ROLE OF URANIUM SPECIATION IN THE UPTAKE AND TRANSLOCATION OF URANIUMBY 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 th e hydroxyl and carbonate U complexes present in the solution at pH 6.0 and 8,0, respectively. A subsequent experiment tested the extent to w hich various monocot acid dicot species take up and translocate the ur anyl cation. Of the species screened, tepary bean (Phaseolus acutifoli us) and red beet (Beta vulgaris) were the species showing the greatest accumulation of U, In addition to providing fundamental information r egarding U uptake by plants, the results obtained also have implicatio ns for the phytoremediation of U-contaminated soils. The initial chara cterization 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-ava ilable form. A pot study using U-contaminated soil was therefore condu cted to assess the extent to which two soil amendments, HEDTA and citr ic acid, were capable of acidifying the soil, increasing U solubility, and enhancing U uptake by red beet, Of these two amendments, only cit ric acid proved effective, decreasing the soil pH to 5.0 and increasin g U accumulation by a factor of 14. The results of this pot study prov ide a basis for the development of an effective phytoremediation strat egy for U-contaminated soils.