Effect of Test Conditions on the Toxicity of Copper to Juvenile Unionid Mussels

Abstract

During the past twnety years, unionid mussels have declined in both abundance and diversity throughout the eastern United States. As a result, there has been an increased call to evaluate the toxicity of various pollutants to unionids in an attempt to separate habitat-caused losses from those precipitated by aquatic contaminants. Few toxicity data for unionids were available until recently because unionids are not easily cultured and no test method had been developed for these animals. Therefore, water quality criteria developed by the USEPA in the 1970s and 1980s were derived from data lacking any information on unionid mussel sensitivities. The Tennessee Valley Authority (TVA) has advocated the use of a 9-day toxicity test method its scientists developed in the late 1980s. This method, which requires the use of silt, an algal mixture for food and daily changes of water, is not only more labor intensive, it also introduces sources of variation with the use of silt and algae, as well as being substantially different from the standard 96-h fathead minnow or Zooplankton tests. The evaluation of TVA's suggested test conditions (24 h darkness, 800 mg/L silt and algal food) indicated that the use of a 16L:8D light regime, with or without silt or algae did not result in a change in the toxicity of dissolved copper to juvenile Utterbackia imbecillis mussels compared to that recorded using TVA's test conditions.