Results of an international round robin study with the Ames fluctuation test

The German mirror committee of ISO TC147 SC 5 WG 9 _eGenotoxicity_f organised an interna-tional round robin study on the Ames >uctuation test (ISO DIS 11350). Nineteen laboratoriesfrom|seven countries participated in the study. The laboratories had to test four coded water sam-ples. Sample one, a river water sample, was used as a negative control water sample and for spikingwith strain-specific mixtures of mutagens (samples two and three). Sample four was an e}uentfrom an industrial waste water plant. Validity criteria were fulfilled in 86 to 100 % of all testconditions (bacterial strain / _} S9-mix). The overall test sensitivity was 100 %. The test specificityranged from 80 to 100 % depending on the test condition. For statistical evaluation an arcsin-square-root transformation was applied to generate a metric data set. An ANOVA was performedto identify samples with a significantly higher numbers of revertants. A threshold value derivedfrom a large set of negative controls was used in a final step to exclude results of individual testswith unexpected low numbers of spontaneous revertants. The lowest ine#ective dilution values(LIDs) were then determined by this new approach. The variability of the LID values among thelaboratories amounted in most cases to no more than two dilution steps around the median. Thedata produced in this round robin study proved a su!cient reproducibility of the test procedureand provide validity data for the finalization of the ISO standardization process.