title: Biogeochemical Controls of Uranium Bioavailability from the Dissolved Phase in Natural Freshwaters.
abstract: To gain insights into the risks associated with uranium (U) mining and processing, we investigated the biogeochemical controls of U bioavailability in the model freshwater species Lymnaea stagnalis (Gastropoda). Bioavailability of dissolved U(VI) was characterized in controlled laboratory experiments over a range of water hardness, pH, and in the presence of complexing ligands in the form of dissolved natural organic matter (DOM). Results show that dissolved U is bioavailable under all the geochemical conditions tested. Uranium uptake rates follow first order kinetics over a range encompassing most environmental concentrations. Uranium uptake rates in L. stagnalis ultimately demonstrate saturation uptake kinetics when exposure concentrations exceed 100 nM, suggesting uptake via a finite number of carriers or ion channels. The lack of a relationship between U uptake rate constants and Ca uptake rates suggest that U does not exclusively use Ca membrane transporters. In general, U bioavailability decreases with increasing pH, increasing Ca and Mg concentrations, and when DOM is present. Competing ions did not affect U uptake rates. Speciation modeling that includes formation constants for U ternary complexes reveals that the aqueous concentration of dicarbonato U species (UO2(CO3)2(-2)) best predicts U bioavailability to L. stagnalis, challenging the free-ion activity model postulate.
authors.affiliation: U.S. Geological Survey , 345 Middlefield Rd, Menlo Park, CA94025, United States.
authors.forename: Marie-Noële
authors.initials: MN
authors.lastname: Croteau
authors.affiliation: U.S. Geological Survey , 345 Middlefield Rd, Menlo Park, CA94025, United States.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Fuller
authors.affiliation: U.S. Geological Survey , 345 Middlefield Rd, Menlo Park, CA94025, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Cain
authors.affiliation: U.S. Geological Survey , 3215 Marine St Suite E-127, Boulder, CO80303, United States.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Campbell
authors.affiliation: U.S. Geological Survey , 3215 Marine St Suite E-127, Boulder, CO80303, United States.
authors.forename: George
authors.initials: G
authors.lastname: Aiken
mesh_terms: D001682:Biological Availability; D005618:Fresh Water; D007700:Kinetics; D014501:Uranium / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000737:chemistry
chemical_list: D014875:Water Pollutants, Radioactive; D014501:Uranium