Water Quality Criteria:Implications for Testing

Russell EricksonU.S. Environmental Protection Agency

Mid-Continent Ecology Division, Duluth, MN, USA

The McKim Conference on the Use of QSARs and Aquatic Toxicology in Risk Assessment

June 27-29, 2006

U.S.EPA Water Quality Criteria for the Protection of Aquatic Life

• Aquatic Life Criteria (ALC) issued by the U.S.EPA Office of Water define limits on chemical exposures which are considered sufficient to preclude unacceptable effects on aquatic communities.

• Procedures are described in “Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses” (Stephan et al., 1985, U.S.EPA).

• Used in regulatory programs to limit discharge of toxic chemicals, in evaluations of aquatic resource condition from monitoring data, and in setting clean-up goals for Superfund sites and other assessments.

• 1-hr average exposure concentrations are allowed to exceed the CMC only once in three years on average.

• The “Criterion Maximum Concentration” (CMC) is set equal to one-half of the FAV.

U.S.EPA Aquatic Life CriteriaAcute Toxicity Data Use

• Mean LC50s for tested species & genera are designated “Species/Genus Mean Acute Values” (SMAVs, GMAVs).

• The “Final Acute Value” (FAV) is set equal to the fifth percentile of GMAVs, or a SMAV of an important species.

• 48- or 96-hr LC50s are required for at least eight aquatic animal species encompassing a specified range of taxa.

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U.S.EPA Aquatic Life CriteriaChronic Toxicity Data Use

• “Chronic values” (CV) are set to the EC20 or the mean of the NOEC&LOEC for the most sensitive of survival, growth, or reproductive endpoints from tests with minimum duration of several days to a few months, depending on species.

• The “Final Chronic Value” (FCV) is set equal to the fifth percentile of GMCVs for at least eight animal genera, the FAV divided by the average SMAV:SMCV ratio for at least three species, or an SMCV of an important species.

• The “Criterion Continuous Concentration” (CCC) is set equal to the FCV or a value based on plant toxicity data.

• 4-day average exposure concentrations are allowed to exceed the CCC only once in three years on average.

• Protection of endangered/threatened species must be based on extrapolations from tested species.

• Testing requirements do not reflect different modes-of-action among chemicals.

U.S.EPA Aquatic Life CriteriaTest Data Issues

• For chemicals barely meeting minimum acute toxicity data requirements, important taxa might not be addressed.

• For chronic toxicity, important response endpoints as well as important taxa might not be addressed.

• Although minimum acute toxicity data requirements are limited, most chemicals do not meet these requirements.

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U.S.EPA Aquatic Life CriteriaBenefits from Predictive Toxicity Tools

• Extrapolation tools for relative effect concentration differences among chemicals, species, and endpoints.

• Methods to predict toxicity mechanisms for different taxonomic groups to guide acute and chronic testing strategies.

• QSARs for point estimates or lower bounds of effect concentrations for species and endpoints of interest.

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