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CHAPTER 8

Environmental Health and Safety

LEARNING OBJECTIVES

By the end of this chapter, the student will be able to:

• define the scope of morbidity and mortality caused by the physical environment.

• identify the range of interactions that occur between human beings and the physical environment.

• identify the components of environmental risk assessment and apply them to an environmental hazard, such as lead.

• distinguish between a risk assessment, a public health assessment, and an ecological assessment.

• discuss the meaning of interactions and how they may impact the size of risks.

• describe how intentional and unintentional injuries can be addressed to prevent their occurrence and diminish their consequences.

• identify successes of outbreak investigations.

Joe grew up in an industrial district of town. His family lived in an old apartment building, and he played in a playground near a major intersection. By the age of 6, Joe was found to have high lead levels in his blood and was not doing well in school. Where could all that lead come from? his mother wondered.

Jill is pregnant and loves fish, which she has eaten almost daily for years as part of her effort to stay healthy. She hears that fish should not be eaten regularly during pregnancy. Why, she wonders, should I cut down on eating something as healthy as fish?

Ralph and Sonya, a prosperous professional couple, and their two children live in an older suburban home. They feel secure that their environment is safe. They were surprised to find when they wanted to put their house up for sale that it did not pass the safety tests for radon. Where did the radon come from, they wondered, and what can be done about it?

Sandra worked for an international agency that had successfully addressed the danger of radiation due to the hole in the ozone layer. She was shocked when she was told that she had a life-threatening skin cancer called melanoma. She asked: What could cause melanoma? Could years of sun exposure have played a role?

You set out on your commute to work, and as you approach the subway station, you see police cars, ambulances, and dozens of emergency responders in hazmat suits. You are told the entire subway system will be shut down indefinitely, as there has been a suspected case of bioterrorism. You wonder how authorities were alerted to this situation and what precautions are being taken to protect the health of those living in the city.

Alex suffered a traumatic brain injury when he was thrown from his motorcycle after colliding with a car in which the driver had an elevated blood alcohol concentration. Alex was not wearing a helmet. His family members wonder what is being done to prevent this from happening to others.

All of these situations are part of what we mean by the burden of environmental disease and injury. In order to understand the impact of the environment on health, we need to define what we mean by “environment” and appreciate the many ways that we interact with it.

WHAT IS MEANT BY “ENVIRONMENT”?

“Environment” is an ambiguous term. It is sometimes used to imply all influences other than genetic influences, including social, economic, and cultural influences. We will define the environment as the physical environment. The physical environment can be thought of in three categories: unaltered (“natural”), altered, and the built environment. a Figure 8-1 diagrams the scope of environmental diseases and injuries. The health of human beings was affected by the physical environment long before we had the capacity to substantially alter the environment. Floods, earthquakes, and volcanoes have always been a part of the physical environment. In addition to these intermittent and often isolated impacts, daily exposures to communicable diseases in water and food have always been a part of the unaltered environment.

FIGURE 8-1 Scope of Environmental Diseases and Injuries

In recent years, we have recognized more subtle impacts of the unaltered environment. Radon, a common naturally occurring breakdown product of uranium, increases the risk of lung cancer. Exposure to naturally occurring sunlight increases the chances of skin cancer, including melanoma—a potentially lethal skin cancer—especially among light-skinned individuals.

Human activity has altered nearly every aspect of our physical environment. Some alterations to our environment may improve human health—from water treatment, to waste management, to mosquito and flood control. Nonetheless, we need to consider the overall impacts that these changes have on the physical environment. The sheer growth in the number of human beings—the planet’s population has exceeded 7 billion—is likely to magnify our impact on all aspects of our physical environment in the future. This population growth and increasing human activity are believed to be contributing to a range of environmental issues, from deforestation to global warming. The observed changes occurring in the climate will likely impact the health of everyone. Box 8-1 outlines some possible health effects of climate change.

We often think of the altered environment as reflecting the impact of chemicals, radiation, and biological products that we introduce into the environment. The list of intentional or unintentional introductions is in fact very long. It ranges from industrial chemicals, such as pesticides, benzene, and chlorofluorocarbons (CFCs), to elements mined from the earth, such as mercury and lead. It also includes radiation from nuclear energy and medical wastes. Biological impacts encompass the introduction of invasive species and the management of biological wastes.

BOX 8-1 Climate Change

Global warming, or climate change, as it is being increasingly referred to, is likely to have expected and unexpected impacts on human health. The most predictable changes are those associated with expanded territory for currently existing communicable diseases. For instance, cases of malaria, dengue fever, and insect-borne encephalitis are likely to increase in the United States. Malaria existed for many years in the country as far north as the mid-Atlantic states. The mosquitoes that transmit malaria are present in the United States, and the disease could readily reestablish itself as a major pathogen. Dengue fever, or “breakbone fever,” is a mosquito-borne disease related to yellow fever. One strain of the disease, hemorrhagic dengue fever, has a high case-fatality rate. The geographic range of the mosquito that carries dengue fever is currently limited because frost kills both the adult insects and their larvae. Rising temperatures are expected to allow the disease to move steadily northward in future decades. Outbreaks of acute encephalitis (inflammation of the brain) transmitted by mosquitoes are already on the rise. We can expect to see more frequent and severe outbreaks in the future.

In addition, more frequent and intense heat waves are likely to occur, especially in currently temperate climates covering much of the United States. Deaths among the very young and the very old can be expected during heat waves. Additional possible impacts of climate change on health are those associated with hurricanes, flooding, forest fires, and drought—all of which are likely to occur with increased frequency and severity in specific areas of the world. The potential for hurricane damage is not just from the acute storm. As demonstrated by Hurricane Katrina, there can be long-lasting impacts on the safety and availability of housing, as well as destruction of the healthcare and public health infrastructure. Rising ocean levels in and of themselves may displace hundreds of millions of people who currently live in low-lying river delta areas throughout the world.

The exact impacts of climate change remain uncertain and controversial. Alterations in ocean currents could potentially lower temperatures in Europe and other highly populated areas. Despite the great uncertainties ahead, it is clear that climate change will affect not only the lives of today’s college students but also people’s lives for centuries to come.

The concept of the built environment is relatively new and includes all the impacts of the physical environment as a result of human construction. The impacts of human construction include injuries and exposures in the home, the transportation system, and where we work and play. They also include factors ranging from the way we build and heat our buildings and cook our food, to the way we travel from place to place. The built environment influences our safety through its impact on injuries and hazardous exposures. It also influences our activity levels and our social interactions, which impact our health. 2

The impact of the built environment is wide ranging throughout the world, but differs greatly by geography and stage of social and economic development. Indoor air pollution from cooking is the most prominent source of air pollution in much of the developing world. Motor vehicle injuries are the most deadly consequences of the built environment in most developed countries. The built environment has subtle impacts as well. The way we build our cities affects the amount of exercise we get and the quantity of noise pollution we experience. Construction methods affect air systems in buildings and can increase our exposure to “sick buildings.” Let us take a look at the burden of disease that results from the physical environment.

WHAT IS THE BURDEN OF DISEASE DUE TO THE PHYSICAL ENVIRONMENT?

Measuring the impact of the physical environment on health is difficult because of the many types of impacts and the often subtle effects that occur. The impacts we experience today may pale in comparison to what we can expect in the future. Nonetheless, it is useful to appreciate the current estimates of the magnitude of the direct and indirect burden.

Motor vehicle injuries and exposure to toxic substances are two important actual causes of death that represent the largest known impact of the physical environment. Together, these incidents are estimated to cause nearly 100,000 deaths per year, representing about 20% of preventable deaths in the United States and approximately 10% of all deaths in the United States, according to the Centers for Disease Control and Prevention’s (CDC) calculations. 3 Motor vehicle injuries and other unintentional injuries have especially heavy impacts on the young; in fact, they are the number one cause of death in the United States among those 1 to 24 years of age. 4 As a cause of disability, injuries also rank high especially considering their disproportionate impact on the young.

The impact of toxic substances on population health extends beyond acute symptoms such as skin and respiratory irritation to chronic conditions. The impact on death and disability is difficult to measure due to the length of time the substances may take to affect the body. It may be years after an exposure before an individual experiences negative health effects on their kidneys, liver, nerves, and other organs. Box 8-2 describes the impact of small particle air pollution on health, including the recent recognition of its long-term effects on the development of coronary artery disease. This link substantially increases the estimated impact the environment has on health outcomes.

Many toxic exposures occur in occupational settings. Approximately 5,000 deaths due to injuries occur in the occupational setting per year. Certain occupations are particularly vulnerable to injuries, including mining, construction, and agriculture. Occupational exposures that result in morbidity and mortality include lung diseases caused by exposures to hazardous dusts, hearing loss from loud noises, and back pain from excessive lifting, as well as a wide range of other mechanical problems, including carpal tunnel syndrome, which is often caused by repetitive motion of the hand and wrist. Occupational injuries have been declining in recent years, but they remain an important cause of death and disability. 6 Cancer caused by occupational exposures has been of particular concern. As much as 5% of cancer deaths in males have been estimated to be due to occupational exposures. 7 Cancers of the lung, bladder, and white blood cells (leukemia) are particularly likely to result from chronic exposures to chemicals, such as formaldehyde, benzene, and organic dyes. Reductions in occupational exposures in the last 30 years have resulted in a declining burden of disease from these exposures in the United States. The opposite is being seen in many newly industrializing countries, where current exposures are increasing and may result in more cases of cancer and other diseases in the not-too-distant future.

Finally, we cannot evaluate the impact of toxic exposures solely by tracing them to human deaths and disabilities. The altered environment has impacts on entire ecosystems of plants and animals. The ecological impact of environmental factors can have long-term and largely irreversible consequences. Once chemicals, radiation, and biological products are released into the environment, the process cannot generally be easily reversed. Thus, we need to take a broad and long-term perspective when we address environmental health.

BOX 8-2 Impact of Small Particle Air Pollution on Health 5

Air pollution occurs when particulate matter, a mix of tiny solid and liquid particles, is suspended in the air. The particles can be comprised of a number of components, including acids, organic chemicals, metals, dust, and pollen and mold spores. The size of the particles makes a difference on their impact on health. Our body’s natural defense mechanisms, such as coughing and sneezing, can dislodge larger particles. However, small particles, less than 10 micrometers in diameter, can be inhaled into the lungs and enter the bloodstream; therefore, they have potential to pose a great risk to health. The smallest of these particles are referred to as fine particles. Fine particles measure less than 2.5 micrometers in diameter and, therefore, can only be seen with an electron microscope. When millions of these particles are suspended in the air, a haze forms, referred to as smog and often seen in cities due to exhaust from motor vehicles.

Everyone’s health is at risk from small particle pollution; however, certain groups are at greater risk. Because children spend more active time outside, their lungs are still developing, and they are more likely to have asthma and acute respiratory disease, they face greater risk. Older adults also have an increased risk for health issues due to small particles because they are more likely to have heart or lung disease, which can be aggravated by inhalation of the particles. People of any age with heart or lung disease are also at increased risk for this reason.

Health effects from short-term exposure can include eye, nose, and throat irritation; shortness of breath; asthma attacks; and bronchitis. Long-term exposure to small particle pollution can contribute to reduced lung function, chronic bronchitis, and premature death.

A number of recent studies demonstrate a link between small particle air pollution and coronary artery disease. It is believed that exposure to fine particulate air pollution leads to thickening of the arteries, disrupting blood flow, which can lead to heart attacks and strokes. Attributing a portion of the many deaths from coronary artery disease to air pollution substantially increases the estimates of the environmental burden of disease.

In an effort to alert individuals to the air quality in their region, the Environmental Protection Agency created an Air Quality Index, which is provided in Figure 8-2 :

FIGURE 8-2 Air Quality Index for Particle Pollution

Reproduced from United States Environmental Protection Agency. Particulate Matter. Availalble at: http://www.epa.gov/airquality/particlepollution/index.html . Accessed July 23, 2013.

HOW DO WE INTERACT WITH OUR PHYSICAL ENVIRONMENT?

To understand how the physical environment—be it the unaltered, altered, or built environment—affects health, we need to explore the myriad ways that we interact with it. Box 8-3 illustrates this concept.

Because of the complexity of the interactions between human beings and the physical environment, a range of approaches has been developed for addressing these issues. We will categorize and examine these approaches as follows:

• Risk assessment

• Public health assessment

• Ecological assessment

• Interaction analysis

We can think of these strategies as a progression of approaches of increasing complexity. We will organize our approach to environmental diseases and injuries starting with risk assessment and proceeding in order to examine each of these strategies.

BOX 8-3 How We Interact with Our Environment

We are exposed to the physical environment every minute of our lives through multiple routes. For each of these routes of exposure, the body has mechanisms for protection. We are primarily exposed to the environment via the skin; the respiratory tract (from the nose to the lungs); the alimentary, or digestive, tract (from the mouth to the anus); and the genital-urinary tract.

Each bodily surface that is directly exposed to the physical environment has developed a form of barrier protection. The skin provides direct protection against radiation, organisms, and physical contact, as well as providing some protections against heat and cold. The respiratory tract is guarded by mucous production and by small hairlike structures called cilia, whose motion in conjunction with coughing removes materials that we breathe into our lungs. Cells called phagocytes literally consume organisms and large particles. Antibodies, along with cell-mediated immunity, also protect against access of harmful particles and organisms through the lungs. The alimentary, or digestive, tract is protected by saliva, mucous membranes, and antibodies, as well as strong acidity in the stomach. The genital-urinary tract is protected by mucous membrane barriers, antibody and cell-mediated immunity, and at times by an acid environment. a

Therefore, we need to recognize that the impacts of the environment on health are very complex. 7 We should expect to find that the following issues affect the risk:

• Route of exposure—The consequences of exposures to heavy metals including mercury, lead, and cadmium, for instance, depend on whether the exposure is via the skin or the respiratory or gastrointestinal tracts.

• Timing of exposure—Short-term high-dose impacts often will not be the same as long-term low-dose impacts, even if the total exposure and the routes of exposure are the same. For instance, a small number of severe episodes of sunburn during childhood have been found to greatly increase the risk of skin cancers far more than multiple milder adult sunburns. Chronic low-dose exposures may produce different and more subtle impacts.

• Stage of life—The impact on the very young and the very old is likely to be different than the impact on people at other stages of life. We need to be especially concerned about exposures during pregnancy, early childhood, and the later years of life.

• Other diseases—The presence of other diseases will affect how the body is impacted by an environmental exposure. We need to be especially concerned about environmental exposures for those with chronic lung diseases and those with suppressed immune systems, such as those living with AIDS.

• Special sensitivities—A few individuals will be hypersensitive to specific environmental exposures that have no measurable impact on the vast majority of individuals. We need to be concerned about how to identify and protect these individuals without depriving them of rights or opportunities.

_______________

a The effectiveness of our bodily defenses depends on a number of factors—for instance, genetic factors. Dark skin pigmentation reduces the penetration of radiation and reduces the risk of skin cancers, including melanoma, the most serious of skin cancers. Other diseases affect how well our defenses operate—for instance, chronic obstructive lung disease and cystic fibrosis can alter the ability of the cilia in the lungs to operate effectively. Age can affect the ability of our skin to serve as an effective barrier as well as the ability of the immune system to respond. The elderly are especially prone to the effects of heat and cold. They are also more susceptible to a range of infections and cancers. Our defense mechanisms can overreact to environmental stimuli and themselves produce ailments, including allergies and autoimmune disease. The impacts of certain environmental exposures may be limited to a small number of susceptible individuals whose immune systems react especially strongly to specific environmental exposures. For instance, allergies to peanuts or household or industrial chemicals can produce unusual, but severe, reactions in a small number of susceptible individuals.

HOW DOES RISK ASSESSMENT ADDRESS THE IMPACTS OF THE PHYSICAL ENVIRONMENT?

Risk assessment is a formal process that aims to measure the potential impact of known hazards. A hazard indicates the inherent danger of an exposure, while a risk assessment aims to take into account not only the inherent danger, but also the quantity, route, and timing of the exposure. 8 The risk assessment approach to environmental hazards represents the mainstay of our current approach. The underlying principles have a long history in public health, often resulting from the investigation of specific occupational exposures.

One of the earliest occupational investigations occurred among chimney sweeps in England during the 1700s. Their high-dose exposure to carbon residues in smokestacks led to early and frequent testicular cancer. In the 1800s, industrializing countries also provided ample opportunities to study the impacts of work-related exposures. For instance, the dangers of radiation came to light after high levels of cancer were detected in workers who painted watches with radiation-containing paint for the purposes of nighttime illumination. The dangers of asbestos became evident after high-dose exposures among ship workers during World War II resulted in cases of lung cancer many years later. The dangers of exposure to polyvinyl chloride (PVC), a common industrial compound, were recognized after five workers from the same manufacturing plant came down with a rare liver tumor in the 1970s.

BOX 8-4 Benzene and Risk Assessment

Benzene is an organic chemical that is used as a solvent in the chemical and pharmaceutical industries. Because it readily becomes a gas at room temperature, airborne exposure is an important concern. Benzene is one of the most widely used organic chemicals. It is estimated that over 250,000 U.S. workers are exposed to benzene, particularly in the chemical, printing, paint, and petroleum industries. a

A range of toxic effects has been documented from benzene over the last 150 years. These include neurological effects of acute and chronic exposure, as well as life-threatening suppression of the production of red blood cells called aplastic anemia.

In the 1960s and 1970s, it was increasingly recognized that benzene causes cancer, particularly leukemia. Early studies of benzene and leukemia were conducted by Muzaffer Aksoy, a Turkish physician, who observed leukemia among many shoemakers in Turkey where benzene was being used as a solvent in the manufacturing of leather products. His large cohort study helped establish the chemical as a presumed cause of leukemia.

Based on a series of studies that documented the risk of leukemia, in 1978, the federal government established a standard for exposure to benzene in the air of 1 part per million (1 ppm), as opposed to the former approach of limiting the exposure to 10 parts per million (10 ppm). One part per million is approximately the equivalent of 1 drop in 40 gallons of liquid. In 1980, the U.S. Supreme Court overturned the new standard based upon the argument that the Occupational Safety and Health Administration (OSHA) had not documented the impact of the new 1 ppm standard in terms of the number of lives saved or compared it to the 10 ppm level. The Supreme Court concluded that “safe” did not mean risk-free, giving the analogies of driving a car and breathing city air. The Supreme Court insisted that standards be set based upon the preponderance of evidence from a formal risk assessment. As a result of this Supreme Court decision, a risk-assessment approach was developed that grew into the current risk-assessment process. The 1 part per million standard was supported by quantitative measures of the impact: the federal government estimated that there would be 14 to 17 excess deaths per 1,000 workers exposed to 10 ppm of benzene for a working lifetime, compared to being exposed to the new 1 ppm standard.

Thus, risk assessment today is a highly technical and quantitative activity designed to establish a maximum level of allowed exposure to one particular hazard. The goal is to protect workers and the public from the most important risks to health.

_______________

a Benzene is also a component of gasoline; therefore, the entire population has some exposure to benzene. This discussion focuses on the hazard assessment of benzene in the occupational setting.

Data from: Feitshans IL, Law and Regulation of Benzene. Environmental Health Perspectives. 1989; 82:299–307.

Risk assessment today has become a complex technical effort requiring quantitative measures of the magnitude of the risk. The history of risk assessment in the United States is closely tied to the investigations and regulations surrounding benzene. Box 8-4 provides an overview of the history of the study and regulation of this chemical hazard. 9 , 10

The formal process of risk assessment represents the current approach to environmental hazards in the United States. 10 ,11 Figure 8-3 illustrates the four-step risk assessment process as used by the U.S. Environmental Protection Agency (EPA).

Risk assessment attempts to evaluate the impact of environmental exposures one at a time and to measure the types and magnitudes of the impacts. If a substantial risk is found to exist, the process then reviews options to protect, detect, and react to the risk to minimize the burden of disease on humans.

The risk assessment process builds in a margin of error designed to provide extra protection for especially vulnerable individuals or populations. Thus, those exposed to levels above the recommended maximum levels of exposure will not necessarily experience adverse effects. Table 8-1 outlines the four steps in the risk assessment process and uses a simplified example of how airborne exposure to benzene in occupational settings may be presented in this framework.

Now let us take a look at what is meant by “public health assessment.”

FIGURE 8-3 The 4-Step Risk Assessment Process

Reproduced from U.S. Environmental Protection Agency. Risk Assessment Portal Available at http://www.epa.gov/risk/hazardous-identification.htm . Accessed August 10, 2013.

WHAT IS A PUBLIC HEALTH ASSESSMENT?

Risk assessment is distinguished from what is called a public health assessment. A public health assessment goes beyond a risk assessment by including data on actual exposure in a community.

Public health assessments have the potential for major impacts on large numbers of people because they address not just the risks in a specific location, such as in an occupational setting, but also the risks to large numbers of individuals and often to the population as a whole. These types of risk assessments have been very controversial and have taken years—often decades—to complete. A classic example of the importance and potential impacts of the public health assessment process and its ongoing challenges is discussed in Box 8-5, which looks at the health risks due to lead. 12 , 13

Risk assessments and public health assessments both focus exclusively on the health impacts on human beings. Let us take a look at an additional type of assessment conducted by the EPA that looks at the impact of an exposure on plants and animals.

WHAT IS AN ECOLOGICAL RISK ASSESSMENT?

Environmental health cannot be viewed solely on the basis of current impacts on human health. The impacts of environmental contamination or pollution on plants and animals and the ecosystems in which they exist often have important long-term consequences.

The modern environmental movement in the United States was ignited in large part by Rachel Carson’s book, Silent Spring, which described how the widespread use of DDT had threatened the American Eagle and other birds as it became deposited in and weakened their eggs. 14 Broader concern about the impacts of contaminants on ecological systems ranging from chemicals, to radiation, to genetically altered crops has made clear the importance of ecological risk assessments. Human health consequences remain an important, but not necessarily direct, consequence of the impacts of environmental contamination or pollution as described in Box 8-6, which explores the impacts of mercury. 15 , 16

TABLE 8-1 Four-Step Risk Assessment and Simplified Example—Benzene

Components

Simplified example—benzene

Hazard identification

What health effects are caused by the pollutant?

Benzene causes leukemia

Strong evidence from cohort studies and supportive animal data exist

Dose-response relationship

What are the health problems at different exposures?

Strong dose-response relationship among occupational workers with level of 1 ppm over a working lifetime

The impact of exposure at 1 ppm is indistinguishable from unexposed, with rapid increase in rates of leukemia above that level

Exposure assessment

How much of the pollutant are people exposed to during a specific time period? How many people are exposed?

Industrial exposures above 1 ppm are common in a range of industries at the time the standard was set

Over 250,000 workers exposed to benzene

Risk characterization

What is the extra risk of health problems in the exposed population?

14–17 excess cases of leukemia per 1,000 workers exposed to 10 ppm throughout a working lifetime

Data from United States Environmental Protection Agency. Human Health Risk Assessment. Available at http://www.epa.gov/risk_assessment/health-risk.htm . Accessed August 10, 2013.

BOX 8-5 Health Risks Due to Lead

Knowledge of the potential for lead poisoning goes back to ancient civilizations, when the metal was widely used—for example, it was a component of water pipes and part of the process of making wine. In Rome, lead was used as a method of abortion, and high-dose exposures led to a range of mental effects. It is said the Roman emperors were affected by the high levels of lead in Roman wine.

Benjamin Franklin listed every known profession for which lead posed a health hazard and predicted that many years would pass before the public health consequences of lead were addressed. Of course, Benjamin Franklin was right. Things were to get worse before they got better.

In the 1920s, lead was added to gasoline to make for smoother driving. It was highly effective in getting the “knocks” out of early versions of the piston engine, as well as elevating the level of lead in the air. Even today, the lead from gasoline lies in the soil of many playgrounds. High levels of lead also improved the performance of paints. Houses built before the 1970s, and especially before the 1950s, still pose a threat to children who often ingest peeling paint.

It was not until the 1970s that the effect of low-dose lead exposure on the development of intellectual function became clear. The studies of Dr. Herbert Needleman and subsequent investigators documented clear-cut negative effects on the intellectual development of young children even at low levels of exposure. This prompted efforts to remove lead from gasoline, paints, and many other products. In recent years, new sources of lead, including toys, pottery, and water, have been given increased attention. In short, lead is a well-recognized hazard that is still with us.

Efforts to protect the environment have been coupled with efforts to detect and react to elevated lead levels. It is now standard practice in pediatrics and public health to monitor blood levels in high-risk children, investigate their home environments, and treat persistently elevated levels. Lead standards for playgrounds, lead abatement programs for homes, and lead monitoring of consumer products all aim to reduce or eliminate the hazards of lead. The system is by no means foolproof, and in recent years, elevated levels of the metal have been found from such divergent sources as toys manufactured in China and water in Washington, D.C. Table 8-2 summarizes the potential exposures to lead, including their sources, and offers potential means of reducing or eliminating the hazard.

TABLE 8-2 Where Does Lead in Our Bodies Come From and What Can Be Done About It?

How lead enters our bodies	Where it comes from	Ways to reduce exposure
Inhalation	Workers in many lead-exposure industries, including mining, smelting, metal repair, or foundry work Demolition and renovation activities that generate fumes and dust, including home renovations and hobby activities Addition of lead to gasoline Once inhaled deep into the lungs, it may remain for long periods and be absorbed into blood over time	Occupational controls Phaseout of lead in gasoline in United States from 1976 to 1996
Ingestion	Children—normal ingestion of dirt and dust by infants and young children, with up to 5% of children who ingest large quantities—a condition called “pica” Children absorb greater percentage of ingested lead than adults	Removal of lead paint from older homes—lead levels in paint in the 1950s and earlier were as much as 50% lead Enforce elimination of lead paint from children’s toys
Ingestion	Children’s toys and objects that are placed in the mouth are especially important sources Soil near old high traffic areas often contaminated from previous lead in gasoline Glazed pottery often includes lead that can leach into food	Monitoring and control of lead levels in soil in young children’s play areas Very high blood levels may require “chelation”—treatment to reduce lead levels in blood
Water	Pipes, especially in older water supplies and homes built before the mid-1980s, often contain lead Lead used in pipes outside and within the home can leach into water—especially warm water—over time	Regulation of levels of lead in public water supply Run home water before use—especially after away for extended period Use cold water for cooking
In utero	Pregnant women absorb higher percentage of ingested lead compared to children, and lead can cross placenta Mother’s previous lead exposure stored in her bones can be resorbed into her blood during pregnancy	Special effort to reduce exposure by pregnant women, including special care with home renovations during pregnancy, especially homes built before 1970

Data from Agency for Toxic Substance and Disease Registry. Case Studies in Environmental Medicine-Lead. Available at http://wonder.cdc.gov/wonder/prevguid/p0000017/p0000017.asp . Accessed July 23, 2013.

Up to this point, we have addressed the impact of environmental exposures one at a time. Increasingly, we find that the interactions between exposures produce unexpectedly large impacts. Let us now look at a strategy that addresses more than one problem at a time and takes into consideration the interaction between multiple exposures. We will call it an interaction analysis.

WHAT IS AN INTERACTION ANALYSIS APPROACH TO ENVIRONMENTAL DISEASES?

The term interaction analysis implies that to understand and control the impacts of environmental exposures, it is necessary to take into account the effect of two or more exposures. Box 8-7 describes the multiple interacting factors contributing to depletion of the ozone layer.

Risk assessment approaches make the assumption that each exposure stands on its own. Thus, if there is more than one type of exposure, we need to make the assumption that the total impact is the sum of the two impacts. For example, if one exposure has a relative risk of 4 and a second has a relative risk of 6, we assume that exposure to both results in a relative risk of 10. Many times, adding together the relative risks does provide an approximation of the risk of two or more exposures. However, in an increasing number of situations, we are recognizing that there are interactions between exposures themselves so that the presence of both exposures results in an overall impact much greater than expected. For instance, we may find that having both exposures results in a relative risk of a bad outcome of 4 times 6, or 24, instead of 10. This type of interaction is called multiplicative interaction. Box 8-8 examines the multiplicative interaction between radon and cigarette smoking. 18

BOX 8-6 Health Risks of Mercury in the Environment

The impact of high-dose mercury on mental function has been recognized since the 1800s. More recently, it was established that much lower levels of mercury pose risks to the fetus. Neurological damage, including learning disabilities and hearing loss, have been documented at low levels of exposure. The human risks of mercury exposure need to be understood as part of the impact of mercury on an entire ecological system.

For much of the late 1800s and the 1900s, mercury was a common product of industry that heavily contaminated the Great Lakes of the United States. The impacts were not appreciated despite the high levels of contamination and the impacts on animal species. Mercury in bodies of water is filtered by fish species and can concentrate in their fat. Thus, certain fish species can and do accumulate high concentrations of mercury. These species may be eaten by fish-eating birds and pose a risk to a number of endangered avian species. There is no technologically feasible method for removing mercury from the Great Lakes or other bodies of water. Your children’s children will most likely be living with mercury contamination.

Recommendations for limiting the consumption of fish, especially by pregnant women, have been the mainstay of efforts to address this problem. These efforts are complicated by the fact that the consumption of fish also carries health benefits. Today, the challenge is how to minimize the amount of mercury consumed by women without losing the benefits of fish consumption. Because some fish have much higher mercury levels than others, the March of Dimes recommends that pregnant women avoid shark, swordfish, king mackerel, and tilefish. They indicate that “it is ok” to eat a limited amount of fish that contain small amounts of mercury, including salmon, pollock, catfish, and canned light tuna. 16 The details of how much fish is safe for pregnant women to eat remains controversial. For today and many years to come, we will be living with the impacts of past environmental contamination on entire ecosystems.

BOX 8-7 Addressing the Problem of the Hole in the Ozone Layer 17

It was first recognized in 1985 that the layer of ozone above Antarctica was being depleted at an alarming rate. Ozone in the upper atmosphere is known to protect against damaging radiation from the sun. Fears were raised that the hole in the ozone would expand progressively, encompass populated areas in the southern hemisphere, and involve the northern hemisphere as well.

It was quickly recognized that the problem was linked to multiple interacting human and naturally occurring systems. The use of chlorofluorocarbons (CFCs) in such products as refrigerators and air-conditioning equipment was quickly identified as a major contributor. In addition, commonly used aerosol sprays from deodorants and hair sprays contained CFCs. More concerning was the use of CFC in devices to deliver medications.

The timely accumulation of data, the rapid understanding of the multiple contributors to the problem, and a worldwide media campaign soon brought together a remarkably effective response to the problem. By 1987, an international agreement, known as the Montreal Protocol, was developed and quickly implemented by most nations. The agreement and subsequent revisions resulted in the rapid phaseout of most uses of CFC, with more gradual elimination of CFCs in medical devices.

The hole in the ozone layer continues to expand due to the extremely long half-life of CFCs. The projections, however, are for a turnaround in the near future and a resolution of the problem by 2050. The coordinated scientific, public health, health communications, and political responses have encouraged future efforts to recognize and jointly address multifactor environmental health problems.

BOX 8-8 Interaction Between Radon and Cigarettes

Radon is a naturally occurring radioactive gas. It is colorless and odorless. Radon is produced by the decay of uranium in soil, rock, and groundwater. It emits ionizing radiation during its radioactive decay. Radon is found all over the country, though there are areas of the country with substantially higher levels than other areas. Radon gets into the indoor air primarily by entering via the soil under homes and other buildings at the basement or lowest level.

Today, it is recognized that radon is the second most important cause of lung cancer after cigarettes and the most common cause of cancer among nonsmokers. The EPA estimates that radon accounts for over 20,000 cases of lung cancer, as compared with the over 100,000 cases attributed to cigarettes. The average indoor level in the United States is about 1.3pCi/L. The EPA has set a level of 2pCi/L as an attainable level and a level of 4pCi/L as the maximum recommended level. Approximately 15% of homes in the United States have basement radon levels above 4pCi/L.

Cigarette smoking and radon exposure are multiplicative; that is, when both are present, the hazard is multiplied. For instance, using the EPA’s figures, the relative risk of lung cancer for the average smoker is approximately 9 times the risk compared to a nonsmoker. The relative risk from radon when the level is 10pCi/L compared to 2pCi/L is over 4.5. When both cigarette smoking and a level of radon exposure of 10pCi/L are present, the relative risk of lung cancer increases over 40 times.

The recognition that radon and also asbestos multiply the impacts of cigarette smoking has had a key impact on the approaches used to address these potential hazards. For smokers with exposure to these hazards, the risk can be greatly reduced by reductions in radon and asbestos, as well as by stopping smoking. Because both radon and asbestos are potentially controllable environmental exposures, there has been a great deal of attention and money given to the control of these hazards. Thus, the recognition of interactions that multiply or greatly increase the risk have become an important tool for setting priorities and developing approaches to risk reduction.

Not all risks for environmental disease require high-level or long-term exposure. In addition to causing lung cancer, asbestos has also been shown to cause a form of cancer called mesothelioma, which originates in the lining of the lung or pleura. Even small and short-term exposures to asbestos may cause mesothelioma, as evidenced by well-documented cases among household members who washed the clothing of those exposed. New technologies, such as nanotechnology, are raising concerns that the risks of low-level exposure need to be investigated as much as those of high-level exposure. Low-dose environmental exposures to estrogen-like substances may pose threats to the reproductive health of animal species and could even affect the human rate of breast cancer. Addressing these types of issues requires us to focus on the interactions between multiple factors.

Now we have taken a look at the basic regulatory approaches we currently use to address the hazards from the physical environment. Let us now take a look at the safety component of environmental health and safety, starting with injuries.

WHAT DO WE MEAN BY “INTENTIONAL AND UNINTENTIONAL INJURIES”?

Injuries can occur in a wide array of settings and circumstances, including actions at work, home, and where we play. They can affect everyone, regardless of age, income, race, or ethnicity. It is estimated that, in the United States, one person dies every three minutes due to violence or injury. Injuries are the leading cause of death among persons aged 1 to 44 years. 20 Injuries do not always result in death and can result in long-term health effects, impacting quality of life.

In public health, we try to avoid the use of the term “accident” because “accident” implies that the reasons for the injury are beyond our control. Injuries can be categorized as intentional and unintentional. Intentional injuries are brought about on purpose, that is, by intention, whether the injury is self-inflicted or meant for others. Intentional injuries can impact entire populations, such as bioterrorist actions that lead to fear and fatalities among a population, or can directly impact individuals, such as with suicide. Harms that occur not on purpose—that is, not by intention—are categorized as unintentional injuries. Unintentional injuries encompass injuries sustained in motor vehicle collisions, drownings, falls, fires, unintentional poisonings, and many other incidents.

WHAT IS BEING DONE TO KEEP THE POPULATION SAFE?

Safety is approached like many other public health issues: the problem is described; risk and protective factors are identified; and interventions and strategies are developed, implemented, evaluated, and disseminated. The formal steps of the evidence-based public health approach are often used to examine specific issues and interventions.

One of the most visible public health tools used to keep populations safe is outbreak investigations. These investigations conjure images of public health professionals serving as “disease detectives,” tracking and responding to outbreaks of acute disease, and these investigations are often viewed as quintessential public health. Box 8-9 discusses some of the successes health departments and the CDC have had in outbreak investigations.

Public health’s role in protecting the health of populations has evolved as new threats have emerged, including bioterrorism. Box 8-10 reviews the anthrax case that occurred shortly after the September 11, 2001, terrorist attack and describes its impact on public health.

In recent years, public health agencies have been increasingly integrated into a National Incident Management System (NIMS), which is part of the Department of Homeland Security (DHS). A central feature of the NIMS is an incident command system (ICS) widely used by police, fire, and emergency management agencies. The ICS attempts to establish uniform procedures and terminology, and an integrated communications system with established and practiced roles for each agency. The goal is to integrate these approaches into ongoing operations and not reserve them solely for emergency situations. 19

The DHS has developed what is called an all-hazards approach. An all-hazards approach to public health preparedness uses the same approach to preparing for many types of disasters, including use of surveillance systems, communications systems, evacuations, and an organized healthcare response. The all-hazards approach has been widely endorsed by public health agencies and organizations in part at least because it recognizes the need for basic public health infrastructure to respond not only to the dramatic crisis or emergency, but to day-to-day needs as well.

Preparing for and responding to emergencies and disasters is key to addressing the expected and unexpected crises that we will inevitably face in the future. In addition to emergency and disaster preparedness and response, public health sets out to ensure safety of the population in everyday tasks. Let us look at the CDC framework used to prevent intentional and unintentional injury and diminish associated consequences.

BOX 8-9 Outbreak Investigations

Outbreak investigations have been a key component of public health’s effort to respond to epidemics and clusters of acute disease. These investigations are often successfully handled by local and state health agencies. The Centers for Disease Control (CDC), however, may be called in to assist with them. The CDC is involved in hundreds of outbreak investigations each year.

Famous investigations include the 1976 outbreak of what came to be called Legionnaires’ disease. Hundreds of military veterans, called Legionnaires, gathering in Philadelphia in July to celebrate the nation’s bicentennial, were infected and many died from pneumonia. The CDC identified the cause as previously unrecognized bacteria—now called Legionella—that can grow in hot water and can be spread through the air.

In the early 1980s, an outbreak of life-threatening cardiovascular shock, known as toxic shock syndrome (TSS), was traced to a new type of absorbent tampon. It brought to light the need for surveillance of new products, even those not suspected of causing disease.

The most important outbreak of the late 1900s was investigated and brought to professional and public attention in 1981 by the CDC. It came to be called acquired immunodeficiency syndrome (AIDS).

Outbreak investigations are not limited to communicable diseases. In fact, the illnesses may originate, for example, from an environmental toxin, a food additive or supplement, or a drug reaction. For instance, eosinophilia-myalgia syndrome (EMS) is an incurable and sometimes fatal neurological condition that often presents with vague flulike symptoms. It was traced by the CDC to poorly produced L-trytophan, an amino acid widely used as a food supplement. Reye’s syndrome, an often fatal acute liver disease of children, was traced to the use of “baby aspirin” for healthy children during acute viral infections.

Thousands of outbreak investigations are conducted in the United States each year and are mostly handled by state and local health departments. These types of investigations can take months or even years to complete. Often the outbreak is over before the investigation can be completed. Outbreak investigations will remain an important part of public health. However, new technologies, new tracking systems, and better communications systems will hopefully make these critical investigations more rapid and efficient.

BOX 8-10 Bioterrorism and Anthrax 20

Shortly after the terrorist attack on the United States on September 11, 2001, a second attack occurred that greatly altered the course of public health in the country. The attack occurred in the form of letters containing a powdered form of anthrax bacteria delivered through the U.S. mail to Congress and national news networks.

Anthrax is bacteria long known for its occasional spread from cattle to humans by close contact and its potential to cause a life-threatening pneumonia. It is considered a particularly deadly agent for bioterrorism, with the potential to kill tens of thousands of people. When prepared in the form of a weapon and delivered in quantity, it has the potential to widely disperse over an entire city or region. Early detection of the substance and treatment of its effects are key to controlling such an attack, including preventing the pneumonia through the early use of antibiotics.

The anthrax attack in 2001 made headlines for weeks, temporarily shutting down Congress and much of Washington, killing five people, and causing severe illness in 17 others. The episode also brought attention and funding to public health programs. It was soon recognized that even large health departments with extensive responsibilities and expertise were not prepared to address bioterrorism and ensure the availability of public health laboratories to diagnose anthrax-related illness and other potential agents of bioterrorism.

Preparation for bioterrorism also focuses on the unique characteristics of bioterrorism and the specific organisms that may be involved with it. The anthrax episode highlighted how terrorism, in general, and bioterrorism, in particular, differ from the types of emergencies and disasters that have become familiar. First, they may involve the military, as well as law enforcement. Second, they require knowledge of agents that are often very rare. Little expertise exists in either the public health or medical communities about agents such as anthrax, botulism, smallpox, and plague. In addition, bioterrorism may not be easily detected, allowing the agent to spread widely before it is noticed and action can be taken. Finally, there is the potential for multiple simultaneous threats at multiple locations. Thus, bioterrorism requires special preparation above and beyond the evolving preparedness system for emergencies and disasters. Public health agencies, including the CDC and local health departments, were on the front lines of the anthrax attack and will continue to be part of the first response to bioterrorism attacks if they occur in the future.

When approaching violence and injury, the CDC:

• Identifies and monitors the injury problem

• Conducts research to guide decision making

• Empowers states through funding and technical assistance

• Builds partnerships for prevention

• Builds awareness through communication and education

• Collaborates with partners around the globe to prevent violence and injuries globally 21

This framework has been applied to motor vehicle safety, which has been identified as 1 of the 10 great public health achievements in the 20th century. That trend has continued though the first decade of the 2000s. From 2001 to 2010, the number of vehicle miles traveled in the United States increased by 8.5%; however, the death rate for motor vehicle travel declined from 14.9 per 100,000 population to 11.0, while the injury rate declined from 1,130 to 722 per 100,000 population. 22

The CDC Injury Center uses comprehensive data systems to track the burden of motor vehicle crashes, studying patterns to understand the problem and identify research, intervention, and policy priorities. This has led to the development of educational tools and resources to raise awareness of the effectiveness of seat belts, supporting efforts to reduce drinking and driving, supporting surveillance and evaluation activities to increase motorcycle helmet use, encouraging state adoption of graduated driver’s licensing programs, and collaborating with the United Nations and World Health Organization to improve road safety across the globe. 23

We have now taken a look at approaches being used to address the issues of environmental disease and injuries. The problems of environmental health and safety require increasingly sophisticated solutions. Lessons learned from these efforts have potential applications to other aspects of public health and health care.

We have now looked at noncommunicable diseases, communicable diseases, and environmental health and safety as ways of organizing the major causes of disability and death. Now, let us turn our attention to the organized systems that have been developed for addressing these problems.

KEY WORDS

• Unaltered environment

• Altered environment

• Built environment

• Risk assessment

• Public health assessment

• Ecological assessment

• Interaction analysis

• Hazards

• Hazard identification

• Dose-response relationship

• Exposure assessment

• Risk characterization

• Interaction analysis

• Multiplicative interaction

• Intentional injuries

• Unintentional injuries

• All-hazards approach