Phytoremediation of a radiocesium-contaminated soil: Evaluation of cesium-137 bioaccumulation in the shoots of three plant species

A field study was conducted to investigate the potential of three plant species for phytoremediation of a Cs-137-contaminated site. Approximately 40-fold more Cs-137 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 Cs-137 removal from the soil by A. retroflexus was associated with both high concentration of Cs-137 in shoots and high shoot biomass production. Approximately 3% of the total Cs-137 was removed from the top 15 cm of the soil (which contained most of the soil radiocesium) in shoots of 3-mo-old A, retroflexus plants. Soil leaching tests conducted with 0.1 and 0.5 M NH4NO3 solutions eluted as much as 15 and 19%, respectively, of the soil Cs-137, Addition of NH4NO3 to the soil, however, had no positive effect on Cs-137 accumulation in shoots in any of the species investigated. It is proposed that either NH4NO3 solution quickly percolated through the soil before interacting at specific Cs-137 binding sites or radiocesium mobilized by NH?NO, application moved below the rhizosphere, becoming unavailable for root uptake. Further research is required to optimize the phytotransfer of the NH4NO3-mobilized Cs-137. With two croppings of A. retroflexus per year and a sustained rate of extraction, phytoremediation of this Cs-137-contaminated soil appears feasible in <15 yr.