es6b02406_si_001.pdf (274 kB)
Biogeochemical Controls of Uranium Bioavailability from the Dissolved Phase in Natural Freshwaters
journal contribution
posted on 2016-07-06, 00:00 authored by Marie-Noële Croteau, Christopher
C. Fuller, Daniel J. Cain, Kate M. Campbell, George AikenTo 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.