most sites designated NFRAP have at best had a preliminary assessment, the quality and quantity of information available usually is inadequate to support a clear conclusion about the potential hazard of the site. Thus, an undetermined number of sites with potentially significant public health hazards are dropped from the CERCLIS inventory each year. Because there is no federal system for tracking sites after they are deferred, no information is available about the subsequent evaluation or remediation of these sites or of changes in their use and associated human exposures.

FEDERAL POLICIES AND ENVIRONMENTAL EPIDEMIOLOGY

The result of the federal programs and policies described here has been to create multiple and overlapping, but incomplete, inventories of hazardous-waste sites. On-site sampling of environmental contamination to estimate off-site human exposure is in some cases inadequate for the assessment of potential human exposure; these cases should be identified and off-site samples obtained. There is no routine review of early site assessments to determine the need for public health interventions or epidemiologic studies. The information used in decisions about subsequent site listing and remediation is inadequate as well. The attendant cost has been a great deal of confusion about the actual risks that hazardous-waste sites pose to human health and the loss of multiple opportunities for epidemiologic research. Clues to the potential scale of human exposure to toxic chemicals released from hazardous-waste sites are emerging, however.

As one of the federal agencies with responsibility for environmental epidemiology, ATSDR has assembled a small professional staff in epidemiology and the related fields of toxicology, environmental medicine, and risk communication. Because the agency has only limited authority and a narrow mandate, and because of its equally limited budget, ATSDR's current programs can do little more than establish a framework for evaluating health effects and for developing research that will be needed to address the issue of hazardous-waste sites adequately in the future. The agency conducts or supports epidemiologic investigations in cases where human exposure to hazardous substances has occurred or is occurring, where a potentially exposed population can be identified, where the exposure can be measured, and where the possible health effects are known or biologically plausible (ATSDR, 1989a).

The broader plan for ATSDR health surveillance activities prepared for FY90 includes site-specific studies at sites that contain compounds of public health importance and for which there are significant data



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