Site-specific derivation of the acute copper criteria for the Clinch River, Virginia

Previous studies indicated that inputs from the Clinch River Plant (CRP), a coal-burning, power-generating facility in Carbo, Virginia, caused impairment to transplanted freshwater mussels. These findings necessitated the examination of instream biological responses to CRP effluents. Therefore, our objective was to derive a site-specific Criterion Maximum Concentration (CMC) for copper (Cu), the toxic constituent of the effluent. This was accomplished by conducting acute toxicity tests with Cu using 17 different genera native to or currently residing in the Clinch River watershed. Four native unionids and a mayfly (Isonychia bicolor) had genus mean acute values of 60 μg/L or lower (ranging from 37 to 60 μg/L). With a GMAV of 88 μg/L, Ceriodaphnia dubia ranked sixth among the 17 genera tested, and the fathead minnow, Pimephales promelas, ranked fourteenth with a GMAV of 310 μg/L. Despite the sensitivity of the indigenous mussels tested, the site-specific CMC of 18 μg/L was not substantially lower than the national CMC for Cu (20 μg/L, hardness = 150 mg/L as CaCO₃). While we conducted acute exposure tests, future investigations should incorporate both biomarker and population or community-level studies to determine low-level contaminant impacts on freshwater mussels.