The role of sediment properties and solution pH in the adsorption of uranium(VI) to freshwater sediments.
Uranium (U) can enter aquatic environments from natural and anthropogenic processes, accumulating in sediments to concentrations that could, if bioavailable, adversely affect benthic organisms. To better predict the sorption and mobility of U in aquatic ecosystems, we investigated the sediment-solution partition coefficients (Kd) of U for nine uncontaminated freshwater sediments with a wide range of physicochemical characteristics over an environmentally relevant pH range. Test solutions were reconstituted to mimic water quality conditions and U(VI) concentrations (0.023-2.3 mg U/L) found downstream of Canadian U mines. Adsorption of U(VI) to each sediment was greatest at pH 6 and 7, and significantly reduced at pH 8. There were significant differences in pH-dependent sorption among sediments with different physicochemical properties, with sorption increasing up until thresholds of 12% total organic carbon, 37% fine fraction (≤50 μm), and 29 g/kg of iron content. The Kdvalues for U(VI) were predicted using the Windermere Humic Aqueous Model (WHAM) using total U(VI) concentrations, and water and sediment physicochemical parameters. Predicted Kd-U values were generally within a factor of three of the observed values. These results improve the understanding and assessment of U sorption to field sediment, and quantify the relationship with sediment properties that may influence the bioavailability and ecological risk of U-contaminated sediments.
Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada. Electronic address: Sarah.Crawford@usask.ca.
Sarah E
SE
Crawford
NERC Centre for Ecology and Hydrology, Library Avenue, Bailrigg, Lancaster, LA1 4AP, United Kingdom.
Stephen
S
Lofts
Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada; School of Environment and Sustainability, 117 Science Place, University of Saskatchewan, Saskatoon, SK, S7N 5C8, Canada; Institute of Loess Plateau, 92 Wucheng Road, Shanxi University, Taiyuan, Shanxi, 030006, PR China. Electronic address: Karsten.Liber@usask.ca.
Karsten
K
Liber
D000327:Adsorption; D002170:Canada; D004784:Environmental Monitoring; D005618:Fresh Water / Q000032:analysis* / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D012525:Saskatchewan; D014501:Uranium / Q000032:analysis* / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry*
D014875:Water Pollutants, Radioactive; D014501:Uranium
Distribution or partition coefficients; Sediment; Sorption; Speciation; Uranium; WHAM; Windermere humic aqueous model