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Technical Report

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Abstract or Description

It was the concern for environmental contamination and human exposure from the growing list of man-made chemicals that led to the set of environmental legislation of the 1970’s which in various ways deals with toxic substances in the environment. Because of the very large number of existing chemicals, and the significant number of new chemicals introduced every year, major regulatory agencies have limited their testing and regulating foci to a small subset of chemicals, presumably those with the greatest perceived threat to human health and environmental contamination.

Priority setting decision processes are being developed, whether systematically or in an ad hoc fashion, as regulatory agencies attempt to set priorities for chemical testing and regulating. These decision processes perforce involve a mix of scientific judgments and value judgments. The outcome of present priority-setting policies and procedures will likely shape regulatory agendas for many years to come and thus determine, for better or worse, the availability of environmental exposure levels of a vast multitude of chemical agents. Some agencies have adopted schemes in which the desired outcome is a ranking of chemicals based on a "hazard index" in order to establish priorities.The objective of the hazard index is to identify those pollutants or chemicals which have the greatest potential for environmental damages, especially to human health. Besides the large number of commercial chemicals, there is also a multiplicity of environmental effects which must be considered in setting priorities for testing.

In all programs for regulating chemicals, two basic categories of information are required: (1) the substance’s production volume, market distribution, usages, and ultimate disposal, and (2) the substance’s physical properties and potential for biological and environmental impacts. The latter category involves testing for physical/chemical properties affecting mobility and transport, degradability, biological accumulation, acute and chronic toxicity, mutagenicity, carcinogenicity, and teratogenicity. The variety of impacts and the large number of available tests have led to the proposal of a hierarchical testing procedure.

With available information on pollutants, ranking schemes have been developed to determine priorities from a mix of objective and subjective information. These have included a subjective allocation of priority points, as well as a scheme based on multiattribute utility theory and other scoring methods for setting priorities on chemical substances. A variety of ranking schemes are in use in federal agencies (Interagency Testing Committee, National Toxicology Program, National Cancer Institute, the pre-manufacture notice of the Toxic Substances Control Act, and others).

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