Environmental Science: BIO_104_

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Biodiversity and Conservation Biology Upon completing this chapter, you will be able to:

➤ Characterize the scope of biodiversity on Earth ➤ Contrast the background extinction rate with periods of mass extinction ➤ Evaluate the primary causes of biodiversity loss ➤ Specify the benefits of biodiversity ➤ Assess the science and practice of conservation biology ➤ Analyze efforts to conserve threatened and endangered species ➤ Compare and contrast conservation efforts above the species level

A Siberian tiger in the Sikhote-Alin Mountains

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CENTRAL CASE STUDY

Saving the Siberian Tiger “Future generations would be truly saddened that this century had so little foresight, so little compassion, such lack

of generosity of spirit for the future that it would eliminate one of the most dramatic and beautiful animals this world has ever seen.”

—George Schaller, Wildlife Biologist, on the tiger

“If you kill a tiger, you can buy a motorbike.” —Anonymous poacher, on selling tiger parts

Historically, tigers roamed widely across Asia from Turkey to northeast Russia to In-donesia. However, people have driven the majestic striped cats from nearly all of their range. Today, tigers are exceedingly rare and are sliding toward extinction. Just over 3,000 tigers survive, down from 100,000 a century ago.

Sikhote-Alin Mountains

RUSSIA

CHINA

MONGOLIA

INDIA

Tigers of the subspecies known as the Siberian tiger are the largest cats in the world. These regal animals today find their last refuge in the forests of the remote Sikhote-Alin Mountains of the Russian Far East. For thou- sands of years the Siberian tiger coexisted with the re- gion’s native people and held a prominent place in their lore. These people viewed it as a guardian of the moun- tains and forests, and they rarely killed a tiger unless it had preyed on a person.

The Russians who moved into the region in the early 20th century had no such cultural traditions. They hunted tigers relentlessly for sport and hides, and the tiger population dipped to perhaps just 20–30 animals. In response, the Russian government banned the hunting of tigers, and the population be- gan to recover. However, poachers started killing ti- gers illegally to sell their body parts to China and oth- er Asian countries, where they are used in traditional medicine and as alleged aphrodisiacs. Meanwhile, logging, road building, and agriculture degraded and fragmented tiger habitat, providing easy access for still more poachers.

International conservation groups got involved just in time, working with Russian biologists to save the

dwindling tiger population. One such group was the Hor- nocker Wildlife Institute, now part of the Wildlife Conserva- tion Society (WCS). In 1992 the group helped launch the Sibe- rian Tiger Project, devoted to studying and conserving the tiger and its habitat. The team put together a plan to protect the tiger, began educating people on the animal’s value, and worked closely with peo- ple who live near the big cats.

Today, WCS biologists track tigers with radio- collars, monitor their movements and health, deter- mine causes of death when they die, and study as- pects of the tiger’s ecosystem. They also work with the region’s people and help fund local wildlife of- ficials to deter and capture poachers.

Thanks to such efforts, the Siberian tiger popu- lation stabilized, even while the world’s other tiger populations were declining. The last range-wide sur- vey, in 2005, found between 428 and 502 Siberian ti- gers in the wild, while 1,500 more survived in zoos and captive breeding programs. However, govern- ment funding and law enforcement to deter poaching were reduced, and data since 2005 suggest that tiger numbers are falling yet again.

Many dedicated scientists, conservationists, and policymakers continue trying to save these

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endangered animals. In November 2010, leaders of the 13 nations where tigers still survive met at a historic summit in St. Petersburg, Russia, marking the first time that multiple heads of state had ever convened to fo- cus on saving a single species of wild animal. Russian prime minister Vladimir Putin, Chinese premier Wen Jiabao, World Bank president Robert Zoellick, and actor Leonardo DiCaprio were among the luminaries participating in the conference. At this International Ti- ger Forum, the leaders signed a declaration that set in motion a strategic multinational plan called the Global Tiger Recovery Program.

This program aims to double the tiger population by 2022 (the next “Year of the Tiger” by the Chinese zodiac) by protecting habitat, cracking down on poach- ing, and addressing illegal trade in pelts and body parts. National governments, conservation organiza- tions, and the World Bank promised millions of dollars, although more is needed—an estimated $350 million over the first 5 years of the program. Representatives of the 13 nations planned to work out details of financ- ing during 2011.

Some proponents of tiger conservation criticized the program, worrying that funding would not be ad- equate, that specific measures to reduce demand for tiger body parts were not spelled out, and that pro- posed actions were not focused enough. Nonetheless, by demonstrating support for tiger conservation at the highest political level, the summit gave tiger conser- vation efforts a clear boost. The struggle to save the tiger from imminent extinction is one of numerous ef- forts around the world today to stem the loss of our planet’s priceless biological diversity. ■

OUR PLANET OF LIFE Our rising human population and resource consumption are putting ever-greater pressure on the flora and fauna of our planet, from tigers to tiger beetles. We are diminishing Earth’s diversity of life, the very quality that makes our planet so special.

Biodiversity encompasses multiple levels Biological diversity, or biodiversity (p. 49), describes the va- riety of life across all levels of biological organization, includ- ing the diversity of species, their genes, their populations, and their communities. Biodiversity is a concept as multifaceted as life itself, and biologists employ different working defini- tions according to their own aims and philosophies. Yet sci- entists agree that the concept applies across the major levels in the organization of life (FIGURE 8.1). The level that is easiest to visualize and most commonly used is species diversity.

Species diversity A species (p. 46) is a distinct type of organism, a set of individuals that uniquely share certain characteristics and can breed with one another and produce fertile offspring. Biologists use differing criteria to distin- guish one species from another. Some emphasize character- istics shared because of common ancestry, whereas others

Ecosystem diversity

Species diversity

Genetic diversity

FIGURE 8.1  The concept of biodiversity encompasses several levels in the hierarchy of life. Species diversity (middle frame of the figure) refers to the number or variety of species. Genetic diversity (bottom frame) refers to variation in DNA composition among individuals within a species. Ecosystem diversity (top frame) and related concepts refer to variety at levels above the species level, such as ecosystems, communities, habitats, or landscapes.

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by the same processes that drive speciation (pp. 49–50) but re- sult when divergence stops short of forming separate species. Scientists denote subspecies with a third part of the scientific name. The Siberian tiger, Panthera tigris altaica, is one of five (or perhaps only four) subspecies of tiger still surviving (FIG- URE 8.3). Tiger subspecies differ in color, coat thickness, stripe patterns, and size. For example, Panthera tigris altaica is taller at the shoulder than the Bengal tiger (Panthera tigris tigris) of India and Nepal, and it has a thicker coat and larger paws.

Genetic diversity Scientists designate subspecies when they recognize substantial, genetically based differences among individuals from different populations of a species. However, all species consist of individuals that vary geneti- cally from one another to some degree, and this genetic di- versity is an important component of biodiversity. Genetic diversity encompasses the differences in DNA composition (p. 28) among individuals.

Genetic diversity provides the raw material for adaptation to local conditions. A diversity of genes for coat thickness in tigers allowed natural selection (pp. 46–48) to favor genes for thin fur in Bengal tigers living in warm regions, and genes for thick fur in Siberian tigers living in cold regions. In the long term, populations with more genetic diversity may be more likely to persist, because their variation better enables them to cope with environmental change.

Populations with little genetic diversity are vulnerable to environmental change because they may happen to lack ge-

emphasize the ability to interbreed. In practice, however, sci- entists generally agree on species identities.

We can express species diversity in terms of the number or variety of species in a particular region. One component of species diversity is species richness, the number of species. Another is evenness or relative abundance, the extent to which species differ in numbers of individuals.

Speciation (pp. 49–50) generates new species, whereas extinction (p. 51) diminishes species richness. Immigration, emigration, and local extinction may change species richness locally, but only speciation and extinction change it globally.

Taxonomists classify species by their similarity into a hi- erarchy of categories meant to reflect evolutionary relation- ships. Related species are grouped together into genera (sin- gular: genus); related genera are grouped into families; and so on (FIGURE 8.2). Every species is given a two-part Latin or Latinized scientific name denoting its genus and species. The tiger, Panthera tigris, is similar to the world’s other species of large cats, such as the jaguar (Panthera onca), the leopard (Panthera pardus), and the African lion (Panthera leo). These four species are closely related in evolutionary terms, and this is indicated by the genus name they share, Panthera. They are more distantly related to cats in other genera such as the chee- tah (Acinonyx jubatus) and the bobcat (Felis rufus), although all cats are classified together in the family Felidae.

Biodiversity exists below the species level in the form of subspecies, populations of a species that occur in separate geo- graphic areas and differ in some characteristics. Subspecies arise

Domain: Eukarya

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Carnivora

Family: Felidae

Genus: Panthera

Species: Panthera tigris

FIGURE 8.2  Taxonomists classify organisms using a hierarchical system meant to reflect evolutionary relation- ships. Species that are similar in their appearance, behavior, and genetics (because they share recent common ancestry) are placed in the same genus. Organisms of similar genera are placed within the same family. Families are placed within orders, orders within classes, classes within phyla, phyla within kingdoms, and kingdoms within domains. For instance, tigers belong to the class Mammalia, along with elephants, kangaroos, and bats. However, the differences among these species, which have evolved and diverged over millions of years, are great enough that they are placed in different orders, families, and genera.

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good gauge for overall biodiversity. Yet we still are profound- ly ignorant of the number of species that exist in the world. So far, scientists have described about 1.8 million species of plants, animals, and microorganisms. However, estimates for the number that actually exist range from 3 million to 100 million, with the most widely accepted estimates in the neighborhood of 14 million.

Our knowledge of species numbers is incomplete for several reasons. First, many species are tiny and easily over- looked. These include bacteria, nematodes (roundworms), fungi, protists, and soil-dwelling arthropods. Second, many organisms are so difficult to identify that ones thought to be identical sometimes turn out, once biologists look more closely, to be multiple species. Third, some areas of Earth remain little explored. We have barely sampled the ocean depths, hydrothermal vents (p. 260), or the canopies and soils of tropical forests. As one example, a 2005 expedition to the remote Foja Mountains of New Guinea discovered over 40 new species of vertebrates, plants, and butterflies in less than a month, while research in marine waters nearby turned up another 50 new species.

Biodiversity is unevenly distributed Some taxonomic groups hold more species than others. In this respect, insects show a staggering predominance over all other forms of life (FIGURE 8.4). Within insects, about 40% are beetles, and beetles alone outnumber all non-insect ani- mals and all plants. No wonder the 20th-century British bi- ologist J.B.S. Haldane famously quipped that God must have had “an inordinate fondness for beetles.”

netic variants that would help them adapt to novel conditions. Populations with low genetic diversity may also be more vul- nerable to disease and may suffer inbreeding depression, which occurs when genetically similar parents mate and produce weak or defective offspring. Scientists have sounded warn- ings over low genetic diversity in species that have dropped to low population sizes, including cheetahs, bison, and elephant seals, but the full consequences of reduced diversity in these species remain to be seen. Diminished genetic diversity in our crop plants is a prime concern to humanity (p. 136).

Ecosystem diversity Biodiversity encompasses levels above the species level, as well. Ecosystem diversity refers to the number and variety of ecosystems, but biologists may also refer to the diversity of biotic communities or habitats within some specified area. If the area is large, scientists may also consider the geographic arrangement of habitats, communities, or eco- systems at the landscape level, including the sizes and shapes of patches and the connections among them. Under any of these concepts, a seashore of rocky and sandy beaches, for- ested cliffs, offshore coral reefs, and ocean waters would hold far more biodiversity than the same acreage of a monocultural cornfield. A mountain slope whose vegetation changes with elevation from desert to hardwood forest to conifer forest to alpine meadow would hold more biodiversity than an equal- sized area consisting of only desert, forest, or meadow.

Many species await discovery Scientists often express biodiversity in terms of species rich- ness because that component is most easily measured and is a

Siberian (Amur) tiger

South China tiger

Indochina tiger

Bengal tiger

Sumatran tiger

Caspian tiger (extinct)

Historical range

Current range

Bali tiger (extinct)

Javan tiger (extinct)

FIGURE 8.3  Three of the eight sub- species of tiger—the Bali, Javan, and Caspian tigers—were driven extinct during the 20th century. Today only the Siberian, Bengal, Indochina, and Sumatran tigers persist, while the South China tiger has not been seen in 25 years and may be extinct. Defor- estation, hunting, and other pressures from people have caused tigers of all subspecies to disappear from 93% of the geographic range they historically occupied. Researchers estimate that the majority of surviving individuals are crowded into less than half of 1% of the species’ original range. This map contrasts the ranges of the eight subspecies in the years 1800 (orange) and 2000 (red). Data from the Tiger Information Center.

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tion zones where habitats intermix; p. 33) often support high biodiversity. Because human disturbance can sometimes in- crease habitat diversity, species diversity may rise in disturbed areas. However, this is true only at local scales. At larger scales, human disturbance decreases diversity because specialists dis- appear when habitats are homogenized and because species that rely on large expanses of habitat disappear when habitats are fragmented.

EXTINCTION AND BIODIVERSITY LOSS Biodiversity at all levels is being lost to human impact, most irretrievably in the extinction of species. Extinction (p. 51) occurs when the last member of a species dies and the species ceases to exist. The disappearance of a particular population from a given area, but not the entire species globally, is re- ferred to as extirpation. The tiger has been extirpated from most of its historic range (see Figure 8.3), but it is not yet ex- tinct. Extirpation is an erosive process that can, over time, lead to extinction.

Human impact is responsible for most cases of extirpa- tion and extinction today, but these processes also occur natu- rally, albeit at a much slower rate. If species did not naturally go extinct, we would be up to our ears in dinosaurs, trilobites, and millions of other creatures that vanished from Earth long before we appeared. Paleontologists estimate that roughly 99% of all species that ever lived are now extinct, and that the

Living things are distributed unevenly across our planet, as well. For instance, species richness generally increases as one nears the equator. This pattern of variation with latitude is called the latitudinal gradient, and hypotheses abound to explain it. A leading idea is that greater amounts of solar en- ergy, heat, and humidity at tropical latitudes lead to more plant growth, making areas nearer the equator more produc- tive and able to support more animals. The relatively sta- ble climates of equatorial regions, in turn, discourage single species from dominating ecosystems and, instead, allow nu- merous species to coexist. Whereas variable environmental conditions favor generalists (species that can tolerate a wide range of circumstances), stable conditions favor specialists (species that do particular things especially well). Another proposed explanation for the latitudinal gradient is that gla- ciation events repeatedly forced organisms toward tropical latitudes, leaving the polar and temperate regions relatively species-poor.

The latitudinal gradient influences the species diversity of Earth’s biomes (pp. 78–84). Tropical dry forests and rainfor- ests support far more species than tundra and boreal forests, for instance. At smaller scales, diversity varies with habitat type. Structurally diverse habitats tend to allow for more eco- logical niches (p. 53) and support greater species richness and evenness. For instance, forests generally support more diver- sity than grasslands.

For any given area, species diversity tends to increase with diversity of habitats, because each habitat supports a somewhat different set of organisms. Thus, ecotones (transi-

Mammals

Arachnids

Fungi

Reptiles

Bacteria

Birds

Insects

PlantsPlants

ArchaeaAmphibians

Annelids

Roundworms

Annelids

Roundworms Echinoderms Fishes

Flatworms

Protists

Jellyfish

Sponges

Molluscs

Crustaceans

FIGURE 8.4  This illustration shows organisms scaled in size to the number of species known from each major taxo- nomic group. This gives a visual sense of the disparity in species richness among groups. However, because most species are not yet discovered or described, some groups (such as bacteria, archaea, insects, nematodes, protists, fungi, and others) may contain far more species than we now know of. Data from Groom- bridge, B., and M.D. Jenkins, 2002. Global

biodiversity: Earth’s living resources in the 21st

century. UNEP-World Conservation Monitoring

Centre. Cambridge, U.K.: Hoechst Foundation.

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of all species. Although similar in scale to previous mass ex- tinctions, today’s ongoing mass extinction is different in two primary respects. First, we are causing it. Second, we will suf- fer as a result.

We are setting the sixth mass extinction in motion Over just the past few centuries, we have recorded hun- dreds of instances of species extinction caused by people. Among North American birds in the past two centuries alone, we have driven into extinction the Carolina para- keet, great auk, Labrador duck, passenger pigeon (pp. 53– 54), probably the Bachman’s warbler and Eskimo curlew, and possibly the ivory-billed woodpecker (FIGURE 8.6). Several more species, including the whooping crane, Kirt- land’s warbler, and California condor (p. 177), teeter on the brink of extinction.

However, species extinctions caused by people precede written history. Archaeological evidence shows that in case after case, a wave of extinctions followed close on the heels of human arrival on islands and continents (FIGURE 8.7). Af- ter Polynesians reached Hawaii, half its birds went extinct. Birds, mammals, and reptiles vanished following human arrival on many other oceanic islands, including large land masses such as New Zealand and Madagascar. Dozens of species of large vertebrates died off in Australia after people arrived roughly 50,000 years ago, and North America lost 33 genera of large mammals once people arrived more than 10,000 years ago.

Today, species loss is accelerating as our population growth and resource consumption put increasing strain on

remaining 1% comprises the wealth of species on our planet today.

Most extinctions preceding the appearance of human beings occurred one by one for independent reasons, at a pace referred to as the background extinction rate (p. 51). By studying traces of organisms preserved in the fossil record (p. 50), scientists infer that for mammals and marine ani- mals, each year, on average, 1 species out of every 1–10 mil- lion vanished.

Earth has experienced five mass extinction episodes Extinction rates rose far above this background rate at sev- eral points in Earth’s history. In the past 440 million years, our planet experienced five major episodes of mass extinc- tion (p. 51; FIGURE 8.5). Each event eliminated more than one-fifth of life’s families and at least half its species. The most severe episode occurred at the end of the Permian pe- riod (see APPENDIX: Geologic Time Scale for Earth’s geologic periods). At this time, 248 million years ago, close to 90% of all species went extinct. The best-known episode occurred 65 million years ago at the end of the Cretaceous period, when an apparent asteroid impact brought an end to the di- nosaurs and many other groups.

If current trends continue, the modern era, known as the Quaternary period, may see the extinction of more than half

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FIGURE 8.5  The fossil record shows evidence for five episodes of mass extinction during the past half-billion years of Earth his- tory. At the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous periods, 50–95% of the world’s species appear to have gone extinct. (This graph shows families, not species, which is why the drops appear less severe.) Each time, biodiversity later rebounded to equal or higher levels, but each rebound required millions of years. Data from Raup, D.M., and J.J. Sepkoski, 1982. Mass extinctions in the marine fossil record. Science 215:1501–1503. Reprinted with

permission from AAAS.

FIGURE 8.6  The ivory-billed woodpecker was one of North America’s most majestic birds and lived in old-growth forests throughout the southeastern United States. Forest clearing and timber harvesting eliminated the mature trees it needed for food, shelter, and nesting, and this symbol of the South appeared to go extinct. In recent years, fleeting, controversial observations in Arkansas, Louisiana, and Florida have raised hopes that the species persists, but proof has been elusive.

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habitats and wildlife. In 2005, scientists with the Millennium Ecosystem Assessment (p. 16 ) calculated that the current global extinction rate is 100 to 1,000 times greater than the background rate. They projected that the rate would increase tenfold or more in future decades.

To monitor endangered species, the International Union for Conservation of Nature (IUCN) maintains the Red List , an updated list of species facing high risks of extinction. The 2010 Red List reported that 21% (1,131) of mammal species, 13% (1,240) of bird species, and 30% (1,898) of amphibian species are threatened with extinction. Among other major groups (for which assessments are not complete), 17% to 73% of species are judged to be at high risk of extinction. In the United States alone over the past 500 years, 237 animals and 30 plants are known to have gone extinct. For all these figures, the actual numbers are without doubt greater than the known numbers.

Among the 1,131 mammals facing possible extinction is the tiger, which despite—or perhaps because of—its tremendous size and reputation as a fierce predator, is one of the most endangered large animals on the planet. In 1950, eight tiger subspecies existed (see Figure 8.3 ). Today, three are extinct. The Bali tiger went extinct in the 1940s, the Caspian tiger in the 1970s, and the Javan tiger in the 1980s. The South China tiger has not been seen in 25 years and little of its habitat remains, so scientists fear it too will soon be extinct, if it is not already.

North America ~10,000–11,500 yr ago 72% of large mammal genera

Eurasia >30,000 yr ago 36% of large mammal genera

Pacific Islands ~1,000–3,000 yr ago 50+% of endemic landbird species

New Zealand ~1,000 yr ago moas, other birds

South America ~10,000–15,000 yr ago 83% of large mammal genera

Africa ~160,000 yr ago 18% of large mammal genera

Madagascar ~1,500 yr ago lemurs, elephant birds, others

Australia ~44,000–72,000 yr ago 88% of large mammal genera

FIGURE 8.7  This map shows for each region the time of human arrival and the extent of the recent extinction wave. Illustrated are representative extinct megafauna from each region. The human hunter icons are sized accord- ing to the degree of evidence that human hunting was a cause of extinctions; larger icons indicate more certainty that humans (as opposed to climate change or other factors) were the cause. Data for South America and Africa are so far too sparse to be conclusive, and future archaeological and paleontological research could well alter these interpretations. Adapted from Barnosky, A.D., et al., 2004. Assessing the causes of late Pleistocene extinctions on the continents. Science 306: 70–75; and Wilson, E.O., 1992. The diversity of life . Cambridge, MA: Belknap Press.

FAQ

Q: If a mass extinction is happening, why don’t I see species going extinct all around me? A: There are two reasons that most of us don’t personally sense the scale of biodiversity loss. First, if you live in a town or city, the plants and animals you see from day to day are generalist species that thrive in disturbed areas. In contrast, the species in trouble are those that rely on less-disturbed habitats, and you may need to go further afield to find them.

S econd, a human lifetime is very short! The loss of populations and species over the course of our lifetime may seem a slow process to us, but on Earth’s timescale it is sudden—almost instantaneous. Because each of us is born into a world that has already lost many species, we don’t recognize what’s already been lost. Likewise, our grandchildren won’t appreciate what we’ve lost in our lifetimes. Each human generation experiences just a portion of the overall phenomenon, so we have difficulty sensing the big picture. Nonetheless, researchers who study biology and naturalists who spend their time outdoors are seeing a great deal of biodiversity loss—and that’s precisely why they feel so passionate about it.

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prairies native to North America’s Great Plains are today al- most entirely converted to agriculture. Less than 1% of prai- rie habitat remains. As a result, grassland bird populations have declined by an estimated 82–99%.

Habitat destruction has occurred widely in nearly every biome (FIGURE 8.9). Over half of the world’s temperate for- ests, grasslands, and shrublands had been converted by 1950 (mostly for agriculture). Across Asia, scientists estimate that 40% of the tiger’s remaining habitat has disappeared just in the last decade. Today habitat is being lost most rapidly in tropical rainforests, tropical dry forests, and savannas.

Because organisms are adapted to the habitats in which they live, any major change in their habitat is likely to render it less suitable for them. Many human activities alter, degrade, or destroy habitat. Farming replaces diverse natural commu- nities with simplified ones composed of only a few plant spe- cies. Grazing modifies the structure and species composition of grasslands. Either type of agriculture can lead to desertifi- cation. Clearing forests removes the food, shelter, and other resources that forest-dwelling organisms need to survive. Hydroelectric dams turn rivers into reservoirs upstream and affect water conditions and floodplain communities down- stream. Urban sprawl supplants natural ecosystems, driving many species from their homes.

Biodiversity loss involves more than extinction Extinction is only part of the story of biodiversity loss. The larger part involves declining population sizes. As a species’ numbers decline, its geographic range often shrinks as it is extirpated from parts of its range. Thus, many species today are less numerous and occupy less area than they once did. Tigers numbered well over 100,000 worldwide in the 19th century but number only 3,000 to 3,500 today. Such declines mean that genetic diversity and ecosystem diversity, as well as species diversity, are being lost.

To measure and quantify this degradation, scientists at the World Wildlife Fund and the United Nations Environ- ment Programme (UNEP) developed a metric called the Liv- ing Planet Index. This index summarizes trends in the popula- tions of 2,544 vertebrate species that are sufficiently monitored to provide reliable data. Between 1970 and 2007, the Living Planet Index fell by roughly 30% (FIGURE 8.8), driven prima- rily by biodiversity losses in tropical regions.

Several major causes of biodiversity loss stand out Scientists have identified four primary causes of popula- tion decline and species extinction: habitat loss, pollution, overharvesting, and invasive species. Global climate change (Chapter 14) now is becoming the fifth. Each of these causes is intensified by human population growth and by our in- creasing per capita consumption of resources.

Habitat loss Habitat loss is the single greatest cause of biodiversity loss today. It is the primary cause of popula- tion declines in 83% of threatened mammals and 85% of threatened birds, according to UNEP data. For example, the

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FIGURE 8.8  The Living Planet Index serves as an indicator of the state of global biodiversity. Index values summarize trends for 7,953 populations of 2,544 vertebrate species. Between 1970 and 2007, the Living Planet Index fell by roughly 30%. The index for terrestrial species fell by 25%; for freshwater species, 35%; and for marine species, 24%. Most losses are in tropical regions, where the index has declined by 60%. In contrast, temperate areas are recov- ering, showing an improvement of 29%. Data from World Wide Fund for Nature, 2010. The Living Planet Report, 2010. Gland, Switzerland.

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FIGURE 8.9  Habitat loss has affected all of Earth’s biomes, as a result of human impacts from housing development (inset photo), agriculture, mining, and other activities. Bars show for each biome the percentage of original area converted for human use through 1990. Temperate grassland and chaparral have lost over 70% of their area, whereas tundra and boreal forest have lost very little. In recent decades, tropical dry forest and savanna have lost the greatest fraction. These data are for outright conversion of habitat and do not include areas indirectly affected by human activity in other ways. Adapted from Millennium Ecosystem Assessment, 2005. Ecosystems and human

well-being: Biodiversity synthesis. World Resources Institute, Washington, D.C.

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Of course, human habitat alteration benefits some spe- cies. Animals such as house sparrows, pigeons, gray squir- rels, rats, and cockroaches thrive in cities and suburbs. How- ever, the species that benefit from our presence are relatively few; for every species that wins, more lose. Furthermore, the species that do well in our midst tend to be weedy generalists that are in little danger of disappearing any time soon.

Habitat loss occurs most commonly through gradual, piecemeal degradation such as habitat fragmentation (FIGURE 8.10). When farming, logging, road building, or development intrude into a forest, they break up a continuous expanse of for- est habitat into an array of fragments, or patches. As habitat fragmentation proceeds across a landscape, animals and plants adapted to the forest habitat disappear from one fragment after

Original habitat1

Gaps form as habitat becomes fragmented

Gaps become larger; fragments become smaller and more isolated

Species disappear due to habitat fragmentation

FIGURE 8.10  Fragmentation of habitat ➊ begins when gaps are created ➋ within a natural habitat. As development proceeds, these gaps expand ➌, join together, and eventually come to domi- nate the landscape ➍, stranding islands of habitat in their midst. As habitat becomes fragmented, fewer populations can persist, and numbers of species in the fragments decline.

FIGURE 8.11  Body parts from tigers are sold as traditional medicines and aphrodisiacs in some Asian cultures. Poachers are il- legally killing tigers to satisfy the surging market demand for these items. Here a street vendor in northern China displays tiger body parts for sale.

another. In response to habitat fragmentation, conservation bi- ologists design landscape-level strategies to prioritize areas to be preserved (pp. 201–203).

Pollution Pollution harms organisms in many ways. Air pollution (Chapter 13) degrades forest ecosystems. Water pol- lution (Chapter 12) impairs fish and amphibians. Agricul- tural runoff (including fertilizers, pesticides, and sediments; Chapters 2 and 7) harms many terrestrial and aquatic species. Heavy metals, polychlorinated biphenyls (PCBs), endocrine- disrupting compounds, and other toxic chemicals poison peo- ple and wildlife (Chapter 10). Plastic garbage in the ocean can strangle, drown, or choke marine creatures (pp. 270–271). The effects of oil and chemical spills on wildlife (pp. 267, 338–340) are dramatic and well known. However, although pollution is a substantial threat, it tends to be less significant than pub- lic perception holds it to be, and it is far less influential than habitat loss.

Overharvesting For most species, hunting or harvest- ing by people will not in itself pose a threat of extinction, but for species like the Siberian tiger, it can. Large in size, few in number, long-lived, and raising few young in its lifetime— a classic K-selected species (p. 59)—the Siberian tiger is just the type of animal to be vulnerable to hunting. The advent of Russian hunting nearly drove the animal extinct, whereas decreased hunting after World War II allowed the population to increase. By the 1980s, the Siberian tiger population was likely up to 250 individuals. The political freedom that came with the Soviet Union’s breakup in 1989, however, brought with it a freedom to harvest Siberia’s natural resources, in- cluding the tiger, without regulations or rules, and poachers illegally killed at least 180 Siberian tigers between 1991 and 1996. This coincided with an economic expansion in many Asian countries, where tiger penises are believed to boost human sexual performance and where tiger bones, claws, whiskers, and other body parts are used to try to treat a va- riety of health problems (FIGURE 8.11). Although no proof of

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Invasive species Our introduction of non-native species to new environments, where some may become invasive (pp. 75–77), also displaces native species (FIGURE 8.12). Some in- troductions are accidental. Examples include aquatic organ- isms transported in the ballast water of ships (such as zebra mussels; Chapter 4), animals that escape from the pet trade, and weeds whose seeds cling to our socks as we travel from place to place. Other introductions are intentional. People have long brought food crops and animals with them as they colonized new places, and today we continue international trade in exotic pets and ornamental plants.

Most organisms introduced to new areas perish, but the few types that survive may do very well, especially if they are freed from the predators and parasites that attacked them back home or from the competitors that had limited their access to resources. Once released from the limiting factors (p. 58) of predation, parasitism, and competition, an introduced species

their effectiveness has been demonstrated, sale of body parts from one tiger fetches at least $15,000 on the black market—a powerful economic temptation for poachers in poor regions.

Hunting has reduced the populations of many K-selected animals. The Atlantic gray whale was driven ex- tinct, and several other whales remain threatened or endan- gered. Gorillas and other primates that are killed for their meat may face extinction soon. Thousands of sharks are killed each year simply so their fins can be used in soup. Today the oceans contain only 10% of the large animals they once did (p. 274).

To combat overharvesting, governments have passed laws, signed treaties, and strengthened anti-poaching efforts. Scientists have begun using genetic analyses to expose illegal hunting and wildlife trade. For instance, DNA testing can re- veal the geographic origins of elephant ivory and determine whether whale meat sold in markets came from animals caught illegally (see THE SCIENCE BEHIND THE STORY, pp. 178–179).

Species Invasive in… Effects

Kudzu (Pueraria montana) Southeastern

United States

(Native to Japan)

Asian long-horned beetles (Anoplophora glabripennis) United States

(Native to Asia)

Rosy wolfsnail (Euglandina rosea)

Hawaii

(Native to Southeastern United States and Latin America)

Invasive Species

European starling (Sturnus vulgaris)

North America

(Native to Europe)

Gypsy moth (Lymantria dispar) Northeastern

United States

(Native to Eurasia)

Cheatgrass (Bromus tectorum) Western United

States

(Native to Eurasia)

Brown tree snake (Boiga irregularis)

Guam

(Native to Southeast Asia)

Kudzu is a vine that can grow 30 m (100 ft) in a single season. The U.S. Soil Conservation Service introduced kudzu in the 1930s to help control erosion. Adaptable and extraordinarily fast-growing, kudzu has taken over thousands of hectares of forests, fields, and roadsides.

Having arrived in imported lumber in the 1990s, these beetles burrow into trees and interfere with the trees’ ability to absorb and process water and nutrients. They may wipe out the majority of hardwood trees in an area. Several U.S. cities, including Chicago and Seattle, have cleared thousands of trees after detecting these invaders.

In the 1950s, well-meaning scientists introduced the rosy wolfsnail to Hawaii to prey upon and reduce the population of another invasive species, the giant African land snail. Within a few decades, however, the carnivorous rosy wolfsnail had instead driven more than half of Hawaii’s native species of banded tree snails to extinction.

In the 1860s, a scientist introduced the gypsy moth to Massachusetts in the belief that it might help produce a commercial-quality silk. The moth failed to start a silk industry, and instead spread through the northeastern United States, where its outbreaks defoliate trees over large regions every few years.

The bird was first introduced to New York City in the late 19th century by Shakespeare devotees intent on bringing every bird mentioned in Shakespeare’s plays to America. It only took 75 years for starlings to spread to all corners of North America, becoming one of the continent’s most abundant birds. Starlings are thought to outcompete native birds for nest holes.

In just 30 years after its introduction to Washington state in the 1890s, cheatgrass has spread across much of the western United States. It crowds out other plants, uses up the soil’s nitrogen, and burns readily. Fire kills many of the native plants, but not cheatgrass, which grows back even stronger amid the lack of competition.

Nearly all native forest bird species on the South Pacific island of Guam have disappeared. The culprit is the brown tree snake, brought to the island inadvertantly as stowaways in cargo bays of military planes in World War II. Guam’s birds had not evolved with tree snakes, and so had no defenses against the snake’s nighttime predation. The snakes have spread to other islands where they are repeating their ecological devastation. The arrival of this snake is the greatest fear of conservation biologists in Hawaii.

FIGURE 8.12  Invasive species are species that thrive in areas where they are introduced, often harming native species. This chart shows a few of the many thousands of invasive species.

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may proliferate and displace native species. Invasive species cause billions of dollars in economic damage each year.

Climate change The preceding four types of human impacts affect biodiversity in discrete places and times. In contrast, our manipulation of Earth’s climate (Chapter 14) is having global impacts. As our emissions of greenhouse gas- es from fossil fuel combustion cause temperatures to warm worldwide, we modify weather patterns and increase the frequency of extreme weather events.

FIGURE 8.13  As Arctic warming melts the sea ice from which they hunt seals, polar bears must swim farther for food. A lawsuit brought by environmental groups forced the U.S. Fish and Wild- life Service in 2008 to list the polar bear as threatened under the Endangered Species Act as a result of climate change.

Extreme weather events such as droughts increase stress on populations, and warming temperatures force organisms to shift their geographic ranges toward the poles and higher in altitude. Some species will not be able to adapt. Mountain- top organisms (such as the cloud-forest fauna at Monteverde in Chapter 3) cannot move further upslope to escape warm- ing temperatures, so they may perish. Trees may not be able to move poleward fast enough. As ranges shift, animals and plants may find themselves among new communities of prey, predators, and parasites to which they are not adapted. In the Arctic, where warming has been greatest, the polar bear (FIGURE 8.13) has been listed as a threatened species under the U.S. Endangered Species Act (p. 176) because thawing ice hinders its ability to hunt seals (p. 314). All in all, scien- tists predict that a 1.5–2.5 ºC (2.7–4.5 ºF) global temperature rise could put 20–30% of the world’s plants and animals at increased risk of extinction.

All five of these causes of biodiversity loss are intensi- fied by human population growth and rising per capita re- source consumption. As researchers gain a solid scientific understanding of the causes of biodiversity loss, we are also coming to appreciate its consequences (FIGURE 8.14). More- over, these causes may interact, resulting in impacts greater than the sum of their parts. The current collapse of amphib- ian populations throughout the world provides an example. Today entire populations of frogs, toads, and salamanders are vanishing without a trace. Nearly 2,500 of the 6,300 known species are in decline, and roughly 170 species stud-

As you progress through this chapter, try to identify as many solutions to biodiversity loss as you can. What could you personally do to help address this issue? Consider how each action or solution might affect items in the concept map above.

Economic loss

Loss of ecosystem services

Degradation of ecosystem function

Health impacts

Social disruption Loss of aesthetic and spiritual ties

with nature

Loss of food sources

Loss of tourism and recreation

Loss of sources of medicines

Overharvesting

Pollution

Habitat alteration

Invasive species

Globalization

Human population growth

Global climate change

More greenhouse gas

emissions

Growth in per capita consumption

Solutions

Biodiversity loss

Causes Consequences

FIGURE 8.14  The loss of biodiversity stems from a variety of causes (ovals on left) and results in a number of consequences (boxes on right) for ecological systems and human well-being. Arrows in this concept map lead from causes to consequences. Note that items grouped within outlined boxes do not necessari- ly share any special relationship; the outlined boxes are intended merely to streamline the figure.

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ied just years or decades ago are thought to be gone. As these creatures disappear before our eyes, scientists are racing to discover the reasons, and they have found evidence impli- cating habitat destruction, chemical pollution, disease, inva- sive species, and climate change. In some cases, researchers surmise that factors in combination are multiplying one an- other’s effects.

BENEFITS OF BIODIVERSITY Biodiversity loss matters from an ethical perspective, be- cause many people feel that organisms have an intrinsic right to exist. However, losing biodiversity is also a problem for human society because of the many tangible, pragmat- ic ways that biodiversity benefits people and supports our society.

Biodiversity provides ecosystem services Contrary to popular opinion, some things in life can indeed be free—as long as we protect the ecological systems that pro- vide them. Intact forests provide clean air and water, and they buffer hydrologic systems against flooding and drought. Na- tive crop varieties provide insurance against disease. Wildlife can attract tourism and boost economies. Intact ecosystems provide these and other valuable processes, known as ecosys- tem services (pp. 2, 36, 90, 95), for all of us, free of charge. According to UNEP, biodiversity:

▶ Provides food, fuel, fiber, and shelter. ▶ Purifies air and water. ▶ Detoxifies and decomposes wastes. ▶ Stabilizes Earth’s climate. ▶ Moderates floods, droughts, and temperatures. ▶ Cycles nutrients and renews soil fertility. ▶ Pollinates plants, including many crops. ▶ Controls pests and diseases. ▶ Maintains genetic resources for crop varieties, livestock

breeds, and medicines. ▶ Provides cultural and aesthetic benefits. ▶ Gives us the means to adapt to change.

In these ways, organisms and ecosystems support vital processes that people cannot replicate or would need to pay for if nature did not provide them. The annual economic val- ue of just 17 of these ecosystem services has been estimated at more than $46 trillion per year (p. 95).

Biodiversity helps maintain ecosystem function Ecological research shows that biodiversity tends to en- hance the stability of communities and ecosystems. Re- search also finds that biodiversity tends to increase the resilience (p. 74) of ecological systems—their ability to

weather disturbance, bounce back from stress, or adapt to change. Thus, when we lose biodiversity this can diminish a natural system’s ability to function and to provide serv- ices to our society.

Will the loss of a few species really make much differ- ence in an ecosystem’s ability to function? Consider a meta- phor first offered by Paul and Anne Ehrlich (pp. 115, 117): The loss of one rivet from an airplane’s wing—or two, or three—may not cause the plane to crash. But as more rivets are removed the structure will be compromised, and eventu- ally the loss of just one more rivet will cause it to fail.

Research suggests that removing a top predator such as a tiger can indeed have a strong impact, because top preda- tors are often keystone species (pp. 71–72). A single tiger may prey on many herbivores, each of which may consume many plants—so the removal of a species like the tiger can have con- sequences that multiply as they cascade down the food chain.

“Ecosystem engineers” (pp. 72–73) such as ants and earthworms can be every bit as influential as keystone species, so the loss of an ecosystem engineer from a system can like- wise set major changes in motion. Ecosystems are complex, and it can be difficult to predict which species are most im- portant. Thus, many people prefer to apply the precautionary principle (pp. 152, 222) in the spirit of Aldo Leopold (p. 14), who advised, “To keep every cog and wheel is the first precau- tion of intelligent tinkering.”

Biodiversity enhances food security Biodiversity provides the food we eat. Throughout history, people have used 7,000 plant species and several thousand animal species for food. Today nutritional experts worry that industrial agriculture has narrowed our diet. Globally, we now get 90% of our food from just 15 crop species and 8 livestock species, and this lack of diversity leaves us vulnerable to fail- ures of particular crops. In a world where 1 billion people go hungry and more are malnourished, we can improve food security (the guarantee of an adequate, safe, nutritious, and reliable food supply; p. 134) by finding sustainable ways to harvest or farm novel or underutilized wild species and rare crop varieties (FIGURE 8.15). For example, the babassu palm of the Amazon produces more vegetable oil than any other plant. The serendipity berry generates a sweetener 3,000 times sweeter than table sugar. Several salt-tolerant grasses and trees are so hardy that farmers can irrigate them with salt water to produce animal feed, a vegetable oil substitute, and other products.

Moreover, crop relatives and wild ancestors of crops hold reservoirs of genetic diversity (p. 136) that can help save our monocultural crops from catastrophe when we transfer help- ful genes by crossbreeding or genetic engineering. We have already received tens of billions of dollars’ worth of disease resistance from the wild relatives of potatoes, wheat, barley, and other crops.

Organisms provide drugs and medicines People have made medicines from plants for centuries, and many of today’s pharmaceuticals are derived from

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chemical compounds from wild plants (FIGURE 8.16). The rosy periwinkle produces compounds that treat Hodgkin’s disease and a deadly form of leukemia. Had this plant from Madagascar become extinct, these two fatal diseases would have claimed far more victims. In Australia, a rare species of cork, Duboisia leichhardtii, provides hyoscine, a compound that physicians use to treat cancer, stomach disorders, and motion sickness. The Pacific yew of North America’s Pacific Northwest produces a compound that forms the basis for the anti-cancer drug taxol. Each year, pharmaceutical products owing their origin to wild species generate up to $150 billion in sales and save thousands of human lives.

The world’s biodiversity holds an even greater treasure chest of medicines still to be discovered. Yet with every spe- cies that goes extinct, we lose one more opportunity to find cures for cancer, AIDS, or other maladies (FIGURE 8.17).

Species Native to… Potential usesand benefits

Food Security and Biodiversity: Potential new food sources

Amaranths (three species of Amaranthus)

Tropical and Andean America

Grain and leafy vegetable; livestock feed; rapid growth, drought resistant

“Tree of life” to Amerindians; vitamin-rich fruit; pith as source for bread; palm heart from shoots

Amazon lowlands

Buriti palm (Mauritia flexuosa)

Cold-resistant root vegetable resembling radish, with distinctive flavor; near extinction

Andes Mountains

Maca (Lepidium meyenii)

A deep-forest pig; thrives on vegetation high in cellulose and hence less dependent on grain

Indonesia: Moluccas and Sulawesi

Babirusa (Babyrousa babyrussa)

World’s largest rodent; meat esteemed; easily ranched in open habitats near water

South America

Capybara (Hydrochoeris hydrochoeris)

Threatened species related to llama; source of meat, fur, and hides; can be profitably ranched

Central Andes

Vicuna (Lama vicugna)

South and Central America

Tropical birds; adaptable to human habitations; fast-growing

Chachalacas (Ortalis, many species)

FIGURE 8.15  By protecting biodiversity, we enhance food security. The wild species shown here are a fraction of the many plants and animals that could supplement our food supply. Adapted from Wilson, E.O., 1992. The diversity of life. Cambridge, MA:

Belknap Press.

Plant Drug Medical application

Pineapple (Ananas comosus)

Medicines and Biodiversity: Natural sources of pharmaceuticals

Autumn crocus (Colchicum autumnale)

Yellow cinchona (Cinchona ledgeriana)

Common thyme (Thymus vulgaris)

Pacific yew (Taxus brevifolia)

Colchicine

Quinine

Thymol

Taxol

Anticancer agent

Antimalarial

Cures fungal infection

Anticancer (especially ovarian cancer)

Velvet bean (Mucuna deeringiana)

L-Dopa Parkinson's disease suppressant

Common foxglove (Digitalis purpurea)

Digitoxin

Bromelain Controls tissue inflammation

Cardiac stimulant

FIGURE 8.16  By protecting biodiversity, we enhance our ability to treat illness. Shown are just a few of the plants found to provide chemical compounds of medical benefit. Adapted from Wilson, E.O., 1992. The diversity of life. Cambridge, MA: Belknap Press.

FIGURE 8.17  We lost opportunities for medical advances when two species of gastric brooding frogs went extinct shortly after their discovery in Australia’s rainforests. Females of these bizarre frogs raised their young inside their stomachs, where the young apparently exuded substances to neutralize their mother’s stomach acids. Any such substance could be of immense value for treating human stomach ulcers, which affect 25 million U.S. citizens. When both frog species went extinct in the 1980s, they took their secrets with them forever.

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direct contact with wild organisms, they suffer what he calls “nature-deficit disorder.” Although it is not a medical condi- tion, Louv argues that this alienation from biodiversity and nature damages childhood development and may lie behind many of the emotional and physical problems young people in developed nations face today.

Do we have ethical obligations toward other species? Aside from all of biodiversity’s pragmatic benefits, many peo- ple feel that living organisms have an inherent right to exist. In this view, biodiversity conservation is justified on ethical grounds alone. As Maurice Hornocker wrote when he and his associates first established the Siberian Tiger Project, “Sav- ing the most magnificent of all the cat species and one of the most endangered should be a global responsibility. . . . If they aren’t worthy of saving, then what are we all about? What is worth saving?”

Today many people are engaged in efforts to save vanish- ing species. The search for solutions to today’s biodiversity crisis is dynamic and exciting, and scientists are developing innovative approaches to maintaining the diversity of life on Earth.

CONSERVATION BIOLOGY: THE SEARCH FOR SOLUTIONS Today, more and more scientists and citizens perceive a need to stop the loss of biodiversity. In his 1994 autobiography, Naturalist, E.O. Wilson wrote:

When the [20th] century began, people still thought of the planet as infinite in its bounty. [Yet] in one lifetime, exploding human populations have reduced wildernesses to threatened nature reserves. Ecosystems and species are vanishing at the fastest rate in 65 million years. Troubled by what we have wrought, we have begun to turn in our role from local conqueror to global steward.

Conservation biology arose in response to biodiversity loss The urge to act as responsible stewards of natural systems, and to use science as a tool in that endeavor, helped spark the rise of conservation biology. Conservation biology is a scientific discipline devoted to understanding the factors, forces, and processes that influence the loss, protection, and restoration of biological diversity.

Conservation biologists aim to develop solutions to such problems as habitat degradation and species loss (see ENVISIONIT, p. 175). Conservation biology is thus an applied and goal-oriented science, with implicit values and ethical standards. Conservation biologists integrate an understanding of evolution and extinction with ecology and the dynamic nature of environmental systems. They use field data, lab data, theory, and experiments to study our impacts on other organisms. They also design, test, and implement ways to alleviate human impact.

Biodiversity boosts economies through tourism and recreation Many people like to travel to observe wildlife and explore natural areas, and in so doing they create economic oppor- tunities for residents living near protected natural areas. Visitors spend money at local businesses, hire local people as guides, and support parks that employ local residents. Such ecotourism (p. 60) can bring jobs and income to areas that otherwise might be poverty-stricken.

Ecotourism has become a vital source of income for Cos- ta Rica, with its rainforests; Australia, with its Great Barrier Reef; Belize, with its reefs, caves, and rainforests; and Kenya and Tanzania, with their savanna wildlife. The United States, too, benefits from ecotourism; its national parks draw mil- lions of visitors from around the world. Although too much development for ecotourism can damage the natural assets that draw people, ecotourism can serve as a powerful financial incentive for nations, states, and local communities to pre- serve natural areas and reduce impacts on the landscape and on native species.

People value and seek out connections with nature Not all of biodiversity’s benefits to people can be expressed in the hard numbers of economics or the practicalities of food and medicine. Some scientists and philosophers argue that people find a deeper value in biodiversity. Harvard Univer- sity biologist and author Edward O. Wilson has popularized the notion of biophilia, asserting that human beings have an instinctive love for nature and feel an emotional bond with other living things (FIGURE 8.18). Wilson and others cite as evidence of biophilia our affinity for parks and wildlife, our love for pets, the high value of real estate with a view of natu- ral landscapes, and our interest in hiking, bird-watching, fishing, hunting, backpacking, and similar outdoor pursuits.

In a 2005 book, writer Richard Louv adds that as today’s children are increasingly deprived of outdoor experiences and

FIGURE 8.18  An Indonesian girl peers into a flower of Rafflesia arnoldii, the largest flower in the world. The concept of biophilia holds that human beings have an instinctive love and fascination for nature and a deep-seated desire to affiliate with other living things.

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Sampling plants in Florida

Tracking rhinos in Africa

Radio tracking birds in Spain

Blood sample from Seychelles Magpie Robin

Sampling insects in Madagascar

You Can Make a Difference

Buy shade-grown coffee, organic produce, and other wildlife-friendly products.

Conservation biologists are racing to save species from decline and extinction.

They work in the �eld, in the lab, at zoos, and with local people in areas that need protecting ...

... striving to recover populations of plants and animals threatened by habitat loss and other causes.

Preserve or restore wildlife habitat in your yard, in your community, or on your campus.

Volunteer time or money to organizations working to save species and habitat.

Sea turtle with transmitter, Hong Kong

En v

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At the genetic level, conservation geneticists ask how small a population can become and how much genetic variation it can lose before running into problems such as inbreeding depression (p. 164). By determining a popula- tion’s minimum viable population size, conservation geneti- cists can help wildlife managers decide how vital it may be to increase the population. Studies of genes, populations, and species inform conservation efforts with habitats, com- munities, ecosystems, and landscapes. Because small and isolated subpopulations are most vulnerable to extirpation, conservation biologists pay special attention to them. By ex- amining how organisms disperse from one habitat patch to another, and how their genes flow among subpopulations, conservation biologists try to learn how likely a population is to persist or succumb in the face of habitat change or oth- er threats.

Endangered species are a focus of conservation efforts The primary legislation for protecting biodiversity in the United States is the Endangered Species Act. Passed in 1973, the Endangered Species Act (ESA) forbids the gov- ernment and private citizens from taking actions that de- stroy endangered species or their habitats. The ESA also forbids trade in products made from endangered spe- cies. The aim is to prevent extinctions, stabilize declin- ing populations, and enable populations to recover. As of 2011, there were 1,061 species in the United States listed as “endangered” and 313 more listed as “threatened,” the status considered one notch less severe than endangered. For about half of these species, government agencies are running recovery plans to protect them and stabilize or increase their populations.

The ESA has had a number of notable successes. Follow- ing the 1973 ban on the pesticide DDT and years of effort by wildlife managers, the bald eagle, peregrine falcon, brown pelican, and other birds have recovered and are no longer listed as endangered (FIGURE 8.19). Intensive management programs with other species, such as the red-cockaded wood- pecker, have held populations steady in the face of continued pressure on habitat. In fact, roughly 40% of declining popula- tions have been stabilized.

This success comes despite the fact that the U.S. Fish and Wildlife Service and the National Marine Fisheries Service, the agencies responsible for upholding the ESA, are perennially underfunded for the job. Reauthorization of the ESA faced stiff opposition from the Republican Congresses in power from 1994 to 2006. Efforts to weaken the ESA by stripping it of its ability to safeguard habitat were narrowly averted in 2006 after 5,700 scientists sent Congress a letter of protest.

Polls repeatedly show that most Americans support protecting endangered species. Yet some opponents feel that the ESA places more value on the life of an endangered organism than it does on the livelihood of a person. This was a common perception in the Pacific Northwest in the 1990s, when protection for the northern spotted owl slowed logging in old-growth rainforest and loggers began to fear for their jobs. In addition, many landowners worry that fed-

eral officials will restrict the use of private land on which threatened or endangered species are found. This has led to a practice described as “shoot, shovel, and shut up” among landowners who want to conceal the presence of such spe- cies on their land.

In fact, however, the ESA has stopped few development projects—and a number of provisions of the ESA and its amendments promote cooperation with landowners. Habitat conservation plans and safe harbor agreements are arrange- ments that allow landowners to harm species in some ways if they improve habitat for them in others.

Today a number of nations have laws protecting species, although they are not always effective. When Canada enacted its Species at Risk Act in 2002, the Canadian government was careful to stress cooperation with landowners and provincial governments, rather than presenting the law as a mandate from the national government. Environmental advocates and many scientists protested that the law was too weak and failed to protect habitat adequately.

In Russia, the government issued Decree 795 in 1995, cre- ating a Siberian tiger conservation program and declaring the tiger a natural and national treasure. In 2007 it established a national park in the Sikhote-Alin Mountains to help protect the tiger, and the next year Prime Minister Vladimir Putin personally visited scientists in the field as they tagged a tiger. However, state funding for tiger conservation remained so meager that the Wildlife Conservation Society felt it necessary to help pay for Russians to enforce their own anti-poaching laws. Whether government support increases in the wake of Russia’s hosting of the 2010 International Tiger Forum in St. Petersburg remains to be seen.

Endangered Species Act passed and DDT banned, 1973

N um

be r

of p

ai rs

2,000

19 63

19 73

19 74

19 81

19 84

19 86

19 88

19 90

19 92

19 94

19 96

19 98

20 00

20 06

Year

4,000

6,000

8,000

10,000

FIGURE 8.19  The recovery of the bald eagle is a success story of the U.S. Endangered Species Act. The national symbol of the United States was close to extinction in the Lower 48 states in the 1960s. Following its protection under the ESA and a ban on the pesticide DDT in 1973, the eagle population began a long re- bound. With its Lower-48 population around 10,000 pairs in 2007, the bald eagle was declared recovered and was removed from the Endangered Species List. Data from U.S. Fish and Wildlife Service, based on annual volunteer eagle surveys. The paucity of data after 2000 is because

surveys began to be discontinued once it became clear that the eagle was

recovering.

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condor, North America’s largest bird (FIGURE 8.20). The suc- cessful program to reintroduce gray wolves to Yellowstone National Park has proven popular with the American public but has met stiff resistance from ranchers, who fear the wolves will attack their livestock. In Arizona and New Mexico, a wolf reintroduction program is making headway, but a number of wolves have been shot.

China is considering a reintroduction program for the Siberian tiger. The Chinese government says it is preparing 600 captive Siberian tigers for release into the far northeast- ern portion of the country. Critics note that forests there are so fragmented that efforts should focus on improving habitat first.

One new idea for saving species from extinction is to cre- ate individuals by cloning them. In this technique, DNA (p. 28) from an endangered species is inserted into a cultured egg without a nucleus, and the egg is implanted into a female of a closely related species that acts as a surrogate mother. Several mammals have been cloned in this way, with mixed results. Some scientists even talk of recreating extinct species from DNA recovered from preserved body parts. Indeed, in 2009 a subspecies of Pyrenean ibex (a type of mountain goat) was cloned from cells taken from the last surviving individual, which had died in 2000. The cloned baby ibex died shortly after birth. Even if cloning can succeed from a technical stand- point, however, such efforts are not an adequate response to biodiversity loss. Without ample habitat and protection in the wild, having cloned animals in a zoo does little good.

Forensics is being used to protect species Forensic science, or forensics, involves the scientific analysis of evidence to make an identification or answer a question relating to a crime or an accident. Conservation biologists are now em- ploying forensics to protect species at risk from illegal harvest- ing. By analyzing DNA from organisms or their tissues sold at

Conservation efforts include international treaties The United Nations has facilitated several international trea- ties to protect biodiversity. The 1973 Convention on Inter- national Trade in Endangered Species of Wild Fauna and Flora (CITES) protects endangered species by banning the international transport of their body parts. When nations enforce it, CITES can protect tigers and other rare species whose body parts are traded internationally.

In 1992, leaders of many nations agreed to the Convention on Biological Diversity. This treaty embodies three goals: to conserve biodiversity, to use biodiversity in a sustainable man- ner, and to ensure the fair distribution of biodiversity’s ben- efits. Among its accomplishments, the treaty has prompted nations to augment protected reserves, has enhanced global markets for shade-grown coffee and other crops grown with- out removing forests, has ensured that African nations share in the economic benefits of ecotourism from wildlife preserves, and has replaced pesticide-intensive farming practices with sustainable ones in some rice-producing Asian nations. Yet the treaty’s overall goal—“to achieve, by 2010, a significant reduction of the current rate of biodiversity loss at the global, regional, and national level”—was not met. Fully 193 nations have become parties to the Convention on Biological Diver- sity. The only ones choosing not to do so are tiny Andorra, the Vatican, and the United States.

Captive breeding, reintroduction, and cloning are being pursued In the effort to save threatened and endangered species, zoos and botanical gardens have become centers for captive breeding, in which individuals are bred and raised in con- trolled conditions with the intent of reintroducing them into the wild. One example is the program to save the California

FIGURE 8.20  To save the California condor from extinction, biologists are raising chicks in captivity. Feeding them with hand puppets designed to look and feel like the heads of adult condors, the biologists shield each chick from all contact with humans, so that when the bird is grown it does not feel an attachment to people. Condors had declined because people killed them, they collided with electrical wires, and they suc- cumbed to lead poisoning after scavenging carcasses of animals killed with lead shot. By 1982, only 22 condors remained, and biolo- gists decided to take all the birds into captiv- ity, in hopes of boosting their numbers and then releasing them. The ongoing program is succeeding. As of 2011, there were 189 birds in captivity and 181 birds living in the wild, having been released at sites in California, Arizona, and Baja California. Several pairs have begun nesting, and so far 24 chicks have been raised in the wild.

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Using Forensics to Uncover Illegal Whaling

The meat from whales has long been a delicacy in Japan and some other nations. Whaling ships deci- mated populations of most species of whales in the 20th century through overhunting, and the International Whaling Commission (IWC) outlawed commercial whaling worldwide beginning in 1986. Yet whale meat continues to be sold at market to wealthy consumers today (see photo). This meat comes legally from several sources:

1. From scientific hunts. Japan and several other nations negotiated with the IWC to continue to hunt limited numbers of whales for research purposes, and this meat may be sold afterwards.

2. From whales killed accidentally when caught in fishing nets meant for other animals (bycatch, p. 274).

3. Possibly from stockpiles frozen before the IWC’s moratorium.

However, conservation biologists long suspected that much of the whale meat on the market was actually caught illegally for the purpose of selling for food and that fleets from Japan and other nations were killing more whales than international law allowed. Once DNA sequencing technology was

developed, scientists could use this tool to find out.

The detectives in this story are conservation geneticists C. Scott Baker, Stephen Palumbi, Frank Cipriano, and their colleagues. For close to two decades they have been traveling to Asia on what have

amounted to top-secret grocery shopping trips.

It began in 1993 when Baker and Palumbi bought samples of whale meat—all labeled simply as kujira, the generic Japanese term for whale meat—from a number of markets in Japan and sequenced DNA from these samples. Law forbids the export of whale meat, so the researchers had to run their analyses in their hotel rooms with portable genetic kits. Once they were back home in the United States, they compared their data with se- quences from known whale species.

By analyzing which samples matched which, they concluded that they had sampled meat from nine minke whales, four fin whales, one humpback whale, and two dolphins. Moreover, because subspecies of whales from different oceans differ genetically, the researchers were able to analyze the genetic variation in their samples and learn that one fin whale came from the Atlantic whereas the other three were from the Pacific, and that eight of the nine minke whales came from the Southern Hemisphere.

Because several of these species and/or subspecies were off-limits to hunting, the data suggested that some of the meat had been hunted, proc- essed, or traded illegally. Baker and Palumbi concluded in a 1994 paper in the journal Science that “the existence of legal whaling serves as a cover for the sale of illegal whale products.” They urged that the international

Dr. C. Scott Baker of Oregon State University running genetic analyses in a Japanese hotel room

Whale meat is sold at this market in South Korea.

market, researchers can often determine the species or subspe- cies and, sometimes, its geographic origin. This can help detect illegal activity, enhancing the enforcement of laws protecting wildlife (see THE SCIENCE BEHIND THE STORY, above).

One example involves African elephants killed for ivory from their tusks. Trade in ivory has been banned globally in an

effort to stop the slaughter of elephants. After airport customs agents seized 6.5 tons of tusks in Singapore in 2002, research- ers led by Samuel Wasser of the University of Washington ana- lyzed DNA from the tusks to determine the geographic origin of the elephants that were killed. The researchers sought to find out whether the tusks belonged to savanna elephants killed in

As any television buff knows, forensic science is a crucial tool in solving mysteries and fighting crime. In recent years conservation biologists have been using forensics to unearth secrets and catch bad guys in the multibillion-dollar illegal global wildlife trade. One such detective story comes from the Pacific Ocean and Japan.

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community monitor catches more closely.

Two years later, Baker, Pa- lumbi, and Cipriano presented results from markets in South Korea and Japan. Again their genetic sleuthing revealed a diversity of whale species, and they stated that their data were “difficult to reconcile” with records of legal catches (scientific whaling by Japan and fishing bycatch by South Korea) reported by these na- tions to the IWC. Among the whales they detected were two specimens of what seemed to be a subspecies or species of whale new to science.

In 2000, the team ana- lyzed 655 samples labeled as whale meat from Japanese and South Korean markets

and found evidence of 12 species or subspecies of whales, along with orcas, porpoises, and dolphins—and even sheep and horses! Seven of the whale species were internationally protected, and together these constituted 10% of the whale meat for sale in Japanese markets.

Genetic analyses of minke whale samples from Japan’s markets also indi- cated that a surprisingly large percent- age came from animals from the Sea of Japan, where Korea and Japan harvest- ed them as fishing bycatch. One-third of the meat on the market was coming from the Sea of Japan, meaning that four times as many whales were being killed there as Japan was reporting (see top figure). The research team calculat- ed that Japan and Korea together were taking so many minke whales from the Sea of Japan that they would eventually wipe out the population (see bottom figure).

In 2007, Baker led a team that combined genetic forensics with eco-

logical methods to estimate numbers of individual whales whose meat was passing through Korean markets. They inferred that meat from 827 minke whales had passed through South Korea’s market in five years. The nation had reported catching only 458 minke whales as fishing bycatch, leading the researchers to conclude that the remainder had been taken illegally.

The governments of Japan and South Korea have tried to refute these findings. Yet the technology and ap- proaches that turn scientists into forensic detectives are now influencing the debate and the negotiation over whaling policy at the interna- tional level.

Genetic types from Sea of Japan

Genetic types from Pacific Ocean

Genetic types from markets in Japan

SOUTH KOREA JAPAN

The distribution of genetic types from minke whale meat in Japanese markets (center pie chart) shows evidence both of whales from the Sea of Japan (left pie chart) and of whales from the open Pacific Ocean (right pie chart). Note how proportions of the types from the market are intermedi- ate between those of each geographic area of ocean. Adapted with permis- sion from Lukoschek, V., et al., 2009. High proportion of protected minke whales sold on Japanese markets due to illegal, unreported, or unregulated exploitation. Animal Conservation 12:385–395.

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Minke whales in the Sea of Japan declined sharply (orange color in graph) until the 1986 moratorium on their capture. Population models forecast that bycatch of 150, 100, or even 50 minke whales per year would be enough to prevent the population’s recovery. Data suggest that actual bycatch from the Sea of Japan has been close to 150 per year. Adapted from Baker, C.S., et al., 2000. Predicted decline of pro- tected whales based on molecular genetic monitoring of Japanese and Korean markets. Proc. Roy. Soc. Lond. B 267:1191–1199.

Zambia (the origin of the shipment), or forest elephants from other locations. The DNA matched known samples from Zam- bian elephants, revealing that many more elephants were be- ing killed there than Zambia’s government had realized. In re- sponse, the government replaced its wildlife director and began imposing harsher sentences on poachers and ivory smugglers.

Some species act as “umbrellas,” protecting habitat and communities Scientists know that protecting species does little good if the larger ecological systems they rely on are not also sus- tained. Yet no law or treaty exists to protect communities

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The nonprofit group Conservation International maps 34 biodiversity hotspots (FIGURE 8.22). The ecosystems of these areas together once covered 15.7% of the planet’s land sur- face but today, because of habitat loss, cover only 2.3%. This small amount of land is the exclusive home for half the world’s plant species and 42% of all terrestrial vertebrate species. The hotspot concept gives incentive to focus on these areas, where the greatest number of unique species can be protected per unit effort.

We can restore degraded ecosystems Protecting natural areas before they become degraded is the best way to safeguard biodiversity and ecological systems. However, we can often restore degraded natural systems to some semblance of their former condition through ecologi- cal restoration (p. 77). Ecological restoration projects aim not just to bring back populations of animals and plants, but also to reestablish the processes that make ecosystems func- tion. By restoring complex natural systems such as Illinois prairies or the Florida Everglades (pp. 77–78), restoration

or ecosystems. Therefore, conservation biologists often use particular species as tools to conserve habitats, com- munities, and ecosystems. Such species are called umbrella species because they serve as a kind of umbrella to protect many other species. Umbrella species often are large ani- mals that roam great distances, such as the Siberian tiger. Because such animals require large areas, meeting their habitat needs helps meet those of thousands of less charis- matic species that might never elicit as much public interest.

Environmental advocacy organizations have found that using large, charismatic vertebrates as spearheads for biodiversity conservation is an effective strategy. This ap- proach of promoting particular flagship species is evident in the longtime symbol of the World Wide Fund for Nature (World Wildlife Fund in North America), the panda. The panda is a large endangered mammal requiring sizeable stands of undisturbed bamboo forest. Its lovable appear- ance has made it a favorite with the public—and an effective vehicle for soliciting support for conservation efforts that protect far more than just the panda.

Protected areas conserve biodiversity at the ecosystem level Although most legislation, funding, and resources for bio- diversity conservation go toward single-species approaches, our practice of preserving areas of undeveloped land in parks and protected areas helps to conserve habitats, communities, ecosystems, and landscapes (pp. 199–203). So far we have set aside 12% of the world’s land area in national parks, state parks, provincial parks, wilderness areas, biosphere reserves, and other protected areas. Many such lands are managed for recreation, water quality protection, or other purposes, not for biodiversity, and many suffer from illegal logging, poach- ing, or resource extraction. Yet these areas offer animals and plants a degree of protection from human persecution, and some are large enough to preserve whole natural systems that otherwise would be fragmented, degraded, or destroyed.

Protected areas alone may not be enough. India has estab- lished reserves to protect its remaining tigers, yet tigers have disappeared from at least two of these reserves. Today a major challenge is to provide linkages among protected areas across the landscape, so that isolated populations of wide-ranging species like tigers can intermix—and so that organisms can move in response to climate change as it alters habitats within protected areas.

Biodiversity hotspots pinpoint regions of high diversity One international approach oriented around geographic regions, rather than single species, is that of biodiversity hotspots. A hotspot is an area that supports an especially great number of species that are endemic (p. 51) to the re- gion: that is, found nowhere else in the world (FIGURE 8.21). To qualify as a hotspot, a location must harbor at least 1,500 endemic plant species (0.5% of the world’s total). In addition, a hotspot must have already lost 70% of its habi- tat as a result of human impact, and be in danger of losing more.

FIGURE 8.21  The ring-tailed lemur is a primate that is endemic to the island of Madagascar. Over 2,000 individuals survive in zoos worldwide thanks to captive breeding, but the lemur’s natural habi- tat is fast disappearing. Madagascar has lost over 90% of its forests because of human population growth, poverty, and resource extraction. One recent president encouraged conservation and ecotourism, but when his government fell, illegal logging resumed, destroying large areas of protected forest. Many lemurs were killed and sold for their meat, and timber was exported to meet demand from wealthy nations.

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Community-based conservation is growing Helping people, wildlife, and ecosystems at the same time, as the Iraqi marsh restoration project intends, is the focus of many current efforts in conservation biology. In past decades, conser- vationists from developed nations, in their zeal to preserve eco- systems in other nations, often neglected the needs of people in the areas they wanted to protect. Developing nations came to view this as a kind of neocolonialism. Today this has largely changed, and many conservation biologists actively engage lo- cal people in efforts to protect land and wildlife (FIGURE 8.23).

This cooperative approach, called community-based conservation, is being pursued to help protect tigers in many places. In India, multiple projects offer education, health care, and development assistance to communities living amid the

ecologists aim to recreate systems that filter pollutants, cleanse water and air, build soil, and recharge groundwater, providing habitat for wildlife and services for people.

Today’s highest-profile restoration project is an effort to restore the vast marshes of southern Iraq. In the 1990s, Iraqi ruler Saddam Hussein drained the marshes, aiming to devastate the region’s people, whom he viewed as dis- loyal. Today ecologists from many nations have joined the people of the marshes in a multimillion-dollar restoration effort. The project was able to restore natural water flow to 75% of the region, so that vegetation grew back and wildlife and people began returning. The effort was on the verge of success when drought descended and Turkey and Syria began diverting water upriver for their own purposes. As of 2011, ecologists and human rights supporters alike were searching for ways to complete this ambitious restoration project.

FIGURE 8.22  Some areas of the world possess exceptionally high numbers of species found nowhere else. Many conservation biologists support prioritizing habitat preserva- tion in these areas, dubbed biodi- versity hotspots. Shown in red are the 34 biodiversity hotspots mapped by Conservation International. Only about 15% of the area in red is actu- ally habitat for these species; most is developed. Data from Conservation International.

Single-Species Conservation? What would you say are some advantages of focus- ing on conserving single species, versus trying to conserve habitats, communities, ecosystems, or landscapes? What are some disadvantages?

Which do you think is the better approach, or should we pursue both?

FIGURE 8.23  In community-based conservation, conserva- tion biologists partner with local people, empowering them to conserve wildlife and habitat in their own region. Here, Costa Rican schoolgirls plant trees in a park in their nation’s capital, San Jose.

shrinking habitat of the Bengal tiger. In Cambodia, people who used to hunt Indochinese tigers are being retrained and paid salaries as forest guards to protect the animals from poachers, or as wildlife technicians to help with science and monitoring. In Russia, the Wildlife Conservation Society is working with local hunters to reduce poaching of Siberian tigers and to in- crease populations of deer and other animals that are prey for both tigers and hunters. The WCS is also establishing a mar- ket in the West for sustainably harvested products from the region that are certified “tiger-friendly.” Proceeds from sales of the products aim to supplement the incomes of up to 1,000 local people by 12–25%.

Making conservation beneficial for local people requires hard work, investment, and trust on all sides. While setting aside land may deprive local people of short-term access to exploitable resources, it also helps ensure that these resources will not be used up or sold to foreign corporations, but can instead be sustainably managed. Moreover, parks and reserves draw ecotourism that supports local economies. Communi- ty-based conservation has not always been successful, but in a world of rising human population, we will require locally based management for biodiversity that sustainably meets people’s needs.

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biodiversity loss. This loss matters, because human society cannot function without biodiversity’s many pragmatic ben- efits. Conservation biologists are rising to the challenge of conducting science aimed at saving endangered species, pro- tecting their habitats, recovering populations, and preserving and restoring natural ecosystems. The innovative strategies these scientists are pursuing hold promise to slow the loss of biodiversity on Earth.

➤ CONCLUSION Data from scientists worldwide confirm what any naturalist who has watched the habitat change in his or her hometown already knows: From amphibians to tigers, biological diver- sity is being lost rapidly and visibly within our lifetimes. This erosion of biodiversity threatens to result in a mass extinc- tion event equivalent to those of the geologic past. Habitat alteration, invasive species, pollution, overharvesting of bi- otic resources, and climate change are the primary causes of

7. Name two successful accomplishments of the U.S. En- dangered Species Act. Now name two reasons some peo- ple have criticized it.

8. Describe how captive breeding can help with endangered species recovery, and give an example. Now explain why cloning will never be, in itself, an effective response to species loss.

9. What is the difference between an umbrella species and a keystone species? Could one species be both an umbrella species and a keystone species?

10. What is a biodiversity hotspot? Describe community- based conservation.

T E S T I N G Y O U R C O M P R E H E N S I O N

1. What is biodiversity? Describe three levels of biodiversity. 2. What are the five primary causes of biodiversity loss?

Give one specific example of each. 3. List three invasive species, and describe their impacts. 4. Define the term ecosystem services. Give three examples

of ecosystem services that people would have a hard time replacing if their natural sources were eliminated.

5. What is the relationship between biodiversity and food security? Between biodiversity and pharmaceuticals? Give three examples of potential benefits of biodiversity conservation for food security and medicine.

6. Describe three reasons why people suggest biodiversity conservation is important.

you want to introduce legislation to protect your nation’s vanishing biodiversity. Consider the U.S. Endangered Species Act and Canada’s Species At Risk Act, as well as international efforts such as CITES and the Convention on Biological Diversity. What strategies would you write into your legislation? How would your law be similar to and different from each of these efforts?

5. THINK IT THROUGH As a citizen and resident of your community, and a parent of two young children, you attend a town meeting called to discuss the pro- posed development of a shopping mall and condo- minium complex. The development would eliminate a 100-acre stand of forest, the last sizeable forest stand in your town. The developers say the forest loss will not matter because plenty of 1-acre stands still exist scattered throughout the area. Consider the develop- ment’s possible impacts on the community’s biodiver- sity, children, and quality of life. What will you choose to tell your fellow citizens and the town’s decision- makers at this meeting, and why?

S E E K I N G S O L U T I O N S

1. Many arguments have been advanced for the importance of preserving biodiversity. Which argument do you think is most compelling, and why? Which argument do you think is least compelling, and why?

2. Some people declare that we shouldn’t worry about endangered species because extinction has always oc- curred. How would you respond to this view?

3. Advocates of biodiversity preservation from developed na- tions have long pushed to set aside land in biodiversity-rich regions of developing nations. Leaders of developing na- tions have responded by accusing these advocates of neo- colonialism. “Your nations attained prosperity and power by overexploiting their environments decades or centuries ago,” these leaders ask, “so why should we now sacrifice our development by setting aside our land and resources?” What would you say to these leaders? What would you say to the environmental advocates? Do you see ways that both preservation and development goals might be reached?

4. THINK IT THROUGH You are an influential legisla- tor in a nation that has no endangered species act, and

C A L C U L A T I N G E C O L O G I C A L F O O T P R I N T S Of the five major causes of biodiversity loss discussed in this chapter, habitat alteration arguably has the greatest impact. In their 1996 book introducing the ecological footprint concept, authors Mathis Wackernagel and

William Rees present a consumption/land use matrix for an average North American. Each cell in the matrix lists the number of hectares of land of that type required to provide for the different categories of a person’s

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consumption (food, housing, transportation, consumer goods, and services). Of the 4.27 hectares required to support this average person, 0.59 hectares are forest,

with most (0.40 hectares) being used to meet the housing demand. Using this information, calculate the missing values in the table.

1. Approximately two-thirds of the forests’ productivity is consumed for housing. To what use(s) would you specu- late that most of the other third is put?

2. If the harvesting of forest products exceeds the sustain- able harvest rate, what will be the likely consequence for the forest? For communities surrounding the forest?

Hectares of forest used for housing

Total forest hectares used

You 0.40 0.59 Your class Your state United States Data from Wackernagel, M., and W. Rees, 1996. Our ecological footprint: Reducing human impact on the earth. British Columbia, Canada: New Society Publishers.

3. What impacts would you expect on biodiversity in each of the following cases, and why? a. The cutting of small plots of forest within a large forest b. The clear-cutting (p. 194) of an entire forest c. The clear-cutting of an entire forest followed by plant-

ing of a monocultural plantation of young trees

Go to www.masteringenvironmentalscience.com for homework assignments, practice quizzes, Pearson eText, and more.

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Environmental Health and Toxicology Upon completing this chapter, you will be able to:

� Identify major environmental health hazards and explain the goals of environmental health ➤ Describe the types of toxic substances in the environment, the factors that affect their toxicity,

and the defenses that organisms possess against them ➤ Explain the movements of toxic substances and how they affect organisms and ecosystems ➤ Discuss the study of chemical hazards, including wildlife toxicology, epidemiology, animal testing,

and dose-response analysis ➤ Compare and contrast risk assessment and risk management

➤ Compare philosophical approaches to risk and how they relate to regulatory policy

Is this baby ingesting toxic substances?

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Bisphenol A: Worldwide

CENTRAL CASE STUDY

Poison in the Bottle: Is Bisphenol A Safe? “Babies in the U.S. are born pre-polluted with BPA. What more evidence do we need to act?”

—Dr. Janet Gray, Director of the Environmental Risks and Breast Cancer Project, Vassar College

“There is no basis for human health concerns from exposure to BPA.” —The American Chemistry Council

H ow is it that a chemical found to alter reproductive development in animals gets

used in baby bottles? How can it be that a substance linked to breast cancer, pros-

tate cancer, and heart disease is routinely used in food and drink containers? The

chemical bisphenol A (BPA for short) has been associated with everything from neurological

effects to miscarriages. Yet it’s in hundreds of products we use every day, and there’s a 90%

chance that it is coursing through your body right now.

To understand how chemicals that may pose health risks come to be widespread in our society, we need to explore how scientists and policymakers study toxic substances and other environmental health risks—and the vexing challenges these pursuits entail.

Bisphenol A is a syn- thetic organic compound (C15H16O2) used in the resins that line metal food cans and drink cans and water supply pipes, and in dental sealants for our teeth. It’s also found in the hard, clear polycarbonate plastic in some water bot- tles, food containers, eating utensils, eyeglass lenses, CDs and DVDs, electronics, baby bottles, and chil- dren’s toys.

Unfortunately, bisphenol A leaches out of these products into our food, air, and bodies. The Centers for Disease Control and Prevention (CDC) reports that 93% of Americans carry detectable concentrations in their urine. Because most of the chemical passes through the body within hours of exposure, its wide- spread presence in urine suggests that most Ameri- cans receive continuous exposure to BPA. Babies and children accumulate the most BPA, because they eat more for their body weight and metabolize the chem- ical less effectively.

What, if anything, is BPA do- ing to us? Over 200 studies with rats, mice, and other animals have shown many apparent ef- fects of BPA, including a wide range of reproductive abnor- malities, and a few recent stud- ies suggest human health im- pacts (see THE SCIENCE BEHIND THE STORY, pp. 214–215). Many of these effects are seen at ex- tremely low concentrations. Sci- entists say this is because BPA mimics the female sex hormone estrogen and can induce some

of estrogen’s effects in animals. Hormones such as estrogen function at very low concentrations in the body, so a synthetic chemical in the body at simi- larly low concentrations can fool the body into re- sponding as it would to estrogen.

In reaction to the burgeoning research, a grow- ing number of researchers, doctors, and consumer advocates are calling on governments to regulate bi- sphenol A and for manufacturers to stop using it. The chemical industry insists that BPA is safe, pointing to industry-sponsored research that finds no health impacts. Expert panels convened to assess the fast- growing body of scientific studies on BPA have strug- gled with the fact that traditional research methods are not geared to test hormone-mimicking substances that exert effects at low doses. These panels have of- ten arrived at divergent conclusions. For instance, the

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U.S. Food and Drug Administration (FDA) insisted in 2008 that it saw no reason to regulate BPA, but its own science advisory committee disagreed, and in 2009 the FDA decided to start a testing program.

In 2008, the Canadian government was the first to declare bisphenol A toxic, banning its sale and impor- tation. As of 2011, the use of BPA in certain products for children was banned in China, Malaysia, and in nine U.S. states. Despite the lack of federal regulation of BPA in the United States, grassroots lobbying efforts have led many companies to voluntarily remove BPA from their products, especially those made for children and infants. The six major U.S. manufacturers of plastic baby bottles promised in 2008 to stop using BPA, and the manufacturer Sunoco stopped selling BPA to compa- nies that use it in children’s products. Nalgene phased out its BPA-containing polycarbonate water bottles. The retailers Walmart and Toys “R” Us decided to stop carrying children’s products with BPA. As a result, con- cerned parents can now more easily find BPA-free prod- ucts for their children, but the rest of us remain exposed through thousands of products (FIGURE 10.1).

Bisphenol A is by no means one of our greatest environmental health threats. However, it provides a timely example of how we as a society assess health risks and decide how to manage them. As scientists and government regulators assess BPA’s potential risks, their efforts give us a window on how hormone- disrupting chemicals are challenging the way we appraise and control the environmental health risks we face. �

ENVIRONMENTAL HEALTH Examining the impacts of human-made chemicals such as bi- sphenol A is just one aspect of the broad field of environmen- tal health. The study and practice of environmental health assesses environmental factors that influence our health and quality of life. These factors include wholly natural aspects of

FIGURE 10.1 ▲ Researchers for Consumer Reports magazine tested these (and more) common packaged foods in 2009; they found that nearly all of them contained bisphenol A that had leached from the linings of their containers.

the environment over which we have little or no control, as well as anthropogenic (human-caused) factors. Practitioners of environmental health seek to prevent adverse effects on human health and on the ecological systems that are essential to our well-being.

We face four types of environmental hazards We can categorize environmental health hazards into four main types: physical, chemical, biological, and cultural. Al- though some amount of risk is unavoidable, much of envi- ronmental health focuses on taking steps to minimize the risks of encountering hazards and to mitigate the impacts of the hazards we do encounter.

Physical hazards Physical hazards arise from processes that occur naturally in our environment and pose risks to human life or health. Some are ongoing natural phenome- na, such as excessive exposure to ultraviolet (UV) radiation from sunlight, which damages DNA and has been tied to skin cancer, cataracts, and immune suppression (FIGURE 10.2A). We can reduce these risks by shielding our skin from intense sunlight with clothing and sunscreen.

(a) Physical hazard (b) Chemical hazard

FIGURE 10.2 ▲ Environmental health hazards come in four types. The sun’s ultraviolet radiation is an example of a physical hazard (a). Excessive exposure increases the risk of skin cancer. Chemical haz- ards (b) include both synthetic and natural chemicals. Much of our exposure comes from pesticides and household chemical products. Biological hazards (c) include diseases and the organisms that trans- mit them. Some mosquitoes, for example, are vectors for pathogenic microbes, including those that cause malaria. Cultural or lifestyle hazards (d) include the behavioral decisions we make, as well as the socioeconomic constraints forced on us. Smoking is a lifestyle choice that raises one’s risk of lung cancer and other diseases.

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Other physical hazards include discrete events such as earthquakes, volcanic eruptions, fires, floods, landslides, hurricanes, and droughts. We cannot prevent many of these hazards, but we can minimize risk by preparing our- selves with emergency plans and avoiding common prac- tices that make us vulnerable to certain physical hazards. For example, clearing vegetation from hillsides increases the chance of landslides, and channelizing rivers pro- motes flooding in some areas while preventing it in others (p. 261).

Chemical hazards Chemical hazards include many of the synthetic chemicals that our society manufactures, such as pharmaceuticals, disinfectants, and pesticides (FIGURE 10.2B). Some natural substances that we process for our use (such as hydrocarbons, lead, and asbestos) are also harmful to human health. Following our overview of environmental health, much of this chapter will focus on chemical health hazards and the ways we study and regulate them.

Biological hazards Biological hazards result from eco- logical interactions among organisms (FIGURE 10.2C). When we become sick from a virus, bacterial infection, or other pathogen, we are suffering parasitism (pp. 66–67). This is what we call infectious disease. Infectious diseases such as malaria, cholera, tuberculosis, and influenza (flu) are major environmental health hazards, especially in developing na- tions with widespread poverty and few resources for health care. As with physical and chemical hazards, it is impossi- ble for us to avoid risk from biological agents completely, but through monitoring, sanitation, and medical treatment we can reduce the likelihood and impacts of infection.

Infectious diseases

14.9 million 23.4%

Cardiovascular diseases 29.0%12.6%

9.8%

6.3%

10.3%

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tetanus, etc.)

Cancers

Maternal and perinatal conditions

Injuries

Respiratory and digestive diseases

Other

(a) Leading causes of death across the world (b) Leading causes of death by infectious disease

FIGURE 10.3 ▲ Infectious disease is the second-leading cause of death worldwide (a), accounting for nearly one-quarter of all deaths. Six types of diseases (b)—respiratory infections, diarrhea, AIDS, tuberculosis (TB), malaria, and childhood diseases—account for 80% of all deaths from infectious disease. Data from World Health Organization, 2009. World health statistics 2009. WHO, Geneva, Switzerland.

Cultural hazards Hazards that result from our place of residence, our socioeconomic status, our occupation, or our behavioral choices can be thought of as cultural hazards or lifestyle hazards. We can minimize or prevent some of these cultural or lifestyle hazards, but others may be beyond our control. For instance, individuals can choose whether or not to smoke cigarettes (FIGURE 10.2D), but exposure to second- hand smoke in the home or workplace may be beyond one’s control. Much the same might be said for other cultural hazards such as drug use, diet and nutrition, crime, and mode of transportation. Environmental justice advocates (pp. 14–15) argue that “forced” risks from cultural hazards, such as living near a hazardous waste site, are often higher for people with fewer economic resources or less political clout.

The biological hazard of disease is a focus of environmental health Despite all our technological advances, we still find ourselves battling disease, which causes the vast majority of human deaths worldwide (FIGURE 10.3A). Over half the world’s deaths result from noninfectious diseases, such as cancer and heart disease. These diseases are not spread from one person to another, but rather are influenced by genetics, environ- mental factors, and lifestyle choices. For instance, whether a person develops heart disease depends not only on his or her genes, but also on lifestyle choices such as diet and exercise.

Infectious diseases account for almost one of every four deaths that occur each year—nearly 14 million people worldwide (FIGURE 10.3B). Some pathogenic viruses, bacteria, and protists attack us directly; others cause infection through a vector, an organism that transfers the pathogen to the host.

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Infectious disease is a greater problem in developing coun- tries, where it accounts for close to half of all deaths. Infec- tious disease causes many fewer deaths in developed nations because their wealth allows their citizens better nutrition, sanitation, hygiene, and access to medical care.

Decades of public health efforts have lessened the impacts of infectious disease and even have eradicated some diseas- es—yet other diseases are posing new challenges. Some, such as acquired immunodeficiency syndrome (AIDS), continue to spread globally despite concerted efforts to stop them. Others, such as tuberculosis and strains of malaria, are evolving resist- ance to our antibiotics, in the same way that pests evolve resist- ance to our pesticides (p. 147). Additionally, human-induced global warming of the climate (Chapter 14) is enabling tropical diseases (such as malaria, dengue, and cholera) to gain foot- holds in temperate regions.

In our world of global mobility and dense human popula- tions, novel infectious diseases (or new strains of old diseases) that emerge in one location are more likely to spread quickly to other locations. Recent examples include severe acute res- piratory syndrome (SARS) in 2003, the H5N1 avian flu start- ing in 2004, and the H1N1 swine flu that spread across the globe in 2009–2010. Diseases like influenza, whose pathogens evolve rapidly, give rise to a variety of strains, making it more likely that one may turn exceedingly dangerous and cause a global pandemic (a widespread outbreak of a disease).

Thousands of dedicated people—from doctors and nurs- es to policymakers to philanthropists—are dedicating their lives to reducing the incidence of disease and improving hu- man health. They use a diversity of approaches to better the living conditions of those most affected by infectious disease by improving access to clean drinking water, sanitation, medi- cal care, and nutritious foods.

Toxicology is the study of chemical hazards Although most indicators of human health are improving as the world’s wealth increases, our modern society is exposing us to more and more synthetic chemicals. Some of these sub- stances pose threats to human health, but figuring out which of them do—and how, and to what degree—is a complicated scientific endeavor. Toxicology is the science that examines the effects of poisonous chemicals on humans and other organisms. Toxicologists assess and compare substances to determine their toxicity, the degree of harm a chemical substance can inflict. A toxic substance, or poison, is called a toxicant, but any chemical substance may exert negative impacts if we ingest or expose ourselves to enough of it. Con- versely, a toxicant in a small enough quantity may pose no health risk at all. These facts are often summarized in the catchphrase, “The dose makes the poison.” In other words, a substance’s toxicity depends not only on its chemical identity, but also on its quantity.

In recent decades, our ability to produce new chemicals has expanded, concentrations of chemical contaminants in the environment have increased, and public concern for health and the environment has grown. These trends have driven the rise of environmental toxicology, which deals specifically

TABLE 10.1 Selected Environmental Hazards

Outdoor Air ▶ Chemicals from automotive exhaust ▶ Chemicals from industrial pollution ▶ Photochemical smog (pp. 288–289) ▶ Pesticide dri ▶ Dust and particulate matter

Water ▶ Pesticide and herbicide runo ▶ Nitrates and fertilizer runo ▶ Mercury, arsenic, and other heavy metals in groundwater

and surface water

Food ▶ Natural toxins ▶ Pesticide and herbicide residues

Indoors ▶ Smoking and secondhand smoke ▶ Radon ▶ Lead in paint and pipes ▶ Asbestos ▶ Toxicants (e.g., PBDEs, phthalates, bisphenol A) in plastics

and consumer products ▶ Dust and particulate matter

with toxic substances that come from or are discharged into the environment. Toxicologists generally focus on human health, using other organisms as models and test subjects. En- vironmental toxicologists study animals and plants to deter- mine the ecological impacts of toxic substances, and to see if other organisms can serve as indicators of health threats that could soon affect people.

People face environmental health hazards indoors Modern Americans spend roughly 90% of their lives indoors. Unfortunately, our homes and workplaces, just like the out- doors, can be rife with physical, biological, chemical, and cultural hazards (TABLE 10.1; also see Figure 13.21, p. 295).

Cigarette smoke and radon are leading indoor hazards (pp. 294–296) and are the top two causes of lung cancer in developed nations. Homes and offices can have problems with toxic compounds produced by mold, which can flourish in wall spaces when moisture levels are high. Asbestos, used in the past as insulation in walls and other products, can be dan- gerous when it is inhaled. Lead poisoning from water pipes or old paint can cause damage to the brain, liver, kidney, and stomach; learning problems and behavioral abnormalities; anemia; hearing loss; and even death. Lead poisoning among U.S. children has greatly declined in recent years as a result of education campaigns and the phaseout of lead-based paints and leaded gasoline (p. 5), which was prompted by govern- ment regulation to protect public health.

There are also indoor chemical hazards that we have yet to discover. One recently recognized hazard is polybrominated diphenyl ethers (PBDEs). These compounds are used as fire retardants in computers, televisions, plastics, and furniture,

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and they may evaporate at very slow rates throughout the life- time of the product. Like bisphenol A, PBDEs appear to act as hormone disruptors. The European Union decided in 2003 to ban PBDEs, but in the United States there has so far been little movement to address the issue.

Risks must be balanced against rewards As we review the impacts of toxic substances throughout this chapter, it is important to keep in mind that artificially produced chemicals have played a crucial role in giving us the standard of living we enjoy today. These chemicals have helped create the industrial agriculture that produces our food, the medical advances that protect our health and pro- long our lives, and many of the modern materials and conven- iences we use every day. It is appropriate to remember these benefits as we examine some of the unfortunate side effects of these advances and as we search for better alternatives.

TOXIC SUBSTANCES AND THEIR EFFECTS ON ORGANISMS Our environment contains countless natural substances that may pose health risks. These include oil oozing naturally from the ground; radon gas seeping up from bedrock; and toxins, toxic chemicals manufactured in the tissues of living organisms—for example, chemicals that plants use to ward off herbivores or that insects use to defend themselves from predators. In addition, we are exposed to many synthetic ( human-made) chemicals.

Synthetic chemicals are all around us—and in us Synthetic chemicals surround us in our daily lives, and each year in the United States we manufacture or import 113 kg (250 lb) of chemical substances for every man, woman, and child. Many of these substances, particularly the pesticides we use to control insects and weeds, find their way into soil, air, and water—and into humans and other organisms (FIGURE 10.4).

As a result of all this exposure, every one of us carries traces of hundreds of industrial chemicals in our bodies. The U.S. government’s latest National Health and Nutrition Examination Survey gathered data on 148 foreign compounds in Americans’ bodies. Among these were several toxic per- sistent organic pollutants restricted by international treaty (p. 223). Depending on the pollutant, these were detected in 41–100% of the people tested. Smaller-scale surveys have found similar results. Our exposure to synthetic chemicals be- gins in the womb as substances our mothers ingested while pregnant were transferred to us. A 2009 study by the nonprof- it Environmental Working Group found 232 chemicals in the umbilical cords of 10 newborn babies it tested. Nine of the 10 umbilical cords contained BPA, leading researchers to note that we are born “pre-polluted.”

All this should not necessarily be cause for alarm. Not all synthetic chemicals pose health risks, and relatively few are

known with certainty to be toxic. However, of the roughly 100,000 synthetic chemicals on the market today, very few have been thoroughly tested. For the vast majority, we simply do not know what effects, if any, they may have on us.

Silent Spring changed public attitudes toward synthetic chemicals It was not until the 1960s that people began to learn about the risks of exposure to pesticides. The key event was the publica- tion of Rachel Carson’s 1962 book Silent Spring (pp. 98–100), which brought the insecticide dichlorodiphenyl-trichlo- roethane (DDT) to the public’s attention. The book was written at a time when large amounts of pesticides virtually untested for health effects were indiscriminately sprayed, on the assumption that the chemicals would do no harm to people (FIGURE 10.5).

Carson synthesized scientific studies, medical case histo- ries, and other data to contend that DDT in particular, and artificial pesticides in general, were hazardous to people, wild- life, and ecosystems. The book became a best-seller and helped generate significant social change in views and actions toward the environment. The use of DDT was banned in the United States in 1973 and is now illegal in a number of nations. U.S. chemical companies still manufacture and export DDT, how- ever, because developing countries with tropical climates use it to control disease vectors, such as mosquitoes that transmit malaria. In these countries, malaria represents a greater health threat than do the toxic effects of the pesticide.

A Circle of Poison? Although the United States has banned the use of DDT, U.S. compa- nies still manufacture and export the compound to developing nations. Thus, it is possible that

pesticide-laden food can be imported back into the United States in what has been called a “circle of poison.” How do you feel about this? Is it unethical for one country to sell to others a substance that it has deemed toxic? Or would it be unethical for the United States not to sell DDT to African nations if they desire it for controlling malaria?

Not all toxic substances are synthetic, and not all synthetic chemicals are toxic Although many toxicologists focus on synthetic chemicals, toxic substances also exist naturally in the environment around us and in the foods we eat. Thus, it would be a mis- take to assume that all artificial substances are unhealthy and that all natural substances are healthy. In fact, the plants and animals we eat contain many chemicals that can cause us harm. Recall that plants produce toxins to ward off animals that eat them. In domesticating crop plants, we have selected (p. 48) for strains with reduced toxin content, but we have not eliminated these dangers. Furthermore, when we consume animal meat, we ingest toxins the ani- mals obtained from plants or animals they ate. Scientists

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FIGURE 10.5  Children on a beach in Long Island, New York, are fogged with DDT from a pesticide spray machine being tested in 1945. Before the 1960s, the environmental and health effects of potent pesticides such as DDT were not widely known. Public parks and neighborhoods were regularly sprayed for insect control without safeguards against excessive human exposure.

Human fetuses and babies

Humans

Non-human biota

Industry and manufacturing

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Consum er products

W orkplace exposure Non-target effects

F oo

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Air for bre athing

A ir for breathing

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Work Medical facilities and public spaces

Agriculture: crops, rangeland, feedlots Soil

Water: surface and groundwater AirHome

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aterials

Pesticides and fertilizers

FIGURE 10.4 ▲ Synthetic chemicals take many routes in traveling through the environment. People take in only a tiny proportion of these compounds, and many compounds are harmless. However, people receive small amounts of toxicants from many sources, and developing fetuses and babies are particularly sensitive.

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ing chemical pathways that produce energy in mitochondria and depriving cells of energy.

Most recently, scientists have recognized endocrine disruptors, toxic substances that interfere with the endocrine system. The endocrine system consists of chemical messen- gers (hormones) that travel through the bloodstream at ex- tremely low concentrations and have many vital functions. They stimulate growth, development, and sexual maturity, and they regulate brain function, appetite, sex drive, and many other aspects of our physiology and behavior. Some hormone-disrupting toxicants affect an animal’s endocrine system by blocking the action of hormones or accelerating their breakdown. Others are so similar to certain hormones in their molecular structure and chemistry that they “mimic” the hormone by interacting with receptor molecules just as the actual hormone would (FIGURE 10.6). Bisphenol A is one of many chemicals that appear to mimic the female sex hor- mone estrogen and bind to estrogen receptors. Phthalates are another class of hormone-disrupting chemicals that are used widely in children’s toys, perfumes and cosmetics, and other items. Health research on phthalates has linked them to birth defects, breast cancer, reduced sperm counts, and other re-

are actively debating just how much risk natural toxicants pose, and it is clear that more research is required on these questions.

Toxic substances come in different types Toxic substances can be classified based on their particular effects on health. The best-known toxicants are carcinogens, which are substances or types of radiation that cause cancer. In cancer, malignant cells grow uncontrollably, creating tumors, damaging the body, and often leading to death. Cancer fre- quently has a genetic component, but a wide variety of envi- ronmental factors are thought to raise the risk of cancer. In our society today, the greatest number of cancer cases is thought to result from carcinogens contained in cigarette smoke. Carcin- ogens can be difficult to identify because there may be a long lag time between exposure to the agent and the detectable on- set of cancer—up to 15–30 years in the case of cigarette smoke.

Mutagens are substances that cause genetic mutations in the DNA of organisms (p. 28). Although most mutations have little or no effect, some can lead to severe problems, in- cluding cancer and other disorders. If mutations occur in an individual’s sperm or egg cells, then the individual’s offspring suffer the effects.

Chemicals that cause harm to the unborn are called teratogens. Teratogens that affect development of human embryos in the womb can cause birth defects. One example involves the drug thalidomide, developed in the 1950s as a sleeping pill and to prevent nausea during pregnancy. Tragi- cally, the drug turned out to be a powerful teratogen. Its use caused birth defects in thousands of babies, and its use by pregnant women was banned in the 1960s.

Other toxicants, known as neurotoxins, assault the nerv- ous system. Neurotoxins include venoms produced by ani- mals, heavy metals such as lead and mercury, and some pes- ticides. A famous case of neurotoxin poisoning occurred in Japan, where a chemical factory dumped mercury waste into Minamata Bay between the 1930s and 1960s. Thousands of people there ate fish contaminated with the mercury and soon began suffering from slurred speech, loss of muscle control, sudden fits of laughter, and in some cases death.

The human immune system protects our bodies from disease. Some toxic substances weaken the immune system, reducing the body’s ability to defend itself against bacteria, viruses, allergy-causing agents, and other attackers. Others, called allergens, overactivate the immune system, causing an immune response when one is not necessary. One hypothesis for the increase in asthma in recent years is that allergenic synthetic chemicals are more prevalent in our environment. Allergens are not universally considered toxicants, however, because they affect some people but not others and because one’s response does not necessarily correlate with the degree of exposure.

Pathway inhibitors are toxicants that interrupt vital biochemical processes in organisms by blocking one or more steps in important biochemical pathways. Rat poisons, for example, cause internal hemorrhaging in rodents by interfer- ing with the biochemical pathways that create blood clotting proteins. Some herbicides, such as atrazine, kill plants by blocking steps in photosynthesis. Cyanide kills by interrupt-

Hormone

Hormone mimic

Receptor

Cell membrane Inside cell

Response (identical to that

caused by hormone)

Inside cell

Response

Receptor

Cell membrane

Hormone

(b) Hormone mimicry

(a) Normal hormone binding

FIGURE 10.6 ▲ Many endocrine-disrupting substances mimic the structure of hormone molecules. Like a key similar enough to fit into another key’s lock, the hormone mimic binds to a cellular receptor for the hormone, causing the cell to react as though it had encountered the hormone.

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The type of exposure can affect the response The risk posed by a hazard often varies according to whether a person experiences high exposure for short periods of time, known as acute exposure , or low exposure over long periods of time, known as chronic exposure . Incidences of acute ex- posure are easier to recognize because they often stem from discrete events, such as accidental ingestion, an oil spill, a chemical spill, or a nuclear accident. Toxicity tests in labo- ratories generally reflect effects of acute toxicity. However, chronic exposure is more common—and more difficult to detect and diagnose. Chronic exposure often affects organs gradually, as when smoking causes lung cancer, or when alco- hol abuse leads to liver or kidney damage. Because of the long time periods involved, relationships between cause and effect may not be readily apparent.

TOXIC SUBSTANCES AND THEIR EFFECTS ON ECOSYSTEMS When toxicants concentrate in environments and harm the health of many individuals, populations (p. 46 ) of the affect- ed species become smaller. This decline can then affect other species. For instance, species that are prey of the affected or- ganism could experience population growth due to lower lev- els of predation. Predators of the poisoned species, however, would decline as their food source became less abundant.

organisms (for example, fetuses, infants, and young children) tend to be much more sensitive to toxicants than are adults. Regulatory agencies such as the U.S. Environmental Protec- tion Agency (EPA) typically set human chemical exposure standards for adults and extrapolate downward for infants and children. However, many scientists contend that these linear extrapolations often do not offer adequate protection to fetuses, infants, and children.

productive effects. Like bisphenol A, phthalates show how a substance can have multiple effects, by being a carcinogen, mutagen, and endocrine disruptor.

Organisms have natural defenses against toxic substances Although synthetic toxicants are new, organisms have been exposed to natural toxicants for millions of years. Mercury, cadmium, arsenic, and other harmful substances are found naturally in the environment. Some organisms produce bio- logical toxins to avoid predators or capture prey. Examples include venom in poisonous snakes, toxins in sea urchins, and the natural insecticide pyrethrin found in chrysanthe- mums. These exposures have provided selection pressure (pp. 46–48 ) for protection from toxins, and over time, organisms able to tolerate these harmful substances have gained an evo- lutionary advantage.

Barriers such as skin, scales, feathers, and fur are the first line of defense against toxic substances because they help the body to resist uptake from the surrounding environment. However, toxicants can circumvent these barriers and enter the body from vital activities such as eating, drinking, and breath- ing. Once in the organism, they are distributed widely by the circulatory and lymph systems in animals, and by the vascular system in plants.

Organisms possess biochemical pathways that use en- zymes to detoxify harmful chemicals. Some pathways break down, or metabolize, toxic substances to render them inert. Other pathways make toxic substances water soluble so they are easier to excrete through the urinary system. In humans, many of these pathways are found in the liver, so this organ is disproportionately affected by intake of harmful substances such as excessive alcohol.

Some toxic substances cannot be effectively detoxified or made water soluble by detoxification enzymes. These chemi- cals are sequestered in fatty tissues and cell membranes to keep them away from vital organs. Heavy metals, dioxins, and some insecticides (including DDT) are stored in body tissue in this manner.

These defenses can protect organisms against low levels of some toxicants but can be overwhelmed if exposure exceeds critical levels. For other toxicants, harm occurs with any ex- posure if organisms have no defense against the substance. Defense mechanisms for natural toxins have evolved over millions of years. Organisms have not had long-term expo- sure to the synthetic chemicals that are so prevalent in today’s environment, so the impacts of these toxic substances can be severe and unpredictable.

Individuals vary in their responses to hazards Some of the defenses described above have a genetic basis. As a result, individuals may respond quite differently to identical exposures to hazards because they happen to have different combinations of genes. Poorer health also makes an individ- ual more sensitive to biological and chemical hazards. Sensi- tivity also can vary with sex, age, and weight. Because of their smaller size and rapidly developing organ systems, younger

FAQ

Q: Does exposure to a toxic substance cause genetic resistance to the substance? A: When a population of organisms is exposed to a toxicant, such as a pesticide, a few individuals often survive while the vast majority of the population is killed. These individuals survive because they possess genes (which others in the population do not) that code for enzymes that counteract the toxic properties of the toxicant. Because the effects of these genes are only expressed when the pesticide is applied, many people think the toxicant “creates” detoxification genes by mutating the DNA of a small number of individuals. This is not the case. The genes for detoxifying enzymes were present in the DNA of resistant individuals from birth, but their effects were only seen when pesticide exposure caused selective pressure (pp. 46–48 ) for resistance to the toxic substance.

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THE SCIENCE BEHIND THE STORY

Testing the Safety of Bisphenol A

At a laboratory at Case Western Reserve University in Ohio in 1998, geneticist Patricia Hunt was mak- ing a routine check of her female lab mice. As she extracted and examined developing eggs from the ovaries, she began to wonder what had gone wrong. About 40% of the eggs showed problems with their chromosomes, and 12% had irregular amounts of genetic material, a dangerous condition called aneuploidy, which can lead to miscar- riages or birth defects in mice and people alike.

A bit of sleuthing revealed that a lab assistant had mistakenly washed the lab’s plastic mouse cages and water bot- tles with an especially harsh soap. The soap damaged the cages so badly that parts of them seemed to have melted.

The cages were made from polycarbonate plastic, which con- tains bisphenol A (BPA). Hunt knew at the time that BPA mimics estrogen and that some studies had linked the chemical to reproductive abnormali- ties in mice, such as low sperm counts and early sexual development. Other research indicated that BPA leaches out of plastic into water and food when

the plastic is treated with heat, acidity, or harsh soap.

Hunt wondered whether the chem- ical might be adversely affecting the mice in her lab. Deciding to re-create the accidental cage-washing incident in a controlled experiment, Hunt in- structed researchers in her lab to wash polycarbonate cages and water bottles using varying levels of the harsh soap. They then compared mice kept in dam- aged cages with plastic water bottles to mice kept in undamaged cages with glass water bottles.

The developing eggs of mice ex- posed to BPA through the deliberately damaged plastic showed significant problems during meiosis, the division of chromosomes during egg forma- tion— just as they had in the original incident (first figure). In contrast, the eggs of mice in the control cages were normal.

In another round of tests, Hunt’s team gave sets of female mice daily oral doses of BPA over 3, 5, and 7 days. They observed the same meiotic abnormali- ties in these mice, although at lower lev- els (second figure). The mice given BPA for 7 days were most severely affected.

Published in 2003 in the journal Current Biology, Hunt’s findings set off a new wave of concern over the safety of bisphenol A. The findings were dis- turbing because sex cells of mice and of people divide and function in similar ways. “We have observed meiotic defects in mice at exposure levels close to or even below those considered ‘safe’ for humans,” the research paper stated. “Clearly, the possibility that BPA exposure increases the likelihood of genetically abnormal offspring is too serious to be dismissed without exten- sive further study.”

Since that time, dozens of other studies of BPA at low doses have docu- mented harmful effects in lab animals,

Dr. Patricia Hunt, Case Western Reserve University

(b)(a)

In normal cell division (a), chromo- somes (red) align properly. Exposure to bisphenol A causes abnormal cell division (b), whereby chromosomes scatter and are distributed improperly and unevenly between daughter cells.

Cascading impacts can cause changes in the composition of the biological community (p. 68) and threaten ecosystem functioning. There are many ways toxicants can concentrate and persist in ecosystems and affect ecosystem services.

Airborne substances can travel widely Toxic substances are released around the world from agricul- tural, industrial, and domestic activities and can sometimes be redistributed far from their emission site. Many chemical substances can be transported by air and exert impacts on ecosystems far from the site of their origin.

Because so many substances are carried by the wind, syn- thetic chemicals are ubiquitous worldwide, even in seemingly pristine areas. Earth’s polar regions are particularly contami- nated because natural patterns of global atmospheric circu- lation (p. 281) tend to move airborne chemicals toward the poles (FIGURE 10.7). Thus, although we manufacture and ap- ply synthetic substances mainly in temperate and tropical re- gions, contaminants are strikingly concentrated in the tissues of Arctic polar bears, Antarctic penguins, and people living in Greenland. Polychlorinated biphenyls (PCBs), which are by- products of chemicals used in transformers and other electri- cal equipment, are one such example.

Of the many studies documenting health impacts of bisphenol A on lab animals, one of the first came about because a lab assistant reached for the wrong soap.

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including not only reproductive disorders related to estrogen mimicry, but also other maladies ranging from thyroid problems to liver damage to obesity. Scientist Frederick vom Saal, whose research in 1997 had shown the first evidence for BPA’s effects, said in 2007, “This chemical is harming snails, insects, lobsters, fish, frogs, rep- tiles, birds, and rats, and the chemical industry is telling people that because you’re human, unless there’s human data, you can feel completely safe.”

Vom Saal did not have to wait long for the first human study to appear.

People with cardiovascular disease and people with diabetes show high concentrations of BPA

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Effects can also occur over relatively shorter distances. Pesticides can be carried by air currents to sites far away from agricultural fields in a process called pesticide drift. Frogs in the mountains of the Sierra Nevada, for example, have experi- enced population declines associated with pesticide drift from agriculture in California’s nearby Central Valley region.

Some toxicants persist Once a toxic substance arrives somewhere, it may degrade quickly and become harmless, or it may remain unaltered and persist for many months, years, or decades. The rate at which

a given substance degrades depends on its chemistry and on factors such as temperature, moisture, and sun exposure. The Bt toxin (p. 150) used in biocontrol and genetically modified crops has a very short persistence time, whereas chemicals such as DDT and PCBs persist for decades.

Persistent synthetic chemicals exist in our environment today because we have designed them to persist. The synthetic chemicals used in plastics, for instance, are used precisely be- cause they resist breakdown. Sooner or later, however, most toxic substances degrade into simpler compounds called breakdown products. Often these are less harmful than the original substance, but sometimes they are just as toxic as

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In this dose-response experiment, the percentage of mice showing chromosomal problems during cell division rose with increasing dose of bisphenol A. In the United States and Europe, regulators have set safe intake levels for people at doses of 50 ng/g of body weight per day. Data from Hunt, P.A., et al., 2003. Bisphenol A exposure causes meiotic aneuploidy in the female mouse. Current Biology 13: 546–553.

In 2008, the Journal of the American Medical Association published research led by Iain Lang and David Melzer of the Peninsula Medical School, Exeter, U.K. Lang and Melzer’s team took an epidemiological approach (p. 218) to assess BPA’s possible effects on peo- ple, using data from the U.S. government’s latest National Health and Nutri- tion Examination Survey. Using data from 1,455 survey participants, they attained a representa- tive sample of adults in the U.S. population. After controlling the data for race/ethnicity, education, income, smoking, body mass, and other variables, they tested for statistical correlations between a series of major health disorders and the concentration of BPA in people’s urine.

These researchers’ analyses showed that Americans with high urine BPA concentrations showed high rates of diabetes and cardiovascular disease (third figure), as well as abnormal concentrations of three liver enzymes. The team found no association with a number of other conditions such as cancer, stroke, arthritis, thyroid disease, and respiratory diseases. The researchers also explored correlations with other estrogenic compounds and found that these did not show the as- sociations that BPA showed.

Previous studies of the mechanisms by which BPA acts in cell cultures and

in rodents’ bodies helped explain how and why BPA might affect liver enzymes and diabetes. However, the reasons for cardiovascular effects remain unclear.

This first direct indication of human health impacts from BPA was a correlative study that does not es- tablish causation. To demonstrate that BPA actually causes the observed ef- fects, researchers would need to track people with low and high BPA levels for years, predict who would most likely get sick, and test these predic- tions with future data. It will take many years to complete such long-term studies. In the meantime, more and more scientists are urging regulators to restrict BPA based on the evidence already at hand.

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be transferred to other organisms as predators consume prey. When one organism consumes another, the predator takes in any stored toxicants and stores them itself. Thus bioaccumu- lation takes place on all trophic levels. Moreover, each indi- vidual predator consumes many individuals from the trophic level beneath it, so with each step up the food chain, concen- trations of toxicants become magnified. This process, called biomagnification, occurred throughout North America with DDT. Top predators, such as birds of prey, ended up with high concentrations of the pesticide because concentrations be- came magnified as DDT moved from water to algae to plank- ton to small fish to larger fish and finally to fish-eating birds (FIGURE 10.8).

Biomagnification of DDT caused populations of many North American birds of prey to decline precipitously from the 1950s to the 1970s. The peregrine falcon was almost total- ly wiped out in the eastern United States, and the bald eagle,

the original chemical, or more so. For instance, DDT breaks down into DDE, a highly persistent and toxic compound in its own right.

Toxicants may concentrate in water Toxic substances are not evenly distributed in the environ- ment, and they move about in specific ways. Runoff in water- sheds (p. 252) concentrates contaminants in small volumes of surface water. Traces of toxins, pharmaceuticals, and detoxi- fication products excreted by people can enter waters from wastewater treatment plants. Many chemicals are soluble in water and enter organisms’ tissues through drinking or ab- sorption. For this reason, aquatic animals such as fish, frogs, and stream invertebrates are effective indicators of pollution. The contaminants that wash into streams and rivers also flow and seep into the water we drink and drift in the air we breathe. Once concentrated in waters, toxicants can move long distances through aquatic systems (pp. 250–251) and af- fect a diversity of ecosystems.

Toxic substances may accumulate and move up the food chain Fat- and oil-soluble toxicants accumulate in fatty tissues in a process termed bioaccumulation, which results in the animal’s tissues having a greater concentration of the sub- stance than exists in the surrounding environment. Toxic substances that bioaccumulate in an organism’s tissues may

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FIGURE 10.8 ▲ Organisms at the lowest trophic level take in fat-soluble compounds such as DDT from water. As animals at higher trophic levels eat organisms lower on the food chain, each organism passes its load of toxicants up to its consumer, such that organisms on all trophic levels bioaccumulate the substance in their tissues. Concentrations increase at higher trophic levels by the process of biomagnification, because consumers each consume many individuals from lower trophic levels. In a classic case of biomagnification, DDT moves from zooplankton through various types of fish, becoming highly concentrated in fish-eating birds such as ospreys.

At high latitudes, deposition of pollutants exceeds evaporation

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to the laboratory to run controlled manipulative experi- ments to test their hypotheses. For instance, biologist Louis Guillette and his collaborators discovered that alligators in lakes in Florida receiving agricultural runoff had higher rates of reproductive problems than alligators in less polluted lakes (FIGURE 10.9A). Based on these field studies, he hypothesized that chemical contaminants were disrupting the endocrine systems of alligators during their development in the egg. Subsequent laboratory studies showed that contaminants

the U.S. national bird, was virtually eliminated from the low- er 48 states. Eventually scientists determined that DDT was causing these birds’ eggshells to grow thinner, so that eggs were breaking in the nest and killing the embryos within. In a remarkable environmental success story, populations of all these birds have rebounded (p. 176) since the United States banned DDT.

Effects from biomagnification still persist, though. Mer- cury bioaccumulates in some commercially important fish species, such as tuna. Polar bears of Svalbard Island in arctic Norway show extremely high levels of PCB contamination from biomagnification. Polar bear cubs suffer immune sup- pression, hormone disruption, and high mortality—and be- cause the cubs receive PCBs in their mothers’ milk, contami- nation persists and accumulates across generations.

In all these cases, biomagnification affects ecosystem composition and functioning. When populations of top pred- ators such as eagles and polar bears are reduced, species inter- actions (pp. 65–68) change, and effects cascade through food webs (pp. 70–71).

Toxic substances can threaten ecosystem services Toxicants can alter the biological composition of ecosystems and the manner in which organisms interact with one anoth- er and their environment. In so doing, harmful compounds can threaten the ecosystem services (pp. 2, 36) provided by nature. For example, pesticide exposure has been implicated as a factor in the recent declines in honeybee populations (p. 149). Honeybees pollinate over 100 economically im- portant crops, and reduced pollination by wild bees has in- creased costs for farmers by forcing them to hire professional beekeepers to pollinate their crops.

Healthy, functioning ecosystems provide the service of nutrient cycling. Decomposers and detritivores in the soil (p. 68) break down organic matter and replenish soils with nutri- ents for plants to utilize. When soils are exposed to pesticides or antifungal agents, the nutrient cycling rates are altered. This affects the quantity of nutrients available to producers, affects their growth, and produces effects throughout the ecosystem.

STUDYING EFFECTS OF HAZARDS Determining the effects of particular environmental hazards on individuals and ecosystems is a challenging job, and scientists rely on several different methods to do this, rang- ing from correlative surveys to manipulative experiments (pp. 9–10).

Wildlife studies integrate work in the field and lab Scientists study the impacts of environmental hazards on wild animals to help conserve animal populations and also to understand potential risks to people. Often wildlife toxicolo- gists work in the field with animals to take measurements, document patterns, and generate hypotheses before heading

(b) Tyrone Hayes in lab with frog

(a) Louis Guillette taking blood sample from alligator

FIGURE 10.9  Researchers Louis Guillette (a) and Tyrone Hayes (b) found that alligators and frogs, respectively, show reproduc- tive abnormalities that they attribute to endocrine disruption by pesticides.

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(a) Linear dose-response curve

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FIGURE 10.10 ▲ In a classic linear dose-response curve (a), the percentage of animals killed or otherwise affected by a substance rises with the dose. The point at which 50% of the animals are killed is labeled the lethal-dose-50, or LD50. For some toxic substances, a threshold dose (b) exists, below which doses have no measurable effect. Some substances, in particular endo- crine disruptors, show unconventional, nonlinear dose-response curves (c) that are U-shaped, J-shaped, or inverted. These curves show that organisms’ responses to toxicants may sometimes be complex.

found in alligator eggs, including the herbicide atrazine, could bind to receptors for estrogen or produce an enzyme that converts testosterone to estrogen.

Building on Guillette’s work, researcher Tyrone Hay- es (FIGURE 10.9B) found in lab experiments that male frogs raised in water containing very low doses of atrazine became feminized and hermaphroditic, developing both testes and ovaries. Field surveys then showed that leopard frogs across North America experienced hormonal problems in areas of heavy atrazine usage. These studies indicated that atrazine, which kills plants by blocking steps in photosynthesis, can also act as an endocrine disruptor in animals.

Human studies rely on case histories, epidemiology, and animal testing Environmental toxicologists also conduct epidemiological studies, large-scale comparisons among groups of people, usually contrasting a group known to have been exposed to some hazard and a group that has not. Epidemiologists track the fate of all people in the study for a long period of time (of- ten years or decades) and measure the rate at which deaths, cancers, or other health problems occur in each group. The epidemiologist then analyzes the data, looking for observa- ble differences between the groups, and statistically tests hy- potheses accounting for differences. When a group exposed to a hazard shows a significantly greater degree of harm, it suggests that the hazard may be responsible. The epide- miological process is akin to a natural experiment (p. 10), in which an event creates groups of subjects that research- ers can study (for example, people exposed to carcinogenic compounds in their drinking water versus those not simi- larly exposed).

Epidemiological studies measure a statistical association between a health hazard and an effect, but they do not con- firm that the hazard causes the effect. To establish causation, manipulative experiments are needed. However, subjecting people to massive doses of toxic substances in a lab experi- ment would clearly be unethical. This is why researchers have traditionally used laboratory strains of rats, mice, and other mammals. Experimenting with these creatures elicits fewer ethical objections in society, and because of shared evolution- ary history, substances that harm mice and rats are reasonably likely to harm us.

Dose-response analysis is a mainstay of toxicology The standard method of testing with lab animals in toxicol- ogy is dose-response analysis. Scientists quantify the toxic- ity of a substance by measuring the strength of its effects or the number of animals affected at different doses. The dose is the amount of substance the test animal receives, and the response is the type or magnitude of negative effects the ani- mal exhibits as a result. The response is generally quantified by measuring the proportion of animals exhibiting negative effects. The data are plotted on a graph, with dose on the x axis and response on the y axis (FIGURE 10.10A). The resulting curve is called a dose-response curve.

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chemicals. Mice exposed to a mixture of nitrate, atrazine, and aldicarb have been found to show immune, hormone, and nervous system effects that were not evident from exposure to each of these chemicals alone.

Traditionally, environmental health has tackled effects of single hazards one at a time. In toxicology, the complex ex- perimental designs required to test interactions, and the sheer number of chemical combinations, have meant that single- substance tests have received priority. This approach is chang- ing, but scientists in environmental health and toxicology will never be able to test all possible combinations.

Endocrine disruption poses challenges for toxicology Unconventional dose-response curves are presenting chal- lenges for scientists studying toxic substances and for policy- makers trying to set safety standards for them. Because so many novel synthetic chemicals exist in very low concentra- tions over wide areas, many scientists suspect that we may have underestimated the dangers of compounds that exert impacts at low concentrations.

Scientists first noted endocrine-disrupting effects dec- ades ago, but the idea that synthetic chemicals might be alter- ing the hormones of animals was not widely appreciated until the 1996 book Our Stolen Future, by Theo Colburn, Dianne Dumanoski, and J.P. Myers. Like Silent Spring, this book in- tegrated scientific work from various fields and presented a unified picture that shocked many readers—and brought crit- icism from some scientists and from the chemical industry.

Today, thousands of studies have linked hundreds of substances to effects on reproduction, development, im- mune function, brain and nervous system function, and other hormone-driven processes. Evidence is strongest so far in nonhuman animals, but many studies suggest impacts on people. Some researchers suggest that endocrine disruptors may account for rising rates of testicular cancer, undescended testicles, and genital birth defects in males. Others argue that the sharp rise in breast cancer rates (one in eight U.S. women today develops breast cancer) may be due to hormone disrup- tion, because an excess of estrogen appears to feed tumor de- velopment in older women. Still other scientists attribute male reproductive problems to elevated BPA exposure. For exam- ple, a 2009 study determined that workers in Chinese facto- ries that manufactured BPA had four times the rate of erectile dysfunction as workers in factories where BPA wasn’t present. A follow-up study in 2010 found that workers with detectable levels of BPA in their urine were 2–4 times more likely to have reduced sperm counts and poorer sperm quality than workers in which no BPA was detected. While the BPA exposure in these workers was far higher than that experienced by the average American, they represent some of the first studies to link bisphenol A exposure to reproductive abnormalities in humans.

Research on hormone disruption has brought about stri- dent debate. This is partly because of the scientific uncertainty inherent in any emerging field of study, but also because of the economic value of the chemicals being tested. The chemi- cal industry has generated research showing that bisphenol A

Once they have plotted a dose-response curve, toxicolo- gists can calculate a convenient shorthand gauge of a sub- stance’s toxicity: the amount of the substance it takes to kill half the population of study animals used. This lethal dose for 50% of individuals is termed the LD50. A high LD50 indicates low toxicity for a substance, and a low LD50 indicates high toxicity.

If the experimenter is interested in nonlethal health ef- fects, he or she may want to document the level of toxicant at which 50% of a population of test animals is affected in some other way (for instance, what level of toxicant causes 50% of lab mice to lose their hair?). Such a level is called the effective- dose-50%, or ED50.

Some substances can elicit effects at any concentration, but for others, responses may occur only above a certain dose, or threshold. Such a threshold dose (FIGURE 10.10B) might be expected if the body’s organs can fully metabolize or excrete a toxicant at low doses but become overwhelmed at higher concentrations. It might also occur if cells can repair damage to their DNA only up to a certain point.

Sometimes a response may decrease as a dose increases. Toxicologists are finding that some dose-response curves are U-shaped, J-shaped, or shaped like an inverted U (FIGURE 10.10C). Such counterintuitive curves contradict toxicology’s traditional assumption that “the dose makes the poison.” These unconventional dose-response curves often occur with endocrine disruptors, likely because the hormone system is geared to respond to minute concentrations of substances (normally, hormones in the bloodstream). Because the endo- crine system responds to minuscule amounts of chemicals, it may be vulnerable to disruption by contaminants that reach our bodies in very low concentrations. In research with bi- sphenol A, a number of studies with lab animals have found unconventional dose-response curves.

The shape of dose-response curves is important because estimating effects on humans often requires extrapolation— extending the dose-response curves beyond the doses tested with laboratory animals. Because these extrapolations stretch beyond the actual data obtained, they introduce uncertainty into the interpretation of what doses are safe for people. As a result, to be on the safe side, regulatory agencies set standards for maximum allowable levels of toxic substances that are well below the minimum toxicity levels estimated from lab studies.

Mixes may be more than the sum of their parts It is difficult enough to determine the impact of a single haz- ard, but the task becomes astronomically more difficult when multiple hazards interact. Chemical substances, when mixed, may act together in ways that cannot be predicted from the effects of each in isolation. Mixed toxicants may sum each other’s effects, cancel out each other’s effects, or multiply each other’s effects. Interactive impacts that are greater than the simple sum of their constituent effects are called synergistic effects.

With Florida’s alligators, lab experiments have indicated that the DDT breakdown product DDE can either help cause or inhibit sex reversal, depending on the presence of other

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one’s sensitivity to the threat. Such factors help determine the overall risk posed.

Risk can be measured in terms of probability, a quantita- tive description of the likelihood of a certain outcome. The probability that some harmful outcome (for instance, injury, death, environmental damage, or economic loss) will result from a given action, event, or substance expresses the risk posed by that phenomenon.

Our perception of risk may not match reality Every action we take and every decision we make involves some element of risk, some (generally small) probability that things will go wrong. We try in everyday life to behave in ways that minimize risk, but our perceptions of risk do not always match statistical reality (FIGURE 10.11). People often worry unduly about smaller risks yet readily engage in other activities that pose higher risks. For instance, most people perceive flying in an airplane as a riskier activity than driv- ing a car, but according to a report by the National Safety Coun- cil, a person’s chance of dying from an automobile accident in 2010 is 69 times higher than from an airplane crash. Psy- chologists agree that this difference between perception and reality stems from the fact that we feel more at risk when we are not controlling a situation and more safe when we are “at the wheel”—regardless of the actual risk involved.

This psychology may help account for people’s anxiety over exposure to BPA, nuclear power, toxic waste, and pes- ticide residues on foods—environmental hazards that are in- visible or little understood and whose presence in our lives is largely outside our personal control. In contrast, people are more ready to accept and ignore the risks of smoking ciga- rettes, overeating, and not exercising—voluntary activities statistically shown to pose far greater risks to health.

does not produce health effects, and regulatory agencies such as the FDA have relied primarily on this research in vouching for the chemical’s safety. However, independent academic sci- entists unaffiliated with industry are reaching different con- clusions. By one count through the end of 2006, 151 of the 178 published studies with lab animals reported harm from low doses of bisphenol A. Almost without exception, the studies reporting harm received public government funding, whereas those reporting no harm were funded by industry.

RISK ASSESSMENT AND RISK MANAGEMENT Policy decisions on whether to ban chemicals or restrict their use generally follow years of rigorous testing for toxicity. Likewise, strategies for combating disease and other health threats are based on extensive scientific research. However, policy and management decisions also incorporate econom- ics and ethics, and all too often these aspects are influenced by political pressure from powerful interests. The steps be- tween the collection and interpretation of scientific data and the formulation of policy involve assessing and managing risk.

We express risk in terms of probability Exposure to an environmental health threat does not in- variably produce a given effect. Rather, it causes some probability of harm, a statistical chance that damage will result. To understand a health threat, a scientist must know more than just its identity and strength. He or she must also know the chance that one will encounter it, the fre- quency with which one may encounter it, the amount of substance or degree of threat to which one is exposed, and

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FIGURE 10.11  Our perceptions of risk do not always match the reality of risk. Listed here are several leading causes of death in the United States, along with a measure of the risk each poses. Risk is measured in days of lost life expectancy, that is, the number of days of life lost by people suffering the hazard, spread across the entire population— a measure commonly used by insurance com- panies. By this measure, one common source of anxiety, airplane accidents, poses 20 times less risk than home accidents, over 50 times less risk than auto accidents, and over 200 times less risk than being overweight. Data from Cohen, B., 1991. Catalog of risks extended

and updated. Health Physics 61: 317–335.

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values. Risk managers assess costs and benefits of addressing risk in various ways, with regard to both scientific and non- scientific concerns, before making decisions on whether and how to reduce or eliminate risk.

In environmental health and toxicology, comparing costs and benefits (p. 90) can be difficult because the ben- efits are often economic, whereas the costs often pertain to health. Moreover, economic benefits are generally known, easily quantified, and of a discrete and stable amount, whereas health risks are hard-to-measure probabilities, of- ten involving a small percentage of people likely to suffer greatly and a large majority likely to experience little effect. When a government agency bans a pesticide, it may mean considerable economic loss for the manufacturer and poten- tial economic loss for the farmer, whereas the benefits accrue less predictably over the long term through healthier people, lower health care costs, and increased worker productivity. Because of the lack of equivalence in the way costs and ben- efits are measured, risk management frequently tends to stir up debate.

In the case of bisphenol A, eliminating plastic linings in our food and drink cans could do more harm than good, because the linings help prevent metal corrosion and the contamination of food by pathogens. Alternative substances exist for most of BPA’s uses, but replacing BPA with alterna- tives will entail economic costs to industry, and these costs get passed on to consumers in the prices of products. Such complex considerations can make risk management deci- sions difficult even if the science of risk assessment is fairly clear. This difficulty may help account for the hesitancy of U.S. regulatory agencies to issue restrictions on BPA so far. As of 2011, both the FDA and the EPA were continuing to review options for managing risk from BPA.

Risk assessment analyzes risk quantitatively The quantitative measurement of risk and the comparison of risks involved in different activities or substances together are termed risk assessment. Risk assessment is a way to iden- tify and outline problems. In environmental health, it helps ascertain which substances and activities pose health threats to people or wildlife and which are largely safe.

Assessing risk for a chemical substance involves several steps. The first steps involve the scientific study of toxicity we examined above—determining whether a substance has toxic effects and, through dose-response analysis, measuring how effects vary with the degree of exposure. Subsequent steps in- volve assessing the individual’s or population’s likely extent of exposure to the substance, including the frequency of contact, the concentrations likely encountered, and the length of en- counter. As discussed in the central case, risk assessments for bisphenol A by expert panels have often arrived at divergent conclusions.

Risk management combines science and other social factors Accurate risk assessment is a vital step toward effective risk management, which consists of decisions and strategies to minimize risk (FIGURE 10.12). In most nations, risk manage- ment is handled largely by federal agencies. In the United States, these agencies include the Environmental Protection Agency (EPA), the Centers for Disease Control and Preven- tion (CDC), and the Food and Drug Administration (FDA). In risk management, scientific assessments of risk are con- sidered in light of economic, social, and political needs and

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FIGURE 10.12 ▲ The first step in addressing the risk of an environmental hazard is risk assessment, a process of quantifying the risk of the hazard and comparing it to other risks. Once science identifies and measures risks, then risk management can proceed. In this process, economic, political, social, and ethical issues are considered in light of the scientific data from risk assessment. The consideration of all these types of information is intended to result in policy decisions that minimize the risk of the environmental hazard.

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Philosophical approaches are reflected in policy The choice of philosophical approach has direct implica- tions for policy, and nations vary in how they blend the two approaches. European nations have recently embarked on a

The Precautionary Principle Industry’s critics say chemical manufacturers should bear the burden of proof for the safety of their products before they hit the market. Industry’s

supporters say that mandating more safety research will hamper the introduction of products that consumers want and increase the price of products. What do you think? Should government follow the precautionary principle and require proof of safety prior to a chemical’s introduc- tion into the market?

These two approaches are actually two ends of a contin- uum of possible approaches. The two endpoints differ mainly in where they lay the burden of proof—specifically, whether product manufacturers are required to prove a product is safe or whether government, scientists, or citizens are required to prove a product is dangerous.

Two approaches exist for determining safety Because we cannot know a substance’s toxicity until we measure and test it, and because there are so many untested chemicals and combinations, science will never eliminate the many uncertainties that accompany risk assessment. In such a world of uncertainty, there are two basic philosophical approaches to categorizing substances as safe or dangerous (FIGURE 10.13).

One approach is to assume that substances are harm- less until shown to be harmful. We might nickname this the “innocent-until-proven-guilty” approach. Because thor- oughly testing every existing substance (and combination of substances) for its effects is a hopelessly long, complicated, and expensive pursuit, the innocent-until-proven-guilty ap- proach has the virtue of facilitating technological innovation and economic activity. However, it has the disadvantage of putting into wide use some substances that may later turn out to be dangerous.

The other approach is to assume that substances are harmful until shown to be harmless. This approach follows the precautionary principle (p. 152). This more cautious ap- proach should enable us to identify troublesome toxicants be- fore they are released into the environment, but it may also impede the pace of technological and economic advance.

Sequence of events

Pre-market testing by industry, government,

and academic scientists

Industrial research and development

Consumer use of products

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Consumer use of safe products

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Rigorous testing demanded Limited testing required

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Limited testing; most products brought to market

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“Innocent-until-proven- guilty” approach

Precautionary principle approach

FIGURE 10.13  Two main approaches can be taken to introduce new substances to the market. In one approach, substances are “innocent until proven guilty”; they are brought to market relatively quickly after limited testing. Products reach consumers more quickly, but some frac- tion of them (blue bottle in diagram) may cause harm to some fraction of people. The other approach is to adopt the precautionary princi- ple, bringing substances to market cautiously, only after extensive testing. Products that reach the market should be safe, but many perfectly safe products (purple bottle in diagram) will be delayed in reaching consumers.

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➤ CONCLUSION

marketed in the United States are not guaranteed to be free of toxic substances, so consumer choice is especially important.

Toxicants are regulated internationally The European Union is taking the world’s boldest step toward testing and regulating manufactured chemicals. In 2007, the EU’s REACH program went into effect (REACH stands for Registration, Evaluation, Authorization, and restriction of CHemicals). REACH largely shifts the burden of proof for testing chemical safety from national governments to industry and requires that chemical substances produced or imported in amounts of over 1 metric ton per year be registered with a new European Chemicals Agency. It is expected that REACH will require the registration of about 30,000 substances. In an impacts assessment in 2003, EU commissioners estimated that REACH will cost the chemical industry and chemical us- ers 2.8–5.2 billion euros (US $3.8–7.0 billion) over 11 years but that the health benefits to the public would be roughly 50 billion euros (US $67 billion) over 30 years. Changes in the program since then have made the predicted cost-to-benefit ratio even better.

The world’s nations have also sought to address chemical pollution with international treaties. The Stockholm Conven- tion on Persistent Organic Pollutants (POPs) came into force in 2004 and has been ratified by over 150 nations. POPs are toxic chemicals that persist in the environment, bioaccumulate and biomagnify up the food chain, and often can travel long distances. The PCBs and other contaminants found in polar bears are a prime example. Because contaminants often cross international boundaries, an international treaty seemed the best way to deal fairly with such transboundary pollution. The Stockholm Convention aims first to end the use and release of 12 POPs shown to be most dangerous, a group nicknamed the “dirty dozen.” It sets guidelines for phasing out these chemi- cals and encourages transition to safer alternatives.

policy course that incorporates the precautionary principle, whereas the United States largely follows an innocent-until- proven-guilty approach.

In the United States, several federal agencies are assigned responsibility for tracking and regulating synthetic chemicals under various legislative acts. The FDA, under an act first passed in 1938, monitors foods and food additives, cosmetics, drugs, and medical devices. The EPA regulates pesticides under a 1947 act and its amendments. The Occupational Safety and Health Administration (OSHA) regulates workplace hazards under a 1970 act. Several other agencies regulate other substances. Syn- thetic chemicals not covered by other laws are regulated by the EPA under the 1976 Toxic Substances Control Act (TSCA).

EPA regulation is only partly effective The Toxic Substances Control Act (TSCA) directs the EPA to monitor the roughly 83,000 industrial chemicals manu- factured in or imported into the United States, ranging from PCBs to lead to bisphenol A. The act gives the agency power to regulate these substances and ban them if they are found to pose excessive risk.

However, many public health advocates view TSCA as being far too weak. They note that the screening required of industry is minimal and that to mandate more extensive and meaningful testing, the EPA must show proof of the chemical’s toxicity. In other words, the agency is trapped in a Catch-22: To push for studies looking for toxicity, it must have proof of toxicity already. The result is that most synthetic chemicals are not thoroughly tested before being brought to market. Of those that fall under TSCA, only 10% have been thoroughly tested for toxicity; only 2% have been screened for carcinogenicity, mutagenicity, or teratogenicity; fewer than 1% are regulated; and almost none have been tested for en- docrine, nervous, or immune system damage, according to the U.S. National Academy of Sciences. As a result, products

International agreements such as REACH and the Stockholm Convention represent a sign that governments may act to pro- tect the world’s people, wildlife, and ecosystems from toxic substances and other environmental hazards. At the same time, solutions often come more easily when they do not arise from government regulation alone. Consumer choice exercised through the market can often be an effective way to influence industry’s decision making. Consumers of products, from plastics to pesticides to cosmetics to kids’ toys, can make deci- sions that influence industry when they have full information from scientific research regarding the risks involved. Once sci- entific results are in, a society’s philosophical approach to risk management will determine what policy decisions are made.

Whether the burden of proof is laid at the door of in- dustry or of government, we will never attain complete sci- entific knowledge of any risk. Rather, we must make choices based on the information available. Synthetic chemicals have brought us innumerable modern conveniences, a larger food supply, and medical advances that save and extend hu- man lives. Human society would be very different without them. Yet a better future, one that safeguards the well-being of both people and the environment, depends on knowing the risks that some hazards pose and on having in place the means to phase out harmful substances and replace them with safer ones.

health experts study to learn how diseases affect human health?

3. Where does most exposure to lead, asbestos, radon, and PBDEs occur?

1. What are the four major types of environmental health hazards?

2. In what way is disease the greatest hazard that people face? What kinds of interrelationships must environmental

T E S T I N G Y O U R C O M P R E H E N S I O N

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Annual pesticide use (pounds of active ingredients)

You

Your class

Your state

United States 1.20 billion World (total) 5.05 billion World (per capita)

Go to www.masteringenvironmentalscience.com for homework assignments, practice quizzes, Pearson eText, and more.

S E E K I N G S O L U T I O N S 1. Describe some environmental health hazards that you

think you may be living with indoors. How do you think you may have been affected by indoor or outdoor haz- ards in the past? How could you best deal with these haz- ards in the future?

2. Do you feel that laboratory animals should be used in experiments in toxicology? Why or why not?

3. Describe differences in the policies of the United States and the European Union toward the study and manage- ment of the risks of synthetic chemicals. Which do you believe are better, the policies of the United States or those of the European Union? Why?

4. THINK IT THROUGH You are the parent of two young children, and you want to minimize the environmental

health risks your kids are exposed to. Name five steps that you could take in your household and in your daily life that would accomplish your goal.

5. THINK IT THROUGH You work for a public health organization and have been asked to educate the public about bisphenol A and to suggest ways to minimize ex- posure to the chemical. You begin by examining your lifestyle and finding ways to use alternatives to BPA-con- taining products. Create a list of five ways you are exposed daily to bisphenol A, and then list approaches that would avoid or minimize these exposures. Do these steps require more time and/or money? What are some costs of em- bracing these changes? What would you tell an interested person about bisphenol A as it relates to human health?

C A L C U L A T I N G E C O L O G I C A L F O O T P R I N T S In 2001, the last year the EPA gathered and reported data on pesticide use, Americans used 1.20 billion pounds of pesti- cide active ingredients, and world pesticide use totaled 5.05 billion pounds of active ingredients. In that same year, the U.S. population was 285 million, and the world’s population totaled 6.16 billion. Pesticides include hundreds of chemicals used by farmers, governments, industries, and individuals to control “pest” organisms. In the table, calculate your share of pesticide use as a U.S. citizen in 2001 and the amount used by (or on behalf of) the average citizen of the world.

1. What is the ratio of your annual pesticide use to the world’s per capita average?

2. In 2007, the average U.S. citizen had an ecological foot- print of 8.0 hectares and the average world citizen’s foot- print was 2.7 hectares (Chapter 1). Compare the ratio of pesticide usage with the ratio of the overall ecological footprints. How do these differ, and how would you ac- count for the difference?

3. Does the per capita pesticide use for you as a U.S. citizen seem reasonable for you personally? Why or why not? Do you find this figure alarming, or of little concern? What else would you like to know to assess the risk associated with this level of pesticide use?

4. List and describe the general categories of toxic sub- stances described in this chapter.

5. Explain the mechanisms found in organisms that protect them from damage from toxic substances.

6. How do toxic substances travel through the environ- ment, and where are they most likely to be found? De- scribe and contrast the processes of bioaccumulation and biomagnification.

7. What are epidemiological studies, and how are they most often conducted?

8. Explain the dose-response curve. Why is a substance with a high LD50 considered safer than one with a low LD50?

9. What factors may affect an individual’s response to a toxic substance? Why is chronic exposure to toxic agents often more difficult to measure and diagnose than acute exposure?

10. How do scientists identify and assess risks from sub- stances or activities?

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Geology, Minerals, and Mining Upon completing this chapter, you will be able to:

� Describe Earth’s internal structure and explain how plate tectonics shapes its surface � Identify the categories of rocks and explain how the rock cycle shapes the landscape around us and the earth

beneath our feet � List the major types of geologic hazards and describe ways to reduce their impacts � Outline types of mineral resources and how they contribute to our products and society � Describe the major methods of mining � Characterize the environmental and social impacts of mining � Assess reclamation efforts and mining policy � Evaluate ways to encourage the sustainable use of mineral resources

Coltan miners in eastern Congo

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AFRICA

Atlantic Ocean

Indian Ocean

Democratic Republic of the Congo

Region of coltan mining

Half a world away, a dirt- poor miner in the heart of Africa toils all day in a jungle streambed, sifting sediment for nuggets of coltan ore, which contain tantalum. At nightfall, rebel soldiers take most of his ore, leaving him to sell what little remains to buy food for his family at the squalid mining camp where they live.

In bedeviling ways, tan- talum links our glossy global high-tech economy with one of the most badly wrecked regions on Earth. The Democratic Republic of the Congo has been em- broiled in a sprawling conflict that has involved six na- tions and various rebel militias. Over 5 million people have lost their lives in this war since 1998. It is the lat- est chapter in the sad history of a nation rich in natu- ral resources—copper, cobalt, gold, diamonds, ura- nium, and timber—whose impoverished people keep losing control of those resources to others.

At the center of the recent conflict is tantalum (Ta), element number 73 on the Periodic Table (APPEN- DIX C). We rely on this metal for our cell phones, com- puter chips, DVD players, game consoles, and digital cameras. Tantalum powder is ideal for capacitors (the components that store energy and regulate current in miniature circuit boards) because it is highly heat resistant and readily conducts electricity.

Tantalum comes from a dull blackish mineral called tantalite, which often occurs with a min- eral called columbite—so the ore is referred to as

columbite-tantalite, or coltan for short. In eastern Congo, men dig craters in rainforest streambeds, panning for col- tan much as early California miners panned for gold.

As information technol- ogy boomed in the late 1990s, global demand for tantalum rose, and market prices for the metal shot up to $500/kg ($230/lb) in 2001. High prices led some Congolese men to mine coltan by choice, but many more were forced into it.

In 1998, local militias, supported by forces from neighboring Rwanda and Uganda, overran eastern Congo. Farmers were chased off their land, villages were burned, and civilians were terrorized. Soldiers from each army seized control of mining operations. They forced farmers, refugees, prisoners, and chil- dren to work, and the soldiers skimmed profits from the coltan the people mined. Children and teachers abandoned school and worked in the mines. The turmoil also caused ecological havoc as miners and soldiers streamed into national parks, clearing rain- forests and killing wildlife for food, including forest elephants, hippopotamuses, endangered gorillas, and the okapi, a rare relative of the giraffe.

Most miners ended up with little, while rebels, soldiers, and bandits enriched themselves by selling coltan to traders, who sold it to processing compa- nies in Europe and the United States. These com- panies refine and sell tantalum powder to capacitor manufacturers, which in turn sell capacitors to Nokia,

CENTRAL CASE STUDY

Mining for . . . Cell Phones? “The conflict in the Democratic Republic of the Congo has become mainly about access, control, and trade of five

key mineral resources: coltan, diamonds, copper, cobalt, and gold.” —Report to the United Nations Security Council, April 

“Coltan . . . is not helping the local people. In fact, it is the curse of the Congo.” —African journalist Kofi Akosah-Sarpong

P ulling a cell phone from her pocket, a student on a college campus in the United States

dials a friend. Inside her phone is a little-known metal called tantalum—just a tiny

amount, but no cell phone could operate without it.

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Oceanic crust Continental crust

Uppermost mantle

Lithosphere

~100 km (62 mi)

~250 km (155 mi)

Asthenosphere Upper mantle

Upper mantle Crust

Lower mantle

Outer core

Inner core

6,370 km (3,950 mi)

5,150 km (3,190 mi)

2,900 km (1,800 mi)

~600 km (370 mi)

FIGURE 11.1  Earth’s three primary layers—core, mantle, and crust—are themselves layered. The inner core of solid iron is sur- rounded by an outer core of molten iron, and the rocky mantle includes the molten asthenosphere near its upper edge. At Earth’s surface, dense and thin oceanic crust abuts lighter, thicker continen- tal crust. The lithosphere consists of the crust and the uppermost mantle above the asthenosphere.

Motorola, Sony, Intel, Compaq, Dell, and other high- tech corporations.

In 2001, an expert panel commissioned by the United Nations Security Council concluded that col- tan riches were fueling, financing, and prolonging the war. The panel urged a U.N. embargo on coltan and other minerals smuggled from Congo and exported by neighboring nations. A grass-roots activist movement advanced the slogan, “No blood on my cell phone!”

Sony, Nokia, Ericsson, and other corporations rushed to assure consumers that they were not using tantalum from eastern Congo—and the region was, in fact, producing less than 10% of the world’s sup- ply. Meanwhile, some observers felt an embargo could hurt the long-suffering Congolese people, rather than help them. The mining life may be miserable, but it pays better than most alternatives in a land where the average income is 20 cents a day.

Soon, however, the high-tech boom went bust, and global demand for tantalum diminished. This occurred just as Australia and other countries were ramping up industrial-scale tantalite mining. As supply outpaced demand, the market price of tantalum fell, and sever- al major producers quit mining tantalum. But nations began to work through their stockpiles, and by 2010 demand had grown, driving prices up once again.

Today, foreign troops are out of Congo, but inter- nal factions still fight viciously over these resources and thousands of people continue to die or to flee their homes. Western electronics companies avoid knowingly purchasing tantalum from Congo, but as a result, much of it ends up being sold to China. In 2010 the U.S. Congress included in its financial reform bill an amendment requiring all electronics companies to report the origin of the tantalum in the products they sell. Yet the trade has so many middlemen and so little transparency that companies will find it very difficult to determine where their tantalum actually comes from.

In the meantime, some Congolese men are return- ing to the coltan mines, while others mine for tin, cop- per, or cobalt. Similar stories are playing out with these and other “conflict minerals” that we in more wealthy nations put to use in our products every day. �

damaging, we first need a working knowledge of some of the physical processes that shape our planet.

Our planet is dynamic, and this is what motivates geology, the study of Earth’s physical features, processes, and history. A human lifetime is just a blink of an eye in the long course of geologic time, and the Earth we experience is merely a snapshot in our changing planet’s long history. We can be- gin to grasp this long-term dynamism as we consider two pro- cesses of fundamental importance to geology—plate tectonics and the rock cycle.

Earth consists of layers Most geologic processes take place near Earth’s surface, but our planet consists of multiple layers (FIGURE 11.1). At Earth’s center is a dense core consisting mostly of iron, solid in the inner core and molten in the outer core. Surrounding the core is a thick layer of dense, elastic rock called the mantle. A por- tion of the upper mantle called the asthenosphere contains especially soft rock, melted in some areas. The harder rock above the asthenosphere is what we know as the lithosphere. The lithosphere includes both the uppermost mantle and

GEOLOGY: THE PHYSICAL BASIS FOR ENVIRONMENTAL SCIENCE Coltan provides just one example of how we extract raw ma- terials from beneath our planet’s surface and turn them into products we use in our everyday lives. To understand the en- vironmental impacts of extracting resources from the earth, and the many ways we can make mineral extraction less

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Juan de Fuca Plate

San Andreas Fault

North American Plate

Eurasian Plate

Arabian Plate

Philippine Plate

Pacific Plate

Caroline Plate

Indian- Australian Plate

Caribbean Plate

Cocos Plate

Pacific Plate

Nazca Plate

Antarctic Plate

Scotia Plate

South American Plate

African Plate

Mid-Atlantic Ridge

Divergent boundary

Transform fault boundary

Convergent boundary

P A N G A E A

Andes M ou ntains

Ap pa

lac hi

M ou

nt ain

Himalaya Mountains

FIGURE 11.2  Earth’s crust consists of roughly 15 major plates (above) that move very slowly by the process of plate tectonics. Today’s continents were joined together in the landmass Pangaea (left) about 225 million years ago.

the entirety of Earth’s third major layer, the crust—the thin, brittle, low-density layer of rock that covers Earth’s surface. The intense heat in the inner Earth drives convection cur- rents that flow in loops in the mantle, pushing the mantle’s soft rock cyclically upward (as it warms) and downward (as it cools), like a gigantic conveyor belt system. As the man- tle material moves, it drags large plates of lithosphere along its surface. This movement of lithospheric plates is known as plate tectonics, a process of extraordinary importance to our planet.

Plate tectonics shapes Earth’s geography Our planet’s surface consists of about 15 major tectonic plates, which fit together like puzzle pieces (FIGURE 11.2). Imagine peeling an orange and then placing the pieces of peel back onto the fruit; the ragged pieces of peel are like the tectonic plates riding atop Earth’s surface. However, the plates are

thinner relative to the planet’s size, more like the skin of an apple. These plates move at rates of roughly 2–15 cm (1–6 in.) per year. This slow movement has influenced Earth’s climate and life’s evolution throughout our planet’s history as the con- tinents combined, separated, and recombined in various con- figurations. By studying ancient rock formations throughout the world, geologists have determined that at least twice, all landmasses were joined together in a “supercontinent.” Sci- entists have dubbed the one that occurred about 225 million years ago Pangaea (see Figure 11.2).

There are three types of plate boundaries The processes that occur at the boundaries between plates have major consequences. We can categorize plate bounda- ries into three types.

At divergent plate boundaries, tectonic plates push apart from one another as magma (rock heated to a molten,

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liquid state) rises upward to the surface, creating new crust as it cools (FIGURE 11.3A). An example is the Mid-Atlantic Ridge, a 16,000-km (10,000-mi) plate boundary that extends from the Arctic Ocean to the southern tip of Africa in the At- lantic Ocean.

Where two plates meet, they may slip and grind along- side one another, forming a transform plate boundary (FIGURE 11.3B). This movement creates friction that generates earthquakes (p. 231) along strike-slip faults. Faults are frac- tures in Earth’s crust, and at strike-slip faults each landmass moves horizontally in opposite directions. The Pacific Plate and the North American Plate rub against one another along California’s San Andreas Fault. Southern California is slowly inching its way toward northern California along this fault, and the site of Los Angeles will eventually reach that of San Francisco.

When plates collide at convergent plate boundaries, either of two consequences may result (FIGURE 11.3C). In the first case, one plate may slide beneath another in a process called subduction. The subducted plate is heated and pres- surized as it dives into the mantle, and water vapor escapes, helping to melt rock above the sinking plate (by lowering its melting temperature). The molten rock rises and may erupt through the surface at volcanoes (pp. 232–233).

Oceanic crust is denser than continental crust, so at sub- duction zones, oceanic crust generally slides beneath conti- nental crust, leading to the formation of volcanic mountain ranges that parallel coastlines. The Cascades, where Mount Saint Helens in Washington (p. 283) erupted violently in 1980 and renewed its activity in 2004, are fueled by magma from subduction. South America’s Andes Mountains (where the Nazca Plate slides beneath the South American Plate) provide another example. When one plate of oceanic crust is subducted beneath another plate of oceanic crust, the result- ing volcanism may form arcs of islands, such as Japan and the Aleutians. This may also create deep trenches, such as the Mariana Trench, our planet’s deepest abyss.

Alternatively, when two plates of continental crust col- lide, this collision may lift material from both plates. The Himalayas, the world’s highest mountains, result from the Indian-Australian Plate’s collision with the Eurasian Plate beginning 40–50 million years ago, and these mountains are still being uplifted today as these plates converge. The Ap- palachian Mountains of the eastern United States, once the world’s highest mountains themselves, result from a more an- cient collision with the edge of what is now Africa.

Tectonics creates Earth’s landforms In these ways, the processes of plate tectonics build moun- tains; shape the geography of oceans, islands, and continents; and give rise to earthquakes and volcanoes. The coltan min- ing areas of eastern Congo are situated along the western edge of Africa’s Great Rift Valley system, a region where the African plate is slowly pulling itself apart. Some of the world’s largest lakes have formed in the immense valley floors, far below towering volcanoes such as Mount Kilimanjaro.

Topography created by tectonic processes, in turn, shapes climate by altering patterns of rainfall, wind, ocean currents, and heating and cooling, all of which affect rates of weathering and erosion and the ability of plants and animals to inhabit different regions. Thus, plate tectonics influences the loca- tions of biomes (pp. 78–84). Moreover, tectonics has affected the history of life’s evolution; for instance, the convergence of landmasses into supercontinents is thought to have helped bring about widespread extinctions by limiting the extent of species-rich coastal areas and by creating an arid continental interior with extreme temperature swings.

Only in the last several decades have scientists learned about plate tectonics—this environmental system of such fun- damental importance was completely unknown to humanity just half a century ago. Amazingly, our civilization was send- ing people to the moon by the time our geologists were ex- plaining the movement of land under our very feet.

Oceanic crust

Oceanic lithosphere

Asthenosphere

Oceanic lithosphere

Subduction Magma

Continental crust

Continental lithosphere

Continental lithosphereVolcano

(a) Divergent plate boundary (b) Transform plate boundary (c) Convergent plate boundary

Rift Strike-slip faultRidge

Trench

Magma

Collision mountains

FIGURE 11.3  Different types of boundaries between tectonic plates generate different geologic processes. At a divergent plate boundary, such as a mid-ocean ridge on the seafloor (a), the two plates move gradually away from the boundary in the manner of conveyor belts, and magma from beneath the crust may extrude as lava. At a trans- form plate boundary (b), two plates slide alongside one another, creating friction that leads to earthquakes. Where plates collide at a convergent plate boundary (c), one plate is subducted beneath another, leading to volcanism. If continental crust from two plates collides, the buckling of rock can form mountain ranges.

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The rock cycle alters rock We tend to think of rock as pretty solid stuff. Yet in the long run, over geologic time, rocks and the minerals that com- prise them are heated, melted, cooled, broken down, and reassembled in a very slow process called the rock cycle (FIGURE 11.4).

A rock is any solid aggregation of minerals. A mineral, in turn, is any naturally occurring solid element or inorganic compound with a crystal structure, a specific chemical com- position, and distinct physical properties. The type of rock in a given region affects soil characteristics and thereby in- fluences the region’s plant community. Understanding the rock cycle enables us to better appreciate the formation and conservation of soils, mineral resources, fossil fuels, and other natural resources.

Igneous rock All rocks can melt. At high enough tem- peratures, rock will enter a molten, liquid state called mag- ma. If magma is released through the lithosphere (as in a volcanic eruption), it may f low or spatter across Earth’s sur- face as lava. Rock that forms when magma or lava cools is called igneous (from the Latin ignis, meaning “fire”) rock (FIGURE 11.4A).

Sedimentary rock All exposed rock weathers away with time. The relentless forces of wind, water, freezing, and thawing eat away at rocks, stripping off one tiny grain (or large chunk) after another. Through weathering (p. 137) and

Melting

Magma and lava

Heating and pressure

Weathering, erosion, transport, deposition

Lithification

(a) Igneous rock

(b) Sedimentary rock

Sediments

Cooling and crystallization

Heating and p

ressu re

Weathering, erosion, transport, deposition W

ea the

rin g, e

rosio n,

tra ns

po rt,

dep osit

ion

FIGURE 11.4  In the rock cycle, igneous rock (a) is formed when rock melts and the resulting magma or lava then cools. Sedimentary rock (b) is formed when rock is weathered and eroded and the result- ing sediments are compressed to form new rock. Metamorphic rock (c) is formed when rock is subjected to intense heat and pressure underground. Through these processes (shown by arrows of different colors), each type of rock can be convert- ed into either of the other two types.

erosion (p. 140), particles of rock blown by wind or washed away by water come to rest downhill, downstream, or down- wind from their sources, eventually forming sediments. Al- ternatively, some sediments form not from the physical ero- sion and accumulation of rock particles, but chemically from the precipitation of substances out of solution. Sediment lay- ers accumulate over time, causing the weight and pressure of overlying layers to increase. Sedimentary rock (FIGURE 11.4B) is formed as sediments are physically pressed together and as dissolved minerals seep through sediments and act as a kind of glue, binding sediment particles.

Processes of physical compaction and chemical trans- formation in sedimentary layers also create the fossils of organisms (p. 50) and the fossil fuels we use for energy (pp. 328–336). Because sedimentary layers, or strata, pile up in chronological order, geologists and paleontologists can assign relative dates to fossils they find in sedimentary rock. By study- ing evidence from sedimentary rock, scientists can thereby make inferences about Earth’s history.

Metamorphic rock Geologic forces may bend, uplift, compress, or stretch rock. When rock is subjected to great heat or pressure, it may alter its form, becoming metamorphic (from the Greek for “changed form”) rock (FIGURE 11.4C). The forces that metamorphose rock generally occur deep underground, at temperatures lower than the rock’s melting point but high enough to change its appearance and physical properties.

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GEOLOGIC AND NATURAL HAZARDS Plate tectonics gives rise to creative forces that shape our planet, but some of the consequences of tectonic move- ment can also pose hazards to us. Earthquakes and volcanic eruptions are examples of such geologic hazards. We can see how such hazards relate to tectonic processes by examining a map of the circum-Pacific belt, or so-called “ring of fire” (FIGURE 11.5). Nine out of 10 earthquakes and over half the world’s volcanoes occur along this 40,000-km (25,000-mi) arc of subduction zones and fault systems.

Earthquakes result from movement at plate boundaries and faults Along tectonic plate boundaries, and in other places where fractures in Earth’s crust known as faults occur, the earth may relieve built-up pressure in fits and starts. Each re- lease of energy causes what we know as an earthquake. Most earthquakes are barely perceptible, but occasionally they are powerful enough to do tremendous damage to hu- man life and property (FIGURE 11.6, TABLE 11.1). Damage is generally greatest where soils are loose or saturated with water; areas of cities built atop landfill are particularly susceptible.

To minimize damage from earthquakes, engineers have developed ways to protect buildings from shaking. They do this by strengthening structural components while also de- signing points at which a structure can move and sway harm-

lessly with ground motion. Just as a flexible tree trunk bends in a storm while a brittle one breaks, buildings with built- in flexibility are more likely to withstand an earthquake’s violent shaking. Such designs are an important part of new building codes in California, Japan, and other quake-prone regions, and many older structures are being retrofitted to meet these codes.

Mt. Pinatubo

Mariana Trench

Japan AleutianIslands

San Andreas fault

Mt. Fuji Mt. St. Helens

Mt. Krakatoa

Mt. Tambora

Mt. Mayon

Mt. Kilauea Mt. Mauna Loa

Mt. Rainier

Mt. Lassen Mt. Popocatepetl

Mt. Cotopaxi

Note how the ring of fire matches patterns of some of the plate boundaries in Figure 11.2

FIGURE 11.5  Most of our planet’s volcanoes and earthquakes occur along the circum-Pacific belt, or “ring of fire,” the system of subduction zones and other plate boundaries that encir- cles the Pacific Ocean. In this map, red symbols indicate major volcanoes, and gray- shaded areas indicate areas of greatest earthquake risk. Compare the distribution of these hazards with the tec- tonic plate boundaries shown in Figure 11.2.

FIGURE 11.6  The 2010 earthquake in Haiti devastated the capital city of Port-au-Prince and killed an estimated 230,000 people. One reason for the high number of fatalities was that many of Haiti’s buildings were not constructed to withstand earthquakes. The structural damage in Japan from a much larger earthquake in early 2011 was less extensive than that seen in Haiti, due to more stringent building codes for earthquake resistance.

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Volcanoes arise from rifts, subduction zones, or hot spots Where molten rock, hot gas, or ash erupts through Earth’s surface, it forms a volcano, which can create a mountain over time as cooled lava accumulates. As we have seen, lava can extrude in rift valleys and along mid-ocean ridges, or over subduction zones as one tectonic plate dives beneath another. Lava may also be emitted at “hot spots,” localized areas where plugs of molten rock from the mantle erupt through the crust. As a tectonic plate moves across a hot spot, repeated eruptions from this source may create a linear series of vol- canoes. The Hawaiian Islands are an example of this process (FIGURE 11.7A).

At some volcanoes, lava flows slowly downhill, such as at Mount Kilauea in Hawaii (FIGURE 11.7B), which has been erupting continuously since 1983! Other times, a volcano may let loose large amounts of ash and cinder in a sudden explo- sion, such as during the 1980 eruption of Mount Saint Helens (p. 283). And sometimes a volcano can unleash a pyroclastic flow—a fast-moving cloud of toxic gas, ash, and rock frag- ments that races down the slopes, enveloping everything in its path. Such a flow buried the inhabitants of the ancient Roman cities of Pompeii and Herculaneum in A.D. 79, when Mount Vesuvius erupted.

Volcanic eruptions also exert environmental impacts (TABLE 11.2). Ash blocks sunlight, and sulfur emissions lead to a sulfuric acid haze that blocks radiation and cools the atmo- sphere. Large eruptions—such as that of Mount Pinatubo in

TABLE 11.1 Examples of Large or Recent Earthquakes

Location Year Fatalities Magnitude1

Shaanxi Province, China 1556 830,000 ~8

Lisbon, Portugal 1755 70,0002 8.7

San Francisco, California

1906 3,000 7.8

Kwanto, Japan 1923 143,000 7.9

Anchorage, Alaska 1964 1282 9.2

Tangshan, China 1976 255,000+ 7.5

Michoacán, Mexico 1985 9,500 8.0

Loma Prieta, California 1989 63 6.9

Northridge, California 1994 60 6.7

Kobe, Japan 1995 5,502 6.9

Northern Sumatra 2004 228,0002 9.1

Kashmir, Pakistan 2005 86,000 7.6

Sichuan Province, China

2008 50,000+ 7.9

Port-au-Prince, Haiti 2010 236,000 7.0

Maule, Chile 2010 500 8.8

Tohoku, Japan 2011 23,6002,3 9.0 1 Measured by moment magnitude; each full unit is roughly 32 times as

powerful as the preceding full unit. 2 Includes deaths from resulting tsunami. 3 Includes people missing and presumed dead.

Pacific Ocean

CANADA

UNITED

MEXICO

ALASKA

RUSSIA

Present-day Hawaiian Islands

Older submerged Islands

Midway Is.

(a) Current and former Hawaiian islands, formed as crust moves over a volcanic hot spot

(b) Mt. Kilauea erupting

Laysan Is.

This location on the crust was over the hot spot 60 million years ago.

This location on the crust is over the hot spot today.

STATES

D irection of plate m

ovement

(Islands get older)

FIGURE 11.7  The Hawaiian Islands (a) have been formed by repeated eruptions from a hot spot of magma in the mantle as the Pacific Plate passes over the hot spot. The Big Island of Hawaii is most recently formed, and it is still volcanically active. The other islands are older and have already begun eroding away. To their northwest stretches a long series of former islands, now submerged. In the future, a new island will one day rise above the sea to the southeast of today’s Big Island. The active volcano Kilauea (b), on the Big Island’s southeast coast, is the youngest of Hawaii’s volcanoes, currently located above the edge of the hot spot.

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the Philippines in 1991—can depress temperatures through- out the world. When Indonesia’s Mount Tambora erupted in 1815, it cooled the planet enough over the following year to cause crop failures worldwide and make 1816 “the year with- out a summer.”

Landslides are a form of mass wasting At a smaller scale than volcanoes or earthquakes, a landslide occurs when large amounts of rock or soil collapse and flow downhill. Landslides are severe, and often sudden, manifes- tations of the more general phenomenon of mass wasting, the downslope movement of soil and rock due to gravity. Mass wasting occurs naturally, but often it is brought about by human land use practices that expose or loosen soil, mak- ing slopes more prone to collapse. Heavy rains may saturate soils and trigger mudslides of soil, rock, and water.

Most often, mass wasting eats away at unstable hillsides, damaging property one structure at a time (FIGURE 11.8). Occasionally mass wasting events can be colossal and deadly; mudslides that followed the torrential rainfall of Hurricane Mitch in Nicaragua and Honduras in 1998 killed over 11,000 people. Mudslides caused when volcanic eruptions melt snow and send huge volumes of destabilized mud racing downhill are called lahars, and they are particularly dangerous. A lahar buried the entire town of Armero, Colombia, in 1985 follow- ing an eruption, killing 21,000 people.

Tsunamis can follow earthquakes, volcanoes, or landslides Earthquakes, volcanic eruptions, and large coastal landslides can all displace huge volumes of ocean water instantaneously and trigger a tsunami, an immense swell, or wave, of water that can travel thousands of miles across oceans. The world’s

attention was drawn to this hazard on December 26, 2004, when a massive tsunami, triggered by an earthquake off Su- matra, devastated coastlines all around the Indian Ocean, from Indonesia to India to Africa. Roughly 230,000 people were killed, 1–2 million were displaced, and whole communi- ties were destroyed.

More recently, a tsunami generated by an offshore earth- quake devastated large portions of northeastern Japan on March 11, 2011 (FIGURE 11.9). The tsunami and earthquake killed more than 23,000 people, caused over $300 billion in economic impacts, and contributed to the release of radioactive material from the Fukushima nuclear power plant (p. 349).

TABLE 11.2 Examples of Notable Volcanic Eruptions

Location Year Impacts Magnitude

Yellowstone Caldera, Wyoming, U.S. 640,000 B.P.1 Most recent “mega-eruption” at site of Yellowstone National Park 8

Mount Mazama, Oregon, U.S. 6,870 B.P. Created Crater Lake 7

Mount Vesuvius, Italy A.D. 79 Buried Pompeii and Herculaneum 5

Mount Tambora, Indonesia 1815 Created “year without a summer”; killed at least 70,000 people 7

Krakatau, Indonesia 1883 Killed over 36,000 people; heard 5,000 km (3,000 mi) away; affected weather for 5 years 6

Mount Saint Helens, Washington, U.S. 1980 Blew top off mountain; sent ash 19 km (12 mi) into sky and into 11 U.S. states; 57 people killed 5

Kilauea, Hawaii 1983–present Continuous lava flow 1

Mount Pinatubo, Philippines 1991 Sulfuric aerosols lowered world temperature 0.5 °C (0.9 °F) 6

Eyjafjallajokull, Iceland 2010 Ash cloud disrupted air travel throughout Europe 1 1B.P. = years before the present. 2Measured by the Volcanic Explosivity Index, which ranges from 0 (least powerful) to 8 (most powerful).

FIGURE 11.8  Landslides are a frequent occurrence in sloping areas along the California coast, particularly after heavy winter rains saturate soils. Homes built on unstable slopes, such as these in Laguna Beach, Orange County, can be damaged or destroyed when slopes give way.

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FIGURE 11.9  The tsunami on March 11, 2011, destroyed entire coastal com- munities in northeastern Japan. Waves up to 10 m (30 ft) high battered the coastline and penetrated up to 9.6 km (6 mi) inland. In this photo, the mas- sive swell crashes over dikes that were thought to be high enough to offer protection.

Those of us who live in the United States and Canada should not consider tsunamis to be something that occurs only in faraway places. The 2011 tsunami from Japan crossed the Pacific and caused some damage and one death in Cali- fornia and Oregon. A large tsunami struck North America’s Pacific coast in 1700 following a huge earthquake in the Pacific Northwest, and one following the Alaskan earthquake of 1964 drowned 100 people, some as far south as California. North America’s Atlantic coast could be at risk if an unstable portion of a Canary Island volcano that researchers are moni- toring were to slump into the sea.

Since the 2004 tsunami, nations and international agen- cies have stepped up efforts to develop systems to give coastal residents advance warning of approaching tsunamis. In addi- tion, we can lessen the impacts of tsunamis if we leave in place natural vegetation such as mangrove forests (p. 257).

We can worsen or reduce the impacts of natural hazards Besides the geologic hazards just described, people face other types of natural hazards that result from conditions in the hydrosphere, atmosphere, or biosphere. Heavy rains can lead to flooding that ravages low-lying areas near rivers and streams (p. 261). Coastal erosion can eat away at beaches (p. 248). Wildfire can threaten life and property in fire-prone areas (p. 196). And tornadoes and hurricanes (p. 282) can cause extensive damage and loss of life.

Although we refer to such phenomena as “natural hazards,” the magnitude of their impacts upon us often depends on choices we make. We tend to worsen the impacts of so-called natural hazards in various ways:

▶ As our population grows, more people live in areas sus- ceptible to natural disasters.

▶ Many of us choose to live in areas that we deem attractive but that are also prone to hazards. For instance, coastlines

are vulnerable to tsunamis and erosion by storms, and mountainous areas may feature volcanoes and mass-wast- ing events.

▶ We use and engineer landscapes around us in ways that can increase the frequency or severity of natural haz- ards. Damming and diking rivers to control f loods can sometimes lead to catastrophic f looding, like the f lood- ing along the Mississippi River in 2011 (p. 261). Suppress- ing natural wildfires puts forests at risk of larger, highly damaging fires. Clear-cutting on slopes (p. 194) and some mining practices (pp. 237–240) can induce mass wasting, speed runoff, compact soil, and change drain- age patterns.

▶ As we change Earth’s climate by emitting greenhouse gas- es (Chapter 14), we alter patterns of precipitation, increas- ing risks of drought, fire, f looding, and mudslides locally and regionally. Rising sea levels induced by global warm- ing increase coastal erosion. And some research suggests that warming ocean temperatures may increase the power and duration of hurricanes.

We can often reduce the impacts of hazards through the thoughtful use of technology, engineering, and policy, informed by a solid understanding of geology and ecol- ogy. Examples already noted include building earthquake- resistant structures; designing early warning systems for tsunamis and volcanoes; and conserving coastal forests, reefs, and salt marshes to protect against tsunamis and coastal erosion (pp. 257–259). In addition, better forestry and mining practices can help prevent landslides. Zon- ing regulations, building codes, and insurance incentives that discourage development in areas prone to landslides, floods, fires, and storm surges can keep us out of harm’s way and decrease taxpayer expense when cleaning up after natural disasters. Finally, addressing global climate change may help reduce the frequency of natural hazards in many regions.

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EARTH’S MINERAL RESOURCES Both gradual geologic processes and catastrophic geologic hazards influence the distribution of rocks and minerals in the lithosphere and their availability to us. We depend on a wide array of mineral resources as raw materials for our prod- ucts, so we mine and process these resources. Without the re- sources from beneath the ground that we use to make building materials, wiring, clothing, appliances, fertilizers for crops, and so much more, civilization as we know it could not exist. Consider a typical scene from a student lounge at a college or university (FIGURE 11.10), and note how many items are made with elements from the minerals we take from Earth.

We use mined materials extensively We often don’t notice how many mined resources we use every day. Using data from the U.S. governement, the Min- eral Information Institute estimated that in 2009 the average American consumed over 17,000 kg (37,000 lb) of new miner- als and fuels every year. At current rates of use, a child born in 2009 will use around 1.3 million kg (2.9 million lbs) over his or her lifetime (FIGURE 11.11).

More than half (9,600 kg or 21,000 lb) of the annual min- eral and fuel use of 17,000 kg is from the coal, oil, and natural gas used to supply our intensive demands for energy. Much of the remaining mineral use is attributable to the sand, gravel, and stone used in constructing our buildings, roads, bridges, and parking lots. Metal use is dwarfed by these other two cat-

egories, but the average American will still use more than 2 tons of aluminum over his or her lifetime. This level of con- sumption clearly shows the potential of recycling and reuse (such as recycling stone and gravel from old highways into new construction) to make our lifestyle more sustainable.

Iron, chromium, manganese, nickel and others in steel

Copper, nickel and zinc in coins

Tungsten in lightbulbGypsum in

wallboardSilica and lithium in glasses Titanium, chromium,

iron, cadmium and others in wall paint

Silver and gold in jewelry

Tantalum in cell phone

Copper and zinc in brass belt buckle

Lead in solder Iron in

pen ink

Titanium, zinc, iron, copper and others in cosmetics

Lead, platinum, hafnium, gallium, indium, tantalum and others in laptop

Nickel and cadmium in batteries for laptop

Zinc and manganese in batteries for radio

Salt in food

Aluminum in can

FIGURE 11.10  Elements from minerals that we mine are everywhere in the products we use in our everyday lives. This scene from a typical college student lounge points out just a few of the many minerals that surround us.

932 lbs. Copper 31,779 lbs.

Salt

12,121 lbs. Clays

544 lbs. Zinc

777 lbs. Lead

41,181 lbs. Cement

14,530 lbs. Iron ore

4,040 lbs. Bauxite (Aluminum)

542,968 lbs. Coal

15,152 lbs. Phosphate rock

1.383 Troy oz. Gold

+ 43,822 lbs. Other minerals and metals

72,499 gallons Petroleum

1.11 million lbs. Stone, sand, and gravel

5.93 million cu. ft. Natural gas

FIGURE 11.11  At current rates of usage, a baby born in 2009 in the United States is predicted to use a stunning 1.3 million kg (2.9 million lb) of mined minerals, metals, and fuels in his or her lifetime. Data from Mineral Information Institute, 2009.

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We obtain minerals by mining We obtain the minerals we use in all these ways through the process of mining. The term mining in the broad sense de- scribes the extraction of any resource that is nonrenewable on the timescale of our society. In this sense, we mine fossil fuels and groundwater, as well as minerals. When used specifically in relation to minerals, mining refers to the systematic removal of rock, soil, or other material for the purpose of ex- tracting minerals of economic interest. Because most miner- als of interest are widely spread but in low concentrations, miners and mining geologists first try to locate concentrated sources of minerals before mining begins.

Metals are extracted from ores Some minerals can be mined for metals. A metal is a type of chemical element that typically is lustrous, opaque, malle- able, and can conduct heat and electricity. Most metals are not found in a pure state in Earth’s crust, but instead are present within ore, a mineral or grouping of minerals from which we extract metals.

Copper, iron, lead, gold, and aluminum are among the many economically valuable metals we extract from mined ore. The tantalum used in the electronic components of computers, cell phones, DVD players, and other devices is a metal that comes from the mineral tantalite (FIGURE 11.12). In nature, tantalite is often found with the mineral columbite within the ore called coltan.

We process metals after mining ore Extracting minerals from the ground is the first step in putting them to use. However, most minerals need to be processed in some way to become useful for our products. For example, after ores are mined, the rock is crushed and pulverized, and the desired metals are isolated by chemical or physical means. The material is then processed to purify the metals we desire. With coltan, processing facilities use acid solvents to separate tantalite from columbite. Other chemicals are then used to

produce metallic tantalum powder. This powder can be con- solidated by various melting techniques and can be shaped into wire, sheets, or other forms.

Sometimes we mix, melt, and fuse a metal with another metal or a nonmetal substance to form an alloy. For example, steel is an alloy of the metal iron that has been fused with a small quantity of carbon. The strength and malleability of this particular alloy make steel ideal for its many applications in buildings, vehicles, appliances, and more. To make steel, we first mine iron ore, which consists of iron-containing com- pounds such as iron oxide. Steelmakers then heat the ore and chemically extract the iron with carbon in a process known as smelting (heating ore beyond its melting point and combin- ing it with other metals or chemicals). They then melt and reprocess the mixture, removing precise amounts of carbon and shaping the product into rods, sheets, or wires. During this melting process, certain other metals may be added to modify the strength, malleability, or other characteristics of the steel.

Processing minerals exerts environmental impacts. Most methods are water-intensive and energy-intensive. Moreover, many chemical reactions and heating processes used for ex- tracting metals from ore emit air pollution, and smelting plants in particular have long been hot spots of toxic air pol- lution. In addition, soil and water commonly become pol- luted by tailings, portions of ore left over after metals have been extracted. Tailings may leach heavy metals present in the ore waste as well as chemicals applied in the extrac- tion process. For instance, we use cyanide to extract gold from ore, and we use sulfuric acid to extract copper. Min- ing operations often store toxic slurries of tailings in large reservoirs called surface impoundments. Impoundment walls are designed to prevent leaks and collapse, but acci- dents can occur if the structural integrity of the impound- ment is compromised. In 2000, a breach of a coal tailings impoundment near Inez, Kentucky, released over 1 billion liters (250–300 million gal) of coal slurry, blackening 120 km (75 mi) of streams, killing aquatic wildlife, and affecting drinking water supplies for many communities.

(a) Tantalite ore (b) Purified tantalum (c) Capacitor containing tantalum

FIGURE 11.12  Tantalite ore (a) is mined from the ground and then processed to extract the pure metal tantalum (b). This metal is used in capacitors (c) and other electronic components in computer chips, cell phones, and many other devices.

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We also mine nonmetallic substances We also mine and use many minerals that do not contain metals. FIGURE 11.13 illustrates the nation of origin and uses for some economically important mineral resources, both metallic and nonmetallic. As you can see, many geologic re- sources in the products you use were mined in faraway nations.

Sand and gravel (the most commonly mined mineral resources) provide fill and construction materials. Phosphates provide us with fertilizer. We mine limestone, salt, potash, and other minerals for a number of diverse purposes.

Gemstones are treasured for their rarity and beauty. For instance, diamonds have long been prized—and like coltan, they have fueled resource wars. Besides the conflict in eastern Congo, the diamond trade has acted to fund, prolong, and intensify wars in Angola, Sierra Leone, Liberia, and elsewhere, as armies exploit local people for mine labor and sell the dia- monds for profit. This is why you may hear the phrase “blood diamonds,” just as coltan has been called a “conflict mineral.”

We also mine substances for fuel. Uranium ore is a min- eral from which we extract the metal uranium, which we use in nuclear power (pp. 345–350). One of the most common fuels we mine is coal. Coal (p. 329) is not a mineral, because it consists of organic matter, but we consider coal mining in this chapter because it has relevance for many general mining issues. Other fossil fuels—petroleum, natural gas, and alterna- tive fossil fuels such as oil sands, oil shale, and methane hy- drates—are also organic and are extracted from the earth (as we will see in Chapter 15).

MINING METHODS AND THEIR IMPACTS Mining for minerals is an important industry that provides jobs for people and revenue for communities in many regions. Mining supplies us raw materials for countless products we use daily, so it is necessary for the lives we lead. However, mining also exerts a price in environmental and social im- pacts. Because minerals of interest often make up only a small portion of the rock in a given area, very large amounts of ma- terial are removed in order to obtain the desired minerals. This frequently means that mining disturbs large areas of land.

Depending on the nature of the mineral deposit, any of several mining methods may be employed to extract the resource from the ground. Mining companies select which method to use based largely on its economic efficiency.

Strip mining removes surface layers of soil and rock When a resource occurs in shallow horizontal deposits near the surface, the most effective mining method is often strip mining, whereby layers of surface soil and rock are removed from large areas to expose the resource. Heavy machinery re- moves the overlying soil and rock (termed overburden) from a strip of land, and the resource is extracted. This strip is then refilled with the overburden, and miners proceed to an adjacent strip of land and repeat the process. Strip mining

Nickel: Cuba, Australia alloy for stainless steel, aerospace applications, batteries

Lead: China batteries, solder, X-ray shields, TV tubes, formerly paints and gasoline additives

Gold: South Africa ingots for monetary value, jewelry, coins, dentistry, medicine

Aluminum: Guinea packaging, building, transportation

Tantalum: Australia electric circuitry, auto parts, steelmaking and alloys

Chromium: Kazakhstan chemical industry, metalworking

Indium: Canada LCDs, solar cells

Cobalt: D.R. of Congo alloys for jet engines, carbides for tools, chemical industry

Phosphates: Morocco, Western Sahara fertilizer, industrial and home chemicals

Platinum: South Africa catalytic converters, chemical industry, capacitors

Silver: Poland jewelry, currency, electronics, photography Titanium: China

airplanes, aerospace, missiles

Tin: China steel plating for cans, alloys, solder, superconductors

Tungsten: China metalworking, machinery, lightbulbs

Uranium: Australia nuclear power, medicine

Zinc: United States, China coatings and alloys, auto parts, batteries, paints

Iron: Ukraine, Russia, Australia steelmaking, metallurgy, auto parts, paints and dyes

Copper: Chile electric wiring, plumbing, machinery, alloys and coatings

FIGURE 11.13  The minerals we use come from all over the world. Shown is a selection of economically important minerals together with their major uses and their main nation of origin. Only a minority of minerals, uses, and origins is shown.

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then mining companies pursue subsurface mining. In this approach, shafts are excavated deep into the ground, and net- works of tunnels are dug or blasted out to follow deposits of the mineral (FIGURE 11.14B). Miners remove the resource sys- tematically and ship it to the surface.

We use subsurface mining for metals such as zinc, lead, nickel, tin, gold, copper, and uranium, as well as for diamonds, phosphate, salt, and potash. In addition, a great deal of coal is mined using the subsurface technique. The scale of subsurface mining can be mind-boggling; the world’s deepest mines (cer- tain gold mines in South Africa) extend nearly 4 km (2.5 mi) underground.

Subsurface mining is the most dangerous form of mining, and fatal accidents are not unusual. In China, coal- mining conditions are so dangerous that in 2010 alone over 2,400 miners lost their lives. Besides risking injury or death from natural gas explosions and collapsing shafts or tunnels, miners inhale toxic fumes and coal dust, which can lead to respiratory diseases, including fatal black lung disease.

Occasionally subsurface mines can affect people long after they are closed. Abandoned mine tunnels can collapse, caus- ing sinkholes at the surface. Both strip mining and subsur- face mining can also pollute waterways through the process of acid drainage, which occurs when sulfide minerals in newly exposed rock surfaces react with oxygen and rainwater to pro- duce sulfuric acid. As the sulfuric acid runs off, it leaches met- als from the rocks, many of which are toxic to organisms. Acid drainage can affect fish and other aquatic organisms when it leaches into streams and it pollutes groundwater supplies peo- ple use for drinking water or irrigating crops (FIGURE 11.15). Although acid drainage is a natural phenomenon, mining greatly accelerates this process by exposing many new rock surfaces at once.

is commonly used for coal (FIGURE 11.14A) and oil sands (p. 335), and sometimes for sand and gravel.

Strip mining can be economically efficient, but it oblit- erates natural communities over large areas, and the soil in refilled areas can easily erode away.

In subsurface mining, miners work underground When a resource occurs in concentrated pockets or seams deep underground, and the earth allows for safe tunneling,

(b) Subsurface mining

(a) Strip mining

Surface

Ventilation

Main Shaft

Ventilation

Main Shaft

Coal seams

Surface Coal seams

FIGURE 11.14  Coal mining involves two types of mining approaches. In strip mining (a), soil is removed from the surface in strips, exposing seams from which coal is mined. In subsurface mining (b), miners work below ground in shafts and tunnels blasted through the rock. These passageways provide access to underground seams of coal or minerals.

FIGURE 11.15  Acidic drainage from an underground coal mine streams down a slope in West Virginia. The yellow-orange color is due to iron from the drainage settling out on the soil surface and forming rust.

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Open pit mining creates immense holes in the ground When a mineral is spread widely and evenly throughout a rock formation, or when the earth is unsuitable for tunneling, the method of choice is open pit mining . This essentially in- volves digging a gigantic hole and removing the desired ore, along with waste rock that surrounds the ore. Some open pit mines are inconceivably enormous. The world’s largest, the Bingham Canyon Mine near Salt Lake City, Utah, is 4 km (2.5 mi) across and 1.2 km (0.75 mi) deep ( FIGURE 11.16 ). Conveyor systems and immense trucks with tires taller than a person carry out nearly half a million tons of ore and waste rock each day.

Open pit mines are terraced so that men and machinery can move about, and waste rock is left in massive heaps out- side the pit. The pit is expanded until the resource runs out or becomes unprofitable to mine. Open pit mining is used for copper, iron, gold, diamonds, and coal, among other re- sources. We also use this technique to extract clay, gravel, sand, and stone such as limestone, granite, marble, and slate, but we generally call these pits quarries .

Open pit mines are so large because huge volumes of waste rock need to be removed in order to extract relatively small amounts of ore, which in turn contain still smaller traces of valuable minerals. The sheer size of these mines means that the degree of habitat loss and aesthetic degrada- tion is considerable.

Once mining is complete, abandoned pits generally fill up with groundwater. If sulfuric minerals are present, acid drain- age can form in the pit and percolate into aquifers.

FAQ

Q: Why would anyone work in a mine when it’s such dangerous work? A: It seems that mining accidents appear regularly in the headlines. In late 2010, for example, 33 miners in Chile were rescued after being trapped 600 m (2,000 ft) underground for 69 days in a gold and copper mine. Four days later, an explosion at an underground coal mine in China killed 37 miners. Similar explosions claimed the lives of 29 miners in a coal mine in West Virginia earlier in 2010 and 45 miners in Pakistan in 2011. Given these dangers, and the chronic health impacts of working in an underground mine, it’s reasonable to wonder why anyone would accept such a job.

Many of the people who work in mines do so because they have few other options. Underground mining often occurs in economically depressed areas, such as Appalachia in the United States, where mining is one of the few well- paying jobs. And for most mining jobs, people can begin working right out of high school. So although the work is dangerous, many miners are willing to accept those risks to provide for themselves and their families because few other career opportunities are available.

Placer mining uses running water to isolate minerals Some metals and gems accumulate in riverbed deposits, hav- ing been displaced from elsewhere and carried along by flow- ing water. To search for these metals and gems, miners sift through material in modern or ancient riverbed deposits, generally using running water to separate lightweight mud and gravel from heavier minerals of value ( FIGURE 11.17 ). This technique is called placer mining (pronounced “plasser”).

FIGURE 11.16  The Bingham Canyon open pit mine outside Salt Lake City, Utah, is the world’s largest human-made hole in the ground. This immense mine produces mostly copper.

FIGURE 11.17  Miners in eastern Congo find coltan by placer mining. Sediment is placed in plastic tubs, and water is run through them. A mixing motion allows the sediment to be poured off while the heavy coltan settles to the bottom.

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Placer mining is the method used by Congo’s coltan miners, who wade through streambeds, sifting through large amounts of debris by hand with a pan or simple tools, search- ing for high-density tantalite that settles to the bottom while low-density material washes away. Today’s African miners practice small-scale placer mining similar to the method used by American miners who ventured to California in the Gold Rush of 1849, and later to Alaska in the Klondike Gold Rush of 1896–1899. Placer mining for gold is still practiced in areas of Alaska and Canada, although today it uses large dredges and heavy machinery.

Besides the many social impacts of placer mining in places like Congo, placer mining is environmentally destruc- tive because most methods wash large amounts of debris into streams, making them uninhabitable for fish and other life for many miles downstream. Gold mining in northern Califor- nia’s rivers in the decades following the Gold Rush washed so much debris all the way to San Francisco Bay that a U.S. district court ruling in 1884 finally halted this mining practice. Placer mining also disturbs stream banks, causing erosion and harming ecologically important plant communities.

Mountaintop mining reshapes ridges and can fill valleys When a resource occurs in underground seams near the tops of ridges or mountains, mining companies may practice mountaintop removal mining, in which several hundred vertical feet of mountaintop may be removed to allow recov- ery of entire seams of the resource (FIGURE 11.18). This meth- od of mining is used primarily for coal in the Appalachian Mountains of the eastern United States. In mountaintop re- moval mining, a mountain’s forests are clear-cut, the timber is sold, topsoil is removed, and then rock is repeatedly blasted away to expose the coal for extraction. Overburden is placed back onto the mountaintop, but this waste rock is unstable and typically takes up more volume than the original rock, so generally a great deal of waste rock is dumped into adjacent valleys (a practice called “valley filling”). So far, mountaintop removal has blasted away an area the size of Delaware and has buried nearly 3,200 km (2,000 mi) of streams.

Scientists are finding that dumping tons of debris into valleys degrades or destroys immense areas of habitat, clogs streams and rivers, and pollutes waterways with acid drainage. With slopes deforested and valleys filled with debris, erosion intensifies, mudslides become frequent, and flash floods rav- age the lower valleys. Further, the Appalachian forests that are cleared in mountaintop mining are some of the richest forests for biodiversity in the nation.

People living in communities near the sites also expe- rience social and health impacts. Blasts from mines crack house foundations and wells, loose rock tumbles down into yards and homes, and floods tear through properties. Coal dust causes respiratory ailments, and contaminated water unleashes a variety of health problems. In fact, a 2009 study documented that people in mountaintop mining areas show elevated levels of lung cancer, heart disease, kidney disease, pulmonary disorders, hypertension, and mortality. In all these ways, the people of Appalachia—already among the poorest in the United States—suffer substantial external costs (p. 92), while the rest of us benefit from the electricity we produce with their coal.

Critics of mountaintop removal mining argue that valley filling violates the Clean Water Act. In 2010 the Environmen- tal Protection Agency introduced new regulations to limit damage from mountaintop mining and valley filling. Legisla- tion introduced in Congress in 2009 sought to restrict some mountaintop mining practices, but failed to become law.

Solution mining dissolves and extracts resources in place When a deposit is especially deep and the resource can be dis- solved in a liquid, miners may use a technique called solution mining or in-situ recovery. In this technique, a narrow bore- hole is drilled deep into the ground to reach the deposit, and water, acid, or another liquid is injected down the borehole to leach the resource from the surrounding rock and dissolve it in the liquid. The resulting solution is then sucked out, and the desired resource is isolated. Sodium chloride (table salt), lithium, boron, bromine, magnesium, potash, copper, and uranium can be mined in this way.

Solution mining generally exerts less environmental impact than other mining techniques, because less area at the surface is disturbed. The primary potential impacts involve accidental leakage of acids into groundwater surrounding the borehole, and the contamination of aquifers with acids, heavy metals, or uranium leached from the rock.

Some mining occurs in the ocean The oceans hold many minerals useful to our society. We extract some minerals from seawater, such as magnesium from salts held in solution. We extract other minerals from the ocean floor. For example, many minerals are concentrated in manganese nodules, small ball-shaped accretions that are scat- tered across parts of the ocean floor. Over 1.5 trillion tons of manganese nodules may exist in the Pacific Ocean alone, and their reserves of metal may exceed all terrestrial reserves. As land resources become scarcer and as undersea mining tech- nology develops, mining companies may turn increasingly to

FIGURE 11.18  In the Appalachians, mountaintop mining for coal takes place on massive scales. Mining trucks like those shown are up 15 m (50 ft) long and 7 m (23 ft) tall.

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the seas. The logistical difficulty of mining offshore resources, however, has kept their extraction limited so far.

Restoration of mined sites is often only partly effective Because of the environmental impacts of mining, govern- ments of the United States and other developed nations now require that mining companies restore, or reclaim, surface- mined sites following mining. The aim of such restoration, or reclamation, is to restore the site to a condition similar to its condition before mining. To restore a site, companies are required to remove buildings and other structures used for mining, replace overburden, fill in shafts, and replant the area with vegetation (FIGURE 11.19). In the United States, the 1977 Surface Mining Control and Reclamation Act man- dates restoration efforts, requiring companies to post bonds to cover reclamation costs before mining can be approved. This ensures that if the company fails to restore the land for any reason, the government will have the money to do so. Most other nations exercise less oversight, and in nations such as the Congo, there is no regulation at all.

The mining industry has made great strides in reclaim- ing mined land and employs many hard-working ecologists and engineers to conduct these efforts. However, even on sites that are restored, impacts from mining (such as soil and water damage from acid drainage) can be severe and long-lasting. Moreover, reclaimed sites do not generally regain the same biotic communities that were naturally present before min- ing. One reason is that fast-growing grasses are generally used to initiate and anchor restoration efforts. This helps control erosion quickly from the outset, but it can hinder the longer- term establishment of forests, wetlands, or other complex nat- ural communities. Instead, grasses may outcompete slower- growing native plants in the acidic, compacted, nutrient-poor soils that usually result from mining. Moreover, many incon- spicuous but vital symbiotic relationships (p. 68) that main- tain ecosystems—such as specialized relationships between plants and fungi or plants and insects—are eliminated by mining and are very difficult to restore.

Water polluted by mining and acid drainage can also be reclaimed, if its pH can be moderated and if toxic heavy metals can be removed. Like the reclamation of land, this is a challenging and imperfect process, but researchers and the mining industry are making progress in improving tech- niques (see THE SCIENCE BEHIND THE STORY, pp. 242–243). The need for treatment can be long-lasting. Mines in Spain from the era of the Roman Empire still leach acid drainage into waterways today.

FIGURE 11.19  More mine sites are being restored today, but restoration rarely is able to recreate the natural community present before mining. Here, reclamation workers in Ghana, West Africa, plant trees in an abandoned gold-mining pit.

An 1872 law still guides U.S. mining policy The ways that mining companies stake claims and use land in the United States is guided by a law that is well over a century old. The General Mining Act of 1872 encourages people and companies to prospect for minerals on federally owned land by allowing any U.S. citizen or any company with permission to do business in the United States to stake a claim on any plot of public land open to mining. The person or company owning the claim gains the sole right to take minerals from the area. The claim-holder can also patent the claim (i.e., buy the land) for only about $5 per acre. Regardless of the profits they might make on minerals they extract, the law requires

Restoring Mined Areas Mining has severe environmental impacts, and restoring a mined site to a condition similar to its state before mining is costly and difficult. How much do you

think we should require mining companies to restore after a mine is shut down, and what criteria should we use to guide restoration? Should we require complete restoration? No restoration? What should our priorities be—to minimize water pollution, health impacts, biodi- versity loss, soil damage, or other factors? Should the amount of restoration we require depend on how much money the company made from the mine? Explain your recommendations.

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THE SCIENCE BEHIND THE STORY

Using Bacteria to Clean Mine Water and Recover Metals

Toxic waters of the Berkeley Pit near Butte, Montana

Let’s set the stage by traveling to western Montana, where in 1982 the Atlantic Richfield Company ceased mining at the Berkeley Pit, a massive open pit copper mine covering just over 1 square mile. Once the mine was shut down and pumps were turned off, groundwater started to fill the 540-m-deep (1,780-ft-deep) crater.

As water bathed the rock walls, it mixed with oxygen from the air and reacted with sulfide minerals in the freshly exposed rock, producing acid drainage (p. 238). Sulfuric acid formed, and water accumulating in the Berkeley Pit became as acidic as lem- on juice, reaching pH values as low as 2.2. The very low pH caused metals in the rock to leach into the acidic water, including ions of iron, zinc, aluminum,

manganese, nickel, cadmium, cobalt, and arsenic, as well as copper. These metals reacted with the sulfuric acid in the water to form metal sulfates, compounds containing a metal ion bonded to a sulfate ion. For instance, zinc formed zinc sulfate (ZnSO4) and iron formed iron sulfate (FeSO4).

Metal sulfates dissolve in water and high concentrations of these dis- solved metals made the water toxic to wildlife. The water here was so unusually acidic and metal-rich that biologists surveying the site discov- ered new species of microbes in the water.

As groundwater continued to fill the pit at a rate of 13 vertical feet per year, experts estimated that by 2015 the water would overflow into the Clark Fork River drainage, polluting

ecosystems and poisoning people’s drinking water. The race was on to find a solution.

Traditionally, mining engineers have tried to treat acid mine drainage by adding a strongly alkaline substance such as lime or sodium hydroxide to raise the water’s pH. When the pH is raised, the dissolved heavy metals precipitate and fall out of solution. In recent years, researchers have begun to put sulfate-reducing bacteria to work in converting soluble metal sul- fates in acid mine drainage to insoluble metal sulfides.

Sulfate-reducing bacteria are microbes that thrive in the absence of oxygen by chemically reducing sulfates to obtain energy. In so doing, they gen- erate sulfides that they expel as waste. In nature, some such bacteria degrade organic materials in the mud of swamps and produce hydrogen sulfide, the gas that gives swamps and mudflats their distinctive rotten-egg odor.

At the Berkeley Pit, EPA scientist Henry Tabak, University of Cincinnati

no payments of any kind to the public, and until recently no restoration of the land after mining was required.

Supporters of the policy say that it is appropriate and desirable to continue encouraging the domestic mining in- dustry, which must undertake substantial financial risk and investment to locate resources that are vital to our econ- omy. Critics counter that the policy gives valuable public resources away to private interests nearly for free. They also point out that many claims made under this law have even- tually led to lucrative land development schemes (such as condominium development) that have nothing to do with mining.

Critics have tried to amend the law many times over the years, mostly without success. The latest effort, the Hardrock Mining and Reclamation Act of 2009, sought to largely end the patenting process, put some public lands off-limits to mining, mandate that mined sites be restored to some semblance of

Mining poses two dilemmas: It exerts environmental impacts, and it can deplete nonrenewable minerals. Now, some scientists are seeking to address both these drawbacks in one fell swoop. They’re aiming to clean up polluted mine sites and amass valuable minerals at the same time. Their secret weapon? Bacteria.

their former condition, and require miners to pay the govern- ment royalties of 4% of profits from new mines and 8% from existing mines. The money would help to fund cleanups of mined sites and reimburse communities affected by mining. The legislation was referred to committee in both houses of Congress but failed to become law.

Reforming the 1872 Mining Law You are a legislator in the U.S. Congress, and your colleagues are asking you to help prepare a bill to reform the General Mining Act of 1872. Would

you join this effort to reform the law? Why or why not? If you would, then what would you seek to include in the bill?

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chemical engineer Rakesh Govind, and three colleagues examined whether they could use sulfate-reducing bac- teria to clean up the water and recover valuable metals.

Highly acidic water harms most bacteria, so Tabak and Govind’s team designed a two-step process (see figure). They grew their bacteria in water kept at a neutral pH and fed them sulfates from the mine water, along with carbon-containing nutri- ents, letting them produce hydro- gen sulfide. They then funneled this hydrogen sulfide into a series of tanks, where it reacted with the acid mine drainage from the Berkeley Pit. The reactions in these tanks caused the dissolved metals in the mine water to precipitate out as insoluble metal

sulfides and settle to the bottom of the tank.

The metal sulfides were then removed from the precipitation tanks. The research team measured its success by calculating the average percent recov- ery for each of several metals (see table). Precipitates of the various metals ranged in purity from 75% to 98%.

Besides recovering high percent- ages of metals that can be processed and recycled, the process cleaned toxic metals from the mine water and also made it less acidic because the reactions produce bicarbonate ions (HCO3–), which raise the pH of the water. After full treatment, the researchers determined that the water was pure enough to meet safety stand- ards for irrigating agricultural crops.

This research, published in 2003, was done in the lab at a small scale. More work remains to scale it up to treat large amounts of water from the mine. Today, a wide variety of similar efforts are ongoing around the world, from Montana to South Africa, as scientists develop better ways of removing metals from acid mine drain- age and as engineers work to scale these systems up. These approaches are showing promise, and give scien- tists new tools to reclaim mined sites around the world.

Hydrogen sulfide gas

Acid mine water

Metal precipitation process

Metal sulfides precipitate

Bioreactor containing bacteria

Treated water

Acidic mine water rich in sulfates is fed into two tanks. Bacteria in the biore- actor produce hydrogen sulfide (H2S), which circulates to the metal precipi- tation tanks. In the presence of hydrogen sulfide, metal ions bond to sulfur to form metal sulfides. The sulfides are not soluble, so they precipitate out of the water. The sulfides are collected and may be processed further to harvest minerals of economic value. The treated water is discharged from the system, clean enough to use for agriculture.

it would last for only 18 years! Most pressing may be dwin- dling supplies of indium. This obscure metal, which is used for LCD screens, might last only another 32 years. Because of these supply concerns and price volatility, industries now are working hard to develop ways of substituting other materials for indium. A lack of indium and gallium would threaten the production of high-efficiency cells for solar power. Platinum is dwindling too, and its unavailability would make it hard- er to develop fuel cells and catalytic converters for vehicles. However, platinum’s high market price encourages recycling, which may keep it available, albeit as an expensive metal.

FIGURE 11.20 shows estimated years remaining for sev- eral selected minerals at today’s consumption rates. Calculat- ing how long a given mineral resource will be available to us is beset by a great deal of uncertainty, for several reasons:

▶ As we discover new deposits of a mineral, the known reserves—and thus the years this mineral is available to

Percent Recovery of Metals from Mine Water Using Sulfate-Reducing Bacteria

Metal

Percent recovery of metal

Aluminum 99.8

Cadmium 99.7

Cobalt 99.1

Copper 99.8

Iron 97.1

Manganese 87.4

Nickel 47.8

Zinc 100.0

Adapted from Tabak, H.H., et al., 2003. Advances in biotreatment of acid mine drainage and biorecovery of metals: 1. Metal precipitation for recovery and recycle. Biodegradation 14: 423–436.

TOWARD SUSTAINABLE MINERAL USE Mining exerts plenty of environmental impacts, but we also have another concern to keep in mind: Minerals are non- renewable resources (p. 2) in finite supply. As a result, it will benefit us to find ways to conserve the supplies we have left and to make them last.

Minerals are limited in supply Some minerals we use are abundant and will likely never run out, but others are rare enough that they could soon become unavailable. For instance, geologists in 2010 calculated that the world’s known reserves of tantalum will last about 164 more years at today’s rate of consumption. If demand for tantalum increases, it could run out faster. And if everyone in the world began consuming tantalum at the rate of U.S. citizens, then

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us—increase. For this reason, some previously predicted shortages have not come to pass, and we may have access to these minerals for longer than currently estimated.

▶ Rising prices for minerals may favor the development of enhanced mining technologies that can reach more min- erals than are currently economically viable to extract.

▶ New societal developments and new technologies can modify demand for minerals. Just as cell phones and computer chips boosted demand for tantalum, fiber- optic cables decreased demand for copper as they replaced copper wiring in communications applications.

▶ Changing consumption patterns alter the speed with which we exploit mineral resources. Economic recession depressed demand and caused a decrease in the produc- tion and consumption of most minerals in 2008 and 2009.

▶ Advances in recycling technologies and increased recy- cling rates can extend the lifetimes of mineral resources by allowing us to reuse them many times.

Despite these sources of uncertainty, we would be wise to be concerned about Earth’s finite supplies of mineral resources and to try to use them more sustainably.

We can make our mineral use more sustainable We can address both major challenges facing us regarding mineral resources—finite supply and environmental dam- age—by encouraging recycling of these resources. Municipal recycling programs handle used items that we as consumers place in recycling bins and divert from the waste stream. In 2009, fully 35% of metals in the U.S. municipal solid waste

stream were diverted for recycling. Car battery recycling pro- grams provide 80% of the lead we need for new products, and 35% of our copper comes from recycled copper sources such as pipes and wires.

In many cases, recycling can decrease energy use sub- stantially. For instance, making steel by remelting recycled iron and steel scrap requires much less energy than produc- ing steel from virgin iron ore. Similarly, over 40% of the alu- minum in the United States today is recycled (FIGURE 11.21). This is a good thing because it takes over 20 times more en- ergy to extract virgin aluminum from ore (bauxite) than it does to obtain it from recycled sources. This reduced energy use also results in lower emissions of greenhouse gases.

We can recycle metals from e-waste Electronic waste, or e-waste, from discarded computers, printers, cell phones, handheld devices, and other electronic products is rising fast—and e-waste contains hazardous sub- stances (Chapter 17, pp. 392–394). Recycling old electronic devices helps keep them out of landfills and also helps us conserve valuable minerals such as tantalum.

Tantalum is recycled from scrap by-products generated during the manufacture of electronic components and also from scrap from tantalum-containing alloys and manufac- tured materials. Currently the industry estimates that recy- cling accounts for 20–25% of the tantalum available for use in products.

When you turn in your old phone to a recycling and reuse center rather than discarding it, the phone may be refurbished and resold in a developing country. People in African nations in particular readily buy used cell phones because they are inexpensive and land-line phone service does not always exist in poor and rural areas. Alternatively, the phone may be dismantled in a developing country and the various parts refurbished and reused, or recycled for their metals. Either way, you are helping to extend the availabil- ity of resources through reuse and recycling and to decrease waste of valuable minerals.

50 100 150 200 250 300 350 4000

Nickel Economically recoverable Technically recoverableMolybdenum

Iron from ore

Zinc

Copper

Cobalt

Titanium

Lead

Years left available, at present rates of consumption

FIGURE 11.20  Minerals are nonrenewable resources, so supplies of metals are limited. Shown in red are the numbers of remaining years that certain metals are estimated to be economi- cally recoverable at current prices, given known global reserves and assuming current rates of consumption. The entire lengths of the bars (red plus orange) show the numbers of remaining years that certain metals are estimated to be available using current technology on all known deposits, whether economically recover- able or not. All these time periods could increase if more reserves are found, or decrease if consumption rates rise. Data are for 2010, from U.S. Geological Survey, 2011. Mineral Commodity Summaries 2011.

USGS, Washington, D.C.

FIGURE 11.21  When you recycle aluminum cans, you contribute to valuable efforts to save mineral resources, money, and energy.

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Throughout the world, using recycling to make better use of the mineral resources we have already mined will help mini- mize the impacts of mining and assure us access to resources further into the future.

Today only about 10% percent of old cell phones are recy- cled. By recycling more, we can reduce demand for virgin ore and decrease pressure on people and ecosystems, such as the miners and natural areas in Africa’s coltan-mining regions.

T E S T I N G Y O U R C O M P R E H E N S I O N

1. Name the primary layers that make up our planet. Which portions does the lithosphere include?

2. Describe how plate tectonics accounts for the formation of (a) mountains, (b) volcanoes, and (c) earthquakes. In your answer, explain the roles that divergent plate boundaries, transform plate boundaries, and convergent plate boundaries play in the formation of each.

3. Name the three main types of rocks, and describe how each type may be converted to the others via the rock cycle.

4. Define each of the following and contrast them with one another: mineral, metal, ore, alloy.

5. A mining geologist locates a horizontal seam of coal very near the surface of the land. What type of mining method will the mining company use to extract it? What is one common environmental impact of this type of mining?

6. How does strip mining differ from subsurface mining? How do each of these approaches differ from open pit mining?

7. What is acid drainage, and why can it be toxic to aquatic organisms?

8. Explain why reclamation efforts after mining frequently fail to effectively restore natural communities. Discuss both soil and vegetation in your answer.

9. List five factors that influence how long global supplies of a given mineral will last, and explain how each affects the time span the mineral will be available to us.

10. Name three types of metal that we currently recycle, and identify the products or materials that are recycled to recover these metals.

S E E K I N G S O L U T I O N S

1. For each of the following natural hazards, describe one thing that can be done to minimize or mitigate their im- pacts on our lives and property:

▶ Earthquakes ▶ Landslides ▶ Flooding

2. List three impacts of mining on the natural environ- ment, and describe how particular mining practices can lead to each of these impacts. How are these impacts be- ing addressed? Can you think of additional solutions to prevent, reduce, or mitigate these impacts?

3. You have won a grant from the U.S. Environmental Pro- tection Agency (EPA) to work with a mining company to develop a more effective way of restoring a mine site that is about to be abandoned. Describe a few preliminary

ideas for carrying out restoration better than it is typi- cally being done. Now describe a field experiment you would like to run to test one of your ideas.

4. THINK IT THROUGH The story of coltan in the Congo is just one example of how an abundance of exploitable resources can often worsen or prolong military conflicts in nations that are too poor or ineffectively governed to protect these resources. In such “resource wars,” civil- ians often suffer the most as civil society breaks down. Suppose you are the head of an international aid agency that has earmarked $10 million to help address conflicts related to mining in the Democratic Republic of the Congo. You have access to government and rebel leaders in Congo and neighboring countries, to ambassadors of the world’s nations in the United Nations, and to rep- resentatives of international mining corporations. Based

➤ CONCLUSION Physical processes of geology such as plate tectonics and the rock cycle are centrally important because they shape Earth’s terrain and form the foundation for living systems. Geologic processes also generate phenomena that can threat- en our lives and property, including earthquakes, volcanoes, landslides, and tsunamis. We depend on a diversity of min- erals and metals from the Earth and we mine these non- renewable resources by various methods, according to how the minerals are distributed. Economically efficient mining

methods have greatly contributed to our material wealth, but they have also resulted in extensive environmental impacts, ranging from habitat loss to acid drainage. Restoration ef- forts and enhanced regulation help to minimize the envi- ronmental and social impacts of mining, although to some extent these impacts will always exist. We can prolong our access to mineral resources and make our mineral use more sustainable by maximizing the recovery and recycling of key minerals.

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mined for coal using the mountaintop removal method. Your parents, who still live there, are worried for their health and safety and do not want to lose the beautiful forested creek and ravine behind their property. How- ever, your brother is out of work and could use a mining job. What would you attempt to do in this situation?

on what you know from this chapter, what steps would you consider taking to help improve the situation in the Congo?

5. THINK IT THROUGH As you finish your college de- gree, you learn that the mountains behind your child- hood home in the hills of Kentucky are slated to be

C A L C U L A T I N G E C O L O G I C A L F O O T P R I N T S

As we saw in Figure 11.20, some metals are in limited enough supply that, at today’s prices, they could be available to us for only a few more decades. After that, prices will rise as they become scarcer. The number of years of total availability (at all prices) depends on a number of factors: On the one hand, metals will be available for longer if new deposits are discovered, new mining technologies are developed, or recycling efforts are improved. On the other hand, if our consumption of metals increases, the number of years we have left to use them will decrease.

Currently the United States consumes metals at a much higher per-person rate than the world does as a whole. If one goal of humanity is to lift the rest of the world up to U.S. living standards, then this will sharply increase pressures on mineral supplies.

The chart shows currently known economically recov- erable global reserves for several metals, together with the amount used per year (each figure in thousands of metric tons). For each metal, calculate and enter in the fourth col- umn the years of supply left at current prices by dividing the reserves by the amount used annually.

The fifth column shows the amount that the world would use if everyone in the world consumed the metal at the rate that Americans do. Now calculate the years of supply left at current prices for each metal if the world were to consume the metals at the U.S. rate, and enter these values in the sixth column.

Metal

Known economic reserves

Amount used per year

Years of economic supply left

Amount used per year if everyone consumed at U.S. rate

Years of economic supply left if everyone consumed at U.S. rate

Titanium 690,000 6,300 33,390

Copper 630,000 16,200 38,510

Nickel 76,000 1,550 5,098

Tin 5,200 261 846

Tungsten 2,900 61 312

Antimony 1,800 135 481

Silver 510 22.2 130

Gold 51 2.50 3.34

Data are for 2010, from U.S. Geological Survey, 2011. Mineral Commodity Summaries 2011. USGS, Washington, D.C. All numbers are in thousands of metric tons. World consumption data are assumed equal to world production data. “Known economic reserves” include extractable amounts under current economic conditions. Additional reserves exist that could be mined at greater cost.

1. Which of these eight metals will last the longest under current economic conditions and at current rates of glo- bal consumption? For which of these metals will eco- nomic reserves be depleted fastest?

2. If the average citizen of the world consumed metals at the rate that the average U.S. citizen does, which of these eight metals’ economic reserves would last the longest? Which would be depleted fastest?

3. In this chart, our calculations of years of supply left do not factor in population growth. All else being equal, how do you think population growth will affect these numbers?

4. Describe two general ways that we could increase the years of supply left for these metals. What do you think it will take to accomplish this?

Go to www.masteringenvironmentalscience.com for homework assignments, practice quizzes, Pearson eText, and more.

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