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Nitrate-stimulated release of naturally occurring sedimentary uranium

February 27, 2023

Groundwater uranium (U) concentrations have been measured above the U.S. EPA maximum contaminant level (30 μg/L) in many U.S. aquifers, including in areas not associated with anthropogenic contamination by milling or mining. In addition to carbonate, nitrate has been correlated to uranium groundwater concentrations in two major U.S. aquifers. However, to date, direct evidence that nitrate mobilizes naturally occurring U from aquifer sediments has not been presented. Here, we demonstrate that the influx of high-nitrate porewater through High Plains alluvial aquifer silt sediments bearing naturally occurring U(IV) can stimulate a nitrate-reducing microbial community capable of catalyzing the oxidation and mobilization of U into the porewater. Microbial reduction of nitrate yielded nitrite, a reactive intermediate, which was further demonstrated to abiotically mobilize U from the reduced alluvial aquifer sediments. These results indicate that microbial activity, specifically nitrate reduction to nitrite, is one mechanism driving U mobilization from aquifer sediments in addition to previously described bicarbonate-driven desorption from mineral surfaces, such as Fe(III) oxides.

Publication Year 2023
Title Nitrate-stimulated release of naturally occurring sedimentary uranium
DOI 10.1021/acs.est.2c07683
Authors Jeffrey P Westrop, Pooja Yadav, PJ Nolan, Kate M. Campbell, Rajesh Singh, Sharon Bone, Alicia Chan, Anthony Hohtz, Donald Pan, Olivia Healy, John Bargar, Daniel D. Snow, Karrie Weber
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Science and Technology
Index ID 70242093
Record Source USGS Publications Warehouse
USGS Organization Geology, Geophysics, and Geochemistry Science Center