"April 15, 2007". Final Includes bibliographical references.

Executive summary -- section 1. Background, aquatic life criteria limitations and needs -- section 2. Toxicity model formulations, binary endpoints -- section 3. Short-term copper lethality to juvenile fathead minnows. "This is the first of a series of reports that will present and evaluate methods for improving how toxic effect levels in aquatic organisms are addressed in the formulation and application of U.S. Environmental Protection Agency (U.S. EPA) water quality criteria for the protection of aquatic life. This work is being conducted in support of efforts by the Aquatic Life Criteria Guidelines Committee of the U.S. EPA Office of Water to develop new guidelines for derivation of aquatic life criteria. Section 1 summarizes the current formulation of aquatic life criteria and identifies certain limitations regarding how well toxic effects on aquatic organisms are quantified in these criteria as a function of the magnitude and time-variability of exposures. It then broadly describes how better quantification of toxic effects could address these limitations and improve criteria utility. Section 2 describes various models for the assessment of binary toxicity endpoints (yes/no responses such as death) that could be useful in better describing such effects in aquatic life criteria. It then broadly describes how these models can be parameterized based on standard toxicity test data and what considerations should go into selecting a model for actual use in criteria. Section 3 presents a case study that establishes the feasibility of model parameterization and demonstrates that these models can adequately describe the observed time-variability of copper lethality to juvenile fathead minnows for relatively short, constant and intermittent exposures. This section also demonstrates how these models can provide information useful to criteria and that this information might be adequate for criteria applications using relatively simple models rather than more complicated models that would be difficult to implements. Subsequent reports will address model formulations for other endpoints; other case 4 studies regarding both acute and chronic exposures and both lethal and sublethal endpoints; and recommendations regarding the application of these models to aquatic life criteria, including minimum data requirements for model parameterization. These reports will provide the technical basis for developing the guidance for using these models to criteria, but are not intended to provide the actual guidance."--Executive summary.