Ion exchange paper chromatography of Tc(IV), Tc(V) and Tc(VII) in hydrochloric acid

Shukla, S.K.

doi:10.1016/s0021-9673(01)91264-6

Cited by 45 publications

(15 citation statements)

References 2 publications

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“…Total Tc in solution was assayed by autoradiography using a phosphorimager as described previously (19). Tc(VII) was also separated from reduced, nonmobile Tc using paper chromatography (19,38), prior to autoradiography and quantification using a Storm 840 PhosphorImager (Molecular Dynamics, Sunnyvale, Calif.) (19). In some experiments, very low concentrations of Tc were quantified using an LS 6500 Liquid Scintillation Analyzer (Beckman Instruments Inc., Fullerton, Calif.).…”

Section: Methodsmentioning

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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Section: Methodsmentioning

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

View full text Add to dashboard Cite

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“…Tc uptake was expressed as the percentage or the concentration of Tc remaining in solution after centrifugation in an Eppendorf 5415C centrifuge (14,000 rpm, 20 min) in comparison with total Tc. Tc(VII) (R f ϭ 0.7) was also separated from reduced, nonmobile [Tc(V); R f ϭ 0.0] and mobile [mainly Tc(IV); R f ϭ 0.9] soluble Tc species using paper chromatography (29) prior to autoradiography and quantification using a PhosphorImager. In most experiments, concentrations of Tc were also quantified using a Packard 1900 TR analyzer.…”

Section: Methodsmentioning

confidence: 99%

Reduction of Technetium(VII) by Desulfovibrio fructosovorans Is Mediated by the Nickel-Iron Hydrogenase

Luca

Philip

Dermoun

et al. 2001

Appl Environ Microbiol

105

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Resting cells of the sulfate-reducing bacterium Desulfovibrio fructosovorans grown in the absence of sulfate had a very high Tc(VII)-reducing activity, which led to the formation of an insoluble black precipitate. The involvement of a periplasmic hydrogenase in Tc(VII) reduction was indicated (i) by the requirement for hydrogen as an electron donor, (ii) by the tolerance of this activity to oxygen, and (iii) by the inhibition of this activity by Cu(II). Moreover, a mutant carrying a deletion in the nickel-iron hydrogenase operon showed a dramatic decrease in the rate of Tc(VII) reduction. The restoration of Tc(VII) reduction by complementation of this mutation with nickel-iron hydrogenase genes demonstrated the specific involvement of the periplasmic nickel-iron hydrogenase in the mechanism in vivo. The Tc(VII)-reducing activity was also observed with cell extracts in the presence of hydrogen. Under these conditions, Tc(VII) was reduced enzymatically to soluble Tc(V) or precipitated to an insoluble black precipitate, depending on the chemical nature of the buffer used. The purified nickel-iron hydrogenase performed Tc(VII) reduction and precipitation at high rates. These series of genetic and biochemical approaches demonstrated that the periplasmic nickel-iron hydrogenase of sulfatereducing bacteria functions as a Tc(VII) reductase. The role of cytochrome c 3 in the mechanism is also discussed.

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“…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).…”

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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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Ion exchange paper chromatography of Tc(IV), Tc(V) and Tc(VII) in hydrochloric acid

Cited by 45 publications

References 2 publications

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

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

Reduction of Technetium(VII) by Desulfovibrio fructosovorans Is Mediated by the Nickel-Iron Hydrogenase

Reduction and removal of heptavalent technetium from solution by Escherichia coli

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