Westrop, and 12 co-authors, reported in early 2023 that uranium (U) concentrations in groundwater 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 (see graphic (here).
However, to date, direct evidence that nitrate mobilizes naturally occurring U from aquifer sediments has not been presented. Here, the authors demonstrated that the influx of high-nitrate groundwater 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 shallow groundwater.
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 (more).
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.2c07683 .
Groundwater geochemical data; descriptive statistics for XANES linear combination fits; measured geochemical parameters from batch adsorption experiments; upflow-column reactor experimental design replicating the sand and silt lithologic interface; ORP, pH, Fe(II), U, and viruses/mL measured from upflow-column reactor effluent; upflow reactor sediment U and Fe; and surface complexation model (PDF)
Managed & Built by I2M Consulting, LLC | © 2010-
