title: Speciation and reactivity of uranium products formed during in situ bioremediation in a shallow alluvial aquifer.
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.
authors.affiliation: Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne , CH-1015, Lausanne, Switzerland.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Alessi
authors.forename: Juan S
authors.initials: JS
authors.lastname: Lezama-Pacheco
authors.forename: Noémie
authors.initials: N
authors.lastname: Janot
authors.forename: Elena I
authors.initials: EI
authors.lastname: Suvorova
authors.forename: José M
authors.initials: JM
authors.lastname: Cerrato
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Giammar
authors.forename: James A
authors.initials: JA
authors.lastname: Davis
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Fox
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Williams
authors.forename: Philip E
authors.initials: PE
authors.lastname: Long
authors.forename: Kim M
authors.initials: KM
authors.lastname: Handley
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmani
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
mesh_terms: D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D003120:Colorado; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry*; D008670:Metals / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D013052:Spectrometry, X-Ray Emission; D013431:Sulfates / Q000378:metabolism; D014501:Uranium / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D008670:Metals; D013431:Sulfates; D014875:Water Pollutants, Radioactive; D014501:Uranium