Assessment criteria for using the sea-urchin embryo test with sediment elutriates as a tool to classify the ecotoxicological status of marine water bodies.

A large, multiyear data set was generated by pooling the sediment elutriate (SET) results collected during previous studies conducted in the Galician Rias (northwest Iberian Peninsula) that met the acceptability criteria in the controls, to ensure optimum quality of data (n=162). Two subsets of equal to reference and lower than reference sites were identified by comparing the Percentage Net Response (PNR) value from each sampling site with nontoxic, cruise-specific, reference sites by using the t test with the unequal variance assumption. Ecotoxicological Assessment Criteria (EAC0, EAC1, EAC2, and EAC3) were then derived from those two subsets to classify the SET results into five categories of ecotoxicological status: high, good, moderate, poor, and bad, in line with the European legislation. The 50th and 5th percentiles of the PNR distribution of the equal to reference sites subset were EAC0=0.879 and EAC1=0.694. An EAC2=0.508 was obtained from the 50th percentile of the lower than reference sites subset. Because the PNR values of the entire database showed a distribution that can be adjusted to two normal populations, the EAC3=0.240 PNR was calculated as the intersection between the first and second normal distributions identified. Power analysis proved that the limit between acceptable and unacceptable status (EAC1) corresponded to a detectable PNR difference to control with a confidence level>99% and a power of 95%. Copyright (c) 2010 SETAC.