title: Uranium reduction in sediments under diffusion-limited transport of organic carbon.
abstract: Costly disposal of uranium (U) contaminated sediments is motivating research on in situ U(VI) reduction to insoluble U(IV) via directly or indirectly microbially mediated pathways. Delivery of organic carbon (OC) into sediments for stimulating U bioreduction is diffusion-limited in less permeable regions of the subsurface. To study OC-based U reduction in diffusion-limited regions, one slightly acidic and another calcareous sediment were treated with uranyl nitrate, packed into columns, then hydrostatically contacted with tryptic soy broth solutions. Redox potentials, U oxidation state, and microbial communities were well correlated. At average supply rates of 0.9 micromol OC (g sediment)(-1) day(-1), the U reduction zone extended to only about35-45 mm into sediments. The underlying unreduced U(VI) zone persisted over 600 days because the supply of OC was diffusion-limited and metabolized within a short distance. These results also suggestthat low U concentrations in groundwater samples from OC-treated sediments are not necessarily indicative of pervasive U reduction because interior and exterior regions of such sediment blocks can contain primarily U(VI) and U(IV), respectively.
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. tktokunaga@lbl.gov
authors.forename: Tetsu K
authors.initials: TK
authors.lastname: Tokunaga
authors.forename: Jiamin
authors.initials: J
authors.lastname: Wan
authors.forename: Jasquelin
authors.initials: J
authors.lastname: Pena
authors.forename: Eoin L
authors.initials: EL
authors.lastname: Brodie
authors.forename: Mary K
authors.initials: MK
authors.lastname: Firestone
authors.forename: Terry C
authors.initials: TC
authors.lastname: Hazen
authors.forename: Steve R
authors.initials: SR
authors.lastname: Sutton
authors.forename: Antonio
authors.initials: A
authors.lastname: Lanzirotti
authors.forename: Matthew
authors.initials: M
authors.lastname: Newville
mesh_terms: D001673:Biodegradation, Environmental; D001692:Biological Transport; D018533:Biomass; D002244:Carbon / Q000032:analysis*; D004058:Diffusion; D004577:Electron Probe Microanalysis; D019015:Geologic Sediments / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D009930:Organic Chemicals / Q000032:analysis*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis; D012988:Soil Microbiology; D012989:Soil Pollutants; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D014501:Uranium / Q000032:analysis*; D017974:Uranium Compounds / Q000032:analysis*; D014502:Uranyl Nitrate / Q000032:analysis
chemical_list: D009930:Organic Chemicals; D012989:Soil Pollutants; D012990:Soil Pollutants, Radioactive; D017974:Uranium Compounds; D014502:Uranyl Nitrate; D014501:Uranium; D002244:Carbon; D014357:Trypsin; D010100:Oxygen