Technetium

Kotegov, K.V.; Pavlov, O.N.; Shvedov, V.P.

doi:10.1016/s0065-2792(08)60165-x

Cited by 62 publications

(42 citation statements)

References 176 publications

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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).…”

mentioning

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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confidence: 99%

Reduction and removal of heptavalent technetium from solution by Escherichia coli

1997

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“…Krupka et al (2006) suggest that this is due to the difference in the standard potential of the Re(VII)/Re(IV) and Tc(VII)/Tc(IV) couples. The oxidation potential of the former is -0.510 V, whereas the latter has a value of -0.738 V (Kotegov et al 1968). …”

Section: Re Reductionmentioning

confidence: 96%

“…The most abundant isotope of Tc present in the wastes is 99 Tc because of its high fission yield (~6%) and long half-life (2.13×10 5 years) (Kotegov et al 1968;Luykx 1986). During the Cold War era, generation of fissile 239 Pu for use in America's atomic weapons arsenal yielded nearly 1900 kg of 99 Tc at the U.S. Department of Energy's (DOE) Hanford Site in southeastern Washington State (Darab and Smith 1996).…”

Section: Introductionmentioning

confidence: 99%

Immobilization and Limited Reoxidation of Technetium-99 by Fe(II)-Goethite

Um¹,

Chang²,

Icenhower³

et al. 2010

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“…Due to these characteristics of Tc, a technique for the removal of Tc from the environment is clearly required. Reduced Tc species, e.g., Tc(IV) and Tc(V) oxides, show a low aqueous solubility (5). Hence, many recent studies have reported the reduction of technetium by microorganisms (4, 6-10, 13, 16).…”

Section: Technetium-99 (mentioning

confidence: 99%