Phytoremediation of a Radiocesium‐Contaminated Soil: Evaluation of Cesium‐137 Bioaccumulation in the Shoots of Three Plant Species

Abstract A field study was conducted to investigate the potential of three plant species for phytoremediation of a 137 Cs‐contaminated site. Approximately 40‐fold more 137 Cs was removed from the contaminated soil in shoots of red root pigweed ( Amaranthus retroflexus L.) than in those of Indian mustard [ Brassica juncea (L.) Czern] and tepary bean ( Phaseolus acutifolius A. Gray). The greater potential for 137 Cs removal from the soil by A. retroflexus was associated with both high concentration of 137 Cs in shoots and high shoot biomass production. Approximately 3% of the total 137 Cs was removed from the top 15 cm of the soil (which contained most of the soil radiocesium) in shoots of 3‐too‐old A. retroflexus plants. Soil leaching tests conducted with 0.1 and 0.5 M NH 4 NO 3 solutions eluted as much as 15 and 19%, respectively, of the soil 137 Cs. Addition of NH 4 NO 3 to the soil, however, had no positive effect on 137 Cs accumulation in shoots in any of the species investigated. It is proposed that either NH 4 NO 3 solution quickly percolated through the soil before interacting at specific 137 Cs binding sites or radiocesium mobilized by NH 4 NO 3 application moved below the rhizosphere, becoming unavailable for root uptake. Further research is required to optimize the phytotransfer of the NH 4 NO 3 ‐mobilized 137 Cs. With two croppings of A. retroflexus per year and a sustained rate of extraction, phytoremediation of this 137 Cs‐contaminated soil appears feasible in <15 yr.