The Environmental Effects Branch (EEB) of the United States Environmental Protection Agency (USEPA) evaluates data to assess the potential effects, inherent toxicity, and hazard posed by industrial chemicals to the environment for the Office of Pollution Prevention and Toxics or OPPT (formerly the Office of Toxic Substances or OTS) under the Toxic Substances Control Act (TSCA). The regulatory framework of TSCA focuses on data submitted by industry and reviewed by EEB. The review process is critical to assessing the ecotoxicological hazard of existing chemicals (TSCA Section 4), new or Pre-manufacture notice (PMN) chemicals (Section 5), and other potentially hazardous existing chemicals (Sections 6 and 8). EEB developed methods for hazard assessment using a tiered testing scheme, test guidelines, environmental endpoints of concern, and assessment factors. The OPPT testing scheme provides a unified, orderly, consistent, economical, and flexible strategy. It is organized into four tiers, each with several toxicity tests. Tiers increase progressively in complexity, testing costs, and duration of the tests. Decision criteria occur at intervals in the scheme and serve to facilitate making choices on whether to proceed with additional testing or to discontinue testing. OPPT test guidelines are state-of-the-art aquatic and terrestrial test methods used to measure toxicity of industrial chemicals. New guidelines (sediment toxicity tests) are promulgated in response to developments in ecotoxicity research, interest in new testing areas, and Agency needs. The testing scheme and test guidelines are used to assess the possible environmental hazard of existing chemicals and new chemicals. Available toxicity data on existing chemicals range from a moderate to a large amount, while limited data usually are available for PMN chemicals. Results of available testing are validated by EEB and incorporated into the hazard assessment. This evaluation identifies qualitative and quantitative effects that may occur from chemical exposure, reports environmental concentrations at which toxic effects may begin to occur, and marshalls arguments to support the analysis. These toxic effect concentrations are used to derive environmental concern levels. For PMN chemicals, assessment factors are used to adjust toxicity data to arrive at environmental concern levels, and to require additional testing to better assess hazard. Concern levels are then compared to predicted exposure concentrations to determine the risk of actually incurring harm, and to obtain a decision on possible regulatory action.