The Agency for Toxic Substances and Disease Registry (ATSDR) is mandated by Congress to address potential public health impacts associated with environmental exposures to hazardous substances from waste sites and releases of hazardous substances into the environment. ATSDR develops in order of priority, a list of hazardous substances most commonly found at facilities on the CERCLA National Priority List. The agency is also directed to prepare toxicological profiles for priority hazardous substances, ascertain significant human exposure levels for these substances in the environment and the associated health effects, and identify research areas needed to fill data gaps.

To further focus these efforts, ATSDR developed a list of priority health conditions (PHCs) to evaluate potential health risks to persons living near hazardous waste sites and to determine needed programs and applied human health activities involving hazardous substances identified at the sites (ATSDR 1993). The PHCs also assist ATSDR programs in the prevention or mitigation of adverse human health effects and diminished quality of life resulting from exposure to hazardous substances in the environment. The selection of PHCs was based on existing knowledge of toxicology and experience in assessing and evaluating hazardous substances and adverse health outcomes. The ATSDR PHCs are:

• Birth defects and reproductive disorders
• Cancer
• Immune function disorders
• Kidney dysfunction
• Liver dysfunction
• Lung & respiratory diseases
• Neurotoxic disorders

In order to address the congressional mandate to ascertain levels of exposure that present a significant risk to human health, ATSDR develops minimal risk levels (MRLs) for priority hazardous substances most frequently found at hazardous waste sites. The MRLs are health guidance values derived based on the most sensitive non-cancer adverse health endpoints. These endpoints are consistent with the ATSDR PHCs. This compendium is comprised of scientific journal publications authored by ATSDR scientists on health implications of environmental exposures and issues concerning health guidance values. The topics cover the precision, uses, and limitations of public health guidance values, methodology for MRL derivation, and evaluation of toxicological end points to derive MRLs. Classification of specific health end points and their roles in the derivation of MRLs are also presented; the end points are neurological, respiratory, developmental, reproductive, hematological, hepatic, renal, and immunological. Other topics dealing with uncertainty factors and reducing uncertainty in the derivation health guidance values are also included. More recent issues on health guidance values for chemical mixtures, and application of computational toxicology methods are also presented.