The Toxic Substances Control Act (TSCA) allows for the regulation of new industrial chemicals if a chemical may present an unreasonable risk toward the environment, or if a chemical has significant exposure toward the environment. Risk assessment under TSCA Section 5 consists of the integration of the hazard assessment for a chemical with the chemical's exposure assessment. The environmental-hazard assessment consists of identifying all of the effects of a chemical toward organisms in the environment, and toward the populations, communities, and ecosystems to which those organisms belong. Toxicity data for a chemical consists of effective concentrations (EC), which indicate the type of effect and the seriousness of that effect on a given organism at a known concentration of chemical. Effective concentrations can be based on test data or predicted using structure activity relationships (SAR). A collection of all of the ECs for a chemical is called a hazard profile or a toxicity profile. Environmental factors which reduce the inherent toxicity of a chemical (that is, mitigation factors), as well as, enhancement factors that increase toxicity are taken into account when the hazard profile is developed. The environmental-exposure assessment consists of predicting the environmental concentrations of a chemical from releases due to its production, processing, uses, and disposal. There are two types of exposure assessment most frequently used under TSCA: the Percen-tile Stream Flow Method and the Probability Dilution Model (PDM) Method. Environmental-risk assessment is done by using the quotient method. This method simply compares an EC or a concern concentration (CC) to the actual or predicted environmental concentrations (PEC). If the PEC is greater than the EC or CC, then you have a potential risk. Case studies for several types of chemicals will be presented: neutral organic chemicals; organic chemicals with excess toxicity; anionic surfactants; nonionic surfactants; cationic surfactants; amphoteric surfactants; anionic polymers; nonionic polymers; poly cationic polymers; amphoteric polymers; acid dyes; neutral dyes; cationic dyes; amphoteric dyes; polyanionic monomers; and compounds which hydrolyze (for example, acid chlorides and alkyloxysilanes); and metals.

Section 5 of the Toxic Substances Control Act (TSCA) requires that manufacturers and importers of new chemicals must submit a Premanufacture Notification (PMN) to the U.S. Environmental Protection Agency 90 days before they intend to commence manufacture or import. Certain information such as chemical identity, uses, etc., must be included in the notification. The submission of test data on the new substance, however, is not required, although any available health and environmental information must be provided. Nonetheless, over half of all PMNs submitted to the agency do not contain any test data; because PMN chemicals are new, no test data is generally available in the scientific literature. Given this situation, EPA has had to develop techniques for hazard assessment that can be used in the presence of limited test data. EPA's approach has been termed "structure-activity relationships" (SAR) and involves three major components: the first is critical evaluation and interpretation of available toxicity data on the chemical; the second component involves evaluation of test data available on analogous substances and/or potential metabolites; and the third component involves the use of mathematical expressions for biological activity known as "quantitative structure-activity relationships" (QSARs). At present, the use of QSARs is limited to estimating physical chemical properties, environmental toxicity, and bioconcentration factors. An important overarching element in EPA's approach is the experience and judgment of scientific assessors in interpreting and integrating the available data and information. Examples are provided that illustrate EPA's approach to hazard assessment for PMN chemicals.

Section 5 of the Toxic Substances Control Act (TSCA) requires that manufacturers and importers of new chemicals must submit a Premanufacture Notification (PMN) to the U.S. Environmental Protection Agency 90 days before they intend to commence manufacture or import. Certain information such as chemical identity, uses, etc., must be included in the notification. The submission of test data on the new substance, however, is not required, although any available health and environmental information must be provided. Nonetheless, over half of all PMNs submitted to the agency do not contain any test data; because PMN chemicals are new, no test data is generally available in the scientific literature. Given this situation, EPA has had to develop techniques for hazard assessment that can be used in the presence of limited test data. EPA's approach has been termed "structure-activity relationships" (SAR) and involves three major components: the first is critical evaluation and interpretation of available toxicity data on the chemical; the second component involves evaluation of test data available on analogous substances and/or potential metabolites; and the third component involves the use of mathematical expressions for biological activity known as "quantitative structure-activity relationships" (QSARs). At present, the use of QSARs is limited to estimating physical chemical properties, environmental toxicity, and bioconcentration factors. An important overarching element in EPA's approach is the experience and judgment of scientific assessors in interpreting and integrating the available data and information. Examples are provided that illustrate EPA's approach to hazard assessment for PMN chemicals.

As testing is not required, ecotoxicity or fate data are available for approximately 5% of the approximately 2,300 new chemicals/year (26,000 + total) submitted to the US-EPA. The EPA's Office of Pollution Prevention and Toxics (OPPT) regulatory program was forced to develop and rely upon QSARs to estimate the ecotoxicity and fate of most of the new chemicals evaluated for hazard and risk assessment. QSAR methods routinely result in ecotoxicity estimations of acute and chronic toxicity to fish, aquatic invertebrates, and algae, and in fate estimations of physical/chemical properties, degradation, and bioconcentration. The EPA's Toxic Substances Control Act (TSCA) Inventory of existing chemicals currently lists over 72,000 chemicals. Most existing chemicals also appear to have little or no ecotoxicity or fate data available and the OPPT new chemical QSAR methods now provide predictions and cross-checks of test data for the regulation of existing chemicals. Examples include the Toxics Release Inventory (TRI), the Design for the Environment (DfE), and the OECD/SIDS/HPV Programs. QSAR screening of the TSCA Inventory has prioritized thousands of existing chemicals for possible regulatory testing of: 1) persistent bioaccumulative chemicals, and 2) the high ecotoxicity of specific discrete organic chemicals.