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Home , Environmental toxicology

14

Environmental Health and

Chapter Objectives

This chapter will help you:

Identify major and explain the goals of environmental health

Describe the types, abundance, distribution, and movement of toxic substances in the environment

Discuss the study of hazards and their effects, including case histories, epidemiology, animal testing, and dose-response analysis

Evaluate and

Compare philosophical approaches to risk

Describe regulatory policy in the and internationally

Lecture Outline

I. Central Case: in the Bottle: Is Bisphenol A Safe?

A. 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 better than 9 in 10 chance that it is coursing through your body right now. B. With so many uses, bisphenol A, an organic compound with the chemical formula C15H16O2, has become one of the world’s most-produced chemicals; each year we make 1 pound of BPA for each person on the planet, and over 6 pounds per person in the United States! C. Bisphenol A leaches out of its many products and into our food, water, air, and bodies. Fully 93% of Americans carry detectable concentrations in their urine,

according to the latest National Health and Nutrition Examination Survey conducted by the Centers for Disease Control and Prevention (CDC). D. Over 200 studies with rats, mice, and other animals have shown many apparent effects of BPA, including a wide range of reproductive abnormalities. E. Scientists say this is because BPA mimics the female sex hormone estrogen; that is, it is structurally similar to estrogen and can induce some of its effects in animals. F. In reaction to the burgeoning research, a growing number of researchers, doctors, and consumer advocates are calling on governments to regulate bisphenol A and for manufacturers to stop using it. G. In 2008, Canada became the first nation to declare bisphenol A toxic. It banned the sale, import, and advertising of baby products using BPA. H. In the face of mounting press coverage and public concern, many companies are choosing to voluntarily remove BPA from their products.

II. Environmental Health 1. The study and practice of environmental health assesses environmental factors that influence human health and quality of life.

A. We face four types of environmental hazards. 1. Physical hazards arise from processes that occur naturally in our environment and pose risks to human life or health. Examples include ultraviolet (UV) radiation from sunlight, or discrete events such as earthquakes, volcanic eruptions, fires, floods, blizzards, landslides, hurricanes, and droughts. 2. Chemical hazards include many of the synthetic chemicals that our society produces, such as disinfectants and , and also include chemicals produced naturally by . 3. Biological hazards result from ecological interactions among organisms. When we become sick from a virus, bacterial infection, or other pathogen, we are suffering parasitism by other species that are simply fulfilling their ecological roles, and this is what we call infectious disease. 4. 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. Choosing to smoke, poor diet, and living in proximity to toxic waste are all cultural hazards.

B. Many environmental health hazards exist indoors. 1. Cigarette smoke and radon are leading indoor hazards and are the top two causes of lung in developed nations.

2. Another indoor is causing a condition called . 3. poisoning is another indoor health hazard. When ingested, lead, a heavy metal, can cause damage to the brain, liver, kidney, and stomach; learning problems and behavioral abnormalities; anemia; ; and even death. 4. A recently recognized hazard is a group of chemicals known as polybrominated diphenyl ethers (PBDEs). These chemicals appear to be endocrine disruptors, affecting thyroid hormones in animals, and have been banned in Europe.

C. Disease is a major focus of environmental health. 1. Many major killers, such as cancer, heart disease, and respiratory disorders, have genetic bases but are also influenced by environmental factors. 2. Malnutrition can foster a wide variety of illnesses, as can poverty, poor hygiene, lifestyle choices, and lack of exercise. 3. Over half the world’s deaths result from non-infectious diseases, such as cancer and heart disease, while 1 death in 11 is due to injuries. 4. In developed nations like the United States, lifestyle trends are altering the prevalence of non-infectious disease in ways both good and bad. 5. Although infectious disease accounts for fewer deaths than non-infectious disease, it robs society of more years of human life because it tends to strike people at all ages, including the very young.

D. Infectious disease interacts with social and environmental influences. 1. Many diseases are spreading because we are so mobile in our modern era of globalization. 2. The changes we cause to our environment can also cause diseases to spread. 3. To predict and prevent infectious disease, environmental health experts assess the complicated relationships among technology, land use, and .

E. Health workers are fighting disease in many ways. 1. Perhaps the best way to reduce disease is to improve the basic living conditions of the world’s poor. Other than providing them food security, this means ensuring their access to safe drinking water and improving sanitation by minimizing exposure to human waste, garbage, and wastewater. 2. Another important pursuit is to expand access to health care. In developing nations, this includes opening clinics, immunizing children against

diseases, providing prenatal and postnatal care for mothers and babies, and making generic and inexpensive pharmaceuticals available. 3. Education campaigns play a vital role in rich and poor nations alike. 4. Such efforts are being spearheaded internationally by the United Nations, the World Health Organization, the U.S. Agency for International Development, and by non-governmental organizations and funding agencies.

F. Toxicology is the study of poisonous substances. 1. Toxicology is the science that examines the effects of poisonous substances on humans and other organisms. 2. Toxicologists assess and compare substances to determine their , the degree of harm a chemical substance can inflict. 3. A toxic substance, or poison, is called a , but any chemical substance may exert negative impacts if we ingest or expose ourselves to enough of it. 4. These trends have driven the rise of environmental toxicology, which deals specifically with toxic substances that come from or are discharged into the environment.

G. Risks must be balanced against rewards.

III. Toxic Substances in the Environment 1. Our environment contains countless natural substances that may pose health risks. These include , toxic chemicals manufactured in the tissues of living organisms, and many synthetic (artificial, or human-made) chemicals.

A. Synthetic chemicals are all around us. 1. Thousands of synthetic chemicals have been manufactured and many have found their way into soil, air, and water.

B. Synthetic chemicals are in all of our bodies. 1. As a result of exposure, every one of us carries traces of numerous industrial chemicals in our bodies. 2. Not all synthetic chemicals pose health risks, and relatively few are known with certainty to be toxic. However, very few have been thoroughly tested.

C. began the public debate over synthetic chemicals. 1. was a naturalist, author, and government scientist.

2. Using scientific studies, medical case histories, and other data, she showed that DDT and artificial pesticides in general were hazardous to people, wildlife, and the environment. 3. Carson’s book was a bestseller and generated significant social changes in views and actions toward the environment. 4. The United States does not use DDT, but manufactures and exports it to countries that still use it, especially for mosquito control. Certain species of mosquitoes are vectors for malaria, which is considered to be a greater risk than the toxic effects of the .

D. come in different types. 1. are substances or types of radiation that cause cancer. 2. are chemicals that cause mutations in the DNA of organisms. 3. Chemicals that cause harm to the unborn are called teratogens. 4. Neurotoxins assault the nervous system. 5. Allergens overactivate the immune system, causing an immune response when one is not necessary. 6. Endocrine disruptors are toxicants that interfere with the endocrine system.

E. Toxicants may concentrate in water. 1. Water runoff often carries low amounts of toxicants from large areas of land and concentrates them in small volumes of surface water. 2. Many chemicals are soluble in water, and thus are very accessible to organisms. This is why aquatic animals such as fish, frogs, and stream invertebrates are especially good indicators of .

F. Airborne substances can travel widely. 1. Because many chemical substances can be transported by air, chemicals can exert impacts far from the site of their origin and use. Airborne transport of pesticides is sometimes termed pesticide drift. 2. Earth’s polar regions are particularly contaminated, because patterns of global atmospheric circulation tend to move airborne chemicals toward the poles. Thus, although we manufacture and apply synthetic substances mainly in temperate and tropical regions, contaminants are strikingly concentrated in the tissues of Arctic polar bears, Antarctic penguins, and people living in Greenland.

G. Some toxicants persist. 1. DDT and PCBs have long persistence times, while Bt has a very short persistence time.

2. Toxicants remain in the environment because they are designed to persist. Some plastics, for example, were developed because they resist breakdown. 3. Some toxicants have breakdown products that are just as toxic as the original chemical, or more so. For example, DDT breaks down into DDE, a highly persistent and toxic compound.

H. Toxic substances may accumulate and move up the food chain. 1. Fat-soluble toxicants such as DDT and DDE are absorbed and stored in fatty tissues and may build up in animals in a process called . 2. Toxic substances that bioaccumulate in the tissues of one may then be transferred to other organisms in the food chain, in a process called . 3. Polar bears in arctic Norway are suffering from PCB contamination because of biomagnification, resulting in high cub mortality, and persistence of toxins across generations.

I. Not all toxicants are synthetic, and not all synthetic chemicals are toxic. 1. Toxic substances exist naturally in the environment around us and in the foods we eat. 2. Scientists have actively debated just how much risk is posed by natural toxicants.

IV. Studying Effects of Hazards A. Wildlife studies integrate work in the field and the lab. 1. Scientists study the impacts of environmental hazards on wild animals to help conserve animal populations and also to understand potential risks to people. 2. Often wildlife toxicologists work in the field to take measurements, document patterns, and generate hypotheses, and then head to the laboratory to run controlled manipulative experiments to test their hypotheses.

B. Human studies rely on case histories, epidemiology, and animal testing. 1. In studies of human health, we gain much knowledge by studying sickened individuals directly. This process of observation and analysis of individual patients is known as a case history approach. 2. Epidemiological studies involve large-scale comparisons among groups of people, usually contrasting a group known to have been exposed to some toxicant with a group that has not.

3. The advantages of epidemiological studies are their realism and ability to enable relatively accurate predictions about risk. Drawbacks include the length of time it takes to obtain results and the inability to address future effects of new hazards. 4. Manipulative experiments are needed to truly nail down causation. However, this is not possible with human subjects, so other animals are substituted.

C. Dose-response analysis is a mainstay of toxicology. 1. The standard method of testing lab animals in toxicology is called dose- response analysis. 2. The dose is the amount of toxicant the test animal receives, and the response is the type or magnitude of negative effects the animal exhibits as a result. The response is generally quantified by measuring the proportion of animals exhibiting negative effects. 3. Once a dose-response curve is plotted, scientists can calculate a convenient shorthand gauge of a substance’s toxicity—the amount of toxicant it takes to kill half the population of study animals used (LD50). 4. Nonlethal health effects are determined by the level of toxicant at which 50% of the population is affected (ED50). 5. Common sense suggests that the greater the dose, the stronger the response will be. However, sometimes responses occur only above a certain dose, called the threshold dose. 6. Sometimes responses decrease with dosage. Some dose-response curves are U-shaped, J-shaped, or shaped like an inverted U; these curves appear to apply to endocrine disruptors. 7. Knowing the shape of the dose-response curve is important for predicting effects. For some toxicants, such as endocrine disruptors, the .U. shaped curve indicates impact at very low concentrations.

D. Endocrine disruption poses challenges for toxicology. 1. Because so many novel synthetic chemicals exist in very low concentrations over wide areas, many scientists suspect that we may have underestimated the dangers of compounds that exert impacts at low concentrations. 2. The idea that synthetic chemicals might be altering the hormones of animals was not widely appreciated until the 1996 publication of the book Our Stolen Future, by Theo Colburn, Dianne Dumanoski, and J.P. Myers. 3. Today, thousands of studies have linked hundreds of substances to effects on reproduction, development, immune function, brain and nervous system function, and other hormone-driven processes in animals. Many studies also suggest impacts on people.

4. Much of the research into hormone disruption has brought about strident debate, partly because a great deal of scientific uncertainty is inherent in any young and developing field, and that negative findings about chemicals pose an economic threat to the manufacturers of those chemicals.

E. Individuals vary considerably in their response to hazards. F. The type of exposure can affect the response. 1. The toxicity of many substances varies according to whether the exposure is in high amounts for short periods of time—acute exposure—or in lower amounts over long periods of time—chronic exposure. 2. Acute exposure is easier to recognize but chronic exposure is more common, and is more difficult to detect and diagnose.

G. Mixes may be more than the sum of their parts. 1. Interactive impacts may arise when toxicants are mixed together, and when these impacts are more than or different from the simple sum of their constituent effects, these are called synergistic effects. 2. Traditionally, environmental health has tackled the effects of single hazards one at a time, and single-substance tests have received priority. This is changing, but scientists will never be able to test all possible combinations.

V. Risk Assessment and Risk Management A. We express risk in terms of probability. 1. Risk can be measured in terms of probability, a quantitative 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.

B. Our perception of risk may not match reality. C. Risk assessment analyzes risk quantitatively. 1. The quantitative measurement of risk and the comparison of risks involved in different activities or substances together are termed risk assessment. 2. Assessing risk for a chemical substance entails 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 involve 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 encounter.

D. Risk management combines science and other social factors. 1. Accurate risk assessment is a vital step toward effective risk management, which consists of decisions and strategies to minimize risk. 2. In most developed nations, risk management is handled largely by federal agencies.

VI. Philosophical and Policy Approaches A. Two approaches exist for determining safety. 1. One approach is to assume that substances are harmless until shown to be harmful—the innocent-until-proven-guilty approach. This approach encourages technological innovation but may put some dangerous substances into wide use. 2. The other approach, called the precautionary principle, is to assume that substances are harmful until shown to be harmless. This enables us to identify toxicants before they are released into the environment, but may also impede technological and economic advances.

B. Philosophical approaches are reflected in policy. 1. Most nations follow a blend of the two approaches. 2. At present, European nations follow the precautionary principle. 3. The U.S. largely follows the innocent-until-proven-guilty approach. 4. In the U.S., the tracking and regulation of synthetic chemicals is shared among several federal agencies.

C. EPA regulation is only partly effective. 1. The EPA also regulates diverse chemicals under the Toxic Substances Control Act (TSCA). a. Many and environmental advocates view TSCA as being too weak. b. The registration process involves risk assessment and risk management. c. Because the registration process takes economic considerations into account, critics say it allows hazardous chemicals to be approved if the economic benefits are judged to outweigh the hazards.

D. Toxicants are regulated internationally. 1. In 2007, the European Union’s REACH (registration, evaluation, authorization and restriction of chemicals) program went into effect. The

burden of proof for chemical safety shifted from governments to industry. REACH will also test previously authorized chemicals for toxicity; 1,500 chemicals could become restricted. 2. These new regulations are expected to cost as much as $7 billion, but the benefits to public health are estimated to be $67 billion. 3. In 2004, an international treaty, the Stockholm Convention, was ratified by over 140 nations. The convention aims first to end the use and release of 12 persistent organic (POPs) called the .dirty dozen.. It appears to be on its way to ratification.

VII. Conclusion A. International agreements such as the Stockholm Convention represent a hopeful sign that governments will act to protect the world’s people, wildlife, and from harm by toxic chemicals and other environmental hazards. B. A society’s philosophical approach to risk management will determine what policy decisions it makes.

Key Terms

infectious disease

acute exposure LD50

allergens mutagens

bioaccumulation neurotoxins

biomagnification REACH

bisphenol A response

carcinogens risk

case history risk assessment chronic exposure risk management dose synergistic effects dose-response analysis teratogens dose-response curve threshold dose

ED50 toxicant endocrine disruptors toxicity environmental health toxicology environmental toxicology Toxic Substances Control Act epidemiological studies toxins