Abstract
Uranium contamination threatens the availability of safe and clean drinking water globally. This toxic element occurs both naturally and as a result of mining and ore-processing in alluvial sediments, where it accumulates as tetravalent U [U(IV)], a form once considered largely immobile. Changing hydrologic and geochemical conditions cause U to be released into groundwater. Knowledge of the chemical form(s) of U(IV) is essential to understand the release mechanism, yet the relevant U(IV) species are poorly characterized. There is growing belief that natural organic matter (OM) binds U(IV) and mediates its fate in the subsurface. In this work, we combined nanoscale imaging (nano secondary ion mass spectrometry and scanning transmission X-ray microscopy) with a density-based fractionation approach to physically and microscopically isolate organic and mineral matter from alluvial sediments contaminated with uranium. We identified two populations of U (dominantly +IV) in anoxic sediments. Uranium was retained on OM and adsorbed to particulate organic carbon, comprising both microbial and plant material. Surprisingly, U was also adsorbed to clay minerals and OM-coated clay minerals. The dominance of OM-associated U provides a framework to understand U mobility in the shallow subsurface, and, in particular, emphasizes roles for desorption and colloid formation in its mobilization.
| Original language | English |
|---|---|
| Pages (from-to) | 1493-1502 |
| Number of pages | 10 |
| Journal | Environmental Science and Technology |
| Volume | 54 |
| Issue number | 3 |
| DOIs | |
| State | Published - Feb 4 2020 |
| Externally published | Yes |
Funding
Use of the Stanford Synchrotron Radiation Lightsource (SSRL) is supported by the US DOE, Office of Basic Energy Sciences. A portion of the research was performed using the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility sponsored by the Office of BER (located at Pacific Northwest National Laboratory). Research described in this paper was performed at beamline 10ID-1 at the Canadian Light Source (CLS), which is supported by Natural Sciences and Engineering Research Council, Canadian Institutes of Health Research, National Research Council, Western Economic Diversification Canada, the University of Saskatchewan, and the Province of Saskatchewan. We are grateful to Ray Johnson and William Dam (Department of Energy-Legacy Management) for their help in obtaining samples from the Riverton Site. We also thank Melanie Cahill for her work in the laboratory while being an undergraduate student at Stanford with S.E.B. Data presented in the manuscript is archived on DOE’s ESS-DIVE at DOI: 10.15485/1582405. Research was supported by the DOE Office of Biological and Environmental Research, Climate and Environmental Sciences Division through the SLAC Groundwater Quality Science Focus Area program (contract no. DE-AC02-76SF00515).
| Funders | Funder number |
|---|---|
| DOE Office of Biological and Environmental Research, Climate and Environmental Sciences Division | |
| DOE Office of Science | |
| Office of BER | |
| Office of Basic Energy Sciences | |
| Province of Saskatchewan | |
| U.S. Department of Energy | |
| University of Saskatchewan | |
| Pacific Northwest National Laboratory | |
| National Research Council | |
| Canadian Institutes of Health Research | |
| Natural Sciences and Engineering Research Council of Canada | |
| Western Economic Diversification Canada |
