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Impact of environmentally based chemical hardness on uranium speciation and toxicity in six aquatic species
- Goulet, Richard R., Thompson, Patsy A., Serben, Kerrie C., Eickhoff, Curtis V.
- Environmental toxicology and chemistry 2015 v.34 no.3 pp. 562-574
- Hyalella azteca, Selenastrum capricornutum, alkalinity, bioassays, calcium, freshwater, hardness, hydrochemistry, magnesium, pH, prediction, toxicity, toxicity testing, uranium
- Treated effluent discharge from uranium (U) mines and mills elevates the concentrations of U, calcium (Ca), magnesium (Mg), and sulfate (SO₄²–) above natural levels in receiving waters. Many investigations on the effect of hardness on U toxicity have been experiments on the combined effects of changes in hardness, pH, and alkalinity, which do not represent water chemistry downstream of U mines and mills. Therefore, more toxicity studies with water chemistry encountered downstream of U mines and mills are necessary to support predictive assessments of impacts of U discharge to the environment. Acute and chronic U toxicity laboratory bioassays were realized with 6 freshwater species in waters of low alkalinity, circumneutral pH, and a range of chemical hardness as found in field samples collected downstream of U mines and mills. In laboratory‐tested waters, speciation calculations suggested that free uranyl ion concentrations remained constant despite increasing chemical hardness. When hardness increased while pH remained circumneutral and alkalinity low, U toxicity decreased only to Hyalella azteca and Pseudokirchneriella subcapitata. Also, Ca and Mg did not compete with U for the same uptake sites. The present study confirms that the majority of studies concluding that hardness affected U toxicity were in fact studies in which alkalinity and pH were the stronger influence. The results thus confirm that studies predicting impacts of U downstream of mines and mills should not consider chemical hardness. Environ Toxicol Chem 2015;34:562–574. © 2014 The Authors. Published by Wiley Periodicals, Inc. on behalf of SETAC