The Application of Biotechnology to the Treatment of Wastes Produced from the Nuclear Fuel Cycle: Biodegradation and Bioaccumulation as a Means of Treating Radionuclide-Containing Streams

Macaskie, Lynne E.

doi:10.3109/07388559109069183

Cited by 222 publications

(105 citation statements)

References 161 publications

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“…Uranium (U) is chemically analogous to other actinides such as plutonium (Pu) and neptunium (Np) in terms of its redox properties and its strong tendency to form complexes with inorganic and organic ligands (Macaskie, 1991;Suzuki and Banfield, 1999;Lloyd and Macaskie, 2000). Thus, U serves as a valuable model for the behavior of actinides in complex natural systems.…”

Section: Introductionmentioning

confidence: 99%

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Suzuki

Suko

2006

Journal of Mineralogical and Petrological Sciences

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Understanding the behavior of uranium (U) in the environment is essential not only for the protection of aquifers from U contamination but also for predicting the fate of U and other actinides disposed of in deep geological settings. It has long been believed that the redox chemistry of U can be simply predicted by thermodynamics and that the development of a low redox potential is a sufficient condition for U reduction. However, recent studies have demonstrated that redox transformations of U are controlled by kinetic factors that are strongly influenced by microbial activity. Although abiological U oxidation proceeds efficiently under oxygenic conditions, abiological reduction of U is inhibited by the formation of negatively charged U(VI) CO 3 complexes that prevail in nature. Phylogenetically diverse microorganisms are capable of enzymatically reducing U(VI) CO 3 complexes to form U(IV) bearing minerals such as uraninite (UO 2+x . This complex is mainly produced by the microbial reduction of Fe(III) in natural systems. Thus, U(VI) reduction is controlled both directly and indirectly, at least in part, by microbial activity. Several mechanisms of U oxidation under anoxic conditions have been revealed recently by laboratory and field studies. U(IV) is abiologically oxidized by Fe(III) and Mn(IV) oxides. Microbial reduction of nitrate to molecular nitrogen, which occurs following the depletion of O 2 , produces nitrogen intermediates including nitrite (NO 2 -), nitrous oxide (NO), and nitric oxide (N 2 O). Although the nitrogen intermediates oxidize U(IV), poorly crystalline Fe(III) oxide minerals resulting from the oxidation of aqueous Fe(II) species by the nitrogen intermediates oxidize U(IV) more efficiently than the nitrogen intermediates alone. Remarkably, the formation of Ca U(VI) CO 3 complexes resulting from increased levels of Ca 2+ and/or HCO 3 -leads to the reoxidation of bioreduced U(IV) under reducing conditions. These geomicrobiological factors pose challenges in manipulating and/or predicting the mobility and fate of U in complex and heterogeneous environmental settings.

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Section: Introductionmentioning

confidence: 99%

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Suzuki

Suko

2006

Journal of Mineralogical and Petrological Sciences

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“…In its most stable form, Tc(VII), typified by the pertechnetate ion (TcO 4 Ϫ ), is highly soluble and mobile in the environment (27). This factor, in combination with a long halflife (2.1 ϫ 10 5 years) and high biological availability as a sulfate analog (3), makes removal at the source necessary.…”

mentioning

confidence: 99%

“…An approach to achieve the removal of Tc(VII) from aqueous solution may be to use metal-reducing microorganisms to reduce the radionuclide to an insoluble oxide (25,27). For example, TcO, TcO 2 , and Tc 2 O 5 all form insoluble precipitates at neutral pH (20,29,41).…”

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confidence: 99%

Reduction and removal of heptavalent technetium from solution by Escherichia coli

1997

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Anaerobic, but not aerobic, cultures of Escherichia coli accumulated Tc(VII) and reduced it to a black insoluble precipitate. Tc was the predominant element detected when the precipitate was analyzed by protoninduced X-ray emission. Electron microscopy in combination with energy-dispersive X-ray analysis showed that the site of Tc deposition was intracellular. It is proposed that Tc precipitation was a result of enzymatically mediated reduction of Tc(VII) to an insoluble oxide. Formate was an effective electron donor for Tc(VII) reduction which could be replaced by pyruvate, glucose, or glycerol but not by acetate, lactate, succinate, or ethanol. Mutants defective in the synthesis of the transcription factor FNR, in molybdenum cofactor (molybdopterin guanine dinucleotide [MGD]) synthesis, or in formate dehydrogenase H synthesis were all defective in Tc(VII) reduction, implicating a role for the formate hydrogenlyase complex in Tc(VII) reduction. The following observations confirmed that the hydrogenase III (Hyc) component of formate hydrogenlyase is both essential and sufficient for Tc(VII) reduction: (i) dihydrogen could replace formate as an effective electron donor for Tc(VII) reduction by wild-type bacteria and mutants defective in MGD synthesis; (ii) the inability of fnr mutants to reduce Tc(VII) can be suppressed phenotypically by growth with 250 M Ni 2؉ and formate; (iii) Tc(VII) reduction is defective in a hyc mutant; (iv) the ability to reduce Tc(VII) was repressed during anaerobic growth in the presence of nitrate, but this repression was counteracted by the addition of formate to the growth medium; (v) H 2 , but not formate, was an effective electron donor for a Sel ؊ mutant which is unable to incorporate selenocysteine into any of the three known formate dehydrogenases of E. coli. This appears to be the first report of Hyc functioning as an H 2 -oxidizing hydrogenase or as a dissimilatory metal ion reductase in enteric bacteria.The long-lived ␤-emitter technetium ( 99 Tc), a fission product of 235 uranium, is produced during the generation of nuclear power. In its most stable form, Tc(VII), typified by the pertechnetate ion (TcO 4 Ϫ ), is highly soluble and mobile in the environment (27). This factor, in combination with a long halflife (2.1 ϫ 10 5 years) and high biological availability as a sulfate analog (3), makes removal at the source necessary. From a recent study, it was concluded that Tc may be the critical radionuclide in determining the long-term impact of the nuclear fuel cycle (45).An approach to achieve the removal of Tc(VII) from aqueous solution may be to use metal-reducing microorganisms to reduce the radionuclide to an insoluble oxide (25, 27). For example, TcO, TcO 2 , and Tc 2 O 5 all form insoluble precipitates at neutral pH (20,29,41). Although there has been much speculation that bacteria may be able to reduce Tc enzymatically, few organisms have been shown conclusively to achieve this biotransformation (25).Anaerobically grown cultures of soil bacteria were shown by Henrot (15)...

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“…As a result of these activities, 99 Tc has been found in groundwaters at sites where nuclear wastes have been reprocessed or stored (32), and it remains a significant contaminant in effluents from nuclear fuel reprocessing plants currently in operation (28). Several factors make Tc contamination a matter of intense concern, principally the long half-life of 99 Tc (2.13 ϫ 10 5 years), its high environmental mobility as the stable pertechnetate anion (TcO 4 Ϫ ), and subsequent uptake of pertechnetate into the food chain as an analog of sulfate (6).…”

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confidence: 99%

Direct and Fe(II)-Mediated Reduction of Technetium by Fe(III)-Reducing Bacteria

Lloyd

Solé

Praagh

et al. 2000

Appl Environ Microbiol

259

208

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The dissimilatory Fe(III)-reducing bacterium Geobacter sulfurreducens reduced and precipitated Tc(VII) by two mechanisms. Washed cell suspensions coupled the oxidation of hydrogen to enzymatic reduction of Tc(VII) to Tc(IV), leading to the precipitation of TcO 2 at the periphery of the cell. An indirect, Fe(II)-mediated mechanism was also identified. Acetate, although not utilized efficiently as an electron donor for direct cell-mediated reduction of technetium, supported the reduction of Fe(III), and the Fe(II) formed was able to transfer electrons abiotically to Tc(VII). Tc(VII) reduction was comparatively inefficient via this indirect mechanism when soluble Fe(III) citrate was supplied to the cultures but was enhanced in the presence of solid Fe(III) oxide. The rate of Tc(VII) reduction was optimal, however, when Fe(III) oxide reduction was stimulated by the addition of the humic analog and electron shuttle anthaquinone-2,6-disulfonate, leading to the rapid formation of the Fe(II)-bearing mineral magnetite. Under these conditions, Tc(VII) was reduced and precipitated abiotically on the nanocrystals of biogenic magnetite as TcO 2 and was removed from solution to concentrations below the limit of detection by scintillation counting. Cultures of Fe(III)-reducing bacteria enriched from radionuclide-contaminated sediment using Fe(III) oxide as an electron acceptor in the presence of 25 M Tc(VII) contained a single Geobacter sp. detected by 16S ribosomal DNA analysis and were also able to reduce and precipitate the radionuclide via biogenic magnetite. Fe(III) reduction was stimulated in aquifer material, resulting in the formation of Fe(II)-containing minerals that were able to reduce and precipitate Tc(VII). These results suggest that Fe(III)-reducing bacteria may play an important role in immobilizing technetium in sediments via direct and indirect mechanisms.Technetium-99, a fission product of uranium, is formed in kilogram quantities during nuclear reactions and has been released into the environment during weapons testing and the disposal of low-and intermediate-level wastes. As a result of these activities, 99 Tc has been found in groundwaters at sites where nuclear wastes have been reprocessed or stored (32), and it remains a significant contaminant in effluents from nuclear fuel reprocessing plants currently in operation (28). Sev-

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The Application of Biotechnology to the Treatment of Wastes Produced from the Nuclear Fuel Cycle: Biodegradation and Bioaccumulation as a Means of Treating Radionuclide-Containing Streams

Cited by 222 publications

References 161 publications

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Reduction and removal of heptavalent technetium from solution by Escherichia coli

Direct and Fe(II)-Mediated Reduction of Technetium by Fe(III)-Reducing Bacteria

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