title: Impact of environmentally based chemical hardness on uranium speciation and toxicity in six aquatic species.
abstract: Treated effluent discharge from uranium (U) mines and mills elevates the concentrations of U, calcium (Ca), magnesium (Mg), and sulfate (SO4 (2-) ) 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.
authors.affiliation: Canadian Nuclear Safety Commission, Ottawa, Ontario, Canada.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Goulet
authors.forename: Patsy A
authors.initials: PA
authors.lastname: Thompson
authors.forename: Kerrie C
authors.initials: KC
authors.lastname: Serben
authors.forename: Curtis V
authors.initials: CV
authors.lastname: Eickhoff
mesh_terms: D033304:Amphipoda / Q000187:drug effects; D000818:Animals; D059001:Aquatic Organisms / Q000187:drug effects*; D002118:Calcium / Q000032:analysis; D000460:Chlorophyta; D017753:Ecosystem; D004777:Environment; D006244:Hardness; D008274:Magnesium / Q000032:analysis; D008906:Mining; D014501:Uranium / Q000302:isolation & purification* / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000633:toxicity; D060753:Water Quality
chemical_list: D014874:Water Pollutants, Chemical; D014501:Uranium; D008274:Magnesium; D002118:Calcium
keywords: Acute toxicity; Chronic toxicity; Freshwater; Speciation; Uranium