Microorganisms and their impact on radionuclide speciation

Microorganisms are ubiquitous in the environment. Hence, for the long-term safety assessment of a nuclear waste repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay) and how these microorganisms can influence the performance of a repository. The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock for nuclear waste disposal [1]. It is well known that indigenous bacteria in such underground environments can affect the speciation and the mobility of actinides [2-5].
From our point of view, the understanding of the speciation and the structure of the actinide (An)/lanthanide (Ln) complexes formed in presence of indigenous bacteria over a wide range of geochemical parameters (e.g., pH, metal concentration) becomes indispensable for predicting the safety of a planned nuclear waste repository.
Our research is focused on broaden the knowledge concerning the bacterial diversity in potential host rocks for nuclear waste storage (e.g., Mont Terri Opalinus Clay) by applying direct molecular culture-independent retrievals and cultivation experiments. After cultivation and characterization of dominant bacterial populations we investigate their influence on the geo-chemical behaviour of selected An/Ln (uranium, plutonium, and curium/europium). The indirect (e.g., actinide mobilization by microbially produced bioligands) and direct (e.g., biosorption, bioaccumulation, biotransformation) influence of microorganisms on the speciation/migration processes of An/Ln will be highlighted during the lecture by using selected examples. This helps to understand the manifold interaction processes in such biological systems on a molecular level.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E9985, 02E10618 and 02E10971) and the BGR for providing the clay samples.

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