Technical Bulletin No. 0588: Precision of the EPA Seven – Day Ceriodaphnia dubia Survival and Reproduction Test Intra- and Interlaboratory Study

In 1985, the U.S. Environmental Protection Agency (EPA) published guidelines for a "Seven-Day Ceriodaphnia dubia Survival and Reproduction Test" to measure the toxicity of effluents. This study evaluated the intra- and inter-laboratory variability of the seven-day Ceriodaphnia test using two reference toxicants (sodium chloride and potassium dichromate), two paper-and-pulp effluents, and two utility effluents. Eleven different laboratories, representing academia, private industry, contractors, and state and federal EPAs participated in the study. The reference toxicants were tested twice during two separate test periods and each industrial effluent was tested once.

Using EPA's criteria for a successful test, 56 percent of the 116 planned tests were completed as valid tests. Most invalid tests were unacceptable either because they were not initiated or because control survival was < 80 percent. Seventy-eight percent of the tests that were initiated were successfully completed. Reproduction NOEC values were generally somewhat lower than those for survival, but had greater variability than survival NOEC values. The interlaboratory variability of the survival and reproduction results, expressed as the coefficient of variation (CV) ranged between 29.8 percent and 30.8 percent and between 28.9 percent and 39.0 percent, respectively.

The study demonstrated that about half (56 percent) of the laboratories participating in the study were able to routinely complete the test successfully. Some of the laboratories experienced with the more well-established effluent toxicity testing procedures were less prepared to successfully complete this test. Overall, the variability of the seven-day Ceriodaphnia test was similar to the variability observed with other toxicity tests and analytical measurements.