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Interactive toxicity of major ion salts: Comparisons among species and between acute and chronic endpoints
Citation:
Mount, Dave, R. Erickson, B. Forsman, T. Highland, R. Hockett, D. Hoff, C. Jenson, AND T. Norberg-King. Interactive toxicity of major ion salts: Comparisons among species and between acute and chronic endpoints. SETAC North America, Salt Lake City, UT, November 01 - 05, 2015.
Impact/Purpose:
not applicable
Description:
Increased concentrations of major ions (Na, K, Ca, Mg, Cl, SO4, HCO3) in freshwater systems can result from a variety of anthropogenic activities, and can adversely affect aquatic organisms if the increase is sufficiently severe. Laboratory tests have indicated that the toxicity of major ion mixtures are dependent on the specific ionic composition of the water. In previous work, we conducted extensive acute toxicity testing with Ceriodaphnia dubia; this work suggested that sodium salts exerted their toxicity additively and that osmolarity provided a good exposure metric that normalized response among exposures of different ion compositions. While they also contribute to osmolarity, Ca and Mg appeared to exert toxicity by a separate mechanism (or mechanisms) that was more potent than, and independent of, effects that could be ascribed to osmolarity. At less than toxic concentrations, increasing Ca was found to ameliorate the toxicity from both Mg and osmolarity. In new work, we evaluated chronic toxicity of major ion salts to C. dubia, as well as comparing acute effects between C. dubia and fathead minnows. With regard to reproductive effects on C. dubia, work thus far suggests that the same basic interactions govern chronic toxicity as were operative for acute toxicity, and that the acute to chronic ratio is fairly similar for different salt mixtures. However, acute studies with fathead minnows demonstrate some notable differences from the results with C. dubia. For example, expressing the aggregate potency of sodium salts via osmolarity does not explain the toxicity of those salts to fathead minnows; instead, sodium sulfate is more toxic than sodium chloride when expressed as osmolarity or as Na activity, suggesting a more specific role of sulfate.. When Na salts are mixed with Mg salts, fathead minnow responses lie between additive and independent response models, whereas acute toxicity of these mixtures to C. dubia indicated independence. These and other findings are discussed in the context of predicting major ion toxicity to freshwater organisms.