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 wholesediment 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.

I n f l u e n c e s on c o p p e r b i o a c c u m u l a t i o n , g r o w t h , a n d survival o f the midge, Chironomus tentans, in m e t a l -c o n t a m i n a t e d s e d i m e n t s * AbstractSediment bioassays with larvae of the midge, Chironomus tentans, were used to evaluate influences on the bioavailability and toxicity of copper (Cu) in sediments with a wide range of concentrations of metals, acid-volatile sulfide (AVS), and other physicochemical characteristics. Sediments were collected from sixteen lakes in Michigan, USA, and from twelve sites in the Clark Fork River drainage of Montana, USA, which are contaminated with metals from mining activities and from other anthropogenic sources. Bioassays with C. tentans larvae were conducted for ten days in a static-renewal test system, with endpoints of survival, growth, and metal bioaccumulation. Bioaccumulation of copper (Cu) was strongly correlated with Cu concentrations in porewater, and was increased significantly at Cu concentrations less than those affecting growth or survival. Midge survival and growth were not significantly correlated with concentrations of Cu in sediment or porewater, and were poorly predicted by ratios of acid-extractable metals to AVS in sediments. Principal components analysis indicated that Cu concentrations in porewater and bioaccumulation of Cu by midge larvae were influenced by AVS, sediment organic carbon, and porewater pH, and that toxicity was associated with high concentrations of Cu, high concentrations of zinc (Zn) and ammonia. No toxicity was observed in several sediments which contained low concentrations of AVS and high concentrations of Cu and Zn. In sediments which contain little AVS, bioavailability of metals may be controlled by constituents other than sulfides, such as organic matter and metal hydrous oxides. These results indicate that assessments of toxicity in metal-contaminated sediments should evaluate the importance of metal-binding phases other than sulfides, and the possible contributions of ammonia or other toxicants to toxicity in sediment bioassays.

No abstract

Abstract-We designed a sediment bioassay using 25% growth inhibition of Hyalella azteca as the end point. Hyalella azteca exhibits size-specific fecundity, so growth is a surrogate of reproductive production. We investigated density effects on growth to address whether crowding could affect test interpretation; amphipods in 14,000/m 2 exposures were 16 to 20% smaller than those at 7,000/m 2 . Using power analysis, we found that 20 to 25 samples are required to determine significance when ␣ ϭ 0.10 and 1 Ϫ ␤ ϭ 0.90. To minimize the need for laboratory resources, we designed a two-step (screening and confirmatory) bioassay, which we tested with fieldcollected sediments. The screening bioassay compared 11 sediments to a reference. Three sediments were ''toxic'' (significant growth inhibition when 1 Ϫ ␤ ϭ 0.66 and n ϭ 5), five sediments were ''nontoxic'' (Ͼ90% of reference), and three sediments were ''possibly toxic'' (growth inhibition was insignificant). In the confirmatory bioassay, three possibly toxic and two nontoxic samples were reevaluated. Two were toxic (1 Ϫ ␤ ϭ 0.91 and n ϭ 20), and the remaining four samples were nontoxic. In summary, five sediments were toxic and six sediments were nontoxic. The two-step analysis used minimal laboratory resources but maximized statistical power, where needed, to discriminate growth effects.

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.