INTERLABORATORY STUDY OF PRECISION - HYALELLA-AZTECA AND CHIRONOMUS-TENTANS FRESH-WATER SEDIMENT TOXICITY ASSAYS

Standard 10-d whole-sediment toxicity test methods have recently been developed by the U.S. Environmental Protection Agency (EPA) for the am phipod Hyalella azteca and the midge Chironomus tentans. An interlabor atory evaluation of method precision was performed using a group of se ven to 10 laboratories, representing government, academia, and environ mental consulting firms. The test methods followed the EPA protocols f or 4-d water-only reference toxicant (KCl) testing (static exposure) a nd for 10-d whole-sediment testing. Test sediments included control se diment, two copper-containing sediments, and a sediment contaminated p rimarily with polycyclic aromatic hydrocarbons. Reference toxicant tes ts resulted in H. azteca and C. tentans median lethal concentration (L C50) values with coefficents of variation (CVs) of 15.8 and 19.6%, res pectively. Whole sediments which were moderately contaminated provided the best estimates of precision using CVs. Hyalella azteca and C. ten tans 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 preci sion limits for the H. azteca survival tests. No samples exceeded the intralaboratory precision limit for H. azteca or C. tentans survival t ests. However, intralaboratory variability limits for C. tentans growt h were exceeded by 80 and 100% of the laboratories for a moderately to xic and control sample, respectively. Interlaboratory variability limi ts for C. tentans survival were not exceeded by any laboratory. The re sults showed these test methods to have relatively low variance and ac ceptable levels of precision in interlaboratory comparisons.