Annual progress Report on research related to our research project “Stabilization of Plutonium in Subsurface Environments via Microbial Reduction and Biofilm Formation” funded by the Environmental Remediation Sciences Division (ERSD) Page: 4 of 7
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M0.4 , -
E0 25 E
- 020 .0 3-
E r 0.15 C
mM (B [Aet2e = 0m P(H4a) .0m .()Lv el wt h lcrndnr j )lv el ihn
U 010 /-
00 0 - - - - - - - - =.
Figure 4. Direct reduction of Pu(OH)4(am) by cell suspension of Shewanella oneidensis MR1 (A) and Geobacter 0
metallireducens GS15 (B) with 0.5 mM FDTA. Conditions: Cell density = 5x108 cell/mL, pH = 7.40, (A) [Lactate] = 10
mM, (B) [Acetate] = 10 m!IV [Pu(OH)4(am)] = 0.50 m!M. (A) Live cells with the electron donor, (A ) live cells with no
electron donor, (o)no cells control, (0) heat killed cells control.
2.1.4 Implications of plutonium reduction for the remediation of Pu and mixed
Pu, U sites. Microbial transformation of Pu hydrous oxides through direct and indirect
reduction can have dramatic consequences on the fate and transport of Pu in the
environment. Pu contamination present in the environment is mainly present as insoluble
Pu(IV) hydrous oxides or associated to colloids and its transport occurs mainly under
these forms. However, if Pu solids are present under anaerobic conditions and under
active bio-reduction conditions, the concentrations of soluble Pu can dramatically
increase. The presence of complexants, which are ubiquitous in biofilms, could
completely change the mode of Pu transport. Metal reducing bacteria examined here
were not able to use Pu species to support their growth and the reduction of
Pu(IV)(OH)4(am) was inefficient in the absence of complexants, but environmental
factors can significantly affect this process. Biogenic chelators are abundant in the
environment and some microorganisms produce large amounts of complexant as a
reaction to contaminants or for nutrient acquisition. For example bacteria and fungi
commonly produce siderophores for nutrient iron acquisition. Other organic complexing
agents such as polysaccharide, organic acids, amino carboxylic acids, and other natural
organic chelators are common is the environment. These ligands can play an important
role in mobilizing plutonium.
Under environmental conditions, it is unlikely that the concentration of Pu species
would be sufficiently high to sustain growth of metal reducing bacteria. However, most
microorganisms use Fe(III), Mn(IV), sulfate or nitrate species that are present in almost
all soil environments to support their growth. It is therefore possible that indirect
reduction of Pu species by reduced forms of Mn, Fe, or any reactive reduced substrates
produced by these organisms would have a big impact on Pu reduction and subsequent
solubilization. It is not known how Pu(III) would interact with various mineral surfaces
and its stability in the environment is also unknown especially in the presence of
complexants. We have demonstrated that Pu(III) can be produced by direct enzymatic
reduction but a lot remains to be done to fully understand the consequences of Pu
hydrous oxides reduction on the fate and transport of Pu in the environment. The
implications of Pu(IV) reduction for possible Pu mobilization at sites containing mixed
Pu, and U contamination needs further fundamental understanding, especially if
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New, Mary. Annual progress Report on research related to our research project “Stabilization of Plutonium in Subsurface Environments via Microbial Reduction and Biofilm Formation” funded by the Environmental Remediation Sciences Division (ERSD), report, June 1, 2006; Los Alamos, New Mexico. (digital.library.unt.edu/ark:/67531/metadc881377/m1/4/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.