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Diagenetic formation of uranium-silica polymers in lake sediments over 3,300 years. Proc Natl Acad Sci U S A 2021; 118:2021844118. [PMID: 33479173 DOI: 10.1073/pnas.2021844118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The long-term fate of uranium-contaminated sediments, especially downstream former mining areas, is a widespread environmental challenge. Essential for their management is the proper understanding of uranium (U) immobilization mechanisms in reducing environments. In particular, the long-term behavior of noncrystalline U(IV) species and their possible evolution to more stable phases in subsurface conditions is poorly documented, which limits our ability to predict U long-term geochemical reactivity. Here, we report direct evidence for the evolution of U speciation over 3,300 y in naturally highly U-enriched sediments (350-760 µg ⋅ g-1 U) from Lake Nègre (Mercantour Massif, Mediterranean Alps, France) by combining U isotopic data (δ238U and (234U/238U)) with U L 3 -edge X-ray absorption fine structure spectroscopy. Constant isotopic ratios over the entire sediment core indicate stable U sources and accumulation modes, allowing for determination of the impact of aging on U speciation. We demonstrate that, after sediment deposition, mononuclear U(IV) species associated with organic matter transformed into authigenic polymeric U(IV)-silica species that might have partially converted to a nanocrystalline coffinite (UIVSiO4·nH2O)-like phase. This diagenetic transformation occurred in less than 700 y and is consistent with the high silica availability of sediments in which diatoms are abundant. It also yields consistency with laboratory studies that proposed the formation of colloidal polynuclear U(IV)-silica species, as precursors for coffinite formation. However, the incomplete transformation observed here only slightly reduces the potential lability of U, which could have important implications to evaluate the long-term management of U-contaminated sediments and, by extension, of U-bearing wastes in silica-rich subsurface environments.
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Asta MP, Beller HR, O'Day PA. Anaerobic Dissolution Rates of U(IV)-Oxide by Abiotic and Nitrate-Dependent Bacterial Pathways. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:8010-8021. [PMID: 32469205 DOI: 10.1021/acs.est.0c01019] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The long-term stability of U(IV) solid phases in anaerobic aquifers depends upon their reactivity in the presence of oxidizing chemical species and microbial catalysts. We performed flow-through column experiments under anaerobic conditions to investigate the mechanisms and dissolution rates of biogenic, noncrystalline UO2(s) by chemical oxidants (nitrate and/or nitrite) or by Thiobacillus denitrificans, a widespread, denitrifying, chemolithoautotrophic model bacterium. Dissolution rates of UO2(s) with dissolved nitrite were approximately 5 to 10 times greater than with nitrate alone. In the presence of wild-type T. denitrificans and nitrate, UO2(s) dissolution rates were similar to those of abiotic experiments with nitrite (from 1.15 × 10-14 to 4.94 × 10-13 mol m-2 s-1). Experiments with a T. dentrificans mutant strain defective in U(IV) oxidation supported microbially mediated U(IV) oxidation. X-ray absorption spectroscopy (XAS) analysis of post-reaction solids showed the presence of mononuclear U(VI) species rather than a solid U(VI) phase. At steady-state U release, kinetic and spectroscopic results suggest detachment of oxidized U(VI) from the UO2(s) surface as the rate-determining step rather than electron transfer or ion diffusion. Under anaerobic conditions, production of nitrite by nitrate-reducing microorganisms and enzymatically catalyzed, nitrate-dependent U(IV) oxidation are likely dual processes by which reduced U solids may be oxidized and mobilized in the aqueous phase.
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Affiliation(s)
- Maria P Asta
- Sierra Nevada Research Institute, University of California Merced, 5200 North Lake Road, Merced, California 95343, United States
| | - Harry R Beller
- Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 3E5, Canada
| | - Peggy A O'Day
- Sierra Nevada Research Institute, University of California Merced, 5200 North Lake Road, Merced, California 95343, United States
- Department of Life and Environmental Sciences, University of California Merced, Merced, California 95343, United States
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3
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Loreggian L, Novotny A, Bretagne SL, Bartova B, Wang Y, Bernier-Latmani R. Effect of Aging on the Stability of Microbially Reduced Uranium in Natural Sediment. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:613-620. [PMID: 31769664 DOI: 10.1021/acs.est.8b07023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Reductive immobilization of uranium has been explored as a remediation strategy for the U-contaminated subsurface. Via the in situ biostimulation of microbial processes, hexavalent U is reduced to less soluble tetravalent species, which are immobilized within the sediment. Although the mineral uraninite (UO2) was initially considered the dominant product of biological reduction, non-crystalline U(IV) species (NCU(IV)) are found to be abundant in the environment despite their greater susceptibility to oxidation and remobilization. However, it has been recently proposed that, through aging, NCU(IV) might transform into UO2, which would potentially enhance the stability of the reduced U pool. In this study, we performed column experiments to produce NCU(IV) species in natural sediment mimicking the environmental conditions during bioremediation. Bioreduced sediment retrieved from the columns and harboring NCU(IV) was incubated in static microcosms under anoxic conditions to allow the systematic monitoring of U coordination by X-ray absorption spectroscopy (XAS) over 12 months. XAS revealed that, under the investigated conditions, the speciation of U(IV) does not change over time. Thus, because NCU(IV) is the dominant species in the sediment, bioreduced U(IV) species remain vulnerable to oxidation and remobilization in the aqueous phase even after a 12-month aging period.
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Affiliation(s)
- Luca Loreggian
- Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland
| | - Agnes Novotny
- Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland
| | - Sophie Louise Bretagne
- Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland
| | - Barbora Bartova
- Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland
| | - Yuheng Wang
- School of Ecology and Environment, Northwestern Polytechnical University, 710129 Xi'an, P. R. China
| | - Rizlan Bernier-Latmani
- Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland
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4
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Li PS, Wu WM, Phillips DH, Watson DB, Kelly S, Li B, Mehlhorn T, Lowe K, Earles J, Tao HC, Zhang T, Criddle CS. Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via. bioreduction followed by reoxidation. J Environ Sci (China) 2019; 85:156-167. [PMID: 31471022 DOI: 10.1016/j.jes.2019.05.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 05/29/2019] [Accepted: 05/30/2019] [Indexed: 06/10/2023]
Abstract
This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation. Field tests (1383 days) at Oak Ridge, Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater. Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L. Aliquots of the bioreduced sediment were reoxidized with O2, H2O2, and NaNO3, respectively, over 285 days, resulting in aqueous U of 0.024, 1.58 and 14.4 mg/L at pH 6.30, 6.63 and 7.62, respectively. The source- and the three reoxidized sediments showed different desorption and adsorption behaviors of U, but all fit a Freundlich model. The adsorption capacities increased sharply at pH 4.5 to 5.5, plateaued at pH 5.5 to 7.0, then decreased sharply as pH increased from 7.0 to 8.0. The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0. The NO3--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0. The pH-dependent adsorption onto Fe(III) oxides and formation of U coated particles and precipitates resulted in U sequestration, and bioreduction followed by reoxidation can enhance the U sequestration in sediment.
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Affiliation(s)
- Peng-Song Li
- Department of Civil and Environmental Engineering, William & Cloy Codiga Resource Recovery Center, Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA 94305-4020, USA; Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China; Institute of New Energy Technology, Tsinghua University, Beijing 100084, China
| | - Wei-Min Wu
- Department of Civil and Environmental Engineering, William & Cloy Codiga Resource Recovery Center, Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA 94305-4020, USA.
| | - Debra H Phillips
- School of Natural and Built Environment, Queen's University Belfast, Belfast BT9 5AG, Northern Ireland, UK
| | - David B Watson
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, P.O. Box 2008, TN 37831, USA
| | | | - Bing Li
- Department of Civil and Environmental Engineering, William & Cloy Codiga Resource Recovery Center, Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA 94305-4020, USA; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, P.O. Box 2008, TN 37831, USA; Department of Civil Engineering, The University of Hong Kong, Hong Kong, China
| | - Tonia Mehlhorn
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, P.O. Box 2008, TN 37831, USA
| | - Kenneth Lowe
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, P.O. Box 2008, TN 37831, USA
| | - Jennifer Earles
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, P.O. Box 2008, TN 37831, USA
| | - Hu-Chun Tao
- Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China
| | - Tong Zhang
- Department of Civil Engineering, The University of Hong Kong, Hong Kong, China
| | - Craig S Criddle
- Department of Civil and Environmental Engineering, William & Cloy Codiga Resource Recovery Center, Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA 94305-4020, USA.
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Dang DH, Wang W, Pelletier P, Poulain AJ, Evans RD. Uranium dispersion from U tailings and mechanisms leading to U accumulation in sediments: Insights from biogeochemical and isotopic approaches. THE SCIENCE OF THE TOTAL ENVIRONMENT 2018; 610-611:880-891. [PMID: 28830048 DOI: 10.1016/j.scitotenv.2017.08.156] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 08/14/2017] [Accepted: 08/15/2017] [Indexed: 06/07/2023]
Abstract
Uranium contamination is a worldwide problem that grows proportionally to human demands for energy and armory. Understanding U cycling in the environment is of eminent interest, mostly concerning ecosystems directly impacted by point sources. In Bow Lake (Ontario, Canada), which is located adjacent to a former U mine, exceptionally high concentrations of U are related to U dispersion from tailings and biogeochemical processes such as biotic reduction and adsorption. This has been shown by a U-Pb isotope composition model. In this study, we use U isotope fractionation (δ238U) to highlight U cycling and the role of bacteria (Geobacteraceae and sulfate-reducing bacteria) in affecting U cycling. Bacteria affected U cycling directly via biotic U reduction and indirectly via reductive dissolution of carrier phases. All the processes are interconnected through diagenetic reactions with the supply of bioavailable organic matter being the primary driving force of the diagenesis. This study is the first to use multiple biogeochemical and isotopic approaches to track U cycling from a contamination point source to U storage in lake sediments.
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Affiliation(s)
- Duc Huy Dang
- School of the Environment, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada.
| | - Wei Wang
- School of the Environment, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada
| | - Philip Pelletier
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Alexandre J Poulain
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - R Douglas Evans
- School of the Environment, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada; Water Quality Center, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada
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6
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Bhattacharyya A, Campbell KM, Kelly SD, Roebbert Y, Weyer S, Bernier-Latmani R, Borch T. Biogenic non-crystalline U (IV) revealed as major component in uranium ore deposits. Nat Commun 2017; 8:15538. [PMID: 28569759 PMCID: PMC5461479 DOI: 10.1038/ncomms15538] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 04/06/2017] [Indexed: 11/09/2022] Open
Abstract
Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U(VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (∼58-89%) of U is bound as U(IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U(VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotope signatures, consistent with largely biotic reduction of U(VI) to U(IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U(IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment. Crystalline uraninite is believed to be the dominant form in uranium deposits. Here, the authors find that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in ore deposits, implying that biogenic processes are more important than previously thought.
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Affiliation(s)
- Amrita Bhattacharyya
- Department of Soil and Crop Sciences, Colorado State University, Fort Collins, Colorado 80523-1170, USA
| | | | | | - Yvonne Roebbert
- Institut für Mineralogie, Leibniz Universitat Hannover, Hannover D-30167, Germany
| | - Stefan Weyer
- Institut für Mineralogie, Leibniz Universitat Hannover, Hannover D-30167, Germany
| | - Rizlan Bernier-Latmani
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland
| | - Thomas Borch
- Department of Soil and Crop Sciences, Colorado State University, Fort Collins, Colorado 80523-1170, USA.,Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA
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7
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Kaplan DI, Kukkadapu R, Seaman JC, Arey BW, Dohnalkova AC, Buettner S, Li D, Varga T, Scheckel KG, Jaffé PR. Iron mineralogy and uranium-binding environment in the rhizosphere of a wetland soil. THE SCIENCE OF THE TOTAL ENVIRONMENT 2016; 569-570:53-64. [PMID: 27328400 PMCID: PMC7388027 DOI: 10.1016/j.scitotenv.2016.06.120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 06/15/2016] [Accepted: 06/15/2016] [Indexed: 06/06/2023]
Abstract
Wetlands mitigate the migration of groundwater contaminants through a series of biogeochemical gradients that enhance multiple contaminant-binding processes. The hypothesis of this study was that wetland plant roots contribute organic carbon and release O2 within the rhizosphere (plant-impact soil zone) that promote the formation of Fe(III)-(oxyhydr)oxides. In turn, these Fe(III)-(oxyhydr)oxides stabilize organic matter that together contribute to contaminant immobilization. Mineralogy and U binding environments of the rhizosphere were evaluated in samples collected from contaminated and non-contaminated areas of a wetland on the Savannah River Site in South Carolina. Based on Mössbauer spectroscopy, rhizosphere soil was greatly enriched with nanogoethite, ferrihydrite-like nanoparticulates, and hematite, with negligible Fe(II) present. X-ray computed tomography and various microscopy techniques showed that root plaques were tens-of-microns thick and consisted of highly oriented Fe-nanoparticles, suggesting that the roots were involved in creating the biogeochemical conditions conducive to the nanoparticle formation. XAS showed that a majority of the U in the bulk wetland soil was in the +6 oxidation state and was not well correlated spatially to Fe concentrations. SEM/EDS confirm that U was enriched on root plaques, where it was always found in association with P. Together these findings support our hypothesis and suggest that plants can alter mineralogical conditions that may be conducive to contaminant immobilization in wetlands.
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Affiliation(s)
- Daniel I Kaplan
- Savannah River National Laboratory, Aiken, SC 29808, United States.
| | - Ravi Kukkadapu
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States
| | - John C Seaman
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, United States
| | - Bruce W Arey
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States
| | - Alice C Dohnalkova
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States
| | - Shea Buettner
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, United States
| | - Dien Li
- Savannah River National Laboratory, Aiken, SC 29808, United States
| | - Tamas Varga
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States
| | - Kirk G Scheckel
- US Environmental Protection Agency, National Risk Management Research Laboratory, Cincinnati, OH 45224, United States
| | - Peter R Jaffé
- Princeton University, Princeton, NJ 08540, United States
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Mikutta C, Langner P, Bargar JR, Kretzschmar R. Tetra- and Hexavalent Uranium Forms Bidentate-Mononuclear Complexes with Particulate Organic Matter in a Naturally Uranium-Enriched Peatland. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:10465-10475. [PMID: 27635434 DOI: 10.1021/acs.est.6b03688] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Peatlands frequently serve as efficient biogeochemical traps for U. Mechanisms of U immobilization in these organic matter-dominated environments may encompass the precipitation of U-bearing mineral(oid)s and the complexation of U by a vast range of (in)organic surfaces. The objective of this work was to investigate the spatial distribution and molecular binding mechanisms of U in soils of an alpine minerotrophic peatland (pH 4.7-6.6, Eh = -127 to 463 mV) using microfocused X-ray fluorescence spectrometry and bulk and microfocused U L3-edge X-ray absorption spectroscopy. The soils contained 2.3-47.4 wt % organic C, 4.1-58.6 g/kg Fe, and up to 335 mg/kg geogenic U. Uranium was found to be heterogeneously distributed at the micrometer scale and enriched as both U(IV) and U(VI) on fibrous and woody plant debris (48 ± 10% U(IV), x̅ ± σ, n = 22). Bulk U X-ray absorption near edge structure (XANES) spectroscopy revealed that in all samples U(IV) comprised 35-68% of total U (x̅ = 50%, n = 15). Shell-fit analyses of bulk U L3-edge extended X-ray absorption fine structure (EXAFS) spectra showed that U was coordinated to 1.3 ± 0.2 C atoms at a distance of 2.91 ± 0.01 Å (x̅ ± σ), which implies the formation of bidentate-mononuclear U(IV/VI) complexes with carboxyl groups. We neither found evidence for U shells at ∼3.9 Å, indicative of mineral-associated U or multinuclear U(IV) species, nor for a substantial P/Fe coordination of U. Our data indicates that U(IV/VI) complexation by natural organic matter prevents the precipitation of U minerals as well as U complexation by Fe/Mn phases at our field site, and suggests that organically complexed U(IV) is formed via reduction of organic matter-bound U(VI).
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Affiliation(s)
- Christian Mikutta
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , 8092 Zurich, Switzerland
- Section for Environmental Chemistry and Physics, Department of Plant and Environmental Sciences, University of Copenhagen , DK-1871 Frederiksberg C, Denmark
| | - Peggy Langner
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , 8092 Zurich, Switzerland
| | - John R Bargar
- Stanford Synchrotron Radiation Lightsource Directorate, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States
| | - Ruben Kretzschmar
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , 8092 Zurich, Switzerland
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Paradis CJ, Jagadamma S, Watson DB, McKay LD, Hazen TC, Park M, Istok JD. In situ mobility of uranium in the presence of nitrate following sulfate-reducing conditions. JOURNAL OF CONTAMINANT HYDROLOGY 2016; 187:55-64. [PMID: 26897652 DOI: 10.1016/j.jconhyd.2016.02.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 02/03/2016] [Accepted: 02/08/2016] [Indexed: 06/05/2023]
Abstract
Reoxidation and mobilization of previously reduced and immobilized uranium by dissolved-phase oxidants poses a significant challenge for remediating uranium-contaminated groundwater. Preferential oxidation of reduced sulfur-bearing species, as opposed to reduced uranium-bearing species, has been demonstrated to limit the mobility of uranium at the laboratory scale yet field-scale investigations are lacking. In this study, the mobility of uranium in the presence of nitrate oxidant was investigated in a shallow groundwater system after establishing conditions conducive to uranium reduction and the formation of reduced sulfur-bearing species. A series of three injections of groundwater (200 L) containing U(VI) (5 μM) and amended with ethanol (40 mM) and sulfate (20 mM) were conducted in ten test wells in order to stimulate microbial-mediated reduction of uranium and the formation of reduced sulfur-bearing species. Simultaneous push-pull tests were then conducted in triplicate well clusters to investigate the mobility of U(VI) under three conditions: 1) high nitrate (120 mM), 2) high nitrate (120 mM) with ethanol (30 mM), and 3) low nitrate (2 mM) with ethanol (30 mM). Dilution-adjusted breakthrough curves of ethanol, nitrate, nitrite, sulfate, and U(VI) suggested that nitrate reduction was predominantly coupled to the oxidation of reduced-sulfur bearing species, as opposed to the reoxidation of U(IV), under all three conditions for the duration of the 36-day tests. The amount of sulfate, but not U(VI), recovered during the push-pull tests was substantially more than injected, relative to bromide tracer, under all three conditions and further suggested that reduced sulfur-bearing species were preferentially oxidized under nitrate-reducing conditions. However, some reoxidation of U(IV) was observed under nitrate-reducing conditions and in the absence of detectable nitrate and/or nitrite. This suggested that reduced sulfur-bearing species may not be fully effective at limiting the mobility of uranium in the presence of dissolved and/or solid-phase oxidants. The results of this field study confirmed those of previous laboratory studies which suggested that reoxidation of uranium under nitrate-reducing conditions can be substantially limited by preferential oxidation of reduced sulfur-bearing species.
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Affiliation(s)
- Charles J Paradis
- Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, United States.
| | - Sindhu Jagadamma
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States
| | - David B Watson
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States
| | - Larry D McKay
- Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, United States
| | - Terry C Hazen
- Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, United States; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States; Department of Microbiology, University of Tennessee, Knoxville, TN 37996, United States; Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN 37996, United States; Center for Environmental Biotechnology, University of Tennessee, Knoxville, TN 37996, United States; Institute for a Secure and Sustainable Environment, University of Tennessee, Knoxville, TN 37996, United States
| | - Melora Park
- School of Civil and Construction Engineering, Oregon State University, Corvallis, OR 97331, United States
| | - Jonathan D Istok
- School of Civil and Construction Engineering, Oregon State University, Corvallis, OR 97331, United States
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10
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Suzuki Y, Mukai H, Ishimura T, Yokoyama TD, Sakata S, Hirata T, Iwatsuki T, Mizuno T. Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer. Sci Rep 2016; 6:22701. [PMID: 26948389 PMCID: PMC4780221 DOI: 10.1038/srep22701] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 02/22/2016] [Indexed: 11/09/2022] Open
Abstract
The stimulation of bacterial activities that convert hexavalent uranium, U(VI), to tetravalent uranium, U(IV), appears to be feasible for cost-effective remediation of contaminated aquifers. However, U(VI) reduction typically results in the precipitation of U(IV) particles less than 5 nanometers in diameter, except for environmental conditions enriched with iron. Because these tiny particles are mobile and susceptible to oxidative dissolution after the termination of nutrient injection, in situ bioremediation remains to be impractical. Here we show that U(IV) nanoparticles of coffinite (U(SiO4)1-x(OH)4x) formed in fracture-filling calcium carbonate in a granitic aquifer. In situ U-Pb isotope dating demonstrates that U(IV) nanoparticles have been sequestered in the calcium carbonate for at least 1 million years. As the microbiologically induced precipitation of calcium carbonate in aquifer systems worldwide is extremely common, we anticipate simultaneous stimulation of microbial activities for precipitation reactions of calcium carbonate and U(IV) nanoparticles, which leads to long-term sequestration of uranium and other radionuclides in contaminated aquifers and deep geological repositories.
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Affiliation(s)
- Yohey Suzuki
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan
| | - Hiroki Mukai
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan
| | - Toyoho Ishimura
- National Institute of Technology, Ibaraki College, 866 Nakane, Hitachinaka-shi, Ibaraki 312-8508, Japan
| | - Takaomi D Yokoyama
- Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan
| | - Shuhei Sakata
- Division of Earth &Planetary Sciences, Kyoto University, Kitashirakawa Oiwakesho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Takafumi Hirata
- Division of Earth &Planetary Sciences, Kyoto University, Kitashirakawa Oiwakesho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Teruki Iwatsuki
- Japan Atomic Energy Agency (JAEA), 1-64 Yamanouchi, Akeyo-cho, Mizunami, Gifu 509-6132, Japan
| | - Takashi Mizuno
- Japan Atomic Energy Agency (JAEA), 1-64 Yamanouchi, Akeyo-cho, Mizunami, Gifu 509-6132, Japan
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11
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Li D, Kaplan DI, Chang HS, Seaman JC, Jaffé PR, Koster van Groos P, Scheckel KG, Segre CU, Chen N, Jiang DT, Newville M, Lanzirotti A. Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:2823-2832. [PMID: 25634067 DOI: 10.1021/es505369g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6-5.8) conditions using U L3-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U-C bond distance at ∼2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulating the SRS wetland processes, U immobilization on roots was 2 orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was reoxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication for the long-term stewardship of U-contaminated wetlands.
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Affiliation(s)
- Dien Li
- Savannah River National Laboratory, Aiken, South Carolina 29808, United States
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12
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Alessi D, Lezama-Pacheco JS, Janot N, Suvorova EI, Cerrato JM, Giammar DE, Davis JA, Fox PM, Williams KH, Long PE, Handley KM, Bernier-Latmani R, Bargar JR. Speciation and reactivity of uranium products formed during in situ bioremediation in a shallow alluvial aquifer. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:12842-50. [PMID: 25265543 PMCID: PMC4224495 DOI: 10.1021/es502701u] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 09/16/2014] [Accepted: 09/29/2014] [Indexed: 05/18/2023]
Abstract
In this study, we report the results of in situ U(VI) bioreduction experiments at the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well at the site and, after a period of conditioning with groundwater, were amended with a mixture of groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous microorganisms. Individual reactors were collected as various redox regimes in the column sediments were achieved: (i) during iron reduction, (ii) just after the onset of sulfate reduction, and (iii) later into sulfate reduction. The speciation of U retained in the sediments was studied using X-ray absorption spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV) comprised about two-thirds of the U(IV) pool, across large changes in microbial community structure, redox regime, total uranium accumulation, and reaction time. A significant body of recent research has demonstrated that noncrystalline U(IV) species are more suceptible to remobilization and reoxidation than crystalline U(IV) phases such as uraninite. Our results highlight the importance of considering noncrystalline U(IV) formation across a wide range of aquifer parameters when designing in situ remediation plans.
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Affiliation(s)
- Daniel
S. Alessi
- Environmental
Microbiology Laboratory, Ecole Polytechnique
Fédérale de Lausanne, CH-1015, Lausanne, Switzerland
| | - Juan S. Lezama-Pacheco
- Chemistry
and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Noémie Janot
- Chemistry
and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Elena I. Suvorova
- Environmental
Microbiology Laboratory, Ecole Polytechnique
Fédérale de Lausanne, CH-1015, Lausanne, Switzerland
| | - José M. Cerrato
- Department
of Energy, Environmental, and Chemical Engineering, One Brookings
Drive, Washington University, Saint Louis, Missouri 63130, United States
| | - Daniel E. Giammar
- Department
of Energy, Environmental, and Chemical Engineering, One Brookings
Drive, Washington University, Saint Louis, Missouri 63130, United States
| | - James A. Davis
- Earth
Sciences Division, Lawrence Berkeley National
Laboratory, 1 Cyclotron
Road, Berkeley, California 94720, United States
| | - Patricia M. Fox
- Earth
Sciences Division, Lawrence Berkeley National
Laboratory, 1 Cyclotron
Road, Berkeley, California 94720, United States
| | - Kenneth H. Williams
- Earth
Sciences Division, Lawrence Berkeley National
Laboratory, 1 Cyclotron
Road, Berkeley, California 94720, United States
| | - Philip E. Long
- Earth
Sciences Division, Lawrence Berkeley National
Laboratory, 1 Cyclotron
Road, Berkeley, California 94720, United States
| | - Kim M. Handley
- Department
of Earth & Planetary Sciences, University
of California, Berkeley, California 97420, United States
| | - Rizlan Bernier-Latmani
- Environmental
Microbiology Laboratory, Ecole Polytechnique
Fédérale de Lausanne, CH-1015, Lausanne, Switzerland
| | - John R. Bargar
- Chemistry
and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
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13
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Abstract
Worldwide industrialization activities create vast amounts of organic and inorganic waste streams that frequently result in significant soil and groundwater contamination. Metals and radionuclides are of particular concern due to their mobility and long-term persistence in aquatic and terrestrial environments. As the global population increases, the demand for safe, contaminant-free soil and groundwater will increase as will the need for effective and inexpensive remediation strategies. Remediation strategies that include physical and chemical methods (i.e., abiotic) or biological activities have been shown to impede the migration of radionuclide and metal contaminants within soil and groundwater. However, abiotic remediation methods are often too costly owing to the quantities and volumes of soils and/or groundwater requiring treatment. The in situ sequestration of metals and radionuclides mediated by biological activities associated with microbial phosphorus metabolism is a promising and less costly addition to our existing remediation methods. This review highlights the current strategies for abiotic and microbial phosphate-mediated techniques for uranium and metal remediation.
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14
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Ding D, Xu F, Hu N, Li S, Tan X, Li G. Uranium speciation in sediments in microcosms before and after incubation under anoxic conditions. J Radioanal Nucl Chem 2014. [DOI: 10.1007/s10967-014-3516-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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15
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Chang HS, Buettner SW, Seaman JC, Jaffé PR, van Groos PGK, Li D, Peacock AD, Scheckel KG, Kaplan DI. Uranium immobilization in an iron-rich rhizosphere of a native wetland plant from the Savannah River Site under reducing conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:9270-9278. [PMID: 25051143 DOI: 10.1021/es5015136] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The hypothesis of this study was that iron plaques formed on the roots of wetland plants and their rhizospheres create environmental conditions favorable for iron reducing bacteria that promote the in situ immobilization of uranium. Greenhouse microcosm studies were conducted using native plants (Sparganium americanum) from a wetland located on the Savannah River Site, Aiken, SC. After iron plaques were established during a 73-day period by using an anoxic Fe(II)-rich nutrient solution, a U(VI) amended nutrient solution was added to the system for an additional two months. Compared to plant-free control microcosms, microcosms containing iron plaques successfully stimulated the growth of targeted iron reducing bacteria, Geobacter spp. Their population continuously increased after the introduction of the U(VI) nutrient solution. The reduction of some of the U(VI) to U(IV) by iron reducing bacteria was deduced based on the observations that the aqueous Fe(II) concentrations increased while the U(VI) concentrations decreased. The Fe(II) produced by the iron reducing bacteria was assumed to be reoxidized by the oxygen released from the roots. Advanced spectroscopic analyses revealed that a significant fraction of the U(VI) had been reduced to U(IV) and they were commonly deposited in association with phosphorus on the iron plaque.
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Affiliation(s)
- Hyun-shik Chang
- Savannah River Ecology Laboratory, University of Georgia , P.O. Drawer E, Aiken, South Carolina 29802, United States
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16
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Latta DE, Mishra B, Cook RE, Kemner KM, Boyanov MI. Stable U(IV) complexes form at high-affinity mineral surface sites. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:1683-91. [PMID: 24404905 DOI: 10.1021/es4047389] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Uranium (U) poses a significant contamination hazard to soils, sediments, and groundwater due to its extensive use for energy production. Despite advances in modeling the risks of this toxic and radioactive element, lack of information about the mechanisms controlling U transport hinders further improvements, particularly in reducing environments where U(IV) predominates. Here we establish that mineral surfaces can stabilize the majority of U as adsorbed U(IV) species following reduction of U(VI). Using X-ray absorption spectroscopy and electron imaging analysis, we find that at low surface loading, U(IV) forms inner-sphere complexes with two metal oxides, TiO2 (rutile) and Fe3O4 (magnetite) (at <1.3 U nm(-2) and <0.037 U nm(-2), respectively). The uraninite (UO2) form of U(IV) predominates only at higher surface loading. U(IV)-TiO2 complexes remain stable for at least 12 months, and U(IV)-Fe3O4 complexes remain stable for at least 4 months, under anoxic conditions. Adsorbed U(IV) results from U(VI) reduction by Fe(II) or by the reduced electron shuttle AH2QDS, suggesting that both abiotic and biotic reduction pathways can produce stable U(IV)-mineral complexes in the subsurface. The observed control of high-affinity mineral surface sites on U(IV) speciation helps explain the presence of nonuraninite U(IV) in sediments and has important implications for U transport modeling.
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Affiliation(s)
- Drew E Latta
- Biosciences Division, Argonne National Laboratory , Argonne, Illinois 60439, United States
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17
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Wu WM, Watson DB, Luo J, Carley J, Mehlhorn T, Kitanidis PK, Jardine PM, Criddle CS. Surge block method for controlling well clogging and sampling sediment during bioremediation. WATER RESEARCH 2013; 47:6566-6573. [PMID: 24070865 DOI: 10.1016/j.watres.2013.08.033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Revised: 08/20/2013] [Accepted: 08/24/2013] [Indexed: 06/02/2023]
Abstract
A surge block treatment method (i.e. inserting a solid rod plunger with a flat seal that closely fits the casing interior into a well and stocking it up and down) was performed for the rehabilitation of wells clogged with biomass and for the collection of time series sediment samples during in situ bioremediation tests for U(VI) immobilization at a the U.S. Department of Energy site in Oak Ridge, TN. The clogging caused by biomass growth had been controlled by using routine surge block treatment for 18 times over a nearly four year test period. The treatment frequency was dependent of the dosage of electron donor injection and microbial community developed in the subsurface. Hydraulic tests showed that the apparent aquifer transmissivity at a clogged well with an inner diameter (ID) of 10.16 cm was increased by 8-13 times after the rehabilitation, indicating the effectiveness of the rehabilitation. Simultaneously with the rehabilitation, the surge block method was successfully used for collecting time series sediment samples composed of fine particles (clay and silt) from wells with ID 1.9-10.16 cm for the analysis of mineralogical and geochemical composition and microbial community during the same period. Our results demonstrated that the surge block method provided a cost-effective approach for both well rehabilitation and frequent solid sampling at the same location.
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Affiliation(s)
- Wei-Min Wu
- Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020, USA; Center for Sustainable Development and Global Competitiveness, Stanford University, Stanford, CA 94305-4020, USA.
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18
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Watson DB, Wu WM, Mehlhorn T, Tang G, Earles J, Lowe K, Gihring TM, Zhang G, Phillips J, Boyanov MI, Spalding BP, Schadt C, Kemner KM, Criddle CS, Jardine PM, Brooks SC. In situ bioremediation of uranium with emulsified vegetable oil as the electron donor. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:6440-6448. [PMID: 23697787 DOI: 10.1021/es3033555] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A field test with a one-time emulsified vegetable oil (EVO) injection was conducted to assess the capacity of EVO to sustain uranium bioreduction in a high-permeability gravel layer with groundwater concentrations of (mM) U, 0.0055; Ca, 2.98; NO3(-), 0.11; HCO3(-), 5.07; and SO4(2-), 1.23. Comparison of bromide and EVO migration and distribution indicated that a majority of the injected EVO was retained in the subsurface from the injection wells to 50 m downgradient. Nitrate, uranium, and sulfate were sequentially removed from the groundwater within 1-2 weeks, accompanied by an increase in acetate, Mn, Fe, and methane concentrations. Due to the slow release and degradation of EVO with time, reducing conditions were sustained for approximately one year, and daily U discharge to a creek, located approximately 50 m from the injection wells, decreased by 80% within 100 days. Total U discharge was reduced by 50% over the one-year period. Reduction of U(VI) to U(IV) was confirmed by synchrotron analysis of recovered aquifer solids. Oxidants (e.g., dissolved oxygen, nitrate) flowing in from upgradient appeared to reoxidize and remobilize uranium after the EVO was exhausted as evidenced by a transient increase of U concentration above ambient values. Occasional (e.g., annual) EVO injection into a permeable Ca and bicarbonate-containing aquifer can sustain uranium bioreduction/immobilization and decrease U migration/discharge.
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Affiliation(s)
- David B Watson
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6038, United States.
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19
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Bioremediation of uranium-contaminated groundwater: a systems approach to subsurface biogeochemistry. Curr Opin Biotechnol 2013; 24:489-97. [DOI: 10.1016/j.copbio.2012.10.008] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2012] [Accepted: 10/09/2012] [Indexed: 11/18/2022]
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20
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Latta DE, Pearce CI, Rosso KM, Kemner KM, Boyanov MI. Reaction of U(VI) with titanium-substituted magnetite: influence of Ti on U(IV) speciation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:4121-4130. [PMID: 23597442 DOI: 10.1021/es303383n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Reduction of hexavalent uranium (U(VI)) to less soluble tetravalent uranium (U(IV)) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for U(VI). Natural magnetites are often impure with titanium, and structural Fe(3+) replacement by Ti(IV) yields a proportional increase in the relative Fe(2+) content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe(2+)/Fe(3+) ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 - xTixO4) reduce U(VI) to U(IV). The U(VI)-Fe(2+) redox reactivity was found to be controlled directly by R but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where U(VI) was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25-0.53) results in the formation of U(IV) species that lack the bidentate U-O2-U bridges of uraninite. Extended X-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound U(IV) phase has a novel U(IV)-Ti binding geometry different from the coordination of U(IV) in the mineral brannerite (U(IV)Ti2O6). The observed U(IV)-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation U(IV) complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced U(IV) phase. The formation of the non-uraninite U(IV)-Ti phase appears to be controlled by availability of surface Ti sites rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of U(IV) and suggests that further work to characterize the long-term stability of U(IV) phases formed in the presence of Ti is warranted.
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Affiliation(s)
- Drew E Latta
- Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
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21
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Tang G, Wu WM, Watson DB, Parker JC, Schadt CW, Shi X, Brooks SC. U(VI) bioreduction with emulsified vegetable oil as the electron donor--microcosm tests and model development. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:3209-3217. [PMID: 23397992 DOI: 10.1021/es304641b] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We conducted microcosm tests and biogeochemical modeling to study U(VI) reduction in contaminated sediments amended with emulsified vegetable oil (EVO). Indigenous microorganisms in the sediments degraded EVO and stimulated Fe(III), U(VI), and sulfate reduction, and methanogenesis. Acetate concentration peaked in 100-120 days in the EVO microcosms versus 10-20 days in the oleate microcosms, suggesting that triglyceride hydrolysis was a rate-limiting step in EVO degradation and subsequent reactions. Acetate persisted 50 days longer in oleate- and EVO- than in ethanol-amended microcosms, indicating that acetate-utilizing methanogenesis was slower in the oleate and EVO than ethanol microcosms. We developed a comprehensive biogeochemical model to couple EVO hydrolysis, production, and oxidation of long-chain fatty acids (LCFA), glycerol, acetate, and hydrogen, reduction of Fe(III), U(VI) and sulfate, and methanogenesis with growth and decay of multiple functional microbial groups. By estimating EVO, LCFA, and glycerol degradation rate coefficients, and introducing a 100 day lag time for acetoclastic methanogenesis for oleate and EVO microcosms, the model approximately matched observed sulfate, U(VI), and acetate concentrations. Our results confirmed that EVO could stimulate U(VI) bioreduction in sediments and the slow EVO hydrolysis and acetate-utilizing methanogens growth could contribute to longer term bioreduction than simple substrates (e.g., ethanol, acetate, etc.) in the subsurface.
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Affiliation(s)
- Guoping Tang
- Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, MS-6038, Oak Ridge, Tennessee 37831-6038, United States.
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22
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Zachara JM, Long PE, Bargar J, Davis JA, Fox P, Fredrickson JK, Freshley MD, Konopka AE, Liu C, McKinley JP, Rockhold ML, Williams KH, Yabusaki SB. Persistence of uranium groundwater plumes: contrasting mechanisms at two DOE sites in the groundwater-river interaction zone. JOURNAL OF CONTAMINANT HYDROLOGY 2013; 147:45-72. [PMID: 23500840 DOI: 10.1016/j.jconhyd.2013.02.001] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 01/10/2013] [Accepted: 02/06/2013] [Indexed: 05/22/2023]
Abstract
We examine subsurface uranium (U) plumes at two U.S. Department of Energy sites that are located near large river systems and are influenced by groundwater-river hydrologic interaction. Following surface excavation of contaminated materials, both sites were projected to naturally flush remnant uranium contamination to levels below regulatory limits (e.g., 30 μg/L or 0.126 μmol/L; U.S. EPA drinking water standard), with 10 years projected for the Hanford 300 Area (Columbia River) and 12 years for the Rifle site (Colorado River). The rate of observed uranium decrease was much lower than expected at both sites. While uncertainty remains, a comparison of current understanding suggests that the two sites have common, but also different mechanisms controlling plume persistence. At the Hanford 300 A, the persistent source is adsorbed U(VI) in the vadose zone that is released to the aquifer during spring water table excursions. The release of U(VI) from the vadose zone and its transport within the oxic, coarse-textured aquifer sediments is dominated by kinetically-limited surface complexation. Modeling implies that annual plume discharge volumes to the Columbia River are small (<one pore volume). At the Rifle site, slow oxidation of naturally reduced, contaminant U(IV) in the saturated zone and a continuous influx of U(VI) from natural, up-gradient sources influence plume persistence. Rate-limited mass transfer and surface complexation also control U(VI) migration velocity in the sub-oxic Rifle groundwater. Flux of U(VI) from the vadose zone at the Rifle site may be locally important, but it is not the dominant process that sustains the plume. A wide range in microbiologic functional diversity exists at both sites. Strains of Geobacter and other metal reducing bacteria are present at low natural abundance that are capable of enzymatic U(VI) reduction in localized zones of accumulated detrital organic carbon or after organic carbon amendment. Major differences between the sites include the geochemical nature of residual, contaminant U; the rates of current kinetic processes (both biotic and abiotic) influencing U(VI) solid-liquid distribution; the presence of detrital organic matter and the resulting spatial heterogeneity in microbially-driven redox properties; and the magnitude of groundwater hydrologic dynamics controlled by river-stage fluctuations, geologic structures, and aquifer hydraulic properties. The comparative analysis of these sites provides important guidance to the characterization, understanding, modeling, and remediation of groundwater contaminant plumes influenced by surface water interaction that are common world-wide.
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Affiliation(s)
- John M Zachara
- Pacific Northwest National Laboratory, Richland, WA 99354, USA.
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23
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Shiel AE, Laubach PG, Johnson TM, Lundstrom CC, Long PE, Williams KH. No measurable changes in (238)U/(235)U due to desorption-adsorption of U(VI) from groundwater at the Rifle, Colorado, integrated field research challenge site. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:2535-2541. [PMID: 23379698 DOI: 10.1021/es303913y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Groundwater samples were collected from the Integrated Field Research Challenge field site in Rifle, Colorado, over the course of a bicarbonate-induced U desorption-adsorption experiment. Uranium concentrations and high precision U isotopic compositions ((238)U/(235)U) of these groundwater samples were determined and used to assess the impact of bicarbonate-induced U(VI) desorption from contaminated sediments on the (238)U/(235)U of groundwater. The (238)U/(235)U of groundwater was not significantly impacted by bicarbonate-induced desorption of U(VI) from mineral surfaces or by adsorption of advecting U(VI) from upgradient locations onto those surfaces after the treatment. Assuming this absence of a significant shift in U isotopic composition associated with desorption-adsorption applies to other systems, reduction of U(VI) to U(IV) is expected to be the dominant source of U isotopic fractionation associated with removal of U(VI) from pore water as a result of natural and stimulated reductive pathways. Thus, changes in the (238)U/(235)U composition of uranium-bearing fluids should be useful in quantifying the extent of reduction.
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Affiliation(s)
- Alyssa E Shiel
- Department of Geology, University of Illinois at Urbana-Champaign , 208 Natural History Building, 1301 West Green Street, Urbana, Illinois 61801, USA.
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24
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Bargar JR, Williams KH, Campbell KM, Long PE, Stubbs JE, Suvorova EI, Lezama-Pacheco JS, Alessi DS, Stylo M, Webb SM, Davis JA, Giammar DE, Blue LY, Bernier-Latmani R. Uranium redox transition pathways in acetate-amended sediments. Proc Natl Acad Sci U S A 2013; 110:4506-4511. [PMCID: PMC3607047 DOI: 10.1073/pnas.1219198110] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/05/2023] Open
Abstract
Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth’s geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing conditions. Based on molecular-scale spectroscopic, pore-scale geochemical, and macroscale aqueous evidence, we propose a biotic–abiotic transition pathway in which biomass-hosted mackinawite (FeS) is an electron source to reduce U(VI) to U(IV), which subsequently reacts with biomass to produce monomeric U(IV) species. A species resembling nanoscale uraninite is also present, implying the operation of at least two redox transition pathways. The presence of multiple pathways in low-temperature sediments unifies apparently contrasting prior observations and helps to explain sustained uranium reduction under disparate biogeochemical conditions. These findings have direct implications for our understanding of uranium bioremediation, ore formation, and global geochemical processes.
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Affiliation(s)
- John R. Bargar
- Chemistry and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
| | - Kenneth H. Williams
- Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | | | - Philip E. Long
- Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Joanne E. Stubbs
- Chemistry and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
| | - ElenaI I. Suvorova
- Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; and
| | - Juan S. Lezama-Pacheco
- Chemistry and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
| | - Daniel S. Alessi
- Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; and
| | - Malgorzata Stylo
- Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; and
| | - Samuel M. Webb
- Chemistry and Catalysis Division, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
| | - James A. Davis
- Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Daniel E. Giammar
- Department of Energy, Environmental and Chemical Engineering, Washington University, Saint Louis, MO 63130
| | - Lisa Y. Blue
- Department of Energy, Environmental and Chemical Engineering, Washington University, Saint Louis, MO 63130
| | - Rizlan Bernier-Latmani
- Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; and
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Llorens I, Untereiner G, Jaillard D, Gouget B, Chapon V, Carriere M. Uranium interaction with two multi-resistant environmental bacteria: Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris. PLoS One 2012; 7:e51783. [PMID: 23251623 PMCID: PMC3520905 DOI: 10.1371/journal.pone.0051783] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Accepted: 11/06/2012] [Indexed: 11/28/2022] Open
Abstract
Depending on speciation, U environmental contamination may be spread through the environment or inversely restrained to a limited area. Induction of U precipitation via biogenic or non-biogenic processes would reduce the dissemination of U contamination. To this aim U oxidation/reduction processes triggered by bacteria are presently intensively studied. Using X-ray absorption analysis, we describe in the present article the ability of Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris, highly resistant to a variety of metals and metalloids or to organic pollutants, to withstand high concentrations of U and to immobilize it either through biosorption or through reduction to non-uraninite U(IV)-phosphate or U(IV)-carboxylate compounds. These bacterial strains are thus good candidates for U bioremediation strategies, particularly in the context of multi-pollutant or mixed-waste contaminations.
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Affiliation(s)
- Isabelle Llorens
- ESRF-CRG-FAME, Polygone Scientifique Louis Néel, Grenoble, France
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26
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Abstract
The in situ stimulation of Fe(III) oxide reduction in the subsurface stimulates the growth of Geobacter spp. and the precipitation of U(VI) from groundwater. As with Fe(III) oxide reduction, the reduction of uranium by Geobacter spp. requires the expression of their conductive pili. The pili bind the soluble uranium and catalyse its extracellular reductive precipitation along the pili filaments as a mononuclear U(IV) complexed by carbon-containing ligands. Although most of the uranium is immobilized by the pili, some uranium deposits are also observed in discreet regions of the outer membrane, consistent with the participation of redox-active foci, presumably c-type cytochromes, in the extracellular reduction of uranium. It is unlikely that cytochromes released from the outer membrane could associate with the pili and contribute to the catalysis, because scanning tunnelling microscopy spectroscopy did not reveal any haem-specific electronic features in the pili, but, rather, showed topographic and electronic features intrinsic to the pilus shaft. Pili not only enhance the rate and extent of uranium reduction per cell, but also prevent the uranium from traversing the outer membrane and mineralizing the cell envelope. As a result, pili expression preserves the essential respiratory activities of the cell envelope and the cell's viability. Hence the results support a model in which the conductive pili function as the primary mechanism for the reduction of uranium and cellular protection in Geobacter spp.
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27
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Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism. Proc Natl Acad Sci U S A 2011; 108:15248-52. [PMID: 21896750 DOI: 10.1073/pnas.1108616108] [Citation(s) in RCA: 149] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The in situ stimulation of Fe(III) oxide reduction by Geobacter bacteria leads to the concomitant precipitation of hexavalent uranium [U(VI)] from groundwater. Despite its promise for the bioremediation of uranium contaminants, the biological mechanism behind this reaction remains elusive. Because Fe(III) oxide reduction requires the expression of Geobacter's conductive pili, we evaluated their contribution to uranium reduction in Geobacter sulfurreducens grown under pili-inducing or noninducing conditions. A pilin-deficient mutant and a genetically complemented strain with reduced outer membrane c-cytochrome content were used as controls. Pili expression significantly enhanced the rate and extent of uranium immobilization per cell and prevented periplasmic mineralization. As a result, pili expression also preserved the vital respiratory activities of the cell envelope and the cell's viability. Uranium preferentially precipitated along the pili and, to a lesser extent, on outer membrane redox-active foci. In contrast, the pilus-defective strains had different degrees of periplasmic mineralization matching well with their outer membrane c-cytochrome content. X-ray absorption spectroscopy analyses demonstrated the extracellular reduction of U(VI) by the pili to mononuclear tetravalent uranium U(IV) complexed by carbon-containing ligands, consistent with a biological reduction. In contrast, the U(IV) in the pilin-deficient mutant cells also required an additional phosphorous ligand, in agreement with the predominantly periplasmic mineralization of uranium observed in this strain. These findings demonstrate a previously unrecognized role for Geobacter conductive pili in the extracellular reduction of uranium, and highlight its essential function as a catalytic and protective cellular mechanism that is of interest for the bioremediation of uranium-contaminated groundwater.
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28
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Du X, Boonchayaanant B, Wu WM, Fendorf S, Bargar J, Criddle CS. Reduction of uranium(VI) by soluble iron(II) conforms with thermodynamic predictions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:4718-4725. [PMID: 21553877 DOI: 10.1021/es2006012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Soluble Fe(II) can reduce soluble U(VI) at rapid rates and in accordance with thermodynamic predictions. This was established by initially creating acidic aqueous solutions in which the sole oxidants were soluble U(VI) species and the sole reductants were soluble Fe(II) species. The pH of the solution was then increased by stepwise addition of OH(-), thereby increasing the potential for electron transfer from Fe(II) to U(VI). For each new pH value resulting from addition of base, values of ΔG for the Fe(II)-mediated reduction of U(VI) were calculated using the computed distribution of U and Fe species and possible half reaction combinations. For initial conditions of pH 2.4 and a molar ratio of Fe(II) to U(VI) of 5:1 (1 mM Fe(II) and 0.2 mM U(VI)), ΔG for U(VI) reduction was greater than zero, and U(VI) reduction was not observed. When sufficient OH(-) was added to exceed the computed equilibrium pH of 5.4, ΔG for U(VI) reduction was negative and soluble Fe(II) species reacted with U(VI) in a molar ratio of ∼2:1. X-ray absorption near-edge structure (XANES) spectroscopy confirmed production of U(IV). A decrease in pH confirmed production of acidity as the reaction advanced. As solution pH decreased to the equilibrium value, the rate of reaction declined, stopping completely at the predicted equilibrium pH. Initiation of the reaction at a higher pH resulted in a higher final ratio of U(IV) to U(VI) at equilibrium.
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Affiliation(s)
- Xin Du
- Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, USA
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29
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Luo W, Gu B. Dissolution of uranium-bearing minerals and mobilization of uranium by organic ligands in a biologically reduced sediment. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:2994-2999. [PMID: 21395303 DOI: 10.1021/es103073u] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The stability and mobility of uranium (U) is a concern following its reductive precipitation or immobilization by techniques such as bioremediation at contaminated sites. In this study, the influences of complexing organic ligands such as citrate and ethylenediaminetetraacetate (EDTA) on the mobilization of U were investigated in both batch and column flow systems using a contaminated and bioreduced sediment. Results indicate that both reduced U(IV) and oxidized U(VI) in the sediment can be effectively mobilized with the addition of EDTA or citrate under anaerobic conditions. The dissolution and mobilization of U appear to be correlated to the dissolution of iron (Fe)- or aluminum (Al)-bearing minerals, with EDTA being more effective (with R2≥0.89) than citrate (R2<0.60) in dissolving these minerals. The column flow experiments confirm that U, Fe, and Al can be mobilized by these ligands under anoxic conditions, although the cumulative amounts of U removal constituted ∼0.1% of total U present in this sediment following a limited period of leaching. This study concludes that the presence of complexing organic ligands may pose a long-term concern by slowly dissolving U-bearing minerals and mobilizing U even under a strict anaerobic environment.
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Affiliation(s)
- Wensui Luo
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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30
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Picard A, Daniel I, Testemale D, Kieffer I, Bleuet P, Cardon H, Oger PM. Monitoring microbial redox transformations of metal and metalloid elements under high pressure using in situ X-ray absorption spectroscopy. GEOBIOLOGY 2011; 9:196-204. [PMID: 21231995 DOI: 10.1111/j.1472-4669.2010.00270.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
X-ray absorption spectroscopy is a well-established method for probing local structural and electronic atomic environments in a variety of systems. We used X-ray absorption near-edge structure (XANES) spectroscopy for monitoring in real-time conditions selenium reduction in situ in live cultures of Shewanella oneidensis MR-1 under high hydrostatic pressure. High-quality XANES data show that Shewanella oneidensis MR-1 reduces selenite Se(IV) to red elemental selenium Se(0) up to 150 MPa without any intermediate redox state. MR-1 reduces all selenite provided (5-10 mM) between 0.1 and 60 MPa. Above 60 MPa the selenite reduction yield decreases linearly with pressure and the activity is calculated to stop at 155 ± 5 MPa. The analysis of cultures recovered after in situ measurements showed that the decrease in activity is linked to a decrease in viability. This study emphasizes the promising potential of XANES spectroscopy for real-time probing in situ microbial redox transformations of a broad range of metal and metalloid elements in live samples, including under high hydrostatic pressure.
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Affiliation(s)
- A Picard
- Laboratoire de Sciences de la Terre, Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS, Université Lyon 1, Lyon, France.
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31
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Bernier-Latmani R, Veeramani H, Vecchia ED, Junier P, Lezama-Pacheco JS, Suvorova EI, Sharp JO, Wigginton NS, Bargar JR. Non-uraninite products of microbial U(VI) reduction. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010; 44:9456-9462. [PMID: 21069950 DOI: 10.1021/es101675a] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A promising remediation approach to mitigate subsurface uranium contamination is the stimulation of indigenous bacteria to reduce mobile U(VI) to sparingly soluble U(IV). The product of microbial uranium reduction is often reported as the mineral uraninite. Here, we show that the end products of uranium reduction by several environmentally relevant bacteria (Gram-positive and Gram-negative) and their spores include a variety of U(IV) species other than uraninite. U(IV) products were prepared in chemically variable media and characterized using transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) to elucidate the factors favoring/inhibiting uraninite formation and to constrain molecular structure/composition of the non-uraninite reduction products. Molecular complexes of U(IV) were found to be bound to biomass, most likely through P-containing ligands. Minor U(IV)-orthophosphates such as ningyoite [CaU(PO(4))(2)], U(2)O(PO(4))(2), and U(2)(PO(4))(P(3)O(10)) were observed in addition to uraninite. Although factors controlling the predominance of these species are complex, the presence of various solutes was found to generally inhibit uraninite formation. These results suggest a new paradigm for U(IV) in the subsurface, i.e., that non-uraninite U(IV) products may be found more commonly than anticipated. These findings are relevant for bioremediation strategies and underscore the need for characterizing the stability of non-uraninite U(IV) species in natural settings.
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Affiliation(s)
- Rizlan Bernier-Latmani
- Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH 1015, Switzerland.
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32
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Significant association between sulfate-reducing bacteria and uranium-reducing microbial communities as revealed by a combined massively parallel sequencing-indicator species approach. Appl Environ Microbiol 2010; 76:6778-86. [PMID: 20729318 DOI: 10.1128/aem.01097-10] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Massively parallel sequencing has provided a more affordable and high-throughput method to study microbial communities, although it has mostly been used in an exploratory fashion. We combined pyrosequencing with a strict indicator species statistical analysis to test if bacteria specifically responded to ethanol injection that successfully promoted dissimilatory uranium(VI) reduction in the subsurface of a uranium contamination plume at the Oak Ridge Field Research Center in Tennessee. Remediation was achieved with a hydraulic flow control consisting of an inner loop, where ethanol was injected, and an outer loop for flow-field protection. This strategy reduced uranium concentrations in groundwater to levels below 0.126 μM and created geochemical gradients in electron donors from the inner-loop injection well toward the outer loop and downgradient flow path. Our analysis with 15 sediment samples from the entire test area found significant indicator species that showed a high degree of adaptation to the three different hydrochemical-created conditions. Castellaniella and Rhodanobacter characterized areas with low pH, heavy metals, and low bioactivity, while sulfate-, Fe(III)-, and U(VI)-reducing bacteria (Desulfovibrio, Anaeromyxobacter, and Desulfosporosinus) were indicators of areas where U(VI) reduction occurred. The abundance of these bacteria, as well as the Fe(III) and U(VI) reducer Geobacter, correlated with the hydraulic connectivity to the substrate injection site, suggesting that the selected populations were a direct response to electron donor addition by the groundwater flow path. A false-discovery-rate approach was implemented to discard false-positive results by chance, given the large amount of data compared.
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