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.