Organisation and performance of an international ringtest for the validation of the enchytraeid reproduction test

The experiences and results of the Enchytraeid Reproduction Test (ERT) ringtest can be summarised as follows: It was performed in line with OECD requirements and was sponsored by the German Federal Environment Agency (Umweltbundesamt; UBA). Twenty-nine institutions (mainly from universities and contract research laboratories) from 15 countries from Europe and North America participated actively in the ringtest. The co-ordinating laboratory centrally distributed the test chemicals, guidance papers and test organisms to all participants. In addition, several training courses were organised. Most participants performed two tests with the fungicide Carbendazim and two tests with 4-Nitrophenol. For each chemical, one test was designed according to an ECx approach and the other according to a NOEC approach. A total of 92 tests were performed (among the highest number ever performed in a ringtest). About 72% of them were valid. A major aspect of the project was the detailed statistical evaluation of the test results, leading to recommendations for an optimised ecotoxicological test design. The effects of the two test chemicals on enchytraeid reproduction were in the range expected from data in the literature on oligochaete toxicity. However, statistical evaluation of the data was sometimes difficult as a result of the high variability in the number of juveniles. This variability was caused by several reasons, e.g. hormesis effects or lack of experience of some participants. Comparison of the data from the NOEC and ECx approaches pointed to a clear advantage in favour of the latter (EC10 values always seem to be lower than NOEC values determined in the same test). As a result of the ringtest, the ERT Draft Guideline was significantly improved. The new guideline version was standardised by OECD, ISO and ASTM in 2004.