Contact

Irene Cardaio

i.cardaioAthzdr.de
Phone: +49 351 260 2251

Ph.D. topics

Interactions between anaerobic microorganisms and technetium for its immobilization through a microbial-induced reduction of the soluble TcVII to TcIV

Promotionsstudent:

Irene Cardaio

Betreuer:

Prof. Dr. Thorsten Stumpf, Dr. Natalia Mayordomo Herranz, Dr. Andrea Cherkouk (HZDR)

Abteilung:

Surface processes

Zeitraum:

09/2022–08/2025

Deep geological repositories for nuclear waste are based on a multiple-barriers concept including the natural host rock, a buffering sealing material, e.g. bentonite, and a metal canister for the radioactive waste, in order to isolate the waste from the biosphere. However, in the long-term disposal of nuclear waste, bentonite is influenced by several processes, such as microbial activity, which in time can affect its physico-chemical properties and therefore, its performance in the repository1, 2. The metabolic production of H2S and FeS2 for instance, can influence the corrosion of the canister and the clay integrity. Microbial metabolic reactions, such as sulfate reduction, are responsible for both the mobilization and immobilization of toxic compounds and radionuclides3, 4.

Nuclear waste represents one of the main sources of hazardous materials, among which technetium (Tc) plays a decisive role. The main oxidation states of Tc in absence of organic molecules are TcIV and TcVII and their species are responsible for the fate of Tc in the environment. Under aerobic or oxidative conditions, Tc forms the highly soluble anion pertechnetate TcVIIO4−, whereas under anaerobic or reducing conditions low-soluble compounds of TcIV, such as Tc-oxides, e.g. TcIVO2, -sulfides or TcIV-mineral sorbed species (pyrite5, FeS2; magnetite6, [FeIIFeIII2O4]; chukanovite7, [Fe2(OH)2(CO3)]) are more likely to be found. Sulfate and iron reducing bacteria may lead to reduced S or Fe species8, 9 that can promote the reduction of TcVII to TcIV. For example, bacteria can generate minerals as result of their metabolic reactions, for instance pyrite10 (FeIIS2) and green rust11 (FeII-FeIII layered double hydroxide), which can immobilize Tc12.

This Ph.D. project aims at providing a comprehensive description and evaluation of the bacterial behaviour towards Tc species and their role in the immobilization of technetium. Two anaerobic bacteria have been selected: Desulfitobacterium sp. G1-213 and Pseudodesulfovibrio äspoeensis14, isolated from FEBEX bentonite and from groundwater samples from Äspo underground research laboratory (Sweden), respectively. These bacteria might occur under repository conditions, but their interplay with Tc has not been studied yet. These two bacterial species are expected to be promising candidates for TcVII reduction by indirect (Desulfitobacterium sp. G1-2) or direct (Pseudodesulfovibrio äspoeensis) pathways. A sound characterization of the reaction mechanisms combining microscopic, spectroscopic, and electrochemical methods will be carried out. The Ph.D. research is developed in the frame of the NukSiFutur Young Investigators group TecRad (02NUK072), funded by the German Federal Ministry of Education and Research (BMBF).

Foto: Desulfitobacterium sp. G1-2 ©Copyright: Irene Cardaio

a) Desulfitobacterium sp. G1-2 in DSMZ 579 after 3 days, 30 °C, magnification: 40X; b) Desulfitobacterium sp. G1-2 in DSMZ 579, close-up of precipitate structure units observed after 10 days after exposure to air, magnification: 100X

References

  1. Matschiavelli, N., Kluge, S., Podlech, C., Standhaft, D., Grathoff, G., Ikeda-Ohno, A., Warr, L. N., Chukharkina, A., Arnold, T., Cherkouk, A. (2019). The Year-Long Development of Microorganisms in Uncompacted Bavarian Bentonite Slurries at 30 and 60 °C. Environmental Science and Technology, 53(17), 10514–10524. DOI: 10.1021/acs.est.9b02670.
  2. Ruiz-Fresneda, M. A., Martinez-Moreno, M. F., Povedano-Priego, C., Morales-Hidalgo, M., Jroundi, F., Merroun, M. L. (2023). Impact of microbial processes on the safety of deep geological repositories for radioactive waste. Frontiers in Microbiology, 14:1134078. DOI: 10.3389/fmicb.2023.1134078.
  3. Rasoulnia, P., Barthen, R., Lakaniemi, A. M. (2021). A critical review of bioleaching of rare earth elements: The mechanisms and effect of process parameters. Critical Reviews in Environmental Science and Technology, 51(4), 378–427. DOI: 10.1080/10643389.2020.1727718.
  4. Lopez-Fernandez, M., Jroundi, F., Ruiz-Fresneda, M. A., Merroun, M. L. (2021). Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications. Microbial Biotechnology, 14(3), 810–828, DOI: 10.1111/1751-7915.13718.
  5. Rodríguez, D. M., Mayordomo, N., Scheinost, A. C., Schild, D., Brendler, V., Müller, K., Stumpf, T. (2020). New Insights into 99Tc(VII) Removal by Pyrite: A Spectroscopic Approach. Environmental Science and Technology, 54(5), 2678–2687, DOI: 10.1021/acs.est.9b0534.
  6. Meena, A. H., Arai, Y. (2017). Environmental geochemistry of technetium. Environmental Chemistry Letters, 15(2), 241–263, DOI: 10.1007/s10311-017-0605-7.
  7. Schmeide, K., Rossberg, A., Bok, F., Shams Aldin Azzam, S., Weiss, S., Scheinost, A. C. (2021). Technetium immobilization by chukanovite and its oxidative transformation products: Neural network analysis of EXAFS spectra. Science of the Total Environment, 770, 145334, DOI: 10.1016/j.scitotenv.2021.145334.
  8. Lloyd, J. R., Sole, V. A., van Praagh, C. V. G., Lovley, A. D. R. (2000). Direct and Fe(II)-Mediated Reduction of Technetium by Fe(III)-Reducing Bacteria. Applied and Environmental Microbiology, 66(9). 3743-3749. DOI: 10.1128/AEM.66.9.3743-3749.2000.
  9. Lloyd, J. R. (2003). Microbial reduction of metals and radionuclides. FEMS Microbiology Reviews, 27(2–3), 411–425, DOI: 10.1016/S0168-6445(03)00044-5.
  10. Duverger, A., Berg, J. S., Busigny, V., Guyot, F., Bernard, S., Miot, J. (2020). Mechanisms of Pyrite Formation Promoted by Sulfate-Reducing Bacteria in Pure Culture. Frontiers in Earth Science, 8:588310, DOI: 10.3389/feart.2020.588310.
  11. O’Loughlin, E. J., Kelly, S. D., Kemner, K. M. (2010). XAFS investigation of the interactions of UVI with secondary mineralization products from the bioreduction of FeIII oxides. Environmental Science and Technology, 44(5), 1656–1661, DOI: 10.1021/es9027953.
  12. McBeth, J. M., Lloyd, J. R., Law, G. T. W., Livens, F. R., Burke, I. T., Morris, K. (2011). Redox interactions of technetium with iron-bearing minerals. Mineralogical Magazine, 75(4), 2419–2430, DOI: 10.1180/minmag.2011.075.4.2419.
  13. J. Drozdowski, et al. Institute of Resource Ecology 2018 annual report. HZDR-096 (2019) p. 40, Hyperlink.
  14. Motamedi M, Pedersen K. (1998) Desulfovibrio aespoeensis sp. nov., a mesophilic sulfate-reducing bacterium from deep groundwater at Aspö hard rock laboratory, Sweden. Int. J. Syst. Bacteriol., 48(1), 311–315. DOI: 10.1099/00207713-48-1-311.