The interlaboratory precision of the ASTM early life-stage toxicity test with the sheepshead minnow (Cyprinodon variegatus) was investigated at five contract and two EPA laboratories using endosulfan and pentachlorobenzene. Each laboratory conducted two tests with each chemical. Tests began with newly fertilized to 48-hour-old embryos, continued through embryonic development, hatching, and growth of fish to the juvenile stage, and were terminated after 28 days. Effects on survival of embryos, survival of hatched fish, and weight of surviving fish were quantified. Criteria were developed for judging acceptability of test results and for selecting the upper and lower chronic values. Using these criteria, 19 of the 28 tests (68%) were judged acceptable.

Results from the early life-stage toxicity test were reasonably reproducible within and between laboratories. Ratios of the high-to-low chronic value from acceptable duplicate tests for each chemical tested within laboratories ranged from 1.04 to 1.99 for eight of nine tests. For nine acceptable paired tests, the average ratio was 1.98; the coefficient of variation was 80%. Variability of chronic values across all laboratories was generally reproducible within a factor of two. Chronic values from all acceptable tests averaged 0.60 μg/L (coefficient of variation 73%) for endosulfan and 82 μg/L (coefficient of variation 54%) for pentachlorobenzene. Neither survival nor weight were consistently the endpoint most sensitive in tests with either chemical. The interlaboratory variability of the results of this test was particularly good relative to variability of other tests considering the following: the test was complex; the laboratories were inexperienced; the embryos were from Atlantic and Gulf Coasts; and test water was from the Atlantic, Gulf, and Pacific Coasts. Variation in this and other toxicity and bioconcentration tests using marine species should be considered when judging the environmental implications of results.