title: Effects of clay minerals and organic matter in formulated sediments on the bioavailability of sediment-associated uranium to the freshwater midge, Chironomus dilutus.
abstract: It is well established that bioavailability influences metal toxicity in aquatic ecosystems. However, the factors and mechanisms that influence uranium (U) bioavailability and toxicity in sediment have not been thoroughly evaluated, despite evidence that suggests different sediment components can influence the sorption and interaction of some metals. Given that dissolved U is generally accepted as being the primary bioavailable fraction of U, it is hypothesized that adsorption and interaction of U with different sediment components will influence the bioavailability of U in sediment. We investigated the effects of key sediment physicochemical properties on the bioavailability of U to a model freshwater benthic invertebrate, Chironomus dilutus. Several 10-day spiked sediment bioaccumulation experiments were performed, exposing C. dilutus larvae to a variety of formulated sediments spiked with different concentrations of U (5, 50 and/or 200 mg U/kg d.w.). Mean accumulation of U in C. dilutus larvae decreased significantly from 1195 to 10 mg U/kg d.w. as kaolin clay content increased from 0% to 60% in sediment spiked with 50 mg U/kg d.w. Similarly, higher organic matter content also resulted in a significant reduction of U bioaccumulation in C. dilutus larvae, indicating a reduction in U bioavailability. Concentrations of U in both the overlying water and sediment pore water displayed a strong positive relationship to U bioaccumulation in C. dilutus larvae (r(2) = 0.77, p<0.001 and r(2) = 0.57, p < 0.001, respectively) for all experiments, while total U concentrations in the sediment had a poor relationship to U bioaccumulation (r(2) = 0.10, p = 0.028). Results from this research confirm that sediment clay and organic matter content play a significant role in altering U bioavailability, which is important in informing risk assessments of U contaminated sites and in the development of site-specific sediment quality guidelines for U.
authors.affiliation: Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK S7N 5B3, Canada. Electronic address: sarah.crawford@usask.ca.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Crawford
authors.affiliation: 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, P.R. China. Electronic address: karsten.liber@usask.ca.
authors.forename: Karsten
authors.initials: K
authors.lastname: Liber
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000818:Animals; D002683:Chironomidae; D000077215:Clay; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D014501:Uranium / Q000032:analysis / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000032:analysis / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D008903:Minerals; D014875:Water Pollutants, Radioactive; D014501:Uranium; D000077215:Clay
keywords: Bioavailability; Clay minerals; Organic matter; Reconstituted sediment; Spiked-sediment tests; Uranium