SYMPOSIA PAPER Published: 01 January 1993

Environmental Risk Assessment of New Chemicals Under the Toxic Substances Control Act TSCA Section Five


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.

Author Information

Nabholz, JV
Office of Toxic Substances, United States Environmental Protection Agency, Washington, DC
Miller, P
Office of Toxic Substances, United States Environmental Protection Agency, Washington, DC
Zeeman, M
Office of Toxic Substances, United States Environmental Protection Agency, Washington, DC
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Developed by Committee: E47
Pages: 40–55
DOI: 10.1520/STP19232S
ISBN-EB: 978-0-8031-5234-2
ISBN-13: 978-0-8031-1860-7