Bioassociation of europium by Phaseolus vulgaris plants

Long-term safety analyses of potential repositories for high-level radioactive waste require the consideration of accident scenarios in which groundwater enters the repository and radionuclides (RN) are released into the groundwater. By this RN contamination of the soil occurs, followed by plant uptake and thus entrance to the human food chain. For humans, RN pose a risk to health (Hall et al., 2021) and for plants, RN are non-essential elements, which affect physiology, development and metabolism (Serre et al., 2019). To protect themselves from stress, plants release root exudates into the rhizosphere to model their environment in the favour of the plant. Additionally, root exudates are important for example to influence bacterial communities, to facilitate nutrient uptake, however root exudates also influence the bioavailability of RN by changing their speciation (Chen et al., 2021). A long list of chemical components, including organic acids, phenolic compounds like flavonoids, DNA, RNA, proteins, amino acids, and many more, can be excreted into the rhizosphere by plants (Lui et al,. 2023). In this study the exposure of Phaseolus vulgaris, a widely used crop plant, with Eu(III) as analogue for trivalent actinides, e.g. Am(III) and Cm(III), is studied in hydroponic culture. The accumulation and translocation of Eu(III) is investigated as a function of time and Eu(III) concentration. In addition, the Eu(III) speciation in hydroponic solution is analyzed by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and chemical microscopy. The RN speciation depends on various parameters, e.g. pH, redox potential and the presence of chelating agents, which can be released by plants as root exudates and may influence the bioavailability of RN (Chen et al., 2021). To characterize their effect on the Eu(III) speciation, root exudates of P. vulgaris plants are isolated from the solutions and characterized by high performance liquid chromatography (HPLC). The bioassoci