ARS | Publication request: POTENTIAL FOR PHYTOEXTRACTION OF 137CS FROM A CONTAMINATED SOIL

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 1997
Publication Date: N/A

Interpretive Summary: Radionuclide contamination of soils in the U.S. has occurred as a result of above ground nuclear testing, accidental release or nuclear energy generation. 137Cs is a long-lived by-product of nuclear fission. Although recent contamination of the en-vironment with 137Cs from the testing of nuclear weapons has been drastically reduced, large areas are still polluted with radiocesium. The projected cost of cleaning up these radionuclide-contaminated soils is 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 to accumulate contaminants in the shoots. Following harvesting, the shoot biomass can be disposed of in a final repository after volume reduction (e.g., ashing). As phytoremediation of radiocesium-contaminated sites is impeded by the marked capacity of soils to tightly adsorb 137Cs & limit its availability for plant uptake, the bio availability of 137Cs in an aged contaminated soil obtained from Brook- haven Natl Lab. was studied. Testing of a number of soil extractants demonstrated that ammonium salts released a large portion of the radiocesium trapped in the soil. This same amendment greatly stimulated the bioaccumulation of 137Cs in plant shoots. Use of the best performing plant species from a species selection trial (cabbage), in conjunction with amending the soil with ammonium nitrate, resulted in dramatic improvements in the accumulation of 137Cs in plant shoots compared with the results of many previous published studies (10 to 300-fold improvement over previous studies). These findings indicate that the phytoremediation of 137Cs con- taminated soils is a very promising green cleanup technology.

Technical Abstract: Phytoremediation of an aged radiocesium-contaminated soil from Brookhaven Natl Lab. was investigated in 3 phases: 1) hydroponic screening for plant species capable of accumulating elevated levels of cesium in shoots, 2) investigation of several amendments for their ability to increase the bioavailability of 137Cs in contaminated soil, & 3) bio-accumulation of radiocesium in shoots of different plant species grown on contaminated soil. Hydroponic screening demonstrated that plants can effectively accumulate Cs in the shoots if it is available for uptake by roots. In studies investigating the bioavailability of 137Cs in contaminated soil, ammonium salts were found to be the most effective at desorbing radioce- sium, releasing approximately 25% of 137Cs. In a pot study in the green- house, there was significant species dependent variability in the ability to accumulate 137Cs in the shoot from contaminated soil. The ability to accumulate 137Cs increased in the order: reed canary grass (Phalaris arundinacea) < Indian mustard (Brassica juncea) < tepary bean (Phaseolus acutifolius) < cabbage (B. oleracea. var. capitata). It was also found that addition of NH4NO3 to the soil elicited a 2- to 12-fold in-crease in 137Cs accumulation in the shoot. 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 soils. These results indicate that careful species selection along with amendments that increase the bioavailability of 137Cs in the soil could greatly enhance the pros-pects for the use of plants to remediate 137Cs contaminated soils.