Biotransformation of PuEDTA: Implications to Pu Immobilization Page: 2 of 3
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assess the distribution of Pu oxidation states in the microbial cultures used in goal 2
Efforts toward objective 2 have thus far used Shewanella oneidensis as the model
organism for establishing incubation parameters and the previously mentioned Pu
oxidation state fractionation protocol. S. oneidensis strain MR-1 was used to test the
hypothesis that it can reduce Pu(IV)O2(am) under anaerobic conditions. The ability of S.
oneidensis MR-1 to reduce Pu(IV) with and without AQDS (an electron shuttle), and
with and without EDTA (a likely co-contaminant) was determined in pure culture at near-
neutral conditions during incubations of less than one week. The electron shuttle AQDS
increased the rate and magnitude of Pu reduction. EDTA also enhanced rates and
magnitudes of biological Pu solubilization and reduction by increasing the solubilization
of Pu(IV) and Pu(III). S. oneidensis MR-1 reduced Pu(IV) to Pu(III) within 2 days of
exposure. AQDS, an electron shuttle, significantly increased reduction (solubilization) of
Pu(IV). In the biological system, EDTA significantly increased Pu(IV) reduction.
The progress toward the third objective is provided in a separate report, prepared by
The overall project outcomes may be briefly summarized,
1. Pu(III) solubility data was collected and used to develop a model that
demonstrated that PuEDTA- is the dominant species occurring within the range of
environmental conditions modeled.
2. S. oneidensis MR-1 rapidly reduced Pu(IV) in dilute aqueous systems. This
reduction was enhanced by the addition of electron donor (H2) and electron
3. Degradability of metal-EDTA is related to the formation of free EDTA to bind to
EppA for transport into the cell
As mentioned above, the experimental work to obtain thermodynamic equilibrium
constants for Pu(III)-EDTA complexes is nearly complete. The main emphasis under this
task for FY 2007 will be the thermodynamic interpretations of the data and drafting of
manuscripts for publication in the open literature. Three different manuscripts (effect of
Fe(III) on Pu(IV)-EDTA complexes important in Pu mobility in geologic environments,
solubility product of PuPO4(s), and Pu(III)-EDTA complexes) are planned.
Objective 2: By the end of December 2006 complete an assessment of the ability of
Geobacter to reduce Pu, and prepare a manuscript comparing this with the observed S.
oneidensis reduction in early 2007. We will also conduct further incubations with S.
oneidensis to determine the scope of its reductive potential in sediments by using
biogenic Fe as reducing agent in January/February 2007, and conduct incubations with a
range of terminal electron acceptors in the months following. We are planning to
determine Pu localization relative to cell physiology using electron microscopy; however,
current technical limitations are requiring us to archive samples while an appropriate lab
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Bolton, Harvey, Jr. Biotransformation of PuEDTA: Implications to Pu Immobilization, report, June 1, 2006; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc883642/m1/2/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.