Bioequivalence approach for whole effluent toxicity testing

Increased use of whole effluent toxicity (WET) tests in the regulatory aren a has brought increased concern over the statistical analysis of WET test d ata and the determination of toxicity. One concern is the issue of statisti cal power. A number of WET tests may pass the current hypothesis test appro ach because they lack statistical power to detect relevant toxic effects be cause of large within-test variability. Additionally a number of WET tests may fail the current approach because they possess excessive statistical po wer, as a result of small within-test variability, and detect small differe nces that may not be biologically relevant. The strengths and limitations o f both the traditional hypothesis test approach and the bioequivalence appr oach for use in the National Pollutant Discharge Elimination System program were evaluated. Data from 5,213 single-concentration, short-term chronic W ET tests with Ceriodaphnia dubia provided the database for analysis. Compar ison of results between the current approach and the bioequivalence approac h indicates that the current approach to WET testing is generally sound but that adopting the proposed bioequivalence approach resolves concerns of st atistical power. Specifically, within this data set, applying the bioequiva lence approach resulted in failure for tests with relatively large test var iability and a pass for tests with relatively small within-test variability .