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Influence of dilution water ionic composition on acute major ion toxicity to the mayfly Neocloeon triangulifer
Citation:
Riecks-Soucek, D., Dave Mount, A. Dickinson, AND R. Hockett. Influence of dilution water ionic composition on acute major ion toxicity to the mayfly Neocloeon triangulifer. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 37(5):1330-1339, (2018).
Impact/Purpose:
This manuscript examines the acute toxicity of major ion salts to a species of mayfly, Neocloeon triangulifer. Analysis of data from natural streams with elevated major ion concentrations have indicated that mayflies are a group of organism with generally high sensitivity to major ion enrichment, but the very limited number of mayfly species that have been adapted for use in laboratory toxicity experiments creates a gap in the understanding of how sensitive this group is to specific major ion salts, and how that sensitivity is influenced by the background composition of the water in which they are exposed. Mayfly were exposed to chloride and sulfate salts of sodium, magnesium, calcium, and potassium in a range of dilution water representing different background hardness. In addition, toxicity was tested in waters whose composition was altered in specific ways to better understand what compositional factors influence response. Data from these experiments will fill an important gap in understanding how to assess and predict the toxicity of major ions to aquatic communities.
Description:
Both field and laboratory studies have shown that mayflies (Ephemeroptera) tend to be relatively sensitive to elevated major ion concentrations, but very little is known about how ionic composition influences these responses. The present study evaluated the toxicity of various major ion salts to the mayfly Neocloeon triangulifer over a range of background water quality conditions. The mayfly was particularly sensitive to Na2SO4, with the median lethal concentration (LC50) of 1,338 mg SO4/L being lower than LC50s reported for seven other species at that hardness. Increasing hardness of the dilution water from 30 to 150 mg/L (as CaCO3; all ions increasing proportionally) resulted in doubling of LC50s for sodium salts, and a ~1.5 fold increase in LC50 for MgSO4. Potassium salt toxicity was not strongly influenced by hardness, consistent with findings for other species. When hardness was held constant, but Ca:Mg ratio was manipulated, the ameliorative effect (relative to Ca activity) on Na2SO4 and NaCl did not appear as strong as when hardness (and other ions) were varied, but for MgSO4 the amelioration relative to Ca activity was similar between the two experiments. The toxicity of K salts to N. triangulifer was very similar to Na salts on a mM basis, which contrasts with several other species for which K salts have been found much more toxic. In addition, the toxicity of KCl to N. triangulifer was not notably affected by the co-occurring Na concentration, as has been shown for Ceriodaphnia dubia. Finally, plotting LC50s in terms of individual ion activity (Cl, SO4, Na, Mg, or K) over the range of Ca activities in dilution water resulted in significant positive relationships, with comparable slopes to those previously observed for C. dubia over the same range of Ca activities.
