Sub-Lethal Effects of Copper on Salmonids: An Avoidance Evaluation Using a Direct Test Method

Avoidance of copper (Cu) by rainbow trout (Oncorhynchus mykiss) was evaluated using a Y-maze exposure system, with data collected over a 1-h exposure period using a digital camcorder. In exposures to five measured concentrations of dissolved copper (<0.3, 1.2, 9.8, 48.3, and 98.6 µg Cu/L), plus control, significant avoidance behavior (p < 0.05) relative to the control was observed at ≥9.8 µg Cu/L, but not at 1.2 µg Cu/L. The chronic value (i.e., geometric mean of these concentrations) was 3.43 µg Cu/L. Estimates of EC50 values for avoidance of Cu ranged from 4.81 to 9.15 µg Cu/L over four 15-min time intervals of exposure to the metal. Based on water quality characterization of the control/diluent water, the U.S. Environmental Protection Agency (USEPA) water hardness- and biotic ligand model (BLM)-based chronic criteria for dissolved Cu were 8.03 and 2.26 µg Cu/L, respectively. This study suggested that enforcement of the BLM-based criterion would provide a higher level of protection of trout for this sensitive response than the hardness-based criterion.