Interlaboratory precision study of a whole sediment toxicity test with the bioluminescent bacterium Vibrio fischeri

The reproducibility of sediment toxicity bioassays using the Microtox® solid‐phase test (SPT) with the luminescent bacterium Vibrio fischeri was estimated in an interlaboratory precision study. A preliminary study, with five labs testing six solid‐phase samples, was used to evaluate proposed method modifications. As a result, it was recommended that the SPT protocol be revised to include whole sample testing with subsequent wet‐weight to dry‐weight correction, and the use of NaNO3, rather than NaCl, as the diluent for freshwater sediment samples. The revised protocol was then examined in a definitive precision study, with 18 laboratories each testing eight samples. Coefficients of variation for the eight samples ranged from 35.8 to 78.0%. One possible source of error is the separate moisture content determination performed by each laboratory in order to calculate the wet‐weight to dry‐weight correction. Out of a total of 143 bioassays performed by the 18 labs, only two results (1.4%) exceeded the critical value of the interlaboratory consistency statistic h. With coefficients of variation comparable to other interlaboratory precision studies, and an extremely low number of results exceeding the critical value of h, it is concluded that the V. fischeri SPT has an acceptable level of precision and can be developed as a standardized test method. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 339–345, 1999