Environmental Epidemiology Research Research Articles

Engaging a Hard-to-Reach Population in Environmental Epidemiology Research: Sampling and Recruitment of California’s Hired Farm Workers

ISEE-0467 Background and Objective: Farm workers provide the majority workforce for California‘s labor-intensive agriculture, but little research has examined the etiology of poor health outcomes that occur disproportionately in this population. To understand occupational/environmental risks, it is critical to obtain representative study samples; however, this poses methodological difficulties. Farm workers are typically mobile, often do not speak English, have little education, may be of undocumented legal status and have complex occupational histories. Therefore, techniques for identifying and recruiting participants for epidemiological studies must utilize different strategies. Methods: MICASA is a cohort investigation of occupational and environmental risks associated with health in 422 farm worker families residing in Mendota, CA. To obtain a representative sample, a two-stage sampling process was employed including identification of eligible census tracts and door-to-door enumeration. The enumeration of residential structures included houses, apartments, trailers and informal structures that housed farm workers. Enumerators visited each mapped dwelling and obtained basic information on residents. Results: 2441 individuals living in 751 households were enumerated. 24% of households were comprised of unaccompanied males, and 9% had 2+ married couples. Among enumerated individuals, 86% engaged in farm work. 66% were men and 34% were women. 55% were Mexican born, 35% were from Central America and 10% were U.S. born. 70% of enumerated households participated in MICASA; 30% declined for reasons including no time, not interested, or don’t want to share personal information. Comparisons between the enumerated and sample populations showed no differences by age, country of birth and years living in U.S. Conclusion: Utilizing a local field team, working with a community advisory board, and involving the community were vital to achieving the research goals. While difficulties in accessing immigrant populations often account for the lack of research, innovative approaches can result in valid samples for epidemiologic study.

Science attracts Spain

The Barcelona Biomedical Research Park (PRBB) in Spain does not resemble the usual research institute (Fig 1). Located on the waterfront, the sophisticated oval building with its wooden panels and open balconies that face the beach looks like a residential or office building rather than the home of, among other facilities, the Centres for Genomic Regulation, for Regenerative Medicine, for Research in Environmental Epidemiology, and the Institute of Advanced Technology. The people of Barcelona took considerable interest in the building and those residing within it during the first PRBB open day in October 2008. Parents, students, passers‐by and tourists visited the laboratories, extracted DNA from kiwi fruit, talked with the scientists and enjoyed refreshments, while they were shown the ways in which their tax money is being spent on scientific research. More recently, on June 16, INDAGANDO TV launched its web‐based television channel (http://www.indagando.tv)—the first Spanish channel dedicated exclusively to scientific communication—that offers news, features and debates, including special reports on women in science. INDAGANDO and the PRBB are just two visible examples of the confidence and optimism that accompany Spain's growing interest and investment in science. Figure 1. The Centre for Genomic Regulation, Barcelona Biomedical Research Park, at the open day in October 2008. © Laura Weill. During the past few years, Spain has made considerable efforts to reinvigorate its research and development (R&D) sector, and to promote an economic model based on knowledge and innovation. Indeed, Spain is a rather late arrival in the international league of countries that regard science as an investment for the future. Since the 1930s, both Spanish society and scientific research have suffered the lasting effects of the ‘dark age’ of Francisco Franco's dictatorship, under which the intellectual potential of the country was suppressed. Many scientists went into exile, including the Nobel Prize winner Severo …

Outside Looking In: Understanding the Role of Science in Regulation

When Rachel Carson took on the task of defining environmental health advocacy in the early 1960s, she made the business of government oversight look simple and straightforward. “Much of the necessary knowledge is now available, but we do not use it,” she wrote in her 1962 book Silent Spring. “We train ecologists in our universities and even employ them in our government agencies, but we seldom take their advice. We allow the chemical death rain to fall as though there were no alternative, whereas in fact there are many, and our ingenuity could soon discover more if given opportunity.” Carson would likely be dazzled by the extent to which governments of all stripes have since called on scientific experts to help populate a regulatory galaxy that extends from the humblest of municipal bailiwicks to the global economy. Nevertheless, the unfolding of this new world of prevention and protection has been neither tidy nor consistent. The scientific community generates volumes of data about potential hazards to human health, but the process of interpretation—resulting ultimately in the development of policy—is often heavily shaped by political, economic, and even cultural interests, which can vary dramatically from one hazard to the next, as well as from one jurisdiction to the next. The outcome of any regulatory deliberation can therefore be unexpected and downright frustrating. A given agent might be labeled a toxic threat in one place while being tolerated without prejudice somewhere else, even as the architects of each policy looked at the very same data. That prospect might puzzle many thoughtful and earnest observers who believe definitive scientific findings should yield equally definitive responses. Daniel Sarewitz recalls his early days as a Congressional Science Fellow in 1989. “The scales fell from my eyes after about a week of being [in Washington, DC],” he says. “When you’re a scientist working in academia, what you see is scientists arguing about difficult problems to try to arrive at the truth. When you’re on the Hill, you realize what’s really going on is these problems are complicated both in terms of the science and in terms of the values. It’s possible to bring many different scientific lenses—interpretations of data, choices of what data to use, what theories to use—to any given complex problem. Not surprisingly, those choices end up mapping onto value preferences and political preferences.” Today Sarewitz is director of the Consortium for Science, Policy, & Outcomes, which, in its own words, seeks to enhance the capacity of public policy to link scientific research to beneficial societal outcomes. But Sarewitz says the consortium faces resistance in moving these perspectives into open public debate. The difficulty, as he outlined in an article in the October 2004 issue of Environmental Science & Policy, stems from a common desire of both advocates and opponents of any given regulation to invoke science to make their respective cases. The former will insist that current knowledge warrants doing something, while the latter point to uncertainties in that same knowledge as justification for doing less, or perhaps nothing.

New Window into Breast Cancer Risk: Assessing Lifetime Exposures to POPs

Persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) are ubiquitous chemical compounds that persist in the environment and bioaccumulate through the food web. Although experiments have shown that POPs stimulate the proliferation of human cancer cell lines, epidemiologic studies of POP-associated cancer risk have yielded inconsistent results, possibly because of the lack of tools for estimating lifetime exposures to these chemicals. Now, however, researchers have developed a new physiologically based pharmacokinetic (PBPK) modeling approach that can potentially be used in epidemiologic studies to simulate lifetime toxicokinetics of POPs in women [EHP 116:886–892; Verner et al.]. Previous biological assessments have been limited to measuring POP levels in blood or tissue samples collected around the time of breast cancer diagnosis. However, such assessments may not reflect the body burden during earlier, potentially critical exposure points in a woman’s life such as the fetal, postnatal, and adolescent periods. In contrast, the new model integrates the relevant processes of absorption, distribution, metabolism, and elimination to estimate lifetime blood and tissue exposure and levels during any hypothesized time window of susceptibility in breast cancer development. The model also predicts how various types of relevant lifetime physiologic changes—such as body weight variation, pregnancy, excretion of POPs through lactation, and aging—will influence the kinetics of a compound in a woman throughout her life. The model enables the estimation of interindividual differences in POP exposures through the use of physiologic information obtained from questionnaires in epidemiologic studies. The researchers found that lactation and weight change histories had the greatest impact on the toxicokinetic profile throughout life. According to the model, the longer and later in life lactation occurred, the lower the woman’s blood POP concentration at age 55 (a surrogate time representing the typical age at breast cancer diagnosis). Similarly, variations in body weight throughout life had a greater impact than average body weight on blood POP concentrations, possibly because weight loss is accompanied by unloading of POPs into the blood via lost adipose tissue. This means that quantitative information on both lactation and body weight histories is critical when evaluating past POP exposures. If, as some researchers hypothesize, breast cancer is related to POP exposures at specific time windows of susceptibility during a woman’s lifetime, lactation and body weight histories must be considered in studies of POP exposures and breast cancer risk. Depending on when such physiologic events occur, women having similar POP concentrations at the age of diagnosis may have had completely different internal levels at a time that may be critical to the formation of breast cancer. The proposed PBPK modeling approach therefore could be used in environmental epidemiology research to circumvent limitations inherent in relying on late-life sampling for past exposure assessments.

Technical Assistance of Environment and Health Ministries to Develop Environmental Epidemiology in Southern Italian Regions

ISEE-543 Objective: The technical assistance activities promoted by Ministry of Environment and Ministry of Health in Italian southern regions, EU Structural Funds 2000–2006, have been investigated to evaluate the impact in developing environmental epidemiology setting. Materials and Methods: The outcome of 3 national conferences organized by the 2 Ministries have been examined, to understand the participation of personnel of competent regional bodies. Scientific papers produced by the regional bodies have been considered as a major result, together with public presentation of results and their impact on media. Other activities are included, like the publication of researches on specific sites, the organization of regional conferences, a national “consensus conference,” and the drafting of research projects still in course. Results: In the framework of the technical assistance activity in 7 Italian regions, aimed at supporting Regional Agencies for the Protection of the Environment and Regional Epidemiological Observatory, to develop environmental epidemiology, the first topic considered was the research in high polluted sites. To build capacity on this issue, being a priority in regional bodies' agenda and in the public attention, methodology and tools were set up and transferred. The regional bodies of 2 out of 7 regions included in the analysis have produced regional surveys on health and the environment in the high polluted sites. A regional Government promoted a “consensus conference” during which a plan was agreed about a site recently identified by an environmental epidemiology research, which played a role in identifying solutions. In the other regions, papers have been published, environmental epidemiology activities have been planned, and regional conferences have been organized. Conclusions: Technical assistance of 2 Ministries helped to implement activities and promoted a culture of collaboration among different bodies in charge of environment and health protection. Environmental epidemiology supplied a common ground to experiment and develop such a cooperation.

Chemicals causing mammary gland tumors in animals signal new directions for epidemiology, chemicals testing, and risk assessment for breast cancer prevention

Identifying chemical carcinogens in animal studies is currently the primary means of anticipating cancer effects in humans. Animal studies to evaluate potential chemical carcinogenicity are particularly important for breast cancer because environmental and occupational epidemiologic research is sparse. Chemicals that increased mammary gland tumors in animal studies were compiled from the International Agency for Research on Cancer (IARC), the U.S. National Toxicology Program (NTP), and other sources. Summary assessments of the carcinogenic potential for each chemical and potentially exposed populations were also compiled. In all, 216 chemicals were identified that have been associated with increases in mammary gland tumors in at least 1 study. These include industrial chemicals, chlorinated solvents, products of combustion, pesticides, dyes, radiation, drinking water disinfection byproducts, pharmaceuticals and hormones, natural products, and research chemicals. Twenty-nine are produced in the U.S. at >1 million pounds/year; 35 are air pollutants, 25 have involved occupational exposures to >5000 women, and 73 have been present in consumer products or as contaminants of food. Thus, exposure is widespread. Nearly all of the chemicals were mutagenic and most caused tumors in multiple organs and species; these characteristics are generally believed to indicate likely carcinogenicity in humans. To our knowledge, this is the most comprehensive list developed of animal mammary gland carcinogens and, along with associated data, is publicly available at URL: www.silentspring.org/sciencereview and at URL: www.komen.org/environment. Valuable information from cancer bioassays is not well utilized in risk assessment and regulatory processes, suggesting a need to strengthen chemicals testing and risk assessment as tools for breast cancer prevention.

Additive versus multiplicative models in ecologic regression

Much research in environmental epidemiology relies on aggregate-level information on exposure to potentially toxic substances and on relevant covariates. We compare the use of additive (linear) and multiplicative (log-linear) regression models for the analysis of such data. We illustrate how both additive and multiplicative models can be fit to aggregate-level data sets in which disease incidence is the dependent variable, and contrast these results with similar models fitted to individual-level data. We find (1) that for aggregate-level data, multiplicative models are more likely than additive models to introduce bias into the estimation of rates, an effect not found with individual-level data; and (2) that under many circumstances multiplicative models reduce the precision of the estimates, an effect also not found in individual-level models. For both additive and multiplicative models of aggregate-level data, we find that, in the presence of covariates, narrow confidence interval are obtained only when two or more antecedent factors are strongly related to the measured covariate and/or the exposure of primary substantive interest. We conclude that the equivalency of fitting additive versus multiplicative models in studies with individual-level binary data does not carry over to studies that analyze aggregate-level information. For aggregate data, we strongly recommend use of additive models.

The need for the “new health geography” in epidemiologic studies of environment and health

Growth during the past decade in what can be broadly referred to as social and environmental epidemiologic research has been an important contributor to an emerging understanding of environment and health relationships. While the incorporation of geographic information systems as well as concepts such as “neighborhoods” might be viewed as evidence of social epidemiology moving closer to health geography, I argue that the two fields are not well aligned. Health geography has much more to contribute to studies of environment and health, and attention by social epidemiologists to those potential contributions could help rectify this misalignment. This paper suggests a number of geographic perspectives on health and environment that could create useful connections between geography and public health, via social epidemiology. To illustrate this potential, I use an ongoing study of a Texas community exposed to a large petrochemical complex—an inquiry constructed in the mode of social epidemiology—as a case in point. I apply several perspectives and concepts from geography to the case study. Cultural ecology, discourse materialized, political ecology, and territoriality are used to assess the Texas City situation and suggest important types of understandings that can enhance the social epidemiology approach to environment and health. I conclude with a discussion of the prospects for a social epidemiology infused with this type of geographic thought and analysis.

Using GIS-Based Approaches to Support Research on Neurotoxicants and Other Children's Environmental Health Threats

Environmental threats to children's health are complex and multifaceted; consequently, children's environmental health research strives to identify areas of elevated exposure, determine whether particular demographic groups are inequitably exposed, and link exposures to incidence of disease. Many environmental health researchers use geographic information systems (GIS) to ex post display the results of their data collection and analysis. This methodological paper shows some ways by which the ex ante integration of GIS into environmental exposure and epidemiological research can significantly enhance: research design; sampling, recruitment, and retention strategies; data management and analysis; and community translation.

Model for the Analysis of Binary Time Series of Respiratory Symptoms

Environmental epidemiologic research on respiratory symptoms presents unique types of data, typically requiring simultaneous analysis of both time- and person-varying factors. In this paper, the authors propose a new, simple model that incorporates such factors and controls for each person's prior history of symptoms. The Yale Mother and Infant Health Study was undertaken to investigate the effects of ambient pollutant concentrations, meteorologic changes, and demographic variables on daily respiratory symptoms in both mothers and infants. This analysis was restricted to 673 mothers followed in southwestern Virginia from June 10 to August 31, 1995. Of the person-varying factors, husband's level of education, nested within marital status, and having pets in the home were related to an increased likelihood of new episodes; however, neither was related to duration of symptoms. Interestingly, women who were unmarried were least likely to have new episodes of respiratory symptoms, while those with the most highly educated spouses were most likely to have new episodes. Having pets in the home increased the likelihood of a new episode. Having a history of allergies and having children in day care were found to be related to the symptom of a runny or stuffy nose, in terms of both incidence and duration. The level of coarse particles was related to the incidence of new episodes of runny or stuffy nose, and a higher level prolonged the duration of symptoms. Sulfate level was not related to the incidence of new episodes but was associated with the duration of the episodes.

Geographic information systems: their use in environmental epidemiologic research.

Advances in geographic information system (GIS) technology, developed by geographers, provide new opportunities for environmental epidemiologists to study associations between environmental exposures and the spatial distribution of disease. A GIS is a powerful computer mapping and analysis technology capable of integrating large quantities of geographic (spatial) data as well as linking geographic with nongeographic data (e.g., demographic information, environmental exposure levels). In this paper we provide an overview of some of the capabilities and limitations of GIS technology; we illustrate, through practical examples, the use of several functions of a GIS including automated address matching, distance functions, buffer analysis, spatial query, and polygon overlay; we discuss methods and limitations of address geocoding, often central to the use of a GIS in environmental epidemiologic research; and we suggest ways to facilitate its use in future studies. Collaborative efforts between epidemiologists, biostatisticians, environmental scientists, GIS specialists, and medical geographers are needed to realize the full potential of GIS technology in environmental health research and may lead to innovative solutions to complex questions.

Applied epidemiology and environmental health: Emerging controversies

This review article assesses the state of the science in environmental epidemiology, not by summarizing current scientific findings but rather by examining conceptual controversies in the study of how environmental factors influence human health. This approach seems necessary because environmental epidemiology presently stands at a crossroads—in fact, at a number of overlapping crossroads. The field teems with epistemologic debates concerning appropriate paradigms for framing research questions, interpreting data, and applying research findings to policy. The present review focuses on emerging controversies related to three questions: What is considered “environmental”? What counts as credible research in environmental epidemiology? And what does “applied epidemiology” mean in the context of environmental health? The goal is to organize the presently fragmented critical literature on these issues and to promote productive dialogue by identifying central themes in current conceptual debates.

Geographic Information Systems: Their Use in Environmental Epidemiologic Research

Advances in geographic information system (GIS) technology, developed by geographers, provide new opportunities for environmental epidemiologists to study associations between environmental exposures and the spatial distribution of disease. A GIS is a powerful computer mapping and analysis technology capable of integrating large quantities of geographic (spatial) data as well as linking geographic with nongeographic data (e.g., demographic information, environmental exposure levels). In this paper we provide an overview of some of the capabilities and limitations of GIS technology; we illustrate, through practical examples, the use of several functions of a GIS including automated address matching, distance functions, buffer analysis, spatial query, and polygon overlay; we discuss methods and limitations of address geocoding, often central to the use of a GIS in environmental epidemiologic research; and we suggest ways to facilitate its use in future studies. Collaborative efforts between epidemiologists, biostatisticians, environmental scientists, GIS specialists, and medical geographers are needed to realize the full potential of GIS technology in environmental health research and may lead to innovative solutions to complex questions.

Biomarkers and mechanistic approaches in environmental epidemiology.

Environmental epidemiological research involves the identification of relationships between previous exposures to putative causative agents and subsequent biological effects with study populations. Such relationships are often hard to fully characterize because of difficulties in accurately quantifying exposure, dose, and effect. Biomarkers are indicators, residing in biological systems or samples, of exposure, dose, effect, or susceptibility. Biomarkers of exposure indicate the presence of previous exposure to an environmental agent; a biomarker of dose bears a quantitative relationship to previous exposure or dose; these include exogenous substances, interactive products, or interactions that change the status of the target molecule. Biomarkers of effect indicate the presence and magnitude of a biological response to exposure to an environmental agent; these include endogenous components, or measures of the functional capacity or state of the system. Biomarkers of susceptibility indicate an elevated sensitivity to the effects of an environmental agent; these include the presence or absence of an endogenous component, or abnormal functional responses to an administered challenge. The development of molecular biomarkers for environmental agents is based upon specific knowledge of metabolism, interactive product formation, and general mechanisms of action. The validation of any biomarker-effect link requires parallel experimental animal and human epidemiological studies.

Biomarkers and Mechanistic Approaches in Environmental Epidemiology

Environmental epidemiological research involves the identification of relationships between previous exposures to putative causative agents and subsequent biological effects with study populations. Such relationships are often hard to fully characterize because of difficulties in accurately quantifying exposure, dose, and effect. Biomarkers are indicators, residing in biological systems or samples, of exposure, dose, effect, or susceptibility. Biomarkers of exposure indicate the presence of previous exposure to an environmental agent; a biomarker of dose bears a quantitative relationship to previous exposure or dose; these include exogenous substances, interactive products, or interactions that change the status of the target molecule. Biomarkers of effect indicate the presence and magnitude of a biological response to exposure to an environmental agent; these include endogenous components, or measures of the functional capacity or state of the system. Biomarkers of susceptibility indicate an elevated sensitivity to the effects of an environmental agent; these include the presence or absence of an endogenous component, or abnormal functional responses to an administered challenge. The development of molecular biomarkers for environmental agents is based upon specific knowledge of metabolism, interactive product formation, and general mechanisms of action. The validation of any biomarker-effect link requires parallel experimental animal and human epidemiological studies.

Problems and priorities in epidemiologic research on human health effects related to wiring code and electric and magnetic fields.

Because of a reported excess of cancers among children living near power lines, there is some concern that electric and magnetic fields (EMFs) induced by electric power sources may affect human health, and this possibility has provoked considerable controversy. The scientific question of whether there are such health effects is far from resolved. Building upon a set of detailed reviews of the available evidence, this paper proposes research priorities and places particular emphasis on epidemiologic research. The most pressing need is to verify the validity of the claim that childhood cancer risk is affected by the type of wiring code in the vicinity of the household. More useful work can be done to verify this in the areas in which such studies have already been carried out, and additional studies should be done elsewhere. Methodological investigation of the interrelationships among different measures and proxies for EMF is needed, and this could feed back to influence the type of EMF measures used in epidemiologic studies. Studies of cancer among adults in relation to EMFs in the work place are needed. Of lower priority are studies of adverse reproductive outcomes in relation to parental EMF exposure and studies of the neurobehavioral impact of chronic EMF exposure. This article also discusses the structural impediments of conducting environmental epidemiology research and argues that bold, large-scale epidemiologic monitoring systems are needed. There is a discussion of the interface between epidemiology and public policy in a topic area as controversial as EMFs.

Use of exposure databases for status and trends analysis.

Exposure databases are useful for monitoring status and trends in environmental health. However, other supporting data are usually needed to infer human exposure or internal dose. Program planning and evaluation, environmental health surveillance, epidemiologic research, and contributions to international efforts are four major purposes for monitoring environmental exposure status and trends. Although databases play an important role in monitoring human exposure, certain methodological problems need to be overcome. The work group developed six criteria for meeting information needs for human exposure assessment. Areas that need attention are (1) specification of location, (2) specification of facility and chemical identifiers, (3) documentation of special populations at risk, (4) provision of early warning of new problems, (5) monitoring changes over time, and (6) enhancement of documentation. We tested these criteria by examining six available databases that might be used for monitoring exposure to contaminants in drinking water. Available data fell short of information needs. We drew four conclusions and offered several recommendations for each. First, available data systems lack adequate measures of human exposure. Second, data for monitoring exposures for many important population subgroups and environmental settings are inadequate. Third, an "early warning" system that monitors human exposures is needed. Fourth, designers of data-collection systems should consider the needs of users who monitor status and trends of human exposure.

Ongoing research in occupational health and environmental epidemiology in developing countries.

Research in occupational health and environmental epidemiology can play an important role in furthering our understanding of occupational and environmental health problems. Research guides us in the recognition, management, and prevention of health problems. However, in developing countries, where rates of occupational and environmental illnesses and injuries are higher and where these problems are often more severe than in developed countries, research capabilities are less developed. In mid-1990, a project was undertaken to (a) document ongoing research in occupational health and environmental epidemiology in developing countries, (b) facilitate the exchange of information among researchers in this field, (c) stimulate research, and (d) avoid unnecessary duplication among researchers in this field. A questionnaire was mailed, the purpose of which was to learn the current status of research in developing countries and to develop a directory of such ongoing research. The questionnaire was sent to 1,528 individuals. Of the 500 research projects identified, 77% were investigating chemical hazards; 26%, physical hazards; 10%, biological hazards; and 10%, psychosocial hazards (some projects addressed multiple hazards). The chemical hazards studied most frequently were dusts, pesticides, and lead. The greatest number of research projects were identified in China, India, Brazil, Korea, and Thailand. Most projects were descriptive or cross-sectional epidemiologic studies or industrial hygiene or exposure-assessment studies. The World Health Organization has published a directory of the specific research projects that were identified in this survey.

The Health of Latin Americans Exposed to Polluted Rivers: A Triple-Blind Observational Study

Accelerating development in South America, with consequent contamination of rivers as the final common pathway of waste, raises concern about adverse effects on the health of riverine populations. We conducted a cross-sectional survey simultaneously in six Latin American nations among people living near a river known to be polluted in each country. Trace metals (arsenic, mercury and lead) were selected as indicators of exposure to industrial effluents. Within each country, we contrasted probability samples from three types of communities: one upstream of point sources of pollution and thus little exposed; one downstream from a site of major development; and one with intermediate exposure. The outcome variables were health status measures elicited by questionnaire and biochemical measures of blood and urine. We examined several possible explanatory and confounding variables, including housing conditions, nutrition, and source of drinking water. The field work was done with triple blinding in that data-gatherers and study subjects were unaware of their group membership and of the study hypotheses, those analysing, specimens and questionnaires were blind to country and community of origin of the material and the investigators reviewed the results in code, committing themselves to conclusions in writing before the codes were broken. Methods were carefully standardized across six countries during training, when pretesting data-gathering instruments and with double coding and extensive accuracy checks of computerized data. There were 900 eligible subjects from 18 communities in six countries. The overall response rate was 92%, the lowest 86%. Results showed an acceptable level of health in all communities and no relationship to exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Issues in environmental epidemiological research: the example of environmental lead and health.

Modern environmental epidemiology encompasses the "traditional" area of physico-chemical hazards, along with health hazards in the societal environment (e.g. noise, stress, social organisation), and, increasingly, supranational problems (e.g. ozone depletion, global warming). As governments undertake environmental management, improved quantitative estimates of environmental risks to health are needed. Methodological difficulties of environmental epidemiological research include problems of exposure measurement, of estimating exposure at the level of the individual, and of detecting relatively small effects (particularly at low exposure levels). The health hazards of occupational lead exposure are well documented. The health hazards of environmental exposure to lead, within the general population, remain a focus of continuing epidemiological research. Indeed, the reported adverse effects upon the developing central nervous system of young children are now central to public health debate about environmental lead exposure standards. Recent evidence from cohort studies in several countries indicates adverse effects of environmental lead exposure upon early childhood mental development. In South Australia, a cohort study of children born in a lead smelter community, Port Pirie, has revealed evidence of such an effect. After controlling for many potential confounding factors (social, behavioural, family, and medical), cumulative postnatal lead exposure was found to be weakly associated with an adverse effect upon mental development at age two years and, more strongly, at age four years. The relations between environmental epidemiological research and public health policy are discussed.