Inter- and intralaboratory variability in <i>Daphnia magna</i> effluent toxicity test results

Abstract

Abstract A nine-laboratory round-robin study of the Daphnia magna static, acute, effluent toxicity test was conducted to examine inter- and intralaboratory variability in test results. A single effluent sample was split and sent to three government, three commercial and three industrial aquatic laboratories. Each laboratory followed a specifically designed test protocol and reported the number of daphnids immobilized in each of seven effluent test concentrations at 24 h and 48 h of exposure. The mean 48-h EC50 value for all data was 5.3% effluent. The range was 3.5 to 9.1% effluent, so there is a factor of 2.6 between the highest and lowest EC50 values. The pooled within-laboratory standard deviation and coefficient of variation were 0.91 and 16%, respectively. Combined inter-and intralaboratory estimates of standard deviation and coefficient of variation were 1.8 and 33%, respectively. The results of this study show that Daphnia magna effluent toxicity data can be reproduced both within and between laboratories when clearly defined test protocols are employed.