Potential for phytoextraction of Cs-137 from a contaminated soil

Potential for phytoremediation of a soil contaminated with radiocesium was investigated in three phases: (1) hydroponic screening for plant species capable of accumulating elevated levels of cesium in shoots, (2) investigation of several amendments for their potential to increase the bioavailability of Cs-137 in the contaminated soil, and (3) bioaccumulation of radiocesium in shoots of plants grown in Cs-137-contaminated soil. The bioaccumulation ratio for Cs in shoots of hydroponically grown plants ranged between 38 and 165. From solution, dicot species accumulated 2- to 4-fold more cesium in shoots than grasses. In studies investigating the bioavailability of Cs-137 in aged contaminated soil, ammonium salts were found to be the most effective desorbing agents, releasing approximately 25% of the Cs-137. The extent of Cs-137 desorption from the soil increased with ammonium concentration up to 0.2 M. In a pot study conducted in a greenhouse, there was significant species-dependent variability in the ability to accumulate Cs-137 in the shoot from contaminated soil. The ability to accumulate Cs-137 from the soil increased in the order: reed canarygrass (Phalaris arundinacea) < Indian mustard (Brassica juncea) < tepary bean (Phaseolus acutifolius) < cabbage (B. oleracea var. capitata). It was also found that addition of NH4NO3 solution to the soil elicited a two-to twelve-fold increase in Cs-137 accumulation in the shoot. The greatest amount of Cs-137 (40 Bq g(-1) dw) was removed in shoots of cabbage grown in contaminated soil amended with 80 mmols NH4NO3 kg(-1) soil. Bioaccumulation ratios of 2-3 were obtained with the best performing plant species. These values are significantly greater than those previously reported in the literature (usually < 0.1) for plants grown on aged contaminated soil. These results indicate that careful species selection along with amendments that increase the bioavailability of Cs-137 in the soil could greatly enhance the prospects for the use of plants to remediate Cs-137-contaminated soils.