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The Toxic Substances Control Act (TSCA) has focused governmental attention on the process of assessing the hazards from commercial chemicals. Environmental behavior and impact must be projected before the chemical is released. This requires a knowledge of the environment, relevancy of laboratory data, extent of necessary data and interpretation of those data for future impacts. The responsibility for the data rests with the manufacturer. The key criterion involves a determination of “unreasonable risk.” Six axiomatic principles of risk assessment are identified. This involves an interactive and interdisciplinary thought process that is both iterative and staged. A generalized procedure for exposure assessment has been developed. An initial risk assessment comparing projected environmental concentrations with probable effect levels determines the type and quantity of laboratory test data needed. As examples, three new and three existing chemicals with widely differing properties and uses have been evaluated for their potential environmental impacts.