Importance of Water Chemistry in Evaluating the Olfactory Effects of Copper in Salmonids
By David DeForest, Joe Meyer, Bill Adams, Bob Dwyer, Bob Gensemer, Joe Gorsuch, and Eric Van Genderen
Several populations of Pacific salmon (Oncorhynchus spp.) are listed as threatened or endangered under the Endangered Species Act, with many of these listed populations using urban streams for spawning and rearing. Concerns have been raised that existing ambient water quality criteria for copper (Cu), which are based on organism-level endpoints such as survival, growth, and reproduction, may not be protective of physiological endpoints, such as olfaction, which has a critical role in predator avoidance and reproduction of salmon populations. The USEPA’s currently recommended Cu criteria are derived using the biotic ligand model (BLM), which is a bioavailability-based model that predicts Cu toxicity as a function of several water chemistry parameters, including dissolved organic carbon (DOC), pH, alkalinity, calcium, and several other ions. To-date, however, the numeric freshwater Cu criteria for western U.S. states are still only adjusted for water hardness, not other more significant natural ligands such as dissolved organic carbon. Given that the effects of Cu on olfactory systems in fish are also modified by water quality factors that influence metal bioavailability (McIntyre et al. 2008a,b), an important question is whether BLM-based criteria are also protective against olfactory impairment.
To evaluate whether Cu criteria are protective against olfactory impairment, a recent paper in Environmental Toxicology and Chemistry (Meyer and Adams 2010) presented an olfactory-based Cu BLM, which can be used to predict olfactory impairment thresholds for Cu over a wide range of freshwater chemistries. The current issue of Integrated Environmental Assessment and Management contains a study in which the olfactory-based Cu BLM of Meyer and Adams (2010) is used to derive olfactory impairment thresholds based on the water chemistry of 133 stream sites in the western U.S. (DeForest et al. 2011). These olfactory impairment thresholds were compared to the corresponding hardness-based and BLM-based Cu criteria for each of the 133 sites. They found that hardness-based Cu criteria were almost always protective against predicted olfactory impairment and that BLM-based Cu criteria were always protective. Therefore, the data available to-date indicate that existing Cu criteria, particularly BLM-based Cu criteria, are protective against olfactory impairment in salmonids.
One uncertainty highlighted in the evaluation of Meyer and Adams (2010) is the lack of water chemistry data reported in most olfactory toxicity studies conducted with Cu. Because water chemistry significantly influences the bioavailability of Cu and other metals, it is imperative that water chemistry is characterized and reported in all studies. Without measuring and reporting appropriate water chemistry it is not possible to accurately assess whether BLM-based Cu criteria–or even hardness-based criteria–are protective against olfactory impairment.
A second uncertainty is the olfactory sensitivity of saltwater salmon life stages to Cu, because the studies to-date have focused on the juvenile freshwater life stage. While relatively few saltwater olfactory studies have been conducted, they indicate that the olfactory sensitivities of freshwater-adapted and saltwater-adapted salmonids when exposed to major ions (e.g., Na+, Ca2+, Mg2+) and amino acids are similar (e.g., Shoji et al. 1996). Assuming this similarity also applies to salmonid responses to Cu, it would be possible to develop an olfactory BLM that can apply to both saltwater and freshwater fish, making it possible to predict the effects of water quality on olfactory impairments under all conditions. We suggest that development of a more generalized olfactory BLM will thus be of great practical value, but given the relative paucity of olfactory studies using saltwater fish, additional study will be needed to validate such a model.
The BLM was developed as a tool for predicting the toxicity of Cu and other metals as a function of site-specific water chemistry. It has also proven to be a flexible tool that can be modified and applied to other endpoints, as in the case of olfactory impairment, as summarized in the Meyer and Adams (2010) and DeForest et al. (2011) studies. This has provided a mechanism to evaluate the protectiveness of Cu criteria relative to olfactory impairment by properly accounting for the influences of water chemistry on Cu bioavailability at the biotic ligand of interest, whether it be at the “gill” in the case of Cu criteria, or at the olfactory receptors in the case of olfactory impairment. However, the importance of measuring and reporting water chemistry in future olfactory studies with Cu (or other metals) cannot be overemphasized because without these data, it will be difficult to adequately understand and predict the influences of water chemistry on the olfactory or related behavioral effects of Cu on salmonids and other fish.
DeForest DK, Gensemer RW, Van Genderen EJ, Gorsuch JW. 2011. Protectiveness of water quality criteria for copper in western United States waters relative to predicted olfactory responses in juvenile Pacific salmon. Integr Environ Assess Manage 7:336-347.
McIntyre JK, Baldwin DH, Meador JP, Scholz NL. 2008a. Chemosensory deprivation in juvenile coho salmon exposed to dissolved copper under varying water chemistry conditions. Environ Sci Technol 42:1352-1358.
McIntyre JK, Baldwin DH, Meador JP, Scholz NL. 2008b. Additions and corrections: Chemosensory deprivation in juvenile coho salmon exposed to dissolved copper under varying water chemistry conditions. Environ Sci Technol 42:6774-6775.
Meyer JS, Adams WJ. 2010. Relationship between biotic ligand model-based water quality criteria and avoidance and olfactory responses to copper by fish. Environ Toxicol Chem 29:2096-2103.
Shoji T, Fujita K-I, Furihata E, Kurihara K. 1996. Olfactory responses of a euryhaline fish, the rainbow trout: Adaptation of olfactory receptors to sea water and salt-dependence of their responses to amino acids. J Exp Biol 199:303-310.
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