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

The reproducibility of sediment toxicity bioassays using the Microtox(R) so lid-phase test (SPT) with the luminescent bacterium Vibrio fischeri was est imated in an interlaboratory precision study. A preliminary study, with fiv e labs testing six solid-phase samples, was used to evaluate proposed metho d modifications. As a result, it was recommended that the SPT protocol be r evised to include whole sample testing with subsequent wet-weight to dry-we ight correction, and the use of NaNO3, rather than NaCl, as the diluent for freshwater sediment samples. The revised protocol was then examined in a d efinitive 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 determinatio n 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 interlaborator y consistency statistic h. With coefficients of variation comparable to oth er interlaboratory precision studies, and an extremely low number of result s exceeding the critical value of h, it is concluded that the V. fischeri S PT has an acceptable level of precision and can be developed as a standardi zed test method. (C) 1999 by John Wiley & Sons, Inc.