Native freshwater mussels are in serious decline and resource managers need more information for their protection and conservation. Nearly 70% of the 300 species in North America are endangered, threatened, of special concern, or already extinct. Previous studies indicate that fresh-water mussels are sensitive to ammonia, metals, and major ions including sodium chloride (NaCl) and sodium sulfate (Na2SO4). As part of a Safe and Sustainable Water Resources Research Project, USEPA-Duluth, the Illinois Natural History Survey (INHS), and the USGS-Columbia Environmental Research Center (CERC) are conducting toxicity tests to help develop a model that predicts the acute and chronic toxicity of mixtures of major ions to commonly tested freshwater organisms. Objectives of the current study were to (1) evaluate acute toxicity of NaCl and Na2SO4 mixtures to juvenile fatmucket tested at CERC and (2) to compare the response of mussels to three other species tested: a crusta-cean Ceriodaphnia dubia and fathead minnow (Pimephales promelas) tested at USEPA-Duluth, and a mayªy (Neocleontriangulifer) tested at INHS. In the current study, 7 treatments were tested at median effect concentra-tion (EC50) ratios of NaCl to Na2SO4 of 1:0, 0:1, 1:1, 1:5, 1:2, 2:1, 5:1. Within each of the 7 treatments, ten exposure concentrations were tested as 20% serial dilutions with a control (100%, 80%, 64%, 50%, 40%, 32%, 25%, 20%, 16%, and 0%). Preliminary results indicate the EC50s for juvenile mussels were at about the 50% dilution in all 7 treatments with a strong 1:1 ratio of NaCl to Na2SO4 toxicity indicating additive acute toxicity for the mixtures of NaCl and Na2SO4 tested. Mussels were more sensitive to the ion mixtures compared to fathead minnows, as sensitive as C. dubia, and less sensitive than mayªies. The relationship between EC50s for NaCl and EC50s for Na2SO4 for each species tested was linear indicating the additive toxicity of the mixtures for all four species, though the slopes of the lines varied among the species indi-cating different relative potency of NaCl and Na2SO4 to the different species. Results from this study will be used to determine the contribu-tion of individual major ions to the overall toxicity of mixtures of major ions, perhaps leading to revisions to regional water quality standards or national ambient water quality criteria for major ions.
|Original language||English (US)|
|Title of host publication||Society of Environmental Toxicology and Chemistry North America 36th Annual Meeting, 1-5 November 2015, Salt Lake City, Utah|
|State||Published - 2015|