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BOS 4201, Toxicology 1

Course Learning Outcomes for Unit III Upon completion of this unit, students should be able to:

3. Assess the environmental risk from the presence of chemical compounds based on their toxicity category. 3.1 Describe the processes by which chemicals move through the

environment. 3.2 Identify the factors affecting the fate of chemicals in the air. 3.3 Identify the factors affecting toxicity in a population.

7. Summarize the impact of exposure to various types of environmental pollution.

Unit Lesson This unit discusses the risks to the environment from chemical contamination. Historic incidents are explored in addition to the factors that affect the fate of chemicals in the environment. In the past it was thought that dilution was the solution to pollution. Chemicals were released into the environment and it was thought that these chemicals would just blow away, until researchers found persistent chemicals in locations where they were not being used. As this became known, new technologies were invented to capture or reduce the amounts of chemicals. Some chemicals are found almost everywhere in our environment. They enter our food chain and can accumulate in animals. As humans, we are at the top of the food chain and the breast-feeding infant is at the highest level. It has been theorized that they are the most exposed group to environmental contaminants. Chapter 5: Environmental Pollutants and Their Fate Pollution is defined as the any change in the characteristic of the air, water, or soil that will adversely affect the health of an organism. A pollutant is any substance released into the environment that may cause adverse effects. The ecosystem is complex, pollutants enter into the ecosystem through discharges into the atmosphere, contamination of land, and entry into water (Richards & Bourgeois, 2014, p. 89). Some examples of common pollutants include:

 gases (nitrogen oxides and sulphur dioxide),

 metals (lead and mercury),

 organics (benzene and toluene),

 noise,

 photochemical oxidants (ozone), and

 radioactive waste.

Reading Assignment Chapter 5: Environmental Pollutants and Their Fate Click here to access the Chapter 5 PowerPoint presentation. Click here to access a PDF version of the presentation.

Suggested Reading See information below.

Learning Activities (Non-Graded) See information below.

UNIT III STUDY GUIDE

Environmental Risks

BOS 4201, Toxicology 2

The fate of chemicals in the environment is affected by the process in which chemicals are moved and transformed in the environment. The processes include:

 persistence in air,

 persistence in water,

 persistence in soil,

 reactivity and degradation,

 migration in ground water, and

 bioaccumulation in aquatic or terrestrial organisms. The persistence of a chemical in the environment is the ability of a chemical to remain unchanged in a particular environment. An example of a persistent substance is PCB (polychlorinated biphenyls). PCBs are a probable human carcinogen. They also have effects on the reproductive system, endocrine system, and the nervous system. The most common effects from exposure to PCBs are acne and rashes. Primary pollutants, such as nitrogen oxides, enter the air directly and can undergo chemical reactions and produce secondary pollutants like ozone. Nitrogen dioxide reacts with oxygen and ultraviolet light to form ozone; ozone and nitrogen dioxide are lung irritants. Particles are also a concern, they vary in concentration and are categorized as PM10 (particles less than 10 microns in diameter) and PM2.5 (particles less than 2.5 microns in diameter) (Richards & Bourgeois, 2014). Particle size is important, as the smaller size penetrates into the gas exchange region of the lungs and contributes to lung disease. The fate of a chemical in the air depends on the rate of disposition and type of pollutant. The mixing with the air through vertical and horizontal transport, the chemical reactions, and the removal through precipitation contribute to this. Pollutants enter the water from run-off, atmospheric disposition, sewage treatment, accidental spills, and industrial discharge. Pollutants move throughout the water and can undergo chemical reactions. In addition, fertilizers from agricultural run-off cause the overgrowth of algae. Pollutants deposited into the soil, either deliberately or accidentally, can also undergo chemical reactions. Mercury is an example of a highly toxic metal found in the environment. Elemental mercury is generally used in scientific instruments and exposure occurs through absorption of the vapor into the body, which affects the central nervous system. Inorganic mercury causes damage to the kidneys. Organic mercury also affects the central nervous system. Mercury is also present in the environment because of the use of organomercury fungicides. It is also used in the manufacture of paper and plastics. Lead has long been recognized as an air pollutant, especially in young children and fetuses (Hodgson, 2010). Lead pollution sources include vehicle emissions and industrial processes. People are exposed to inorganic lead by ingestion and inhalation. Historically, lead poisoning in children came from paint and the effect in children was usually encephalopathy with mental retardation. Lead is taken up by the red blood cells and distributed to the kidneys and liver. Some lead is also deposited into the bones. Lead also interferes with red blood cell production and causes the destruction of red blood cells, both of which lead to anemia. Organic lead, such as tetraethyl lead, is rapidly absorbed through the skin. The effects include delusions and hallucinations.

BOS 4201, Toxicology 3

Arsenic is a metalloid found everywhere on earth. Exposures usually occur through contaminated ground water. Long term exposure to arsenic can result in various cancers (e.g., skin, lungs, and lymph glands), and hyperpigmentation of the skin (Hodgson, 2010). Noise is another type of pollution that is often overlooked. Noise pollution can come from automobile traffic, airplanes, trains, and machinery. In addition to hearing loss, noise can cause other health effects such as hypertension, tinnitus, and cardiovascular disease. Poor urban planning has been a contributing factor to residential noise exposure. Endocrine-disrupting chemicals cause changes in the endocrine system. It has been demonstrated that these chemicals are responsible for reproductive system dysfunctions. These chemicals can act as estrogen, anti-estrogen, or anti-androgens; they all result in an imbalance of hormones. Some examples of endocrine disrupting chemicals include DTT (organochlorine pesticides), PCBs (polychlorinated biphenyls), and alkylphenols. There has been an increase in breast cancer and testicular cancer since the 1940s, and it has been suggested that sperm counts are decreasing because of exposure to these chemicals. The food chain is another source of exposure to pollutants. An animal may not be able to eliminate a substance and therefore it will accumulate in the body. When that animal becomes a prey for a predator, the predator is then exposed to the accumulated substance. Exposure to environmental pollutants occurs through the pollution of the air, water, and soil. The fate of pollutants if affected by many factors and, as we have seen, there are primary and secondary pollutants. Metals are a common environmental pollutant of high toxicity. Endocrine-disrupting chemicals are becoming more of a concern as some cancer rates on the increase.

References

Hogdson, E. (2010). A textbook of modern toxicology (4th ed.). Hoboken, NJ: Wiley. Richards, I. S., & Bourgeois, M. M. (2014). Principles and practice of toxicology in

public health (2nd ed.). Burlington, MA: Jones & Bartlett.

Suggested Reading Review the recent reports about the drinking water crisis in Toledo, Ohio and Lake Erie by reading The Weather Channel website. Retrieved from: http://www.weather.com/news/toledo-ohio-lake-erie-water-supply-20140803

Learning Activities (Non-Graded) Research two extreme cases of environmental hazards, preferably in your county or state. Find the reported source and include any actual or potential health effects. Non-graded Learning Activities are provided to aid students in their course of study. You do not have to submit them. If you have questions, contact your instructor for further guidance and information.