Increased awareness of the value of effluent toxicity test data has stimulated regulatory agencies to develop and implement quality assurance (QA) programs for laboratories performing effluent toxicity tests. As part of a QA program, a standard reference toxicant program should be conducted to verify the health and acceptability of a particular population of test organisms. The recently issued EPA manual for the evaluation of laboratories performing aquatic testing, a pilot study in 1990 to evaluate performance of aquatic toxicology laboratories in New Jersey and North Carolina, and the first study (DMR-QA Study 11) involving laboratories from all states providing data for the National Pollutant Discharge Elimination System (NPDES) program represent examples of proposed practices that specify quality-control parameters to ensure the acceptability of biological data used in the permitting process.
Two reference toxicants, hexavalent chromium and copper, were tested extensively over a two year period in our laboratory. The mean 48-h LC50 for D. pulex was 188 μg Cr+6/L and 3 μg Cu/L, while the mean 96-hour LC50 for fathead minnows was 83 mg Cr+6/L and 180 μg Cu/L. The coefficient of variation (CV) of LCW values for daphnids were similar for both compounds. However, the CV for fathead minnows test results with copper was approximately three times greater than that for hexavalent chromium.
Comparable to multipoint calibration curves used to define the accuracy of a chemical method, results of toxicity tests conducted on a regular basis using reference toxicants can be used as criteria for accuracy and precision of biological effects studies. Because performance standards for testing laboratories are based on the results from reference tests, this study also provided an opportunity to evaluate current EPA criteria for acceptance. For this evaluation the results of 88 toxicity tests were selected (44 tests with chromium and 44 tests with copper using D. pulex). In our opinion, the results of this study indicated that both biological performance and the results from reference tests are equally important for the evaluation of the health of test organisms.