Protectiveness of Water Quality Criteria for Copper in Western United States Waters Relative to Olfactory Responses in Pacific Salmon

At elevated concentrations copper (Cu) can impair olfaction in salmonid fishes, thus inhibiting the ability of salmonids to avoid elevated Cu concentrations and/or predators. Several salmonid species are listed as threatened or endangered in the western US, including many in urban watersheds. Because Cu is commonly elevated in stormwater runoff in urban environments, storm events may result in elevated Cu concentrations in salmon-bearing streams. Accordingly, there is concern that existing Cu criteria, which were not derived using data for olfactory-related endpoints, may not be adequately protective of salmonids. However, a reparameterized olfactory-based biotic ligand model (BLM) was recently proposed as a modification of the US Environmental Protection Agency’s ionoregulatory-based BLM for deriving site-specific Cu criteria. This revision, based on olfactory inhibition in coho salmon (Oncorhynchus kisutch) exposed to Cu in various combinations of pH, hardness, alkalinity, and dissolved organic carbon (DOC) levels, was used to derive Cu IC20 values for 133 stream locations in the western US. The olfactory BLM-based criteria were compared to the existing hardness-based Cu criteria for western US states and the USEPA’s BLM-based Cu criteria. Of the 133 sampling locations, hardness-dependent acute and chronic Cu criteria were below the olfactory BLM-based IC20 in 124 (93%) and 130 (98%) of the waters, respectively (i.e., <20% olfactory impairment would have been predicted at the hardness-based Cu criteria concentrations). Waters characterized by high hardness and very low DOC are most likely to have hardness-based Cu criteria that are not lower than the olfactory-based IC20, as DOC strongly influences Cu bioavailability in the BLM. In all waters the USEPA’s current BLM-based criteria were less than the olfactory-based IC20 values, indicating that adoption of the USEPA’s BLM-based criteria by western states should ensure protection of salmonids from olfactory impairment.