assessments at the very frontiers of the environmental sciences (Davis, 1985). Thus, under terms of the Toxic Substances Control Act, the EPA was charged with developing policies to control new and existing chemicals. To effect this control, EPA must incorporate evidence on whether agents pose or could pose an unreasonable risk of causing significant adverse health effects, including birth defects, neurological disease, synergistic effects, environmental effects, and other not-well-specified harms to public health and the environment. To make such assessments, EPA relies on a series of risk assessment models that use animal and other experimental data to estimate effects on humans. Unfortunately, many important synthetic and natural chemicals have not been adequately tested and most have not been tested at all. Risk assessment techniques are highly speculative, and almost all rely on multiple assumptions of fact—some of which are entirely untestable (NRC, 1983; 1986b). The anticipatory, preventive intention of these environmental laws has resulted in their heavy reliance on experimental models and theoretical inferences.

As recognition mounted that past disposal practices had contaminated neighborhoods near disposal sites, Congress promulgated the Superfund law (the Comprehensive Environmental Response, Compensation, and Liability Act, CERCLA, Public Law 96-510, 94 Statute 2767) in 1980 to provide a short-term remedy for abandoned hazardous-waste sites. The precise number of these sites is unknown, although estimates go as high as the tens of thousands—an issue discussed in more detail in Chapter 2. Reauthorizing amendments in 1986 further strengthened the provisions of the Superfund law to address the issue of assessing health effects of persons exposed to hazardous wastes.

In 1980, a Congressional Research Service report for the Senate Committee on Environment and Public Works noted that in many cases adequate data on the extent of contamination and its effects on public health and the environment could not readily be obtained (CRS, 1980). A decade later, the congressional Office of Technology Assessment reiterated that conclusion, faulting the regulatory process and the failure to seek scientific and technical studies of many key questions, including the health effects attendant to exposure to hazardous wastes (OTA, 1989).

The original Superfund law, in 1980, established ATSDR as a new agency of the Public Health Service within the U.S. Department of Health and Human Services. The agency's “mission is to prevent or mitigate adverse human health effects and diminished quality of life