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Environ Sci Technol. 2016 Aug 2;50(15):8120-7. doi: 10.1021/acs.est.6b02406. Epub 2016 Jul 21.

Biogeochemical Controls of Uranium Bioavailability from the Dissolved Phase in Natural Freshwaters.

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U.S. Geological Survey , 345 Middlefield Rd, Menlo Park, CA94025, United States.
U.S. Geological Survey , 3215 Marine St Suite E-127, Boulder, CO80303, United States.


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.

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