SummaryDetailed knowledge of the nature of uranium complexes formed after the uptake by plants is an essential prerequisite to describe the migration behavior of uranium in the environment. This study focuses on the determination of uranium speciation after uptake of uranium by lupine plants. For the first time, time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy were used to determine the chemical speciation of uranium in plants. Differences were detected between the uranium speciation in the initial solution (hydroponic solution and pore water of soil) and inside the lupine plants. The oxidation state of uranium did not change and remained hexavalent after it was taken up by the lupine plants. The chemical speciation of uranium was identical in the roots, shoot axis, and leaves and was independent of the uranium speciation in the uptake solution. The results indicate that the uranium is predominantly bound as uranyl(VI) phosphate to the phosphoryl groups. Dandelions and lamb´s lettuce showed uranium speciation identical to lupine plants.
Biosorption of actinides like uranium by fungal cells can play an important role in the mobilization or immobilization of these elements in nature. Sorption experiments of U(VI) with Schizophyllum commune at different initial uranium concentrations and varying metal speciation showed high uranium sorption capacities in the pH range of 4–7. A combination of high angle annular dark-field and scanning transmission electron microscopy analysis (HAADF-STEM) showed that living mycelium cells accumulate uranium at the cell wall and intracellular. For the first time the fluorescence properties of uranium accumulates were investigated by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) beside the determination of corresponding structural parameters using X-ray absorption fine structure spectroscopy (EXAFS). While the oxidation state of uranium remained unchanged during sorption, uranium speciation changed significantly. Extra and intracellular phosphate groups are mainly responsible for uranium binding. TRLFS spectra clearly show differences between the emission properties of dissolved species in the initial mineral medium and of uranium species on fungi. The latter were proved to be organic and inorganic uranyl phosphates formed depending on the uranyl initial concentration and in some cases on pH.
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