Vegetation is often the primary method of recovery in mining areas to stabilize radioactive waste and to minimize downward translocation of contaminants. However, plants may increase radionuclide mobilization through complexation with rhizosphere organic acids exuded by the roots under moderate nutrient stress. But overall fate of the mobilized radionuclides under natural environment remains uncertain. If the mobilization capacity of radionuclides by plants exceeds their uptake capacity, the excess of mobilized radionuclides will percolate down the soil profile as the chelation precludes any immediate immobilization of radionuclide in the soil matrix. This work examines plant mediated uranium (U) mobilization and fate of mobilized U in soils as influenced by nutrient availability. Andropogon virginicus, exposed to different mineral forms of phosphorus (KH2PO4, FePO4 and no P) was examined with respect to their potential for U mobilization followed by its transportation in the plant - soil system. Accidental versus intentional mobilization was determined using two different sources of U; UO2HPO4 4H2O (Chernikovite) and UO2 (Uraninite). The presence of plant significantly increased the mobilization of U from parental mineral forms to leachate, predominantly in the presence of sparingly available form of P (FePO4) in the system. The amount of U in plant tissues and leachate indicated that the plant uptake was 33% lower as compared to leaching (0.0001% to 7 % leached from initial source). Within the plant, U preferentially retained in roots. The highest amount of U (7% from initial source) was removed from the column with plants exposed to chernikovite (uranyl-phosphate) source, located along with FePO4. Among different uranium sources, higher amount of uranium transported downward from Chernikovite source (27% higher) compared to UO2. Our study highlights that plant-mediated mobility and subsequent downward migration of radioactive contaminants under nutrient stress condition is an important factor that should be considered in management at legacy contamination sites, nuclear waste repositories, and nuclear material processing facilities.

Enhanced leaching of uranium from stable mineral forms by plants under phosphorus stress

2019 Spring National Meeting

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