Anaerobic metal/radionuclide biooxidation (AM/ROx) has been demonstrated in a variety of environments. Subsurface sediments and groundwater (20-64ft.) were collected from a shallow aquifer near Alda, NE, containing nitrate (from fertilizer) and natural iron and uranium in order to evaluate the potential of AM/ROx and U mobility. The reduction potential revealed a reduced environment and was confirmed by the presence of Fe(II) and U(IV). Although sediments were reduced, nitrate persisted in the groundwater. Nitrate concentrations decreased, 38mg/L to 30mg/L, with increasing concentrations of Fe(II) and U(IV). Dissolved U, U(VI), increased with depth, 30.3�g/L to 302�g/L. Virtually all U in sediments existed as U(IV). The increase in aqueous U concentrations with depth suggests active U cycling. Tetravalent U (U(IV)) phases are stable in reduced environments; however oxidants such as oxygen or nitrate would oxidize reduced U. Co-occurrence of nitrate suggests that nitrate could serve as a U(IV) oxidant. Most probable number enumeration of nitrate-dependent U(IV) oxidizing microorganisms demonstrated an abundant community, 1.61x104 to 2.74x104 cells g-1 sediment. Enrichments initiated verified microbial U reduction and U oxidation coupled to nitrate reduction, oxidation (0-4,554�g/L) and reduction (0-55�g/L) of U. The oxidation of U(IV) could contribute to U mobilization and result in decreased drinking water quality.

Anaerobic metal/radionuclide biooxidation in shallow subsurface sediments

243rd National Meeting (2012)

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