Interactions of radionuclides with plants: Identification of metabolites and their influence on bioavailability and transport of actinides in the environment.
For a long-term safety assessment of repositories for high-level radioactive waste, it is necessary to consider processes that may lead to a release of radionuclides into the environment. Released radionuclides can be accumulated by plants via near-surface groundwater and soil and thereby enter the food chain. The interaction processes that take place have so far been scarcely understood and are usually only described on a macroscopic level using transfer factors. With regard to a risk assessment for humans and the environment, however, it is necessary to understand these processes on a molecular level and to obtain information on the available radionuclide species in order to be able to estimate their behavior in the environment.
This work focuses on the interaction of actinides with plants. Especially model studies with plant cell metabolites are planned. The aim is to investigate the influence of released metabolites on actinide speciation in the rhizosphere and thus to allow statements on the bioavailability and transport of actinides in the environment. In addition to uranium, the experiments will be performed with plutonium. Furthermore, europium is used as an analogue for the trivalent actinides curium and americium, because their radiotoxicity - especially that of americium - is of high relevance in repositories. Based on previous studies on the time and concentration dependence of the bioassociation of U(VI) and Eu(III) with plant cells, the release of plant cell metabolites is investigated. Potential ligands for the complexation of radionuclides are metabolites formed and released by plants in response to heavy metal stress. Possible metabolites will therefore be isolated and identified and the complexing behaviour of these with actinides in different oxidation states will be investigated. Spectroscopic methods such as TRLFS and UV/VIS spectroscopy will be used for speciation studies. In addition, measurements using X-ray absorption spectroscopy (XAS) will be performed to obtain information on the oxidation state of the actinides in the presence of plant cells (XANES) and on the structure of the complexes formed (EXAFS).
The work is part of the project "Trans-LARA" (Transport and transfer behaviour of long-lived radionuclides along the pathway groundwater - soil - surface - plant under consideration of long-term climatic changes), which is funded by the Federal Ministry of Education and Research under contract number 02NUK051B.