The objective of the present study was to determine acute toxicity of copper, ammonia, or chlorine to larval (glochidia) and juvenile mussels using the recently published American Society for Testing and Materials (ASTM) Standard guide for conducting laboratory toxicity tests with freshwater mussels. Toxicity tests were conducted with glochidia (24- to 48-h exposures) and juveniles (96-h exposures) of up to 11 mussel species in reconstituted ASTM hard water using copper, ammonia, or chlorine as a toxicant. Copper and ammonia tests also were conducted with five commonly tested species, including cladocerans (Daphnia magna and Ceriodaphnia dubia; 48-h exposures), amphipod (Hyalella azteca; 48-h exposures), rainbow trout (Oncorhynchus mykiss; 96-h exposures), and fathead minnow (Pimephales promelas; 96-h exposures). Median effective concentrations (EC50s) for commonly tested species were >58 microg Cu/L (except 15 microg Cu/L for C. dubia) and >13 mg total ammonia N/L, whereas the EC50s for mussels in most cases were <45 microg Cu/L or <12 mg N/L and were often at or below the final acute values (FAVs) used to derive the U.S. Environmental Protection Agency 1996 acute water quality criterion (WQC) for copper and 1999 acute WQC for ammonia. However, the chlorine EC50s for mussels generally were >40 microg/L and above the FAV in the WQC for chlorine. The results indicate that the early life stages of mussels generally were more sensitive to copper and ammonia than other organisms and that, including mussel toxicity data in a revision to the WQC, would lower the WQC for copper or ammonia. Furthermore, including additional mussel data in 2007 WQC for copper based on biotic ligand model would further lower the WQC.

The objectives of the present study were to develop methods for conducting chronic toxicity tests with juvenile mussels under flow‐through conditions and to determine the chronic toxicity of copper and ammonia to juvenile mussels using these methods. In two feeding tests, two‐month‐old fatmucket (Lampsilis siliquoidea) and rainbow mussel (Villosa iris) were fed various live algae or nonviable algal mixture for 28 d. The algal mixture was the best food resulting in high survival (≥90%) and growth. Multiple copper and ammonia toxicity tests were conducted for 28 d starting with two‐month‐old mussels. Six toxicity tests using the algal mixture were successfully completed with a control survival of 88 to 100%. Among copper tests with rainbow mussel, fatmucket, and oyster mussel (Epioblasma capsaeformis), chronic value ([ChV], geometric mean of the no‐observed‐effect concentration and the lowest‐observed‐effect concentration) ranged from 8.5 to 9.8 μg Cu/L for survival and from 4.6 to 8.5 μg Cu/L for growth. Among ammonia tests with rainbow mussel, fatmucket, and wavy‐rayed lampmussel (L. fasciola), the ChV ranged from 0.37 to 1.2 mg total ammonia N/L for survival and from 0.37 to 0.67 mg N/L for growth. These ChVs were below the U.S. Environmental Protection Agency 1996 chronic water quality criterion (WQC) for copper (15 μg/L; hardness 170 mg/L) and 1999 WQC for total ammonia (1.26 mg N/L; pH 8.2 and 20°C). Results indicate that toxicity tests with two‐month‐old mussels can be conducted for 28 d with >80% control survival; growth was frequently a more sensitive endpoint compared to survival; and the 1996 chronic WQC for copper and the 1999 chronic WQC for total ammonia might not be adequately protective of the mussel species tested. However, a recently revised 2007 chronic WQC for copper based on the biotic ligand model may be more protective in the water tested.

The present study evaluated the performance and variability in acute toxicity tests with glochidia and newly transformed juvenile mussels using the standard methods outlined in American Society for Testing and Materials (ASTM). Multiple 48-h toxicity tests with glochidia and 96-h tests with juvenile mussels were conducted within a single laboratory and among five laboratories. All tests met the test acceptability requirements (e.g., >or=90% control survival). Intralaboratory tests were conducted over two consecutive mussel-spawning seasons with mucket (Actinonaias ligamentina) or fatmucket (Lampsilis siliquoidea) using copper, ammonia, or chlorine as a toxicant. For the glochidia of both species, the variability of intralaboratory median effective concentrations (EC50s) for the three toxicants, expressed as the coefficient of variation (CV), ranged from 14 to 27% in 24-h exposures and from 13 to 36% in 48-h exposures. The intralaboratory CV of copper EC50s for juvenile fatmucket was 24% in 48-h exposures and 13% in 96-h exposures. Interlaboratory tests were conducted with fatmucket glochidia and juveniles by five laboratories using copper as a toxicant. The interlaboratory CV of copper EC50s for glochidia was 13% in 24-h exposures and 24% in 48-h exposures, and the interlaboratory CV for juveniles was 22% in 48-h exposures and 42% in 96-h exposures. The high completion success and the overall low variability in test results indicate that the test methods have acceptable precision and can be performed routinely.

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