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Environmental exposure assessment, an intermediate step in risk analysis, ties projected volumes of toxic materials entering the environment to specific environmental effects. Thus, prediction of the environmental fate and distribution of a toxic compound is an integral part of any hierarchical scheme of risk analysis.
Environmental exposure assessment is a new and emerging science, and, although some processes have not been adequately characterized, tests for the most significant ones (volatilization, hydrolysis, oxidation, etc.) are available. Both screening tests and detailed protocols are presently available for determining the process kinetics for selected chemicals exposed to differing environmental conditions. Preliminary exposure assessments can be made from the screening data if the following rate processes are estimated: microbial degradation, chemical transformation, photolysis, hydrolysis, ionization, and partitioning. Because these processes can act either synergistically or competitively, depending upon the chemical structure of the material and the conditions of the environment, great care must be taken to conduct the tests in sequential order.
The greatest unrealized potential for exposure assessment lies in the use of mathematical modeling techniques. When environmental exposure models are coupled with environmental effects models, powerful tools for risk assessment emerge. Such sophisticated models need to be refined and verified, however, before risk analysis becomes accurate and cost-effective.
analysis, chemical properties, environment, mathematical models, risk analysis, exposure analysis, toxicology, pollution, aquatic toxicology
Associate director for Water Quality Research, Environmental Research Laboratory, U.S. Environmental Protection Agency, Athens, Ga.