Gina M. Solomon, MD, MPH
Physicians are increasingly called upon to address questions related to environmental health. Pollution of air and water, contamination of food, releases from industrial facilities or waste sites, and hazards in the home are all common causes for concern among patients, community members, the media, and public officials. All health care providers should understand how to approach clinical and public health problems in environmental health, as well as the similarities and differences between occupational health and environmental health.
Although environmental issues are important worldwide, the severity and nature of the problem differs geographically, with especially serious hazards in newly industrializing countries. Many developed countries have taken significant steps in recent decades to address pervasive problems such as air pollution and contamination of drinking water. These countries continue to face issues around the safety of chemicals in consumer products, legacy contamination from historic industrial uses, and emerging concerns about recently identified chemical hazards.
Developing countries, in contrast, have faced enormous increases in industrial pollution. The dramatic expansion in motor vehicles worldwide, the shift of industrial production to nations where environmental laws are less stringent and their enforcement is often nonexistent, and the practice of shipping hazardous waste to less-developed countries for recycling or storage, have all created massive and relatively new environmental problems around the globe. In particular, air pollution and contamination of the water and food supply are very serious concerns in the developing world. Meanwhile global threats such as climate change, depletion of natural resources, and the pervasive presence of persistent bioaccumulative chemicals in the environment threaten health throughout the world.
AN APPROACH TO ENVIRONMENTAL HEALTH
Although workplace exposures to industrial chemicals are often far higher than environmental pollution levels, the latter may still be a significant concern. Lower-level exposures are an issue when the size of the exposed population is sufficient to suggest that even fairly rare or subtle health effects may have public health importance. For example, a chemical that confers a cancer risk at environmental exposure levels of one extra case per 10,000 people is of considerable importance when the base population exposed includes millions of people. Similarly, a 10 μg/dL increase in blood lead is associated with a 2–3 point decrease in IQ of exposed children. A slight decrease in IQ may not seem significant on an individual basis, but across a population of children exposed to lead such a decrement shifts the entire distribution of child IQ scores downward, resulting in a substantial increase in the number of children falling into categories that require special education services.
Although environmental exposures are often significantly lower than exposures in the workplace, there are many exceptions. For example, the populations most highly exposed to organic mercury compounds are heavy fish consumers, not industrial workers. Exposures to arsenic are frequently higher from naturally occurring arsenic contamination in drinking water worldwide than in workplace settings. Inhalation of radon gas is primarily a problem in the residential environment. In addition, the widespread popularity of chemical-intensive hobbies can lead to significant environmental exposures. Art products, home-improvement products, automotive products, solders, dyes, adhesives, and solvents are often used in similar ways in workplace and home settings; in the home, people may be less likely to have adequate safety training, personal protective equipment, ventilation, and disposal practices so exposures may even be higher than in the workplace.
Many workers in chemically exposed industries are healthy adult males. In contrast, the general population includes pregnant women, young children, those with underlying disease or poor nutritional status, and the elderly. Each of these groups may face increased risk from lower environmental levels of exposure. Children, for example, are more exposed to contaminants because they breathe more air, drink more water, and eat more food per kilogram of body weight than do adults. Toddlers engage in frequent hand-to-mouth activity, meaning that they consume contaminants (such as lead, pesticides, polycyclic aromatic hydrocarbons [PAHs], or flame retardants) in house dust or soil. Fetuses and young children are more susceptible to long-term damage from neurotoxicants or endocrine disruptors because of the critical phases of brain and reproductive system development during gestation and infancy. Low-level exposures to certain carcinogens, such as ionizing radiation, are known to be more likely to cause cancer when exposure occurs in childhood. Finally, a child has a lifetime in which to manifest delayed health effects, and there is increasing scientific consensus that numerous diseases of adulthood and aging have their origins very early in life.
Environmental health issues can be very difficult to assess. Exposures are often complex, cumulative, and unquantifiable; diseases are often multifactorial with long latencies; important information is often patchy or absent. For example, due to confidential business information (CBI) claims, it can be difficult or impossible to get full ingredients information for many consumer products. Current law in the United States does not mandate toxicity testing before chemicals are introduced into consumer products, so even if ingredients are known, little or no toxicity information may be available. Of the roughly 100,000 chemicals on the market today, of which about 3000 are produced and used in amounts over 1 million pounds per year, only a few hundred have been tested for toxicity. Standard reporting of chemical releases to the environment from industry—in countries where reporting is mandated—includes a short list of several hundred toxic chemicals, and analytical chemistry testing of environmental media focuses on a similar subset of chemicals. The result is that many potentially hazardous chemicals have not undergone toxicity testing, and are not prioritized for emissions reporting or environmental monitoring, and the result is a complete lack of information on the potential health risk from these thousands of chemicals.
In addition to the limitations of animal toxicity testing, population-based studies in environmental health are difficult to perform. Retrospective studies almost universally suffer from very large exposure uncertainty, which tends to bias toward null results. Prospective studies are often prohibitively expensive because they require following a cohort of individuals for years or decades to assess health effects over time. Cross-sectional studies, which assess both exposure and health status at the same time point, can be useful for generating hypotheses for future research, but are often subject to confounding by multiple variables, and cannot demonstrate a cause-effect relationship.
Clinicians may encounter patients known to have been exposed to an environmental hazard, or who believe they may have sustained such an exposure. In some cases, an entire community may become concerned because of a natural or technological disaster, or because of a discovery such as contaminants in the water supply or an apparent disease cluster. These situations require careful evaluation, including a thorough exposure history and quantification—where possible—of exposure levels. A basic understanding of major issues in environmental health can help to address individual patient and community issues, and can help identify potential public health threats that may exist.
THE MAGNITUDE OF ENVIRONMENTAL CONTAMINATION
In the United States in 2011, over 4 billion pounds of toxic chemicals were disposed of or released into the environment (ie, air, water or land), an 8% increase from 2010. Although over 92% of community water systems met health-based standards in 2010, 14 million people in the United States are still served by one of the 4000 drinking water systems that reported at least one violation of a health-based drinking water standard. Although air quality in the United States has significantly improved in recent years, and air pollution emissions have dropped, nearly 124 million people in the United States still live in areas that exceed one or more of the primary air pollution standards. Although many toxic waste sites have been cleaned up or controlled, more than 9.2 million people still live in neighborhoods within 3 km of the 413 commercial hazardous waste facilities in the United States. Nonwhite people are between 1.7 and 2.3 times more likely to live in a neighborhood with a hazardous waste facility compared with white residents of the United States. Significant racial and income disparities have also been reported for proximity to other environmental pollutants.
Globally, the situation is dire; according to the World Health Organization, air pollution from outdoor sources kills about 3 million people per year, including 1.2 million people in China, and a loss of 25 million years of healthy life in that country alone. Indoor air pollution from use of solid fuels is estimated to cause over 4.5 million deaths annually, or 7% of the global burden of disease. Ninety countries are facing water stress, with polluted or over-drawn water supplies. Globally, 1.2 billion people lack clean water, and waterborne infections account for 80% of all infectious diseases worldwide.
Over 1 billion pounds of pesticides are used in the United States each year and approximately 5.6 billion pounds are used worldwide. In many developing countries, programs to control exposures are limited or nonexistent. An estimated 25 million agricultural workers worldwide, and unknown numbers of bystanders and food consumers, experience unintentional pesticide poisonings each year. An estimated 40% of deaths globally are due in some way to environmental degradation.
MAJOR ENVIRONMENTAL HEALTH ISSUES
Many significant environmental health issues are discussed elsewhere in this textbook. Preceding chapters on international occupational and environmental health, occupational and environmental exposures, and occupational and environmental illness all contain major environmental health issues, as do all the chapters that follow in this section. Several issues of global importance cut across the various environmental health concerns. Global energy use and transportation are major drivers of air pollution, resource-depletion, global warming, and health. Global warming itself poses significant planet-wide human health challenges. Finally, certain chemical contaminants should be considered of global concern due to the fact that they have potential for very widespread exposures and subtle, population-wide effects.
Energy Use & Transportation
The world’s environmental challenge is evident from the continued growth in energy demand, especially in Asian countries. Global oil consumption reached 88 million barrels per day in 2011, which accounts for 33.1% of global energy consumption. Coal consumption grew by 5.4% in 2011, which outstripped the growth in oil consumption, and coal now accounts for 30.3% of global energy consumption, with the largest increases in Asian countries. Coal is associated with the largest carbon emissions of any fossil fuel, as well as the largest emissions of air pollutants. In marked contrast, renewable forms of energy accounted for only 2.1% of global energy consumption in 2011.
A report from the National Research Council (NRC) estimated the costs of US energy production and use—especially the damage air pollution imposes on human health—that are not reflected in market prices. The total damages the committee was able to quantify added up to an estimated $120 billion in the United States in 2005, primarily from the health effects of air pollution associated with electricity generation and motor vehicle transportation. The report was unable to quantify damage from climate change, harm to ecosystems, effects of some air pollutants such as mercury, and risks to national security. The total annual damage from sulfur dioxide, nitrogen oxides, and particulate matter created by burning coal at 406 coal-fired power plants, which produce 95% of the US coal-generated electricity, was about $62 billion.
Transportation, which relies almost exclusively on oil, accounts for nearly 30% of US energy demand and 20% of US emissions of carbon dioxide (CO2). Vehicles are a major contributor to air pollution around the world, accounting for most of the carbon monoxide (CO), and a large share of the hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter in major urban areas. The NRC estimated that in the United States in 2005, motor vehicles produced $56 billion in health and other non-climate-related damage. Worldwide, the number of motor vehicles surpassed the 1 billion mark in 2010, and over 60 million passenger cars are projected to be produced worldwide in 2012; use of motor vehicles is increasing especially fast in industrializing countries, with resulting adverse effects on air quality and public safety.
Climate Change
Certain gases effectively trap heat in the atmosphere and impair radiation of that heat into space. Although a certain amount of heat-trapping is essential to life on earth, the system has been in delicate balance for millennia, and the massive emissions of “greenhouse gases” released by human activities in the last century is disrupting that balance. From the pre-industrial era to 2010, concentrations of carbon dioxide (CO2) have increased globally by nearly 40%; concentrations of methane, a greenhouse gas that is 21 times more potent than CO2, increased by 158%. In the United States, total greenhouse gas emissions, in CO2 equivalents, increased 8.7% between 1990 and 2011. The top greenhouse gas emitters worldwide are China, the United States, the European Union, India, the Russian Federation, Japan, and Canada. Together, these sources represent the vast majority of total global CO2 emissions.
Two major climate shifts are predicted based on these emissions: overall temperature increases, and more extreme variability in the weather due to the increased heat energy in the atmosphere, with resulting effects on other natural systems from phenomena such as drought and flooding.
Global average temperatures are projected to increase between 1.4°C and 5.8°C by the end of this century due to climate change. Research so far has mostly focused on the health effects of heat, extreme weather events, and infectious diseases; some studies have also looked at the effects of climate change on crop yields and resulting hunger and population displacement. Climate change is projected to result in significant sea level rise, and the number of people at risk globally from flooding by coastal storm surges is projected to increase from the current 75 to 200 million in a scenario of mid-range climate change.
Heat stress is projected to substantially affect labor capacity, especially among workers whose jobs involve exertion outdoors; a decline to 80% of current labor capacity is projected worldwide by 2050 due to decreased productivity from heat, with resulting economic effects. Heat waves have significant effects on health, including substantial increases in mortality, hospitalizations, and emergency room visits during days of extreme heat. Areas that are normally cooler, where people and the built environment are less acclimatized, have larger increases in heat-related morbidity during extreme heat events.
Greenhouse Gases
• Carbon dioxide is produced through burning fossil fuels and is removed from the atmosphere (“sequestered”) when it is absorbed by plants, or into the ocean where it reacts to form carbonic acid, leading to acidification of the ocean and resulting threats to marine organisms.
• Methane primarily comes from livestock, and from landfills, composting facilities, and sewage treatment plants. Fugitive methane emissions also come from natural gas drilling and pipeline transport. Methane is produced naturally from decaying vegetation in marshlands; melting of the arctic permafrost is expected to result in significant increases in methane production over the coming decades.
• Nitrous oxide is emitted from fertilizer use and industrial activities, as well as during combustion of fossil fuels and solid waste.
• Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (eg, chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).
• Although black carbon is not a gas, it is important because it directly absorbs sunlight and infrared radiation. It also deposits on and darkens snow and ice, increasing absorption of sunlight and accelerating snow melt. The major source of black carbon is diesel engines, but it also comes from wood smoke, power plants, and other industrial facilities.
Persistent, Bioaccumulative Toxicants
Numerous industrial chemicals and pesticides are a particular problem for human health and the environment due to their resistance to environmental degradation and propensity to bioaccumulate. Chemicals in this category are not only a hazard to workers and individuals who are directly exposed, but also to ecosystems and people far away from sites where these chemicals are used or emitted. Chemicals that fall in the category of persistent, bioaccumulative toxicants (PBTs) include some metals such as methyl mercury, cadmium, and lead; some halogenated organic chemicals such as PCBs, dioxins, and polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides such as DDT. Other groups of chemicals such as certain perfluorinated chemicals (used as stain-repellants, waterproofing agents, and in grease-proof coatings), short-chain chlorinated paraffins (used as flame retardants, plasticizers, additives in metal working fluids, sealants, paints, and coatings), and musk xylenes (used as fragrances) have also been identified as PBTs.
Although some PBTs (such as most organohalogens) are lipophilic and tend to accumulate in fatty tissue of biota at increasing concentrations up the food chain, other PBTs (such as many metals) accumulate in muscle, bone, or other tissues. These chemicals can be transported globally in air, water, and biota, and have been detected at locations far from where they were manufactured or used. For example, many PBT chemicals are found at especially high concentrations in the arctic, and are major contaminants in marine mammals and polar bears. Inuit populations generally have among the highest exposures to these chemicals in the world, due to their dietary patterns, and adverse health effects in these populations have been associated with exposures to PCBs and other PBT chemicals in epidemiologic studies. Dioxins, PCBs, and other lipophilic chemicals also concentrate in breast milk lipids, resulting in disproportionately large exposures among nursing infants compared to adults. The Institute of Medicine (IOM) reviewed dietary intakes of dioxins and related chemicals in the United States and concluded that although concentrations have been generally declining, the typical levels in women of reproductive age are still higher than advisable. Dioxins are potent endocrine disruptors and carcinogens, raising concerns about exposures during fetal development and infancy. The IOM panel recommended educational efforts directed toward young girls to encourage them to eat a diet low in animal fat as a way of reducing dioxin exposures. It is unclear that these recommendations have been followed. Dioxins are not produced intentionally, but are by-products of incineration, combustion, chlorine-based bleaching, and other industrial processes; some dioxins are also produced naturally in forest fires and volcanic eruptions.
Many PBT chemicals are on the list of substances subject to international reduction efforts under the Stockholm Convention on Persistent Organic Pollutants, effective in 2004. Although the United States has not ratified this treaty, it has been signed by 178 countries and has resulted in significant success in globally reducing or eliminating many of these chemicals.
Endocrine Disruptors
In the mid-1990s, scientists from various fields began to realize that they were all seeing toxic effects on the endocrine system from environmental exposures. Some common chemicals were found to activate the estrogen receptor in a manner that mimics estrogen itself. Many of these chemicals were subsequently tested in breast cancer cells and found to promote proliferation; studies in laboratory animals, wildlife populations living in contaminated areas, and even humans have confirmed estrogenic effects. In the intervening years, numerous hormonally active pesticides and industrial chemicals have been identified, including chemicals that are antiandrogenic, antithyroid, and others with more complex effects on endocrine pathways. Although there was initial skepticism about the theory that environmental chemicals could cause endocrine disruption in wildlife and humans, the existence of this problem is now a matter of general consensus.
Numerous chemicals have now been recognized as endocrine disruptors. Hormonally active agents can occur naturally in the diet, such as the phytoestrogen coumestrol and isoflavones such as genistein; these phytoestrogens are found in soy, nuts, cereals, and legumes, with the highest concentrations in foods such as flax and tofu. Numerous studies have weighed the risks and benefits of dietary phytoestrogens, with concerns mostly centering on potential risks to women with estrogen receptor positive breast cancer, and to infants consuming soy formula. Neither of these issues has been fully resolved, but the rapid metabolism and excretion of phytoestrogens, along with their modulatory effect on endogenous estradiol, have suggested that the effects of these chemicals may be modest or beneficial in many circumstances. In contrast, some industrial chemicals and pesticides with endocrine activity are more persistent in the body and may be more likely to cause adverse effects in living organisms.
The European Commission created a priority chemical list and a strategy on endocrine disruptors, considering both potential for exposure, and evidence of endocrine disrupting activity. Clear evidence of endocrine disrupting activity was noted for 66 chemicals, including pesticides, detergents, plasticizers, and combustion by-products. Of the 66 chemicals, humans were considered likely to be exposed to 60. An additional 52 chemicals showed some evidence suggesting potential endocrine activity. Well-established endocrine disruptors with widespread human exposures include alkylphenols, bisphenol A, dioxins, PCBs, polybrominated diphenyl ethers (PBDEs), perchlorate, phthalates, and triclosan.
The main concerns around endocrine disrupting chemicals relate to prenatal and childhood exposures. The adult endocrine system is relatively resilient, with endogenous hormones generally at higher concentrations than the chemicals at issue, and feedback loops that regulate hormone levels. In early life, however, background levels of sex hormones are much lower, and endogenous regulatory mechanisms are not fully developed. At the same time, hormonally sensitive organs, including the brain, are actively developing and therefore sensitive to permanent developmental damage from biological perturbations. As a result, fairly subtle endocrine fluctuations during fetal and child development may lead to permanent structural and functional deficits. For example, prenatal phthalate exposure has been associated with testicular dysgenesis syndrome, an entity first described in 2001 that is a result of disrupted gonadal development during fetal life, resulting in poor semen quality and higher rates of undescended testis, hypospadias, and testicular cancer. Exposure to antithyroid chemicals such as the PCBs and PBDEs has been associated with neurodevelopmental delays and reduced IQ in children.
APPROACHING DIFFICULT ENVIRONMENTAL HEALTH PROBLEMS
Environmental Justice
Low-income communities of color have become increasingly concerned about a disproportionate and unfair burden of environmental risk in their communities. Even a relatively small risk may be seen in the context of a history of racial and socioeconomic disparities in the distribution of environmental risks, and is perceived as adding to an already unacceptable background of risk. In the mid-1980s, a coalition emerged among civil rights activists and environmentalists working for the rights of low-income communities of color to clean and healthy environments; this collaboration is known as the environmental justice movement.
A groundbreaking 1987 report by the United Church of Christ’s Commission on Racial Justice found that three-fifths of African-Americans or Hispanics lived in communities with uncontrolled toxic waste sites, and that the most significant predictor for the location of hazardous waste facilities nationwide was the race of the local community. In the intervening years, numerous studies have documented the presence of disproportionately large numbers of polluting industrial facilities, sewage treatment plants, busy roadways, and other undesirable land uses in low-income communities populated by racial or ethnic minorities. Such communities also frequently lack healthy food options, have greater numbers of fast food restaurants and liquor stores, few green spaces, degraded housing quality, and limited recreational opportunities. High levels of community violence and stress add further to the risk profile in such neighborhoods.
Reviews of research in this area have shown that children of color suffer disproportionate burdens of disease with potential environmental aspects, ranging from lead poisoning to asthma and childhood cancer. In addition, African-Americans children are at greater risk of preterm birth or low birth weight. Although these health conditions may be caused or exacerbated by some environmental factors, the causes are multifactorial and cannot be attributed to any specific set of conditions.
The Presidential Executive Order on environmental justice, signed in 1994, mandates that every federal agency “make achieving environmental justice part of its mission.” In an effort to help guide implementation of the Executive Order on environmental justice, the National Academy of Sciences (NAS) produced a report in 1999 offering guidance to government agencies, scientists, and the medical community. The NAS report identified a lack of knowledge among health care professionals, researchers, and communities about environmental hazards, and recommended “enhanced efforts in the training of health professionals and education of the public.”
The NAS panel recommended that education and risk communication efforts be directed toward four main goals: (1) increasing individual and community awareness of environmental health issues and resources, (2) involving the community in the identification of problems related to environmental exposures, (3) soliciting community involvement in research approaches, (4) and improving links between community members, health care providers, and researchers. Due to the historic and national pattern of disparities, any discussion of risk in a particular community must consider environmental justice.
Risk Communication
Risk communication can be defined as the exchange of information about the nature, magnitude, significance, and control of a risk. Physicians have emerged as one of the most trusted and credible sources of information about occupational and environmental health risks.
Understanding different perceptions of risk is important to help understand how to communicate about risk. If the physician who is attempting to explain a risk does not realize that the audience or individual may perceive risks very differently, risk communication is less likely to be productive and effective. Failure to recognize these differences in perception and deal with them appropriately can cause risk communication to fail. Factors influencing risk perception include differences in the nature of the hazard itself, differences among individuals or groups in how they react to the hazard, and factors related to the social context in which the risk communication occurs.
In the patient care setting, environmental health concerns tend to focus on questions about individual risk. Because the science on environmental health does not pertain to individual risk but rather to population risk, the challenge to the health care professional is substantial. Even assuming that the health care provider is familiar with the scientific data relevant to the issue in question, there remains a challenge in translating a combination of complex and sometimes conflicting results from a variety of sources such as in vitro assays, laboratory rodent studies, and limited human epidemiological research to practical advice for a patient’s individual situation. This problem is further complicated by difficulties in exposure assessment, the fact that individuals are exposed to mixtures rather than single chemicals, and differing effects of chemicals when exposure occurs during vulnerable periods during the lifespan. The resulting conversation must therefore move away from a focus on trying to “answer the question” toward a more open discussion of scientific uncertainty, risk, and prevention.
Individuals may come to their health care provider after an adverse event (such as a miscarriage, or cancer diagnosis), or they may have concerns about potential future harm. They may have had exposure to an occupational or environmental hazard, or there may be no obvious exposures. Patients who have already suffered from an adverse event are generally focused on exploring causation. They may be trying to understand what happened, to assign blame, or to recover compensation for the event. Individuals who have suffered a known hazardous exposure, irrespective of dose or of whether an adverse event has occurred, may require counseling about their future risk and may have questions about biological monitoring for the chemical, and potential treatment options to reduce their risk.
Many patients believe that science “proves” or “disproves” links between potential environmental hazards and health effects. The many shades of uncertainty, data gaps, and data quality problems are not issues most people have grappled with in their personal or professional lives. Yet communicating about risk requires the clinician to convey these uncertainties as a way of explaining why there are no clear answers to most questions.
Many scientific links between exposure and adverse effects are based on animal toxicology studies. People respond to rodent data based on their preconceptions about risk, with some people dismissing such results as irrelevant to humans, and others finding any such results alarming, irrespective of data quality. The clinician can point out the animal toxicology findings and add cautions appropriate to the situation, either to encourage precautionary action to reduce exposure, or to indicate the difficulty of establishing causation based on limited animal toxicology data.
Even when the hazard associated with an environmental agent is known, the dose a patient may have received is often unknown. Route of exposure, dose, and timing of exposure are important determinants of risk. Some people may be falsely reassured, for example, learning that an exposure was below the OSHA Permissible Exposure Limit (PEL), even though these limits are generally outdated and are not designed to protect against all health effects in all populations. Other people may be extremely anxious about a single low-dose, short-term exposure and require extensive counseling and reassurance.
Even with well-understood toxicants such as lead, and known blood lead levels, it remains difficult to communicate risk, since epidemiological studies allow prediction of neurodevelopmental deficits on a population level, but are not predictive for an individual. For example, if a mother has a blood lead level of 10 micrograms per deciliter (μg/dL), it is not possible to predict that her child will lose 3 IQ points and will be more hyperactive, inattentive, and prone to violent behavior, even though many epidemiologic studies have shown these associations on a population level. Due to the multifactorial determinants of health, the child of such a mother could grow up to be a genius or could be profoundly developmentally delayed. Predicting or attributing risk on an individual basis must be done with great caution.
Some characteristics of a hazard serve to magnify apparent risk irrespective of the outcome of a risk assessment. Hazards that are seen as potentially catastrophic, although unlikely, are generally perceived as greater than hazards that are more likely but would result in less serious or reversible outcomes. For example, the risk from a nuclear power plant may be seen as greater than the risk from coal power plants although the likelihood of emissions that are hazardous to health is higher from coal plants. Similarly, the risk of a dreaded outcome (such as cancer, birth defects, or brain damage) is often seen as worse than the risk of a disease that is less universally dreaded (such as liver, lung, or kidney disease). Unfamiliar hazards are generally seen as riskier than familiar hazards, and manmade hazards may be perceived as riskier than those that occur naturally. The population affected by the hazard is also important. For example, a hazard to children is often judged worse than a similar hazard to adults. Finally, hazards that are involuntary are almost always judged more serious than hazards that are faced by choice. Thus, comparison of the risks associated with skiing or drinking alcohol with risks from a hazardous waste incinerator will not be seen as equivalent because the former are voluntary and under the control of the individual, whereas the latter is imposed from outside and not controlled by the individual.
Estimates of risk used for comparison and the order in which they are presented can affect how risks are perceived. Compression refers to the tendency to overestimate the frequency of risks that are rare and underestimate those that are frequent. Availability refers to the tendency to base the expected likelihood of an event on the ability to recall instances of a similar event. As a result, events that draw media attention tend to be perceived as more likely.
Different groups within the population often have different perceptions of risk. In particular, experts and scientists often view many risks as less significant than do nontechnically trained individuals. Among scientists and professionals, where one works is relevant to risk perception. For example, toxicologists who work for industry rate risks from chemicals significantly lower than toxicologists who work for universities. Men frequently rate risks lower than do women. This difference is not explained by differences in familiarity with scientific issues because the difference is present even between male and female toxicologists. Interestingly, the gender difference in risk rating is only seen in whites. Black men, black women, and white women all rate risks similarly, whereas white males tend to rate virtually all risks as less serious.
The social context of risk communication efforts is extremely important to perceptions of risk. If the individual or organization imposing the risk is trusted by the community (ie, a local company that has provided jobs in the community for many years and is well known to the community) the risk is often perceived as less than if the risk is imposed by an outsider. Similarly, the level of trust in government regulatory officials and in the risk communicator is important in the perception of risk. Risks seen as unfair are often seen as larger than risks seen as fairly distributed. For example if an individual or community perceives significant benefits from submitting to a risk, that risk seems smaller than if the benefits will only accrue to a distant corporation. Human right issues such as the right to personal integrity, to privacy, and to informed consent all play into risk perception.
Disease Clusters
Sometimes a cluster of illnesses can signal a workplace or community hazard requiring attention. In the United States, physicians are legally required to report work-related illnesses or injuries, and some states have additional requirements. For example, the State of California requires that health care providers report all pesticide-related illnesses and that laboratories report blood lead levels to the state. Likewise, many industrialized countries require reporting of occupational illnesses and injury and some have occupational disease registries designed for capturing sentinel events. Cancer or birth defects surveillance programs can also sometimes be helpful in assessing disease patterns. There is no reporting or tracking system for potential environmental disease clusters, but these are often reported anecdotally to county or state health departments, or to the Centers for Disease Control and Prevention (CDC).
Due to a lack of resources for conducting investigations, epidemiologic limitations that make it difficult to investigate small communities or rare diseases, and a lack of tools for accurately measuring exposures retroactively, it has been difficult for state and federal agencies to shed light on the causes of most disease clusters. Most disease clusters are never investigated, and most cluster investigations that are done fail to provide clear answers for the community. Most public health experts recognize that many disease clusters are likely to be due to chance; statistical probabilities show that events (such as rates of disease) vary around the mean, and some geographic areas will inevitably have rates that are significantly above the mean for some period of time due to chance alone. On the other hand, sometimes there will be reasons for unusually high rates of disease during a time period, or sometimes the rates are so high that chance is an unlikely explanation. It is often difficult to discern when a cluster represents a statistical fluke and when it represents a sentinel event that could provide an important clue to occupational or environmental factors and disease.
Many important chemical hazards were initially identified because of clusters of adverse events. For example, the pesticide dibromochloropropane (DBCP) was first identified as a potent testicular toxicant in 1977 when a group of workers at a chemical plant realized through word-of-mouth that they all had been unable to father children. Subsequent investigation revealed that most of the production workers had oligospermia or azoospermia, and that prior animal tests identifying this effect in rats had been disregarded. The teratogenic and neurotoxic effects of methyl mercury were first discovered in the 1950s when numerous severely developmentally disabled children were born in the fishing village of Minamata, Japan at the same time as cats in the town were exhibiting bizarre behavior, and some adults were experiencing neurological symptoms. Initially an infectious disease was suspected, but the cause was ultimately discovered to be mercury discharged from a nearby chemical facility into Minamata Bay, methylated by bacteria in the sediment of the Bay, and concentrated in fish which was the dietary staple in that town. The reproductive toxicity of several glycol ethers was first identified due to reports of spontaneous abortions among women working in “clean rooms” at semiconductor manufacturing facilities. The link between n-methyl-2-pyrrolidone (NMP), a common solvent used in many consumer products, and stillbirth was first described in a case report.
Although it is often more difficult to identify carcinogens from disease cluster investigations due to the generally longer latency of cancer compared to reproductive effects, some carcinogens have famously been identified in this manner. For example, vinyl chloride was shown to cause cancer in humans because of a cluster of hepatic angiosarcoma in 1974 at a vinyl chloride production facility in Louisville, Kentucky. As with DBCP, there were previously published rodent toxicology studies demonstrating liver toxicity and liver tumors, but these were largely disregarded until the outbreak of liver cancers in workers was established and linked to vinyl chloride.
In more recent years, outbreak investigations have linked nylon flock exposure to interstitial lung disease, and diacetyl flavoring agent to bronchiolitis obliterans. An important review of occupational disease clusters identified 87 reports that established new disease-agent connections from 1775 to 1990. This review pointed out that there are some important advantages to the workplace in identifying new disease-agent connections, including natural denominator boundaries, shared exposures, the ability to form intermediate hypotheses, and the possibility of locating comparable populations in which to study these hypotheses.
Some investigators, however, have pointed out that the limited number of workers at any given worksite, the latency period of many diseases, and the mobility of the workforce make it very difficult to identify sentinel outbreaks. For a disease to be noticed against the general background, it would generally need to be acute or rare, or the causative agent would need to be extremely potent. Chemicals or other substances that cause a subtle increase in a common disease would tend not to be identified through workplace clusters.
Clusters of environmental disease have historically been less likely to yield answers than in the occupational context. In community situations, exposure pathways are often more complex than in the workplace, exposures are generally lower, and it can be very difficult to do dose-reconstruction in an investigation. One notable exception was the discovery in 1999 of a lung cancer and restrictive lung disease cluster associated with asbestos contamination at a vermiculite mining operation in Libby, Montana. This investigation uncovered the associated deaths of about 400 workers and community residents, prompted the first declaration of a public health emergency by the U.S. EPA, and triggered a cleanup that has cost hundreds of millions of dollars.
Health care providers should remain alert to disease clusters, as they can sometimes be sentinel events. The decision to report a potential problem and to intervene may prevent many future adverse outcomes in the population. However, clinicians should also recognize that many clusters occur by chance alone, and even if there is an occupational or environmental cause, cluster investigations often end with no clear answers due to scientific limitations such as small sample size and difficulty categorizing exposure. As a community is engaged in working with researchers on a cluster investigation, these factors should be discussed early in the investigation and frequently during the course of the investigation, to prepare the community for the possibility of equivocal or negative results.
Knowing the Community
Clinicians should learn about potential occupational and environmental hazards in the communities they serve so that they are better prepared to prevent and respond to potential issues that may arise. For example, clinicians who practice in agricultural communities should be aware of the crops grown in their area and the pesticides most commonly used on those crops, so they have the ability to recognize potential symptoms of overexposure to those pesticides. Familiarity with the major industries in a local catchment area can be helpful in appropriately diagnosing or treating both occupational and environmental exposures, including in emergency situations. Anticipatory guidance can also link to local issues. For example, clinicians who practice in areas where radon levels tend to be high should be aware of this public health threat, and should advise patients to test for radon in their homes, thereby preventing many potential cases of lung cancer.
Water source is an important environmental health issue. In the United States, every water utility is required to distribute an annual report detailing the levels of regulated contaminants in the system. These reports are publicly available and health providers should check them for any contaminants that exceed the Maximum Contaminant Level Goal (MCLG), which is the health-based exposure limit and is generally lower than the enforceable legal limit.
It is also important to know what fraction of the community is supplied by private wells. If that fraction is significant, it will be important to identify whether there are any local or state agencies that offer free or subsidized testing of well water. Well water is not regulated by any government agency, and it is difficult to know what contaminants it may contain. In many cases, individuals must pay for their own water to be tested by private labs; such testing should be done by labs that are state certified and it is reasonable to screen for total coliform, metals, and nitrates. Depending on local land uses, it may sometimes be advisable to also test for pesticides, chlorinated solvents, or other contaminants.
In some regions in the world, there is no universal standard for regulating drinking water contaminants or for reporting requirements. The World Health Organization has recommended drinking water standards and the United Nations Environment Program has a database on international water quality.
Local industrial facilities may expose their workers to hazards and may also pollute the community. Routine emissions to air or water, storage and transport of hazardous materials, and accidental releases are all issues that can cause public health concerns. In the United States, facilities that emit any of over 650 federally listed toxic chemicals over certain quantity thresholds are required to report emissions; the approximately 20,000 sites around the country with significant releases are mapped and their emissions data are readily available online through the Toxics Release Inventory (TRI). In the EU, the European Pollutant Release and Transfer Register (E-PRTR) reports on the emissions from industrial facilities into air and water, and maintains an online database. The EU report covers more than 90 pollutants and over 29,000 facilities. Other air quality issues relate to ambient pollutants that are not emitted from local industrial sources. For example, particulate matter, ozone, and other pollutants come from a variety of sources especially including motor vehicles. It is possible to sign up for alerts from the AirNow program in the United States or the AirQualityNow program in the European Union, or to use a mobile app for regular updates on local air quality. This information is very useful to clinicians, since many acute respiratory and cardiovascular health outcomes have been linked temporally to air quality. Health care providers who are attuned to local environmental conditions are better positioned to identify patterns, anticipate potential issues, and respond quickly and appropriately when needed. Fortunately, there is extensive information available on the Internet to allow clinicians to gather significant information relatively quickly and easily.
REFERENCES
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Bellinger DC: Comparing the population neurodevelopmental burdens associated with children’s exposures to environmental chemicals and other risk factors. Neurotoxicol 2012;33:641 [PMID: 22525934].
Boucher O: Response inhibition and error monitoring during a visual go/no-go task in Inuit children exposed to lead, polychlorinated biphenyls, and methylmercury. Environ Health Perspect 2012;120:608 [PMID: 22142904].
Center for Environmental Systems Research. Water > Severe water stress by country. University of Kassel, WaterGap 2.1. http://www.NationMaster.com/graph/env_wat_sev_wat_str-environment-water-severe-stress.
EPA: Air Quality Trends, http://www.epa.gov/airtrends/aqtrends.html.
EPA. Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks, 2013. http://www.epa.gov/climatechange/ghgemissions/sinventoryreport.html.
EPA: Toxics Release Inventory National Analysis Overview, http://www.epa.gov/tri/tridata/tri11/nationalanalysis/index.htm.
European Union Strategy on Endocrine Disruptors. http://ec.europa.eu/environment/endocrine/strategy/substances_ en.htm.
Gilbert ME: Developmental thyroid hormone disruption: prevalence, environmental contaminants and neurodevelopmental consequences. Neurotoxicol 2012;33:842 [PMID: 22138353].
Lim SS: A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010. The Lancet 2012;380:2224 [PMID: 23245609].
Morello-Frosch R: Understanding the cumulative impacts of inequalities in environmental health: Implications for policy. Health Aff (Millwood) 2011;30:879 [PMID: 21555471].
National Research Council. Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use, 2010. http://www8.nationalacademies.org/onpinews/newsitem.aspx?recordid=12794.
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SELF-ASSESSMENT QUESTIONS
Select the one correct answer to each question.
Question 1: Oil
a. accounts for less than half of global energy consumption
b. consumption is exceeded by coal consumption
c. creates the largest carbon emissions of any fossil fuel
d. causes the largest emissions of air pollutants
Question 2: Transportation
a. relies almost exclusively on oil
b. accounts for nearly 50% of US energy demand
c. produces 40% of US emissions of carbon dioxide
d. by automobiles is on the decline
Question 3: Dioxins
a. are suspected to be endocrine disruptors and carcinogens
b. are produced intentionally
c. are by-products of industrial processes
d. are excluded from international reduction efforts
Question 4: Testicular dysgenesis syndrome
a. is a result of disrupted pituitary development
b. may include undescended testis but not hypospadias
c. is an early form of testicular cancer
d. has been associated with prenatal phthalate exposure
Question 5: A disease cluster was the very first indication of the link between
a. DBCP and male infertility
b. vinyl chloride and liver cancer
c. diacetyl and bronchiolitis obliterans
d. inorganic mercury and neurodevelopmental toxicity
Question 6: Risks are perceived as more serious if they
a. are within individual control
b. primarily affect otherwise healthy adults
c. are imposed by a locally-owned company
d. are linked to a dreaded disease such as cancer
Question 7: Environmental justice is
a. purely a social movement with no significant relevance to health care providers
b. not based on any real data showing disproportionate environmental hazards in low-income and nonwhite communities
c. not something US government agencies need to consider when they make decisions
d. something the Institute of Medicine recommends for inclusion in education for all levels of health professionals
Question 8: Health care providers do not need to know
a. whether the region may have elevated radon levels
b. which homes have carbon monoxide detectors
c. the source of local drinking water and contaminants that have been reported in the water
d. major local industries and pesticide use patterns