UPTAKE AND RELEASE OF CESIUM-137 BY FIVE PLANT SPECIES AS INFLUENCED BY SOIL AMENDMENTS IN FIELD EXPERIMENTS

Authors: FUHRMANN, M - BROOKHAVEN NATIONAL LAB; LASAT, M - USEPA; EBBS, S - SOUTHERN ILLINOIS UNIV; CORNISH, J - MSE TECH APPLICATIONS; Kochian, Leon

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2004
Publication Date: 7/1/2004
Citation: Fuhrmann, M., Lasat, M., Ebbs, S., Cornish, J., Kochian, L.V. 2004. Uptake and release of cesium-137 by five plant species as influenced by soil amendments in field experiments. Journal of Environmental Quality. 32:2272-2279.

Interpretive Summary: Radionuclide contamination of soils poses serious problems to both human health and agriculture in the U.S. Soils have become contaminated with radionuclides as a result of above ground nuclear testing, accidental release or nuclear energy generation. 137Cs is a long-lived by-product of nuclear fission. Large areas of land in the US are still polluted with 137Cs and the projected cost of cleaning up these radionuclide-contaminated soils is very high, in excess of 300 billion dollars. Phytoremediation is emerging as an attractive alternative to energy-intensive, high-cost traditional cleaning methods. This new technology employs the use of higher plants capable of accumulating high levels of contaminants in shoots. Following harvesting, the shoot biomass can be disposed of in a final repository after volume reduction (e.g., ashing). In this field study of a 137Cs contaminated site at the Brookhaven National Laboratory, 5 different plant species and 3 different soil amendments aimed at increasing 137Cs soil bioavailability for plant uptake were tested. It was found that Amaranthus retroflexus was by far the most effective at sequestering 137Cs in the shoot biomass. None of the soil amendments (ammonium ion, manure, or manure + ammonium) stimulated 137Cs uptake. In fact, the manure + ammonium amendment significantly reduced 137Cs uptake. It appears that this specific change in soil chemistry triggered a transfer of accumulated 137Cs from the shoots to the roots. These findings indicate that Amaranthus retroflexus shows considerable promise for the phytoremediation of 137Cs-contaminated soils, but soil amendments previously suggested to facilitate 137Cs phytoextraction may actually inhibit this process.

Technical Abstract: Phytoextraction field experiments were conducted on soil contaminated with 0.39 to 8.7 Bq/g of 137Cs to determine the capacity of 5 plant species to accumulate 137Cs and the effects of 3 soil treatments on uptake. The plants tested were redroot pigweed (Amaranthus retroflexus L. var. aureus); a mixture of redroot pigweed and spreading pigweed (A. graecizans L.); purple amaranth hybrid; Indian mustard (Brassica juncea); and cabbage (Brassica oleracea L. var. capitata). For control plants, the concentration ratios (CR) of 137Cs were greatest for redroot pigweed and the amaranth hybrid, with average CR values of 1.0 more or less 0.24 and 0.95 more or less 0.14, respectively. The lowest value was for Indian mustard at 0.36 more or less 0.10. The soil treatments included (i) application of NH4NO3 solution to the soil after plants had matured, (ii) addition of composted manure to increase organic matter content of the soil, (iii) combination of the manure and ammonium solution treatments, and (iv) controls. The ammonium solution yielded little overall increase in 137Cs accumulation. The use of composted manure also had little influence, but the combination of the composted manure with application of ammonium solutions had a distinctly negative effect on plant uptake of 137Cs. On average, the fraction of 137Cs taken up from the soil was reduced by 57.4 more or less 1.2% compared with controls. This was the result of release of competing ions, primarily Ca, from the manure and was observed across all five plant species tested. The application of ammonium solution took place in the last two weeks before harvest. The reduction of plant 137Cs content, by addition of the ammonium solution, as it interacted with the manure, indicates that substantial quantities 137Cs can be released from the shoots of plants as a result of sudden changes in soil solution chemistry.