PRECISION AND SENSITIVITY OF A 7-DAY GROWTH AND SURVIVAL TOXICITY TEST USING THE WEST-COAST MARINE MYSID CRUSTACEAN HOLMESIMYSIS-COSTATA

A 7-d growth and survival toxicity test using the west coast marine my sid crustacean Holmesimysis castata (Holmes) was evaluated to determin e test precision and sensitivity, The intralaboratory coefficient of v ariation (CV) among six reference toxicant test median lethal concentr ations (LC50s) was 25%, whereas the mean intralaboratory CV for side-b p-side effluent test LC50s was 7%. The mean intralaboratory CV for the concentration at which growth was inhibited bq 25% (IC25) was 19%. In terlaboratory CVs for effluent LC50s averaged 14%, whereas variation a mong growth IC25s averaged 15%. Test precision and sensitivity compare d favorably with literature values for a number of commonly used toxic ity tests and chemical methods. Toxicity increased slightly with incre ased mysid exposure from 4 to 7 d (mean effluent LC50s of 9.9% for 4 d of exposure and 7.5% for 7 d), and more significantly from 7 to 24 d (zinc LC50 values were 50 mu g/L and 7.8 mu g/L for concurrent 7-d and 24-d tests). Although growth was a less sensitive endpoint than survi val in tests with individual chemicals (zinc and sodium azide), growth was the more sensitive endpoint in seven of nine tests with complex e ffluents. Seventy-five percent of tests conducted at all participating laboratories met protocol test acceptability criteria (n = 40).