Adverse effects from increased concentrations of major geochemical ions (Na, K, Ca, Mg, Cl, SO4, HCO3) to aquatic organisms have been demonstrated or implied in many settings. However, experimental work has shown that the toxicity of ion mixtures is dependent on the specific mixture of ions present, and these vary according to both the source of the enrichment and the underlying geology of the waterbody. To date, we have conducted extensive acute toxicity testing of major ion salts (and mixtures of thereof) with a variety of aquatic species, including cladoc-eran (Ceriodaphnia dubia), fathead minnow (Pimephales promelas), amphipod (Hyalella azteca), mayfly (Neocloeon triangulifer), midge (Chironomus dilutus), oligochaete (Lumbriculus variegatus), and snail (Lymnaea stagnalis). While we expected overall sensitivity to vary across taxa, we have been surprised at the number of differences in how spe-cies respond to different ionic compositions. For example, response of some organisms to Na salts appears related to solution osmolarity, while responses of others appear more governed by Na concentration, and perhaps to SO4 at lower Ca concentrations. For several (but not all) inver-tebrate species, mixtures of Na and Mg salts show independent behavior suggesting separate toxic mechanisms, but for fathead minnows and mayfly the interaction appears more additive. Toxicity of K salts is highly dependent on Na concentration in Ceriodaphnia, but not in fathead min-now, mayfly or amphipod. On the other hand, some responses do appear more generalizable, such as lower toxicity from Na or Mg salts at elevated (but less than directly toxic) Ca concentration. We discuss the risk assess-ment challenges posted by these differing characteristics in response across species. 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|