Biogeochemical controls of uranium bioavailability from the dissolved phase in natural freshwaters

Environmental Science & Technology
By: , and 

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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 speciesLymnaea 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.

Publication type Article
Publication Subtype Journal Article
Title Biogeochemical controls of uranium bioavailability from the dissolved phase in natural freshwaters
Series title Environmental Science & Technology
DOI 10.1021/acs.est.6b02406
Volume 50
Issue 15
Year Published 2016
Language English
Publisher ACS Publications
Contributing office(s) Colorado Water Science Center, National Research Program - Western Branch, Toxic Substances Hydrology Program, National Research Program - Central Branch
Description 8 p.
First page 8120
Last page 8127
Online Only (Y/N) N
Additional Online Files (Y/N) N
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