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Anaerobic Biotransformation and Mobility of Pu and of Pu-EDTA

Anaerobic Biotransformation and Mobility of Pu and of Pu-EDTA, poster
Anaerobic Biotransformation and Mobility of Pu and Pu-EDTA. Download poster (PDF, 775K).

Harvey Bolton, Principal Investigator

The complexation of radionuclides, such as plutonium (Pu) and cobalt-60, by co-disposed ethylenediaminetetraacetate (EDTA) has enhanced radionuclide transport in sediments at U.S. Department of Energy (DOE) sites. In our previous Environmental Remediation Sciences Program (ERSP) studies, we investigated the aerobic biodegradation and biogeochemistry of Pu (IV)-EDTA. Plutonium(IV) forms stable complexes with EDTA under aerobic conditions and an aerobic EDTA-degrading bacterium can degrade EDTA in the presence of Pu and decrease Pu mobility. However, our recent studies indicate that while Pu (IV)-EDTA is stable in simple aqueous systems, it is not stable in the presence of relatively soluble iron(III) (Fe(III)) compounds. Since most DOE sites have Fe(III)-containing sediments, Pu(IV) cannot be the mobile form of Pu-EDTA in groundwater. The only other Pu-EDTA complex stable in groundwater relevant to DOE sites is Pu(III)-EDTA, which only forms under anaerobic conditions. Therefore, research is needed to investigate the biotransformation of Pu and Pu-EDTA under anaerobic conditions.

The Anaerobic Biotransformation and Mobility of Pu and Pu-EDTA project team at Pacific Northwest National Laboratory (PNNL) is addressing knowledge gaps about the biotransformation of Pu and Pu-EDTA under anaerobic conditions. By understanding these processes better, researchers can assess, model, and design approaches to stop Pu transport in groundwater at DOE sites. We are studying many aspects of the biotransformation of Pu and Pu-EDTA under various anaerobic conditions including:

  • the reduction kinetics of Pu(IV) to Pu(III) from soluble (Pu(IV)-EDTA) and insoluble Pu(IV) as PuO2(am) by metal-reducing bacteria
  • the redox conditions required for this reduction
  • the strength of the Pu(III)-EDTA complex
  • how the Pu(III)-EDTA complex competes with other dominant anoxic soluble metals (e.g., Fe(II))
  • the oxidation kinetics of Pu(III)-EDTA.

The formation of a stable, soluble Pu(III)-EDTA complex under anaerobic conditions would require degradation of the EDTA complex to limit Pu(III) transport in geologic environments. As part of this project, we are also working to isolate anaerobic EDTA-degrading microorganisms.

Information regarding the Anaerobic Biotransformation and Mobility of Pu and of Pu-EDTA project was obtained from its ERSP project page.

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