Environmental Epidemiology: Where We’ve Been and Where We’re Going

The International Society for Environmental Epidemiology (ISEE) held its first meeting in Brookhaven, NY, in September 1989. Three months later, the first issue of Epidemiology was published. Beginning with the November 1994 issue, this Journal became the official publication of ISEE. The Journal and the Society both have flourished through their interaction. We take this opportunity in the pages of the Journal to reflect on the past and future of environmental epidemiology. The traditional concerns of environmental epidemiology have been the contamination of air, water, and food. In western countries, as sanitary measures reduced the burden of disease from biological pathogens, the focus increasingly shifted to chemical and physical agents. Several accomplishments during the last half of the 20th century can be attributed to environmental epidemiology, although each achievement is accompanied by some unfinished business. Lead The primary sources of lead burdens in the general population are the result of human activity, with the largest contribution coming from leaded additive in gasoline and paints used in housing. 1 These findings, coupled with the identification of adverse effects from low-level exposures on the neurodevelopment of young children, 2 led to source reductions. These reductions, in turn, resulted in observable, dramatic declines in blood lead levels on a population-wide basis in the United States and elsewhere, 3–7 a major achievement. Other adverse health effects of lead have been suggested, such as elevations in blood pressure and adverse reproductive outcomes, 8,9 but the evidence here is less firm. Large-scale monitoring of blood lead levels in children is conducted on an ongoing basis in some areas; however, many populations worldwide are still being exposed at dangerously high levels because of the continued use of leaded gasoline and the lack of protections from industrial processes, wastes and consumer products. Air Pollution Air pollution from fossil fuel combustion (for both industrial and motor vehicle uses) can impair respiratory and cardiovascular functions. Early studies, in which severe episodes of air pollution were associated with increased morbidity and mortality in several western countries, 10,11 led to legislation, monitoring programs, and other measures that reduced ambient levels of pollutants in those countries. 12 As the 20th century closed, concerns about similar adverse effects at lower level exposures have dominated, 13 although many questions remain unresolved, including biological mechanisms of action and the determination of which chemical or physical components are responsible for health effects. Also, rapid urbanization, the emergence of mega-cities, and industrialization in developing regions have produced serious air pollution in areas of the world where resources for cleaning up the environment are minimal or nonexistent. Widespread burning of forests in the developing world has created huge clouds of pollution that can persist for months, resulting in exposures and adverse effects on an unprecedented scale. In addition, billions of people still use low-grade biomass fuels in simple stoves, thereby experiencing very high indoor levels of particulates, polycyclic aromatic hydrocarbons (PAHs), and other airborne pollutants. 14 Halogenated Compounds Improper disposal of highly persistent, non-pesticide chlorinated and brominated compounds has produced bioconcentration up the food chain, leading to widespread contamination of animal and fish products. 15 Associations with cancer, reproductive outcomes, and child development have been observed, but for most of these endpoints, definitive evidence is still elusive. Despite bans implemented in the 1970s in many western countries on production and discharges of, for example, polychlorinated biphenyls, 16 these substances remain ubiquitous. Due to their persistence in biological ecosystems (half-lives in humans can be as long as a decade or more), resolution for these halogenated compounds is slower than for air pollution. New episodes of contamination of food products are still occurring (eg, with dioxin 17). Pesticides Recognition of pesticides as potential human toxins has, in contrast to the above three groups of contaminants, resulted in only small steps either to limit or monitor human exposures. This is despite the fact that these compounds are developed precisely for their toxicity to pests. Concern over adverse health effects has led in some instances to substitution with compounds of different structures, even though safety, even in relative terms, is often unknown. Because thousands of substances from a vast array of chemical classes are involved, larger efforts at documentation of exposure 18 should be undertaken as a first step toward scientific determination of which compounds are safe and which are not. What Lies Ahead In recent years, “globalization” has become a buzzword throughout society, and the ramifications of this phenomenon for environmental epidemiology are not difficult to see. First, issues such as motor vehicle exhaust that previously were of high priority only in western countries are now on the agendas of less industrialized nations. Second, pollution does not respect political borders, as the industrial waste that one country pours into its rivers, lakes and oceans washes up on the shores of other nations, and toxins released into the air are deposited thousands of miles away. In some cases, there has been deliberate transport of waste from high pollution-producing countries to less developed countries; this practice highlights the problem of environmental injustice, whereby population groups that are economically or socially disadvantaged sometimes are also the ones experiencing a disproportionate burden from environmental degradation. Third, localized problems such as overuse of fertilizers are frequently repeated in one region after the next. As for future directions, several themes are emerging at the opening of the 21st century. Infectious Diseases Infectious diseases are re-emerging as major threats to public health. In dealing with threats from pathogenic microorganisms, new problems can occur with chemical and physical hazards. A quintessential example was the discovery during the last decade that tens of millions of people in India, Bangladesh, and other countries are being exposed to arsenic at levels likely to produce noticeable, perhaps dramatic, increases in cancer. 19–21 The source of the arsenic is the microbially safe drinking water delivered by millions of tube wells that were dug during the 1970s to combat diarrheal and other water-borne diseases. At present, there is no quick fix for this major public health disaster. Global Warming and Other Ecologic Shifts In addition to the “traditional” concerns about microbial or chemical threats to the environment (problems most certainly not solved), fresh concerns about planetary changes that have a potential for large-scale ecologic and health impact have come to the fore. The depletion of the ozone layer due to the use of chlorofluorocarbons is increasing exposure to UV-B radiation. This in turn is expected to bring about rising rates of skin cancers and cataracts, as well as changes in immune function, over the next century. 22–24 Global warming is predicted to cause changes in the distribution of vector-borne diseases such as malaria and tick-borne encephalitis 25,26; alterations in food productivity; a possible rise in the oceans and a consequent flooding of coastal areas (where a substantial portion of the world’s population resides); and problems stemming from increased climatic variability. 27–30 Deforestation of a large proportion of the earth’s land mass is predicted to change weather patterns drastically. Exhaustion of fresh water supplies leads to falling water tables in many areas of the world, with potentially far-reaching consequences for the sustainability of food production. These environmental alterations are occurring at the same time as major demographic shifts, in which the populations of cities in less developed regions of the world are swelling far beyond the capacity of the infrastructure to provide clean water, adequate housing, and sanitation. 31 Thus, as the physical environment is undergoing massive change, so too is the social environment. Together, these changes may bring about a very different pattern of health and disease from the one with which we are familiar. 32 The appropriate epidemiologic and public health responses to these changes have yet to be delineated. One thing is clear, however: public policy will require much new scientific data. To meet this need, we must put in place surveillance systems that can document changes in time and space for both exposure and health outcomes. 33 We also need more detailed, focused epidemiologic studies to address questions about the complex intersection of culture and behavior with physical, chemical and biologic factors; such studies will require interdisciplinary teams of investigators. In tandem with the creation of extensive databases will be a second need: the development of creative epidemiologic methods that enable us both to understand these phenomena and to help devise policies that can prevent potentially catastrophic effects on human health and well-being. As some of the potential adverse health effects of global change cannot yet be observed, forward-looking strategies should include some type of “scenario epidemiology” that will allow us to make reliable, quantitative estimates of the effects of future global changes in climate, land use, and social conditions on population health. 34,35 The reader may have noticed that the words “genetics” and “molecular” have not yet been mentioned. It is true that the tools developed by geneticists, toxicologists, and other (more) basic scientists have an important role to play in understanding the associations between the environment and disease. Environmental epidemiology is, however, mainly about the environment. The future of our field must lie as much in strenuous efforts to improve the identification, characterization, and quantification of hazardous environmental exposures as it does in the integration of tools developed by basic science. 36 Ultimately, the success of environmental epidemiology rests on the improvement of public health. This in no way implies that high quality science is not essential; the efforts of “hired guns” to discredit our work is alarming, and rock-solid research papers (our bullet-proof vests), published in the most critical and respectable journals, are the only appropriate basis for effective prevention and intervention. Now that Epidemiology has established itself among the leading journals in public health, we are convinced that the continued synergism between ISEE and the Journal is good for both of us, but, most importantly, is good for public health on a global scale.