Power analysis for the NOEC: What is the probability of detecting small toxic effects on three different species using the appropriate standardized test protocols?

The power to detect small toxic effects with ecotoxicity tests is investiga ted on the basis of ring tests for the protocols of three standardized repr oduction tests. The test species are Daphnia magna, Eisenia fetida and Fols omia candida, respectively. The coefficient of variance for reproduction in the controls of these tests is about 14.4% for D. magna, and 19% for both E, fetida and E candida. Giv en the standardized test protocols this implies that a reduction inhibition of 20% will be observed in 80% of the D, magna tests and in only 18% of th e tests with either E. fetida or E candida. Comparing 5 different concentra tions with one control, 12 replicas are needed per concentration and 27 in the control for D. magna, and 21 and 47, respectively, for both E. fetida a nd F. candida to observe an effect of 20% in at least 95% of the experiment s. The power analysis is based on a one-sided Dunnett test. This test assumes normal distributed data with equal variance at all treatments. These assump tions are checked for the D, magna test using ring test data. The distribut ion of these data does not deviate substantially from normal. For small tox ic effects, no significant correlation between mean and variance of reprodu ction was observed.