Role of uranium speciation in the uptake and translocation of uranium by plants

Uranium (U) uptake and translocation by plants was characterized using a computer speciation model to develop a nutrient culture system that provided U as a single predominant species in solution. A hydroponic uptake study determined that at pH 5.0, the uranyl (UO22+) cation was more readily taken up and translocated by peas (Pisum sativum) than the hydroxyl and carbonate U complexes present in the solution at pH 6.0 and 8,0, respectively. A subsequent experiment tested the extent to which various monocot acid dicot species take up and translocate the uranyl cation. Of the species screened, tepary bean (Phaseolus acutifolius) and red beet (Beta vulgaris) were the species showing the greatest accumulation of U, In addition to providing fundamental information regarding U uptake by plants, the results obtained also have implications for the phytoremediation of U-contaminated soils. The initial characterization of U uptake by peas suggested that in the field, a soil pH of <5.5 would be required in order to provide U in the most plant-available form. A pot study using U-contaminated soil was therefore conducted to assess the extent to which two soil amendments, HEDTA and citric acid, were capable of acidifying the soil, increasing U solubility, and enhancing U uptake by red beet, Of these two amendments, only citric acid proved effective, decreasing the soil pH to 5.0 and increasing U accumulation by a factor of 14. The results of this pot study provide a basis for the development of an effective phytoremediation strategy for U-contaminated soils.