Rothman (1990) noted estimates of exposure are very often heterogenious, poorly described, and involve low concentrations of toxicants. Although essential to well-designed epidemiologic investigations, exposure assessment has been and continues to be an inadequately developed component of environmental epidemiology, because
the temporal characteristics of site discovery and investigation make it difficult;
the conceptual framework and techniques for evaluation have only recently been established;
epidemiologists often have not understood or given sufficient attention to exposure evaluation.
This chapter has three sections. The first describes the potential for human exposure by identifying toxic chemicals found at hazardous-waste sites. This includes direct site contamination, contamination by unidentified or uncharacterized pollutants, and groundwater contamination from other sources. The second section discusses approaches to exposure assessment and their attendant problems. The third section examines reported exposure assessments associated with hazardous-waste sites and reviews the strengths and weaknesses of the reports.
Although much of the waste produced annually in the U.S. is not listed as hazardous, the U.S. Environmental Protection Agency (EPA) estimated in 1988 that the amount of hazardous waste managed by approximately 3000 licensed facilities was 275 million metric tons (EPA, 1988). In addition, there are a substantial number of uncontrolled disposal sites that contain hazardous wastes and that could present serious environmental or public health problems. For example, municipal waste sludge and incinerator ash can contain toxic materials such as lead, cadmium, mercury, and other toxic materials.
In the late 1970s there was widespread publicity about the indiscriminate dumping of waste that was resulting in release of toxic agents into the environment. The national failure to address the many known and suspected hazards from uncontrolled hazardous waste sites led Congress to pass the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), generally known as the Superfund law. Under CERCLA's terms, more than 31,000 sites have been reported to EPA's CERCLA Information System (CERCLIS) inventory of sites that could require cleanup. EPA