The Office of Toxic Substances (OTS), United States Environmental Protection Agency (USEPA), is responsible for administering the Toxic Substances Control Act of 1976 (TSCA). Under Section 5 of TSCA, all new chemicals must be submitted to the USEPA for review and evaluation before entering commerce. The Environmental Effects Branch (EEB) of the Health and Environmental Review Division (HERD) is responsible for the ecological-hazard assessment of new chemicals. Submitters of new chemicals are not required to provide any ecotoxicological data. To date, less than 10% of Sec. 5 submissions contain environmental toxicity data. In the early years, the EEB used analogs, chemical class similarities and literature searches to evaluate the potential ecological hazards of new chemicals. The use of Quantitative Structure Activity Relationships (QSARs) was added to the hazard assessment process in 1981. These QSARs were applied to three broad categories of organic chemicals: (1) neutral organics that are nonreactive and nonionizable, (2) neutral organics that are reactive or ionizable organics (for example, anilines), which show excess toxicity in addition to narcosis, and (3) surface-active compounds such as surfactants and polycationic polymers. Currently, over 50 QSARs are available to estimate the toxicity of new chemicals to fish, aquatic invertebrates and algae. These QSARs can be applied to about 40 classes and subclasses of organic chemicals.
This paper describes the development and application of QSARs by the OTS in the hazard assessment of new chemicals under TSCA.