You are here:
Transepithelial potential as a predictor of major ion toxicity in fish
Citation:
Po, B., K. Brix, M. Grosell, D. McDonald, D. Mount, W. Adams, AND C. Wood. Transepithelial potential as a predictor of major ion toxicity in fish. SETAC North America, Toronto, ON, CANADA, November 03 - 07, 2019.
Impact/Purpose:
This work improves understanding of the aquatic toxicity of major geochemical ion mixtures by linking whole organism responses to physiological mechanisms that may underpin variation in toxicity of different ions (or mixtures) and across different organisms. If successful, this approach should support development of aquatic life criteria for these ions by Office of Water.
Description:
One of the stressors faced by freshwater ecosystems is salinization, for which there are no guidelines that rigorously address the contributions of different ions and their potential interactive effects including sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+) cations paired with chloride (Cl-), sulphate (SO42-), and (bi)carbonate (HCO3- / CO3-) anions. These major ions at elevated concentrations may, to different extents and in interactions, alter the balance of blood ions, acid-base status, and internal fluid volume regulation in freshwater animals in complex ways. To address this complexity, an ongoing modelling approach relates major ion toxicity to the predicted depolarization of transepithelial potential (TEP) across the gills, utilizing the Goldman-Hodgkin Katz (GHK) Equation and assumed permeability values and internal concentrations to estimate TEP. However, at present there is a critical lack of data relating actual TEP changes to changes in major waterborne ion concentrations, to blood ions, and to mortality. Our research addresses this gap, and so far has examined 5 teleost species - Pimephales promelas (fathead minnow), Oncorhynchus mykiss (rainbow trout), Ictalurus punctatus (channel catfish), Lepomis macrochirus (bluegill), and Carassius auratus (goldfish) under acute exposures to different salts (Cl-, SO42- and HCO3- salts of Na+, K+, Ca2+ and Mg2+). In general, there was qualitative consistency among species and salts such that ?TEP above baseline increased with the concentration of the ions until it became close to a maximum at the 4-day LC50. Furthermore, there was much greater consistency in this ?TEP value than in the absolute concentrations of the different salts at the LC50, lending support to the modelling approach. At present we are extending the data set by tests with additional salts, measurements of blood ions, and calculation of relative permeabilities by the GHK equation. Our findings work towards providing an integrative measure of salt toxicity based on physiological measurements relevant to the mechanism(s) of impact. They also support an ongoing modelling effort to develop water quality criteria based on prediction of interactive effects among different ion combinations (EPRI, Rio Tinto, EcoTox, NSERC).