Interlaboratory study of precision: Hyalella azteca and Chironomus tentans freshwater sediment toxicity assays

Abstract

Standard 10‐d whole‐sediment toxicity test methods have recently been developed by the U.S. Environmental Protection Agency (EPA) for the amphipod Hyalella azteca and the midge Chironomus tentans. An interlaboratory evaluation of method precision was performed using a group of seven to 10 laboratories, representing government, academia, and environmental consulting firms. The test methods followed the EPA protocols for 4‐d water‐only reference toxicant (KCl) testing (static exposure) and for 10‐d whole‐sediment testing. Test sediments included control sediment, two copper‐containing sediments, and a sediment contaminated primarily with polycyclic aromatic hydrocarbons. Reference toxicant tests resulted in H. azteca and C. tentans median lethal concentration (LC50) values with coefficents of variation (CVs) of 15.8 and 19.6%, respectively. Whole sediments which were moderately contaminated provided the best estimates of precision using CVs. Hyalella azteca and C. tentans tests in moderately contaminated sediments exhibited LC50 CVs of 38.9 and 13.5%, respectively. The CV for C. tentans growth was 31.9%. Only 3% (1 of 28) of samples exceeded acceptable interlaboratory precision limits for the H. azteca survival tests. No samples exceeded the intralaboratory precision limit for H. azteca or C. tentans survival tests. However, intralaboratory variability limits for C. tentans growth were exceeded by 80 and 100% of the laboratories for a moderately toxic and control sample, respectively. Interlaboratory variability limits for C. tentans survival were not exceeded by any laboratory. The results showed these test methods to have relatively low variance and acceptable levels of precision in interlaboratory comparisons.

Interlaboratory evaluation of Hyalella azteca and Chironomus tentans short‐term and long‐term sediment toxicity tests

“…Toxicol. The previous interlaboratory evaluations of the 10-d sediment tests with these organisms [20] had CVs for the WB sediment that were comparable to those obtained in the 10-d tests conducted as part of the present evaluation. 25, 2006 2671 us the opportunity to undertake a second evaluation of the standard 10-d test [20] with more laboratories.…”

“…Chem. In that previous study [20], all 10 laboratories met the 80% survival TAC in tests with H. azteca, achieving a mean survival of 95% and a CV of 5.8%. The majority of laboratories (Ͼ88%) met the 10-d TACs for survival (H. azteca and C. tentans) and growth (C. tentans).…”

“…Whereas the CV is the most commonly applied statistic for assessing test precision, it is not used exclusively, because extremely toxic or nontoxic samples may result in very low CVs [20]. The term precision was defined as the degree of mutual agreement among individual measurements of the same property of sample data generated from replicate measurements, recognizing that interlaboratory variance may depend on how the laboratories followed the test protocol.…”

“…A second objective was to conduct a second interlaboratory evaluation of the 10-d H. azteca and C. tentans tests [20,21]. One objective of the interlaboratory study was to have laboratories representing both regulators and the regulated communities characterize the variability with the newly developed long-term test methods.…”

Statistical Results and Implications of the Enchytraeid Reproduction Ringtest

“…To our knowledge, this index has not been used in terrestrial ecotoxicology so far; hence, it is briefly described. The h value equals the standard normal variable z and is determined (12) by dividing the sample deviation (i.e., the difference between a laboratory NOEC or ECx from the mean NOEC or ECx obtained from all valid tests) by the standard deviation of the considered sample statistic (i.e., the standard deviation of the laboratory NOECs from the mean NOEC of all laboratories or the standard deviation of the laboratory ECx from the mean ECx of all laboratories from which valid results were obtained; eq 2).…”