concern. Such studies are designed to discern relationships between health effects and potential causes. In his recent review of environmental justice, Foreman asserts, "For environmental justice to contribute measurably to public health in low-income and minority communities, it would almost certainly have to stress an epidemiologic perspective … to a far greater extent than is currently the case" (Foreman, 1998, p. 70). Here, again, much of the research to date has been undertaken in occupational health. Two of the biggest challenges to an epidemiologic analysis of health effects are the existence of multiple exposures in the community of interest and the possibility that an adverse health outcome may have multiple determinants.

Multiplicity of Hazards

A community of concern may be exposed to multiple environmental hazards, which may act cumulatively or which may even interact in complex ways to magnify their risks to human health. Researchers have long recognized the need for knowledge about the separate and collective health effects of multiple chemicals (National Research Council, 1988). Recent research into the risks from mixtures has begun to provide some insight into the toxicological issues underlying the interactions of chemical and physical agents and the interactions of external exposures and chemotherapeutic drugs, as discussed in the recent report Interactions of Drugs, Biologics, and Chemicals in U.S. Military Forces (Institute of Medicine, 1996).

Research on multiple exposures has tended to focus on the occupational setting. It is important for new research, however, to take other settings into account, especially residential settings (see Box 3-1). Although it will never be feasible to study the health effects of every specific mixture that may occur because the possible number of combinations is very large, it should not be difficult to select those combinations that should be given priority because of their larger concentrations or greater likelihood of having toxic effects.

Multiplicity of Potential Determinants

A given health condition identified in a community of concern may have several possible etiologies. A major challenge for conducting research on a population with a high prevalence of diseases with multiple causes, such as asthma, is to identify the important environmental determinants from the multiple other factors that affect that disease's expression in populations or individuals. Current models of exposure assessment do not adequately capture this type of interaction. Existing health or environmental exposure databases do not include information on all the relevant factors that need to be investigated to answer many of the research questions posed. Allergens, for example, are notably absent from the majority of environmental exposure databases. Even if a

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