Juvenile freshwater mussel (bivalvia: unionidae) responses to acute toxicity testing with copper

The sensitivities of newly metamorphosed juveniles of Villosa iris and Anodonta grandis to copper were determined using 24-h static bioassays. Two methods of assessing postexposure response were compared: direct visual examination and the use of vital staining with neutral red. Both species responded to copper exposures, exhibiting valve closure at concentrations as low as 24 μg Cu per liter for Villosa iris and 17 μg Cu per liter for Anodonta grandis. EC50 values of 27 μg Cu per liter (Villosa iris) and 33 μg Cu per liter (Anodonta grandis) were calculated on the basis of the valve closure response. Use of vital staining with neutral red provided an EC50 of 29 μg Cu per liter for Villosa iris. The amber coloration of Anodonta grandis valves prevented determination of an EC50 using the vital staining. LC50 values of 83 μg Cu per liter (Villosa iris) and 44 μg Cu per liter (Anodonta grandis) were calculated from the results of vital staining. Neutral red was found to be effective in assessing postexposure mortality and sublethal responses after acute exposures to copper.