This study was performed to evaluate the inter- and intra-laboratory variability of the U.S. EPA-developed short-term chronic survival and growth test with fathead minnow larvae. Two reference toxicants (potassium dichromate and sodium pentachlorophenate) and three effluents (both petroleum and utility in origin) were used as the test materials. To initiate this study, private, government, and university laboratories experienced with conducting the test were evaluated, and ten laboratories were selected to participate. A detailed Standard Operating Procedure for conducting the test (based on the EPA Guidelines) was supplied to each laboratory, as were specific instructions for preparing test concentrations of reference toxicants and effluents. Both of the reference toxicants were tested twice by each laboratory and each of the three effluents was evaluated once (seven test materials per laboratory). Each laboratory conducted two concurrent toxicity tests with each test material to evaluate intralaboratory variability. A total of 140 7-day toxicity tests (10 laboratories x 7 test materials x 2 concurrent tests/test material) were conducted. The two endpoints that were evaluated were survival and average dry-weight/fry. The concentration-effects relationships were characterized by several different parameters including: the no-observed-effect-concentration (NOEC), the median lethal concentration (LC50), and the slope of the concentration-effects curve. The total variability was split into variability attributed to test laboratory, replicate tests, and test beakers. For the reference toxicants, temporal variability was also evaluated. Variability estimates for each component were obtained and used to determine the overall precision of the test to identify which components were responsible for the greatest loss in precision (i.e., those with the largest variance). Based on the results of this study, the utility of this test was assessed and improvements were recommended.
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