Revisiting the aquatic impacts of copper discharged by water-cooled copper alloy condensers used by power and desalination plants

Power generation and desalination plants have used water-cooled copper alloy condensers since the 1960s. During the late 1970s some copper discharges associated with these condensers were implicated as a cause of adverse aquatic impacts and water quality criteria (WQC) exceedances. Given recent advances in monitoring and impact assessment techniques, it was therefore decided to complete an updated review of the aquatic impacts of copper alloy condenser discharges. In conducting such a review, it is necessary to accurately define both the exposure and effect levels of concern, and to consider bioavailability. The evaluation of copper exposure levels requires use of clean sampling and analytical techniques. A review of historical data showed that some previously reported copper data probably overstated actual levels due to failure to use these techniques. Further, the regulatory effect levels of concern, the WQC, have often been found to be overly protective relative to the level of protection intended by regulatory guidelines. Thus, WQC refinements have been introduced, including: a revision of the saltwater copper criterion, a recommendation to use dissolved copper to assess compliance, and development of procedures to set site-specific WQC. Considering the latter, the biotic ligand model, an evaluative tool that considers copper bioavailability, is introduced as a computational alternative to setting bioassay-based site-specific criteria. Based on the preceding considerations, bioavailable copper exposure levels are lower than previously believed, effect levels of concern (applicable site-specific WQC) have increased, and the desired level of protection has been achieved more frequently than previous analyses have indicated.