Copper toxicity in Bristol Bay headwaters: Part 2-Olfactory inhibition in low-hardness water.

We investigated the olfactory toxicity of copper (Cu) to rainbow trout in low-hardness (27 mg/L as CaCO ) water formulated in the laboratory over a 120-h period using a flow-through design. The fish's response to an alarm cue (e.g., reduction in activity) was recorded to determine the exposure concentrations and durations that inhibited olfactory detection of the cue after 3, 24, 48, and 96 h of Cu exposure and after 24 h of clean water recovery following the 96-h exposure period. Exposures were conducted with a range of Cu concentrations from 0.13 (control) to 7.14 μg Cu/L (dissolved Cu). We observed a dose-dependent response in olfactory inhibition with a 20% reduction in the probability of responding to the alarm cue, relative to controls, at 2.7 and 2.4 μg Cu/L after 24 or 96 h of exposure, respectively. Olfactory inhibition manifested between 3 and 24 h of exposure. Our 24- and 96-h 20% olfactory inhibition estimates fell between the criteria derived using the biotic ligand model (BLM; criterion maximum concentration [CMC] and criterion continuous concentration [CCC] values were 0.63 and 0.39 μg Cu/L, respectively) and water hardness-based criteria (CMC and CCC values were 3.9 and 2.9 μg Cu/L, respectively). Therefore, the hardness-based criteria do not appear to be protective and the BLM-derived criteria do appear to be protective against Cu-induced olfactory inhibition given our test water chemistry. Neither the hardness-based criteria nor the BLM-derived criteria appear to be protective against our estimated Cu behavioral avoidance response concentrations at 24- and 96-h exposures (0.54 and 0.50 μg Cu/L, respectively). Environ Toxicol Chem 2019;38:198-209. © 2018 SETAC.