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Microbial reduction of intragrain U(VI) in contaminated sediment
Chongxuan Liu1, John M Zachara, Lirong Zhong
1Pacific Northwest National Laboratory, Richland, Washington 99352, USA. Chongxuan.liu@pnl.gov
Environmental Science & Technology
|August 14, 2009
Summary
Microbial reduction of uranium (U(VI)) in Hanford sediment is slow due to intragrain precipitates and geochemical factors. Two pathways control U(VI) bioavailability and bioreduction rates.
Area of Science:
- Environmental Science
- Geochemistry
- Microbiology
Background:
- Uranium (U(VI)) contamination at DOE sites like Hanford poses environmental risks.
- Intragrain uranyl precipitates within sediment fragments limit U(VI) accessibility.
- Understanding U(VI) bioavailability is crucial for remediation strategies.
Purpose of the Study:
- Investigate the accessibility of intragrain U(VI) to microbial reduction.
- Determine geochemical and microscopic transport phenomena controlling U(VI) bioavailability.
- Elucidate mechanisms of U(VI) bioreduction in contaminated sediments.
Main Methods:
- Collected sediment from the U.S. Department of Energy Hanford site.
- Utilized Shewanellea oneidensis strain MR-1 for bioreduction experiments.
- Measured uranium concentration, speciation, and valence in aqueous and solid phases.
Main Results:
- Microbial reduction of intragrain U(VI) occurred via two pathways: dissolution-diffusion-reduction and intragrain reduction by biogenic reductants.
- Bioreduction rates were over 3 orders of magnitude slower than in aqueous solutions.
- Slower rates were linked to calcium release altering U(VI) speciation and alternative electron transfer pathways.
Conclusions:
- Reactive mass transfer and geochemical reactions significantly influence intragrain U(VI) bioreduction rates.
- U(VI) bioavailability is controlled by complex interactions between microbial activity and sediment geochemistry.
- Findings inform strategies for managing uranium-contaminated sediments.
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