Environmental Health and Toxicology PDF

8 Environmental Health and Toxicology How dangerous are new, synthetic chemicals like those in Learning Outcomes non-stick pans...

8 Environmental Health and Toxicology How dangerous are new, synthetic chemicals like those in Learning Outcomes non-stick pans? Do we need to worry? Paul Bradbury/OJO images/Getty Images After studying this chapter, you should be able to: 8.1 Describe health and disease and how the global disease burden is now changing. 8.2 Summarize the principles of toxicology. “To wish to become well is a part 8.3 Discuss the movement, distribution, and fate of toxic of becoming well.” substances in the environment. 8.4 Explain ways we evaluate toxicity and risk. – Seneca 8.5 Relate how we establish health policy. 152  C A S E S T U D Y PFAS: Miracle or Menace? killing his dairy cows. The unlined waste dump turned out to have 7,000 tons of Many of us have non-stick cookware and food packaging, or stain- PFOA residues from Teflon production in resistant fabrics and furniture. These products are familiar, but do a DuPont factory in nearby Parkersburg, West we understand how they avoid sticking and staining? Many use Virginia. The farmer sued DuPont, and the court ordered the com- coatings from a large family of manufactured chemical substances pany to turn over all documentation related to PFOA. known as PFAS, or per- and polyfluoroalkyl substances. Among Surprisingly, the records included confidential medical and PFAS, two of the most wildly used are PFOA (perfluoroacto- health studies, some dating back half a century, documenting a noic acid) and PFOS (perfluorooctane sulfonate). The names are variety of illnesses associated with PFOA. Major manufacturers, unwieldy, but the products are in countless items we buy daily. such as DuPont and 3M, had documented associations of PFOA The PFAS group of compounds are useful because they are slip- exposure with birth defects and cancer in laboratory animals in the pery and durable and widely used. They last well, without breaking 1960s. They also knew that factory workers had high concentra- down, and their non-sticky properties prevents cookware and fabrics tions of PFOA in their blood, and that workers, as well as residents from absorbing stains or oils. PFAS appear in stain-repellent and near industrial facilities and waste disposal sites, suffered from a water-repellent coatings, cleaning solvents, hydraulic fluids, seal- variety of cancers, as well as kidney, liver, and skin ailments. ants, and refrigerants. They are As in many environmental used in cosmetics, fire-fighting health issues, irresponsible waste foam, computer parts, carpeting, disposal caused much of the prob- pizza boxes, and popcorn bags lem. DuPont dumped PFOA and (fig. 8.1). other waste materials into public There’s also a dark side to sewers, waterways, and open waste these technological wonders. dumps. These expedient methods Because they’re so persistent avoided the much higher costs of and widely used, they are now incinerating waste or sending it to found throughout the world, secure, contained landfills. even in the most remote and In the West Virginia law suit, it seemingly pristine sites. They quickly became apparent that DuPont accumulate in birds, mam- had long recognized the adverse health mals, fish, and humans. They effects of PFOA. They also knew that can be found in the blood of the chemicals were widespread in the most people in industrialized environment and were present in local nations at 2 to 8 parts per bil- water supplies at unsafe concentra- lion (ppb). In Korea, average FIGURE 8.1 It’s estimated that 20 percent of the PFOA in American tions. The company had been search- blood comes from anti-grease coatings in pizza and popcorn containers. levels are about 60 ppb. In the ing for an alternative to PFOA, and Creatista/Shutterstock United States, nearly everyone had announced in 1993 that they had is thought to have PFAS levels in their blood about ten times a compound that appeared to be less toxic, and that stayed in the higher than the EPA (Environmental Protection Agency) limits body for a much shorter time. Nevertheless, the company decided suggested for drinking water. against shifting away from PFOA, which was worth an estimated These compounds were not regulated in the United States $1 billion a year in profits. until recently because they were not legally designated as hazard- Coming up with alternatives for the substances that we use ous. There’s a common misperception that if a chemical is danger- so widely is not easy. The major manufacturers of PFOA and ous, it will be regulated to protect public health. Under the 1976 related materials have promised to eliminate PFOA and related Toxic Substances Control Act, however, the EPA can investigate compounds. But the substitutes they have come up with so far, a chemical only when it is proven harmful. But proving harm is while less long-lasting, seem to be just as toxic. difficult, when we have long-term exposure to many different This case study demonstrates a number of themes in envi- compounds. This standard, therefore, largely eliminates public ronmental health. We have produced amazing array of synthetic oversight of new chemicals. The EPA has restricted only five syn- chemicals with highly useful properties. But monitoring, evalu- thetic chemicals in the last 40 years, out of an estimated 60,000 or ating, and regulating new compounds and understanding their more on the market. effects is extremely difficult. How dangerous is low-level but The landmark case that brought these substances into the public widespread exposure to the thousands of new materials we’ve spotlight began in 1999, when a farmer in West Virginia suspected released? This is a central question of environmental health and that water draining from a DuPont waste dump was sickening and toxicology. CHAPTER 8 Environmental Health and Toxicology 153 8.1 Environmental Health and ­mortality (death). Environmental health focuses on external factors that cause disease, including elements of the natural, social, ∙ The global disease burden is changing. Infectious diseases are cultural, and technological worlds in which we live. ­We encoun- decreasing while chronic conditions, such as heart disease, ter many different environmental health risks (fig. 8.2). Deciding stroke, and diabetes, are increasing. which are most urgent, and how to avoid them, is a matter of both personal and public policy. Ever since the publication of Rachel ∙ We can evaluate health concerns in terms of DALYs as well as Carson’s Silent Spring in 1962, the discharge, movement, fate, and death rates. effects of synthetic chemicals have been a special focus of envi- ∙ Emergent diseases are appearing with increasing frequency as ronmental health. Later in this chapter, we’ll study these topics we travel more, move into new habitats, and share our germs in detail. First, however, let’s look at some of the major causes of with others around the world. illness worldwide. In recent years, the COVID-19 pandemic has dramatically increased public discussion of health risks. Rapidly spreading The global disease burden is changing viruses are important health concerns, but contagious diseases are just one of many other environmental risk factors. Often these Although there are many worries about pollution, toxic sub- environmental factors are hard to notice, but cumulatively they can stances, emerging diseases, and other health threats, we should have important impacts. take a moment to consider the remarkable progress we’ve made Fifty years ago, leading environmental health risks included over the past hundred years in controlling many terrible diseases. infections and diarrhea from contaminated water and parasites. Epidemics that once killed millions of people have been reduced or Life was precarious, especially for very young children, and life eliminated. Smallpox was completely wiped out in 1977. Polio has spans were short in many places. Improving access to food, clean been eliminated everywhere in the world except for a few places water, sanitation, and health care has revolutionized health and in Afghanistan, Pakistan, Laos, and Madagascar. Guinea worms, health care. Today, our leading health concerns have to do with river blindness, and yaws appear to be on their way to elimination. diet and conditions associated with age. Epidemics of typhoid fever, cholera, and yellow fever that regu- Our exposure to environmental contaminants, such as PFAS, larly decimated populations a century ago are now rarely encoun- is more complicated, than it was, however. Novel diseases, includ- tered in developed countries. AIDS, which once was an immediate ing coronaviruses and influenza viruses, spread farther and faster than ever before. We encounter new chemical compounds in our environment, including pesticides, petrochemicals, and heavy Infectious metals. We produce new toxic compounds every year. We test a Agents small subset. We also write laws intended to protect ourselves and our environments from substances that are especially harmful (see chapter 24). In many ways, the world is safer than ever before; in Bacteria, some ways it is less safe. protozoa We also face environmental health threats from air and water Trauma pollution, which cause illness or death for millions each year. These risks are discussed in chapters 16 (air pollution), and 18 Viruses (water pollution). Climate change is also emerging as an impor- tant environmental health threat: Hotter temperatures amplify air and water quality issues, and heat stress is a growing concern for Air Accidents populations around the world. These and many other issues are important factors in environmental health. Pollution Noise What is health? Water The World Health Organization (WHO) defines health as a state of complete physical, mental, and social well-being, not merely Chemicals the absence of disease or infirmity. By that definition, we all are UV ill to some extent. But we all can improve our health to live hap- Lead Toxic pier, longer, more productive, and more satisfying lives if we think Smoking Substances about what we do. What is disease? A disease is an abnormal change in the Ionizing Radiation body’s condition that impairs important physical or psychological functions. Diet and nutrition, infectious agents, toxic substances, genetics, trauma, and stress all play roles in morbidity (illness) FIGURE 8.2 Major sources of environmental health risks. 154 Environmental Science  260 terms of the total number of DALYs in a population. For example, 240 a teenager permanently paralyzed by a traffic accident will have many years of suffering, health care costs, and lost potential. Simi- 220 larly, many years of expected life are lost when an infant dies from 200 an infectious disease. A senior citizen who has a stroke has lost far Sub- fewer years to disease or disability. 180 Sahara nA Deaths per 1,000 births fric Look at the changes in the relative ranking of the major causes 160 a of disease burden in table 8.1, listed in order of DALYs. Just a few 140 So uth decades ago, communicable diseases and malnutrition were high As ia in the list of illness. Today, chronic disorders related to age and 120 diet are becoming more common. Much of this change in disease Wo 100 rld burden is occurring in the low-income regions, where people are Ea adopting the habits and diets of richer countries. Malnutrition has 80 st A s ia & Pa declined in both frequency and ranking, indicating dramatically 60 Euro cific p e& improved access to food resources in much of the world. Cen 40 tra l Asia 20 North Ame rica Major causes of death have also changed 0 About 56 million people die each year, worldwide. Chronic condi- 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 tions, such as cardiovascular disease, diabetes, and cancer, once Year dominant only in wealthy countries, are now among the leading FIGURE 8.3 Child mortality has fallen dramatically over the past causes of death in lower- and middle-income regions. Those con- 50 years and is expected to continue to decline. East Asia has reached a ditions result from multiple risk factors: Diet ranks first, respon- level matching that of Europe and Central Asia, while sub-Saharan Africa sible for about 11 million of the world’s total 56 million deaths has lagged behind—mainly because of wars, poverty, and poor health. per year. High blood pressure ranks second, associated with about Death rates for children under 5 years old are shown. 10.5 million deaths. Tobacco use is the third most important risk Source: Data from the World Health Organization, 2012. factor, associated with over 8 million deaths annually, mainly from heart disease, cancer, or chronic respiratory disease. At least death sentence, has become a highly treatable disease, if people 1.3 billion people smoke, mostly in low- and middle-income coun- have access to health care. tries, and this number continues to climb. Tragically, the WHO One of the best indicators of health gains is a worldwide calculates that about 1.2 million tobacco-related deaths are non- increase in child survival. In 1960, in South Asia, for example, smokers exposed to second-hand smoke. Diabetes, air pollution, nearly one child in four died before their fifth birthday. Today, the 5-year survival rate is over 96 percent (fig. 8.3), the same as the global average. In the West African country of Mali in 1960, an Table 8.1 Global disease burden, ranked by incredible 44 percent of children died before the age of 5. Today, percentage of DALYs1 that number has fallen to 10 percent. Much of this progress is due 1990 % 2019 % simply to better nutrition, improved sanitation, and clean water, 2 which keep children healthy. According to the WHO, half of all Childbirth 9.4 Heart disease 13.3 gains in child survival are brought about by increases in women’s Heart disease 9.0 Childbirth 6.3 education, which informs and empowers mothers. Only sub- Respiratory, TB3 8.6 Diabetes, CKD 4.4 Saharan Africa has lagged in this health revolution, for a number Intestinal infections 7.2 Tumors 4.1 of reasons that include political instability and poverty. Malnutrition 3.1 Respiratory, TB 3.6 Chronic conditions now outweigh infectious Tumors 2.5 Intestinal infections 3.0 4 diseases COPD 2.2 COPD 2.5 Infectious diseases 2.0 Malnutrition 1.8 The decrease in many infectious illnesses, along with an aging population, is producing a shift in global disease burden. Many Diabetes, CKD5 1.9 HIV/AIDs, STDs 1.5 people now live for years with chronic illness or disability. Accord- Substance abuse 0.9 Substance abuse 1.4 ing to the WHO, chronic diseases now account for about half of 1 Disability adjusted life years. Data source: Institute for Health Metrics and Evaluation, 2021. the global disease burden. To account for the costs of chronic ill- 2 Maternal and neonatal disorders. ness, health agencies calculate disease burden for a population in 3 Respiratory illnesses and tuberculosis. terms of disability-adjusted life years (DALYs). One DALY rep- 4 Chronic obstructive pulmonary disorders. resents 1 lost year of healthy life. We can compare risk factors in 5 Chronic kidney disease. CHAPTER 8 Environmental Health and Toxicology 155 over-weight, and high cholesterol each contribute to over 4 million one third of the global population may have been infected, and up deaths per year. to 50 million may have died. The transition in causes of deaths largely represents improved health care and sanitation, which helps more people live long Emergent diseases often come from wildlife enough to develop chronic conditions. Intestinal infections, which contact can cause severe diarrhea and dehydration in young children, have declined everywhere. Respiratory conditions, mainly an effect of Many people became aware of the concept of emergent diseases air pollution, have declined but remain an important cause of dis- (newly occurring or spreading illnesses) with the COVID-19 pan- ability and death globally. demic that began in 2019–2020. Epidemiologists, however, were In much of the world, a leading cause of death that remains not particularly surprised to see COVID-19 appear. They have urgent is neonatal and maternal illnesses. Among children under 5, long warned that close human contact with wild animals, includ- neonatal conditions cause almost a third of all deaths globally. For ing bats, birds, and especially wild meat animals, provides a ready women in low-income countries, the Institute for Health Metrics reservoir of novel viruses. Viruses evolve rapidly and can occa- and Evaluation reports that complications of childbirth and neo- sionally jump from one species to another. Some of our most seri- natal conditions caused over 9 percent of deaths in 2019, about ous viruses originate in birds, which spread to other animals. the same as in 1990. Ready access to doctors and midwives makes This is the pattern epidemiologists suspect drove the 1918– this risk far lower, about 0.2 percent, in wealthier countries. These 1919 global influenza pandemic, which has genetic markers of deaths represent a continuing crisis of access to reproductive and originating in birds. How it transmitted to humans is unknown, infant health. Even in wealthy countries, this disparity occurs but when a virulent mutation emerged, it spread with astonish- among low-income and under-served groups. In the United States, ing speed. Similarly, In 2002, a severe acute respiratory syndrome for example, women of color die in childbirth at four to five times (SARS-CoV-1) appeared in Guangdong, southern China. This was the rate of white women. a coronavirus like that in 2019 (originally called SARS-CoV-2). This outbreak may have come from palm civets in wild meat Infectious diseases still kill millions of people Although the ills of modern life are becoming more important Benchmark Data almost everywhere in the world, communicable diseases still Among the ideas and values in this chapter, the following are kill millions of people, especially children (fig. 8.4). Humans a few worth remembering. are afflicted by a wide variety of pathogens (disease-causing 1 in 6 Chance of dying from heart disease organisms), including viruses, bacteria, protozoans (single-celled 1 in 188,364 Chance of dying in airplanes animals), parasitic worms, and flukes. Pandemics (worldwide epi- 1 in 5 Number of children in poorest countries who die before demics) have changed the course of history. In the mid-fourteenth age 5 century, the “Black Death” (bubonic plague) swept out of Asia 1 in 100 Number of children in richest countries who die before and may have killed half the people in Europe. When Europe- age 5 ans reached the Americas in the late fifteenth and early sixteenth 50% Percentage of antibiotics prescribed for inappropriate centuries, they brought with them diseases, such as smallpox, conditions measles, cholera, and yellow fever, that killed up to 90 percent 20% Estimate of PFOA in American blood from pizza and pop- of the native population in many areas. The largest loss of life in corn containers a pandemic in the past century was in the great influenza pan- 2x Increase in skin cancer risk from using tanning bed demic of 1918–1919. Epidemiologists now estimate that nearly FIGURE 8.4 (a) A group of influenza viruses magnified about 300,000 times. (b) Pathogenic bacteria magnified about 50,000 times. (c) Giardia, a parasitic intestinal protozoan, magnified about 10,000 times. (a) CDC/SCIENCE PHOTO LIBRARY/Getty Images; (b) Image Source/Getty Images; (c) Dr. Stan Erlandsen/CDC 156 Environmental Science  more virus into the body. Notably, the 1918–1919 flu never went away. Less virulent descendants still circulate, causing seasonal flu every year. This is the flu for which you should get a new immunization each year, to protect against new variants of the constantly mutating virus. Transmission from wildlife to people is increasingly likely as people travel deeper into wildlife habitat, clear forests, and hunt and trade wildlife, the likelihood of exposure multiplies. The wild meat trade is an important source of novel viruses, as wild animals, alive and dead, are increasingly marketed around the world. Normally, humans and wild species have little close contact, but in the wildlife trade, close contact is constant, as people hunt, trade, handle, and eat diverse species. In live mar- kets, multiple species are kept in close concentrations, allowing FIGURE 8.5 Ebola workers need complete protection from bodily c­ ontact, cross-species spread. Epidemiologists observe that virus out- which is difficult in a hot, humid climate. Protective gear also a ­ lienates locals, breaks like this are likely to happen again. Conservation biolo- who tend to be suspicious of strangers and authority. gists say this is a good reason to leave wild animals and their Kenzo Tribouillard/AFP/Getty Images habitat alone. The severity of a new infectious disease (fig. 8.6) depends on markets. Palm civets, however, probably picked up the virus from how rapidly we suppress it. While the COVID-19 pandemic was other species in the live-animal market, likely horseshoe bats, dire, it was far less lethal than the flu outbreak a century earlier. which evidently acquired the coronavirus from wild birds. Follow- The astonishingly rapid development of vaccines certainly reduced ing the same pattern was the 2014 emergence of Ebola hemor- illness and death. Also critical, health experts can now coordinate rhagic fever in West Africa. This deadly virus probably infected efforts, share resources, and exchange information. Agencies like some 20,000 people in 2014 and killed as many as 8,000 (fig. 8.5). the Centers for Disease Control and Prevention now exist, unlike It is thought to have originated in wild chimps or monkeys, and it a century earlier, to distribute information and support. Similarly, probably jumped to humans in the bushmeat trade. in a 2019 Ebola outbreak, health care systems mobilized much A coronavirus is a virus (basically a small package of faster than in the 2014 epidemic, delivering resources and provid- genetic material) studded with a spikes, like a solar corona. Once ing health care, including simple hydration and nourishment. It attached to a living cell in the lungs or other tissues, a virus uses is clear that coordinated, rapid responses are key to reducing the the energy and resources of the cell to reproduce and send out impacts of new types of viruses. Mumps Drug-resistant TB Bourbon virus Europe 2012 Myanmar, Nigeria, Kansas Russia 2016 2014 Middle East Respiratory syndrome Measles Saudi Arabia California 2017 2014 Chagas Avian flu U.S. 2013 H7N9 2017 Ebola Liberia 2014 India Swine flu Chikungunya 2015 Lta Am, Caribbean Zika 2013 Brazil 2016 Polio Sudan 2013 AIDS Orapouche Congo virus 1920s Peru 2016 Plague Flu H3N2 Madagascar Australia 2017 2017 FIGURE 8.6 Some recent outbreaks of highly lethal infectious diseases. Why are supercontagious organisms emerging in so many different places? Source: Data from U.S. Centers for Disease Control and Prevention. CHAPTER 8 Environmental Health and Toxicology 157 Novel diseases also threaten wild species fungus Batrachochytrium dendrobatidis, commonly called chy- trid fungus, causes the disease. It was first recognized in 1993 Humans aren’t the only ones to suffer from new and devastating in dead and dying frogs in Queensland, Australia, and now is diseases. Domestic animals and wildlife also experience sudden spreading rapidly, perhaps because the fungus has become more and widespread epidemics, which are sometimes called ecological virulent or amphibians are more susceptible due to environmen- diseases. We are coming to recognize that the delicate ecological tal change. Most of the world’s approximately 6,000 amphibian balances that we value so highly—and disrupt so frequently—are species appear to be susceptible to the disease. Amphibians are important to our own health. Conservation medicine is an emerg- especially vulnerable because water aids the movement of the ing discipline that attempts to understand how our environmental fungal spores, and most amphibians live in damp or aquatic envi- changes threaten our own health as well as that of the natural com- ronments. At least 2,000 species have declined or even become munities on which we depend for ecological services. extinct in their native habitats as part of this global epidemic. Ebola hemorrhagic fever, for example, is one of the most viru- Temperatures above 28°C (82°F) kill the fungus, and treating lent viruses ever known, is a leading example of a disease that frogs with warm water can cure the disease in some species. passes among species and affects other primate species. In 2002 Topical application of the drug chloramphenicol also has success- researchers found that 221 of the 235 western lowland gorillas they fully cured some frogs. And certain skin bacteria seem to con- had been studying in the Congo disappeared in just a few months. fer immunity to fungal infections. In some places, refuges have Many chimpanzees also died. Although the study team could find been established in which frogs can be maintained under antisep- only a few of the dead gorillas, 75 percent of those tested positive tic conditions until a cure is found. Biologists hope that survivors for Ebola. Altogether, researchers estimate that 5,000 gorillas died can eventually be reintroduced to their native habitat and species in this small area. Extrapolating to all of central Africa, it’s pos- will be preserved. sible that Ebola has killed one-third of all the gorillas in the world. Still more lethal was a disease discovered in 2006, when people living near a cave west of Albany, New York, reported something Multiple stressors aid novel parasites peculiar: Little brown bats (Myotis lucifugus) were flying outside Climate change also facilitates expansion of parasites and diseases during daylight in the middle of the winter. Inspection of the cave into new territories. Tropical diseases, such as malaria, cholera, by the Department of Environmental Conservation found numer- yellow fever, and dengue fever, have been moving into areas from ous dead bats near the cave mouth. Most had white fuzz on their which they were formerly absent, as mosquitoes, rodents, and other faces and wings, a condition now known as white-nose syndrome vectors expand into new habitat. This is just one of many ways (WNS). Little brown bats are tiny creatures, about the size of your climate change is complicating questions of environmental health thumb. They depend on about 2 grams of stored fat to get them (see What Do You Think? p. 159) Climate-related expansion of through the winter. Hibernation is essential to making their energy diseases affects other species, as well. A disease called dermo is resources last. Being awakened just once can cost a bat a month’s spreading northward through oyster populations along the Atlan- worth of fat. tic coast of North America. This disease is caused by The white fuzz has now been identified as filamentous fungus a protozoan parasite (Perkinsus marinus) that was (Pseudogymnoascus destructans), which thrives in the cool, moist first recognized in the Gulf of Mexico about conditions where bats hibernate. We don’t know where the fun- 70 years ago. In the 1950s the disease gus came from, but, true to its name, the pathogen has spread like was found in Chesapeake Bay. Since wildfire, reaching 33 states and 7 Canadian provinces. Biologists estimate that at least 7 million bats already have died from this disease. It isn’t known how the pathogen spreads. Perhaps it moves from animal to animal through physical contact. It’s also possible that humans introduce fungal spores on their shoes and clothing when they go from one cave to another. Biologists have stated that WNS is the worst epidemic ever to affect bat populations, with over 6 million killed. So far, 12 species of bat, five of them endangered species, are known to be susceptible to this plague. In infected colonies, mortality can be 100 percent. Some researchers fear that bats could be extinct in 20 years in the eastern United States. Losing these important spe- cies would have devastating ecological consequences. Amphibians are especially vulnerable FIGURE 8.7 Frogs and toads throughout the world are succumbing to a deadly disease called chytridiomycosis. Is this a newly virulent fungal An even more widespread epidemic is wiping out amphibians disease, or are amphibians more susceptible because of other environ- worldwide: a disease called chytridiomycosis, which causes dra- mental stresses? matic losses or even extinctions of frogs and toads (fig. 8.7). The Rosalie Kreulen/Shutterstock 158 Environmental Science then the parasite has been moving northward, probably assisted by parts of Europe. Because bees are essential crop pollinators, at higher sea temperatures caused by global warming. It is now found least 70 crops worth at least $15 billion annually are at risk. Many as far north as Maine. This disease doesn’t appear to be harmful to factors have been suggested to explain the mysterious bee die-off, humans, but it is devastating oyster populations. including pesticides, parasites, viruses, fungi, malnutrition, genet- Another persistent epidemic, known as colony collapse dis- ically modified crops, and long-distance shipping of bees to pol- order, is destroying honey bee colonies across North America and linate crops. What Do You Think? High temperatures and heat stress: How does We can assess risk of heat and humidity in terms of “wet bulb tem- perature.” Normally, temperature readings represent readings from a ther- global warming affect our health? mometer with its bulb surrounded by air, a “dry bulb” temperature. In Climate change is a threat multiplier. It enhances environmental hazards, contrast, a wet bulb temperature represents the reading if the thermometer from increased storm intensity and stronger heat waves to greater drought bulb were wrapped in a moist cloth, with air moving past it. Moving air risks for food crops. How is climate change likely to affect our health? evaporates moisture from the cloth, cooling the thermometer and lower- Climate change is expanding the range of infectious diseases and para- ing the temperature reading. When the surrounding air is dry, moisture sites, increasing water pollution, and making the effects of air pollution evaporates easily, and the wet bulb temperature is lower than the dry bulb more severe. temperature. When the air is humid, evaporation slows, and the wet bulb The physical stress of heat itself is also an important health impact of temperature approaches the dry bulb temperature. At 100 percent humid- global warming. Recent summers have seen extraordinary temperatures in ity, there is no evaporation, and the two readings are equal. places that normally have relatively mild summers: Seattle, WA, and Port- This approach approximates the way your body responds to tem- land, OR, saw temperatures above 46 °C (115 °F) in the summer of 2021. peratures, as your skin, like the wet bulb, cools through evaporation. Central British Columbia had the highest temperatures ever recorded in If the wet bulb temperature is about the same as your body tempera- Canada, at 49.6 °C (121 °F) in a regional heat wave that caused at least ture, above 35 °C (above 95 °F), then you lose the ability to stay cool 1,400 deaths and an estimated US $9 billion in damages to agriculture, by sweating. This temperature is considered the extreme of what the hydroelectric generation, forests, and infrastructure. human body can survive with prolonged exposure. But lower wet bulb In areas accustomed to heat, summers are getting longer and hot- temperatures, above 30 °C (86 °F) can also be deadly. Currently, wet ter. Parts of the American Southwest that normally see 30–50 days above bulb temperatures above 35 °C are rare around the globe, but a warming 100 degrees in a year can expect triple that number before the end of climate may produce these extremes in many places around the world. the century. India’s capital, Delhi, an urban region of 30 million people, The effects of heat stress and other climate-related risks on our own has exceeded 42 °C (110 °F) for multiple days in recent summers, while health depends on where we live, and on how insulated we are from envi- Jacobabad, Pakistan, has reached 52 °C (125 °F). Climatologists expect ronmental change. What sorts of vulnerabilities do you think might affect that other cities may start recording temperatures that high in coming your community? What sorts of responses are wealthier communities responsible to offer, to help reduce health impacts of climate stress in low- decades (fig. 1). income communities, or world regions? How does heat affect health? Heat stress can cause exhaustion, diz- ziness, nausea, and muscle cramping. In high temperatures, your heart pumps more blood to your skin, in an attempt to release heat. In extreme cases, this deprives organs of blood and oxygen. If unrelieved, strain on the pumping heart can cause cardiac arrest, or a combination of high tem- perature and pressure can reduce blood flow to the brain, potentially lead- ing to a stroke. As with many health concerns, risks are greatest for individuals with chronic heart or respiratory conditions, and older people. Your vulnerabil- ity also depends on whether you have access to indoor air conditioning. In Portland and Seattle, few people have historically needed air condition- ing. In India and Pakistan, few can afford it. For those who work outside, as in agriculture, construction, and for those who lack air conditioning, heat stress can be life-threatening. But less extreme suffering extends more broadly. Imagine the difficulty of young children trying to study in extreme temperatures. A combination of heat plus humidity creates the greatest risk. The human body keeps cool by sweating—that is, by evaporating water from the skin. Evaporation takes heat from the skin, and evaporation works best when the air around you is dry or breezy. This is why you fan yourself when you are hot, to move air past your skin and increase evaporation. FIGURE 1 In warming climates, keeping cool is critical for surviving summer But high humidity slows evaporation from the skin. heat CHAPTER 8 Environmental Health and Toxicology 159  Mutation Resistant bacterium understand that antibiotics combat only bacterial infections, not Antibiotic viruses, and they insist on receiving prescription from doctors. By Antibiotic some estimates, more than 20 ­percent of antibiotics prescribed for adults are for colds, upper respiratory tract infections, and bronchitis, three conditions for which antibiotics have little or no benefit. Fur- thermore, many people who start antibiotic treatment fail to carry it Bacterial colony Resistant colony out for the time prescribed. Failing to complete an antibiotic treat- (a) Mutation and selection create drug-resistant strains ment just aids the development of resistant strains of a disease. Hospitals are key centers of antibiotic resistance, but practices have begun to change. They are tracking prescriptions more closely, Harmless and they are examining closely how they clean and disinfect rooms, drug-resistant equipment, and the hands of doctors and nurses. Among the most bacterium lethal antibiotic-resistant bacteria are CRE (­carbapenem-resistant enterobacteriaceae), which have been identified in health care facil- ities in 42 states. While CRE cause only 1 to 4 percent of all hospi- tal-acquired infections, the CDC has dubbed them the “nightmare Harmful Conjugation Harmful drug-resistant Resistant colony bacteria” because they are fatal in half of all cases. bacterium bacterium Another serious infection is methicillin-resistant Staphylococ- (b) Conjugation transfers drug resistance from one strain to another cus aureus (MRSA). One U.S. study found that 60 percent of the FIGURE 8.8 How microbes acquire antibiotic resistance. (a) Random estimated 80,000 MRSA infections in 2011 were related to outpa- mutations make a few cells resistant. When challenged by antibiotics, tient hospital procedures, and another 22 percent occurred in the only those cells survive to give rise to a resistant colony. (b) Sexual repro- general community. duction (conjugation) or plasmid transfer moves genes from one strain or Clostridioides difficile (C. diff.) is a bacterium that causes species to another. colon inflammation. Diarrhea and fever that can lead to other lethal complications are among the most common symptoms. In Overuse of antibiotics breeds super bugs 2019 this species was estimated to cause about 224,000 infec- tions in the United States and over 12,000 deaths. Those most at Population biologists have long known that constant exposure risk were older adults. C. diff. infections are extremely difficult to to a toxic substance produces resistance to it. Constant use of eradicate. antibiotics, for example, kills off all but the resistant strains of The cost of treating antimicrobial-resistant infections is enor- microbes that tolerate the antibiotic. The surviving strains multi- mous. The CDC reports that C. diff. alone costs over $1 billion a ply and come to dominate the population (fig. 8.8a). For bacteria, year in added health care costs. In total, the direct cost of treating this problem is especially challenging: Bacteria readily exchange resistant infections exceeds $8 billion per year in the United States. genes, increasing the likelihood of producing resistant popula- Dire as these hospital infections are in rich countries, the situ- tions (fig. 8.8b). Widespread overuse of antibiotics, in people and ation is much worse in poorer places. India may be the epicenter especially in livestock, is producing a rapidly growing problem for antibiotic overuse and multidrug-resistant infections. Bacteria of antibiotic-resistant infections. The Centers for Disease Control spread easily because at least half the population defecate out- reports that more than 2.8 million antibiotic-resistant infections doors, and much of the sewage generated by those who do use occur in the United States each year, resulting in 35,000 deaths. toilets is dumped, untreated, into rivers. As a result, Indians have Antibiotic resistance is expanding because we raise most of among the highest infection rate in the world, and they collectively our cattle, hogs, and poultry in densely packed barns and feedlots. take more antibiotics, which are sold over the counter, than any Confined animals are dosed constantly with antibiotics to keep other people. In 2016 at least 60,000 Indian babies died of multi- them disease-free, and to make them gain weight faster. At least drug-resistant infections. India’s poor sanitation and uncontrolled 80 percent of all antibiotics used in the United States are fed to antibiotic use, coupled with substandard housing and a complete livestock. Monitoring in and around livestock operations consis- lack of monitoring of the problem, have created a tsunami of anti- tently finds multidrug-­resistant pathogens in soil, water, and air. biotic resistance that is spreading throughout the world, say epide- These multiple-­resistant pathogens are increasingly found in peo- miologists. Researchers have recently found “super bugs” carrying ple, a major public health worry. In some countries, such as Den- a genetic code first identified in India around the world, including mark, livestock have been raised for decades with only emergency to France, Japan, and the United States. uses of antibiotics. Close attention to sanitation helps keep animals healthy, and national policies against routine feeding of antibiotics help ensure farmers act responsibly. After years of debate, U.S. What would better health cost? livestock growers are beginning to explore this approach. The heaviest burden of illness is borne by the poorest people, In humans, millions of unnecessary courses of antibiot- who can afford neither a healthy environment nor adequate ics are prescribed every year. In part, this is because people don’t health care. Women in sub-Saharan Africa, for example, suffer 160 Environmental Science six times the disease burden per 1,000 persons as women in Table 8.2 Top 20 Toxic and Hazardous most European countries. The WHO estimates that 90 percent Substances of all disease burden occurs in developing countries, where less MATERIAL MAJOR SOURCES than one-tenth of all health care dollars are spent. The group Médecins Sans Frontiéres (MSF, or Doctors Without Borders) 1. Arsenic Treated lumber calls this the 10/90 gap. While wealthy nations spend billions to 2. Lead Paint, gasoline treat cosmetic problems in humans or the ailments of their pets, 3. Mercury Coal combustion billions of people are sick or dying from treatable infections and 4. Vinyl chloride Plastics, industrial uses parasitic diseases to which little attention is paid. To counter this trend, benefactors such as the Bill and Melinda Gates Foun- 5. Polychlorinated biphenyls Electric insulation dation have pledged $200 million for medical aid to developing (PCBs) countries to help fight AIDS, TB, and malaria. 6. Benzene Gasoline, industrial use Dr. Jeffrey Sachs of the Columbia University Earth Institute 7. Cadmium Batteries says that disease is as much a cause as a consequence of poverty 8. Benzo(a)pyrene Waste incineration and political unrest, yet the world’s richest countries now spend 9. Polycyclic aromatic just $1 per person per year on global health. He predicts that raising Combustion ­hydrocarbons (PAHs) our commitment to about $25 billion annually (about 0.1 percent of the annual GDP of the 20 richest countries) not only would save 10. Benzo(b)fluoranthene Fuels about 8 million lives each year, but would boost the world economy 11. Chloroform Water purification, industry by billions of dollars. 12. DDT Pesticide use Section Review 13. Aroclor 1254 Plastics 1. What is PFAS or PFOA and how might you be exposed to it? 14. Aroclor 1260 Plastics 2. What are emergent diseases? Give a few examples, and describe 15. Trichloroethylene Solvents their cause and effects. 15. Dibenz(a, h)anthracene Incineration 3. How does antibiotic resistance arise? How do hospitals and feed- 17. Dieldrin Pesticides lots contribute to this phenomenon? Paints, coatings, welding, 18. Chromium, hexavalent ­anticorrosion agents 8.2 Environmental Toxicology 19. Chlordane Pesticides 20. Hexachlorobutadiene Pesticides ∙ Many toxic substances are harmful in concentrations as low as Source: Data from U.S. Environmental Protection Agency. billionths, or even trillionths, of a gram. ∙ Allergens, carcinogens, and toxic substances occur in many common products. innocuous by dilution, neutralization, or other physical treatments. They don’t react with cellular components in ways that make them ∙ Hormone disruptors can interfere with growth, development, and poisonous at low concentrations. physiology at very low doses. Exposure to toxic or hazardous substances can be acute, Toxicology is the study of toxic substances (poisons) and their involving a short-term, often single exposure event, or chronic, effects, particularly on living organisms. Because many substances involving repeated exposures over time. Responses can also be are known to be poisonous (whether plant, animal, or microbial), acute (sudden and severe) or chronic (long-lasting, or even per- toxicology is a broad field, drawing from biochemistry, histol- manent). Both acute and chronic exposures can cause severe or ogy, pharmacology, pathology, and many other disciplines. Toxic permanent damage. Often an acute reaction, while it involves an agents damage or kill living organisms because they react with immediate crisis, can be reversed over time. cellular components to disrupt metabolic functions. Because of Environmental toxicology, or ecotoxicology, focuses on this reactivity, many are harmful even in extremely diluted con- the effects of toxic substances on living organisms, and on the centrations. In some cases, billionths, or even trillionths, of a gram way these substances interact and are transformed as they move can cause irreversible damage. Toxic substances produced natu- through populations and ecosystems. In aquatic systems, special rally are generally known as toxins. Those made by human activi- attention is devoted to the ways pollutants act at the interface of ties are called toxicants. sediment and water, or of water and organisms, or at the water/air All toxic substances are hazardous, but not all hazardous interface. In terrestrial environments, the emphasis tends to be on materials are toxic. Some substances, for example, are dangerous the effects of metals on the soil fauna community and population because they’re flammable, explosive, acidic, caustic, irritants, or characteristics. sensitizers. Many of these materials must be handled carefully in Table 8.2 presents a list of the top 20 toxic and hazardous large doses or high concentrations, but can be rendered relatively substances considered the highest risk by the U.S. Environmental CHAPTER 8 Environmental Health and Toxicology 161  Attic Asbestos (vermiculite insulation) Protection Agency. Compiled from the 275 substances regulated by the Compre- Formaldehyde (furniture, carpeting, particle board) hensive Environmental Response, Com- Fungicides (carpeting) pensation, and Liability Act (CERCLA), Nitrogen oxide (fireplace) commonly known as the Superfund Act, these materials are listed in order of assessed importance in terms of human and environmental health. The Superfund Act directs the EPA to monitor these sub- stances in order to identify and clean up sites contaminated with toxic compounds. Tetrachloroethylene Living Room (dry cleaning) How do toxic substances Bedroom affect us? Tobacco smoke (cigarettes, pipes) Allergens are substances that activate Lead (candle wicks, paint) the immune system. Some allergens act directly as antigens; that is, they are rec- ognized as foreign by white blood cells Mothballs and stimulate the production of specific antibodies (proteins that recognize and Oven cleaner bind to foreign cells or chemicals). Other Nitrogen oxides (unvented stove) allergens act indirectly by binding to and Bathroom changing the chemistry of foreign mate- Mold Kitchen rials so they become antigenic and cause an immune response. Formaldehyde is a good example of a widely used chemical that is a power- ful sensitizer of the immune system. It is directly allergenic and can also trig- Toilet bowl ger reactions to other substances. Widely cleaner used in plastics, wood products, insula- tion, glue, and fabrics, formaldehyde Chloroform (chlorine-treated water in shower) concentrations in indoor air can be thou- Basement Disinfectants, pesticides sands of times higher than in normal Cleansers, ammonia outdoor air. Some people suffer from what is called sick building syndrome: Paints, solvents, paint stripper, glue Pesticides (garden products) headaches, allergies, chronic fatigue, and other symptoms caused by poorly vented Herbicides indoor air contaminated by mold spores, carbon monoxide, nitrogen oxides, form- Carbon aldehyde, and other toxic substances monoxide released from carpets, insulation, plas- tics, building materials, and other sources Garage (fig. 8.9). The Environmental Protection Agency estimates that poor indoor air quality may cost the United States $60 billion a year in absenteeism and reduced Mold, bacteria Rust remover Paint, glue productivity. Radon (cracks in floor, foundation) Immune system depressants are pol- Nitrogen oxide } (furnace, water heater) lutants that suppress the immune system Carbon monoxide rather than activate it. Little is known about how this occurs or which chemi- Gasoline from auto, lawnmower cals are responsible. Immune system FIGURE 8.9 Some sources of toxic and hazardous substances in a typical home. failure is thought to have played a role, 162 Environmental Science  Estrogen Plasma What Can You Do? estrogen carrier Estrogen-like Tips for Staying Healthy compound Enters cell ∙ Eat a balanced diet with plenty of fresh fruits, vegetables, legumes, and whole grains. Wash fruits and vegetables carefully; they may have pesticide residues. Binds to receptor Intracellular and blocks estrogen receptor ∙ Use unsaturated oils such as olive or canola oil rather than hydro- estrogen uptake genated or semisolid fats such as margarine. Protein synthesis ∙ Cook meats and other foods at temperatures high enough to kill pathogens; clean utensils and cutting surfaces; store food properly. ∙ Wash your hands frequently. You transfer more germs from hand s cle u mRNA to mouth than by any other means of transmission. Nu ∙ When you have a cold or flu, don’t demand antibiotics from your doctor—they aren’t effective against viruses. ∙ If you’re taking antibiotics, continue for the entire time prescribed— e quitting as soon as you feel well is an ideal way to select for an br antibiotic-resistant germs. em ∙ Practice safe sex. m Ce ll ∙ Don’t smoke, and avoid smoky places. ∙ If you drink, do so in moderation. Never drive when your reflexes FIGURE 8.10 Steroid hormone action. Plasma hormone carriers or judgment are impaired. deliver regulatory molecules to the cell surface, where they cross the ∙ Exercise regularly: walk, swim, jog, dance, garden. Do something cell membrane. Intracellular carriers deliver hormones to the nucleus, you enjoy that burns calories and maintains flexibility. where they bind to and regulate the expression of DNA. Estrogen-like ∙ Get enough sleep. Practice meditation, prayer, or some other form compounds bind to receptors and either block the uptake of endogenous of stress reduction. hormones or act as a substitute hormone to disrupt gene expression. ∙ Make a list of friends and family who make you feel more alive and happy. Spend time with one of them at least once a week. however, in the widespread deaths of seals in the North Atlantic and of dolphins in the Mediterranean. These dead animals gen- erally contain high levels of pesticide residues, polychlorinated biphenyls (PCBs), and other contaminants that are suspected of billion to 70 parts per billion. However, Philippe Grandjean of damaging the immune system and making it susceptible to a vari- the Harvard School of Public Health suggests that a “safe” level ety of opportunistic infections. should be only 1 part per trillion. Endocrine disrupters are chemicals that disrupt hormone Because these chemicals often cause sexual dysfunction functions. Hormones are chemicals that living organisms use (reproductive health problems in females or the feminization of to regulate the development and function of tissues and organs males, for example), these chemicals are sometimes called envi- (fig. 8.10). You undoubtedly have heard about sex hormones and ronmental estrogens or androgens. They are just as likely, how- their powerful effects on how we look, behave, and develop, but ever, to disrupt other important regulatory hormone functions. these are only one example of the many regulatory hormones that Neurotoxins are a special class of metabolic poisons that rule our lives. Insulin is a hormone that controls our uptake of sug- specifically attack nerve cells (neurons). The nervous system is ars from food, and adrenaline is a hormone that elevates our breath- so important in regulating body activities that disruption of its ing and circulation in moments of stress. The hormone thyroxine activities is especially fast-acting and devastating. Different types helps regulate many functions, including heart rate, temperature, of neurotoxins act in different ways. Heavy metals such as lead and growth. Chemicals that disrupt any of these normal hormone and mercury kill nerve cells and cause permanent neurologi- functions can severely damage an organism’s health or reproduction. cal damage. Anesthetics (ether, chloroform, halothane, etc.) and PFAS (opening case study) are among the many compounds chlorinated hydrocarbons (DDT, Dieldrin, Aldrin) disrupt nerve that can disrupt hormone function. Endocrine disruptors can inter- cell membranes necessary for nerve action. Organophosphates fere with normal growth, development, and physiology of a vari- (­Malathion, Parathion) and carbamates (carbaryl, zineb, maneb) ety of animals—including humans—at very low doses. For some inhibit acetylcholinesterase, an enzyme that regulates signal trans- materials, picogram concentrations (trillionths of a gram per liter) mission between nerve cells and tissues or organs, such as mus- may be enough to cause developmental abnormalities in sensitive cles. Failure to regulate nerve signals to muscles, for example, can organisms. The EPA under the Biden administration lowered the cause muscle convulsions. Most neurotoxins are both extremely acceptable limit of PFOS in drinking water from 400 parts per toxic and fast-acting. CHAPTER 8 Environmental Health and Toxicology 163  Mutagens are agents that damage or alter genetic material effects—these components include pectins; vitamins A, C, and (DNA) in cells. Chemicals and radiation can both act as muta- E; substances produced in cruciferous vegetables (cabbage, broc- gens. Damage to DNA can lead to birth defects if it occurs during coli, ­cauliflower, Brussels sprouts); and selenium, which we get embryonic or fetal growth. Later in life, genetic damage may trig- from plants. ­Vegetables, dietary fiber, and complex carbohy- ger neoplastic (tumor) growth. When damage occurs in reproduc- drates also contribute to a healthy microbiome—the microbial tive cells, the results can be passed on to future generations. Cells community that keeps your digestive system functioning. Having have repair mechanisms to detect and restore damaged genetic a healthy microbiome is shown to contribute to emotional well- material, but some changes may be hidden, and the repair process being and healthier brain function, as well as physical health itself can be flawed. It is generally accepted that there is no “safe” (see chapter 4). threshold for exposure to mutagens. Any exposure has some pos- Eating too much food is a significant dietary health factor sibility of causing damage. in developed countries and among the well-to-do everywhere. Teratogens cause birth defects. These are chemicals or other ­Seventy percent of all U.S. adults are now considered overweight, factors that cause abnormalities during embryonic growth and and the worldwide total of obese or overweight people is estimated development. Some compounds that are not otherwise harmful to be over 1 billion. Every year in the United States, 300,000 can cause tragic problems in these sensitive stages of life. Perhaps deaths are linked to obesity (chapter 9). the most prevalent teratogen in the world is alcohol. Drinking dur- The U.S. Centers for Disease Control and Prevention in ing pregnancy can lead to fetal alcohol syndrome—a cluster of Atlanta warn that one in three U.S. children will become diabetic. symptoms that includes craniofacial abnormalities, developmental Diet-related health concerns are strongly related to socioeconomic delays, behavioral problems, and mental defects that last through- status. Low-income families often have less access to healthy out a child’s life. Even one alcoholic drink a day during pregnancy foods, or less time to cook them. In the United States, race and eth- has been associated with decreased birth weight. nicity also contribute to dietary risk factors, in part because people Similarly, by some estimates, 300,000 to 600,000 children of color are more likely to suffer from poverty. Some Indigenous born every year in the United States are exposed in the womb to communities are also thought to have historical predispositions to unsafe levels of mercury. The effects are subtle, but include reduced accumulate weight, as an ability to accumulate body fat could be intelligence, attention deficit, and behavioral problems. The total essential for surviving lean seasons. Today that survival mecha- cost of these effects is estimated to be $8.7 billion per year. nism may be more of a liability. Among the Pima tribe of Arizona, Carcinogens are substances that cause cancer, invasive, nearly 80 percent of all adults are diabetic. For more discussion, ­out-of-control cell growth that results in malignant tumors. Can- see chapter 9. cer rates rose in most industrialized countries during the twentieth century, and cancer is now the second leading cause of death in Section Review the United States, killing 600,000 people in 2018. According to 1. What are endocrine disrupters and why are they dangerous? the American Cancer Society, one in two males and one in three 2. What are teratogens and mutagens? females in the United States will have some form of cancer in their 3. How does diet influence health? lifetime. Some authors blame this cancer increase on toxic syn- thetic chemicals in our environment and diet. Others attribute it mainly to lifestyle (smoking, sunbathing, alcohol) or simply liv- 8.3 The Movement, Distribution, ing longer. The U.S. EPA estimates that 200 million U.S. residents and Fate of Toxic Substances live in areas where the combined lifetime cancer risk from envi- ronmental carcinogens exceeds 1 in 100,000, or ten times the risk ∙ Solubility and mobility determine where and when chemicals normally considered acceptable. move through the environment and in our bodies. ∙ Persistent materials, such as heavy metals and some organic How does diet influence health? compounds, concentrate in food webs and reach toxic concen- trations in top predators. Diet also has an important effect on health. For instance, there is a ∙ Bioaccumulation and biomagnification concentrate pollutants strong correlation between cardiovascular disease and the amount in the food chain. of salt and animal fat in one’s diet. Public health agencies increas- ingly encourage us to reduce the amount of high fructose corn The danger of a toxic or hazardous substance often depends on how syrup, refined sugar, red meat, and saturated (solid) fats. While easily we can be exposed to it. Likelihood of exposure depends on these components of our diet can be hard to avoid, nutritionists how long the substance persists in the environment, and on how eas- have found that they contribute to depression and other mental ily it moves through waterways, air, soil, or food webs (table 8.3). health concerns. We can think of both individuals and ecosystems as sets of interact- Fruits, vegetables, whole grains, complex carbohydrates, ing compartments between which chemicals move (fig. 8.11). The and dietary fiber (plant cell walls) often have beneficial health different pathways and types of exposure strongly influence how effects. Certain dietary components seem to have anticancer serious a risk they are. 164 Environmental Science  Air Table 8.3 Factors in Environmental Toxicity Photolysis Source Factors Related to the Toxic Agent Oxidation Industry Precipitation Agriculture 1. Chemical composition and reactivity Domestic, etc. 2. Physical characteristics (such as solubility, state) 3. Presence of impurities or contaminants 4. Stability and storage characteristics of toxic agent 5. Availability of vehicle (such as solvent) to carry agent 6. Movement of agent through environment and into cells Biota Factors Related to Exposure Metabolism Storage 1. Dose (concentration and volume of exposure) Excretion 2. Route, rate, and site of exposure 3. Duration and frequency of exposure 4. Time of exposure (time of day, season, year) Factors Related to Organism 1. Resistance to uptake, storage, or cell permeability of agent 2. Ability to metabolize, inactivate, sequester, or eliminate agent 3. Tendency to activate or alter nontoxic substances so they become toxic 4. Concurrent infections or physical or chemical stress 5. Species and genetic characteristics of organism 6. Nutritional status of subject Soil and Sediment 7. Age, sex, body weight, immunological status, and maturity Photolysis and metabolism Water Source: U.S. Department of Health and Human Services, 1995 Evaporation Hydrolysis Oxidation Microbial degradation Evaporation Sedimentation Compounds dissolve either in water or in fat FIGURE 8.11 Once toxic substances enter the environment (orange Solubility is one of the most important characteristics in deter- arrows), they travel through ecosystems and living organisms in many mining how, where, and when a toxic material will move through ways. the environment or through the body. Chemicals can be divided into two major groups: those that dissolve more readily in water and those that dissolve more readily in oils or fats. Water-soluble more ill health than any other exposure source. We breathe far compounds move rapidly and widely through the environment more air every day than the volume of food we eat or water we because water is everywhere around us. Water-soluble sub- drink. In addition, the cellular lining of our lungs is designed stances also tend to have ready access to most cells in the body, to exchange gases very efficiently, but this also means for- because aqueous solutions bathe all our cells. Molecules that are eign substances move easily from our lungs into our blood- oil- or fat-soluble (usually these are organic, carbon-based mol- stream. Epidemiologists estimate that millions of people die ecules) generally need a carrier to move through the environment each year from diseases caused or exacerbated by air pollution and into, and within, the body. Once inside the body, however, (see ­chapter 16). oil-soluble compounds penetrate readily into tissues and cells, Food, water, and skin contact also can expose us to a wide because the membranes that enclose cells are themselves made variety of toxic substances. The greatest exposures to many of of similar oil-soluble chemicals. Once they get inside cells, oil- these toxicants are found in industrial settings (including indus- soluble materials are likely to be accumulated and stored in lipid trial agriculture), where workers may encounter doses thousands deposits, where they may be protected from metabolic break- of times higher than would be found anywhere else. In the open- down and persist for many years. ing case study for this chapter, workers in factories that synthe- How do these dangerous substances enter our bodies? There size perfluorocarbon products had much higher exposure to these are many routes, although some cause damage more frequently chemicals and a greater incidence of cancers and other diseases than others (fig. 8.12). Airborne toxic particles generally cause than the general public. CHAPTER 8 Environmental Health and Toxicology 165  Water Cosmetics, (drinking) household accidents (incidental and accidental exposure) 100 Medicinal drugs (oral, intravenous, intramuscular) Food 60 (eating) Air DDT (ppm) (breathing) 40 Occupational exposure (oral, dermal, inhalation) 20 0 FIGURE 8.12 Routes of exposure to toxic and hazardous environmen- Bottom Small Fishes Gulls tal factors. mud insects (3–6 ppm) (99 ppm) (0.014 ppm) (0.41 ppm) Children have higher sensitivity FIGURE 8.13 Biomagnification in a Lake Michigan food chain. The DDT tissue concentration in gulls, a tertiary consumer, was about Condition of the organis