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Exploring drivers of sodium salt toxicity to the mayfly Neocloeon triangulifer, and comparing trends in mayfly and daphnid responses to major ions
Citation:
Riecks-Soucek, D., A. Dickinson, Dave Mount, R. Erickson, AND R. Hockett. Exploring drivers of sodium salt toxicity to the mayfly Neocloeon triangulifer, and comparing trends in mayfly and daphnid responses to major ions. SETAC North America, Orlando, FL, AFGHANISTAN, November 06 - 10, 2016.
Impact/Purpose:
not applicable
Description:
Field studies have shown that mayflies (Ephemeroptera) tend to be more sensitive than other benthic macroinvertebrates to elevated levels of total dissolved solids in streams. While work with other species has shown that major ion toxicity is dependent on the ionic composition of the water, little is known about how ionic composition influences responses of mayflies to elevated major ions. We tested the toxicity of a variety of major ion salts to the parthenogenetic mayfly Neocloeon triangulifer using dilution waters in which we manipulated either the concentrations of all background ions, Ca:Mg ratios, or sodium and potassium concentrations. We also conducted acute toxicity tests with D-mannitol and sodium gluconate to investigate potential effects of high osmolarity in the absence of “toxic” cations or anions (D-mannitol) or in the absence of a “toxic” anion (sodium gluconate). Finally, we conducted full-life chronic toxicity tests with two sodium salts. In the case of the sodium salts, expressing LC50s (acute tests) or EC20s (chronic tests) in terms of sodium activity (mM) produced a much narrower range of effect levels than when expressing the same data in terms of the anion activity. Furthermore, exposing mayflies to high osmolarity using D-mannitol resulted in a minor effect on survival, whereas the sodium gluconate test resulted in a sodium activity effect level similar to those produced with inorganic sodium salts. This suggests that sodium, rather than overall osmolarity, was responsible for observed toxicity. Comparing general trends in major ion toxicity for Neocloeon to those observed for Ceriodaphnia dubia revealed similarities on some cases but differences in others. For example, while Na activity appears to be the driver of toxicity to the mayfly in sodium salt tests (NaCl, Na2SO4, NaHCO3), for C. dubia Na salt toxicity appears to have some anion dependence and may be better explained by osmolarity. While the two species are similar in that it appears that the acute toxicity of magnesium and potassium salts may be driven by the cation as well, the species are different in terms of their relative responses to Na, K, and Mg. The acute toxicity of potassium to the mayfly is similar to that of sodium on a mM activity basis, and LC50s for Na and K are ~4-fold greater than those for Mg on a mM activity basis, whereas for C. dubia, K and Mg LC50s are similar, and they are ~4 to 6-fold lower than those for Na on a mM activity basis.