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, and initial results of laboratory acute and chronic tests with the parthenogenetic mayfly Neocloeon triangulifersupport the findings of field assessments. We previously presented data for single salts that suggested that dilution water composition influences the toxicity of major ion salts to N. triangulifer,as has been observed for other species. In the present study, we used binary mixtures and in one case a ternary mixture, plus D-mannitol and Na, K, and Mg gluconate salts to investigate potential drivers of toxicity in solutions with elevated major ions. D-mannitol and gluconate were used to increase osmolar-ity in solutions without introducing ions (or anions specifically in the case of gluconate) that can cross membranes and cause toxic effects by mechanisms other than external osmolarity. None of the single salt or mixture toxicity tests had a median lethal concentration (LC50) in terms of osmolarity that was more than 50% of the LC50 in terms of osmolar-ity for D-mannitol. This suggests that while osmolarity is correlated with toxicity, it does not appear to be the cause, in contrast to what has been observed for Ceriodaphnia dubia. We conducted acute tests with various proportions of the following binary mixtures: NaCl and Na2SO4; Na2SO4 and MgSO4; NaCl and MgCl2; KCl and K2SO4. In each case, evidence of additivity was observed, which suggested that both salts were contribut-ing to a common mechanism of action. The additivity of the Na and Mg salts for the mayfly was in contrast to what has been documented for C. dubia, for which Na and Mg acted independently. This may suggest a stronger role for toxicity to the mayfly from the anions sulfate and chlo-ride. Most published literature on major ion toxicity reports data in terms of anions (i.e., chloride or sulfate toxicity), while recent work with other species (Duluth lab) suggested that cations may be more important than anions in causing toxicity. For the mayfly, it appears that both cations and anions may cause toxicity, depending on the mixture involved and which particular ion reaches its toxic threshold activity. This abstract does not necessarily reflect USEPA policy.
|Original language||English (US)|
|Title of host publication||Abstracts of the 38th Annual Meeting, Society for Environmental Toxicology and Chemistry|
|State||Published - 2017|