Dissolved copper (dCu) is a ubiquitous surface water pollutant that causes a range of adverse effects in fish as well as in aquatic invertebrates and algae. This technical memorandum is a summary and targeted synthesis regarding sensory effects to juvenile salmonids from lowlevel exposures to dCu. As such, the material presented here serves to summarize scientific research on dCu and its impacts on salmonid sensory systems. In addition, this document provides a benchmark analysis of empirical data generated in recent National Marine Fisheries Service investigations that have focused on salmon olfactory function. The review section, Appendix A, discusses peer reviewed and gray literature on the effects of dCu on salmonid sensory systems, associated sensory-mediated behaviors, and physiology. It is intended to facilitate understanding of the effects of dCu on sensory system–mediated behaviors that are important to survival, reproduction, and distribution of salmonids. The review does not address the effects of dCu on salmonid habitats, although copper is also highly toxic at low μg/L concentrations to aquatic primary producers and invertebrates (i.e., the aquatic food web). Undoubtedly, new information will become available that enhances our current understanding of copper’s effect on threatened and endangered salmonids and their supporting habitats. A large body of scientific literature has shown that fish behaviors can be disrupted at concentrations of dCu that are at or slightly above ambient concentrations (i.e., background).
In this document, background is operationally defined as surface waters with less than 3 μg/L dCu, as experimental water had background dCu concentrations as high as 3 μg/L dCu. Sensory system effects are generally among the more sensitive fish responses and underlie important behaviors involved in growth, reproduction, and (ultimately) survival (i.e., predator avoidance). Recent experiments on the sensory systems and corresponding behavior of juvenile salmonids contribute to more than four decades of research and show that dCu is a neurotoxicant that directly damages the sensory capabilities of salmonids at low concentrations. These effects can manifest over a period of minutes to hours and can persist for weeks. To estimate toxicological effect thresholds for dCu in surface waters, benchmark concentrations (BMCs) were calculated using a U.S. Environmental Protection Agency methodology. This paper presents examples of BMCs for juvenile salmonid olfactory function based on recent data. BMCs ranged 0.18–2.1 μg/L, corresponding to reductions in predator avoidance behavior of approximately 8–57%. The BMC examples represent the dCu concentration (above background) expected to affect the ability of juvenile salmonids to avoid predators in freshwater. These concentration thresholds for juvenile salmonid sensory and behavioral responses fall within the range of other sublethal endpoints affected by dCu such as behavior, growth, and primary production, which is 0.75–2.5 μg/L.
The paper also discusses the influence of water chemistry on the bioavailability and toxicity of copper to fish sensory systems. Studies exploring behavioral avoidance as well as representative studies of other effects to salmonids are also summarized. Salmon may be able to avoid dCu in environmental situations where distinct gradients occur. However, avoidance of dCu originating from nonpoint sources appears unlikely. Given the large body of literature on copper and responses of aquatic ecosystems, we focused on a subset of fish sensory system studies relevant to anadromous salmonids.
Point and nonpoint source discharges from anthropogenic activities frequently exceed these thresholds by one, two, and sometimes three orders of magnitude, and can occur for hours to days. The U.S. Geological Survey ambient monitoring results for dCu representing 811 sites across the United States detected concentrations ranging 1–51 μg/L, with a median of 1.2 μg/L. Additionally, typical dCu concentrations originating from road runoff from a California study were 3.4–64.5 μg/L, with a mean of 15.8 μg/L. Taken together, the information reviewed and presented herein indicates that impairment of sensory functions important to survival of juvenile salmonids is likely to be widespread in many freshwater aquatic habitats. Impairment of these essential behaviors may manifest within minutes and continue for hours to days depending on concentration and exposure duration. Therefore, dCu has the potential to limit the productivity and intrinsic growth potential of wild salmon populations by reducing the survival and lifetime reproductive success of individual salmonids.