POTENTIAL REMEDIATION OF CS-137 AND SR-90 CONTAMINATED SOIL BY ACCUMULATION IN ALAMO SWITCHGRASS

Cesium-137 (Cs-137) and Strontium-90 (Sr-90) are radionuclides charact eristic of nuclear fallout from nuclear weapons testing and nuclear re actor accidents. Alamo switchgrass (Panicum virginatum L.) is a perenn ial C-4 species native to central North America that produces exceptio nally high biomass yields in short periods of time. In three separate experiments, Alamo switchgrass plants were tested for their ability to accumulate Cs-137 and Sr-90 from a contaminated growth medium. Plants in experiment 1 were grown in 33 x 20 x 7 cm plastic pans containing 2.5 kg sand. Plants in experiments 2 and 3 were grown in 30 x 3 cm dia meter test tubes containing 0.3 kg growth medium. After 3 months of pl ant growth, either 102 Bq Cs-137 or 73 Bq Sr-90 g(-1) soil were added to the growth medium. Plants in all three experiments were grown withi n a greenhouse that was maintained at 22 +/- 2 degrees C with a photos ynthetic active radiation of 400-700 mu mol m(-2) s(-1) and a 14-16 h photoperiod, Above-ground plant biomass did not differ between plants that were not exposed to these radionuclides (controls) and those that were exposed to growth medium containing Cs-137 or Sr-90 over the cou rse of the experiment. Plants accumulated 44 and 36% of the total amou nt of Sr-90 and Cs-137 added to growth medium after the first 5 harves ts. After the first two harvests, the concentration of Cs-137 and Sr-9 0 in plant tissue and the amount of Cs-137 or Sr-90 removed from growt h medium declined with each successive harvest. Duration of exposure c orrelated curvilinearly with accumulation of both Sr-90 and Cs-137 by plants (r(2) = 0.95 and 0.78, respectively). As concentration of both Cs-137 and Sr-90 in growth medium increased, plant accumulation of bot h radionuclides increased and correlated curvilinearly in seedlings (r (2) = 0.83 and 0.89 respectively).