Phyto extraction of 99Tc on soil cores with aged contamination

99Tc is an artificial radionuclide which is found in high-activity and long-lived nuclear waste. This work was designed to study the phyto-extraction of 99Tc in soils that had received aged contamination and to monitor the resulting 99Tc concentrations in the soil solution of undisturbed soil cores in a greenhouse. Undisturbed soil cores had been sampled previously from a Rendzic Leptosol (R), a Fluvic cambisol (F) and a Dystric cambisol (D), using 0.5-m diameter PVC tubing (3 samples/soil type) without disturbing soil structure (1). Each core was equipped with two nylon porous cups (respectively 20 and 35 cm deep) and a final leachate collector. A 99TcNO3 solution had been supplied at the soil surface of each core during the two previous years (4200 kBq in total) in which maize and wheat had been successively cropped. These two crops had already removed 30-65% of total contamination before the present study. After the second year no more 99Tc was added to the cores. Thereafter, Lolium perenne was cultivated for 20 successive months. 99Tc was determined in both plant aerial parts and water samples (from both cups and collectors), and the balance of 99Tc in the system was established after phyto-extraction. Results showed that transfer of 99Tc to plants vary among soils: 7% on soil R to 11% on soil D. Concentration of 99Tc in the porous cups dramatically decreased in all soils. The plants maintained low and stable concentration levels of 99Tc in the soil solution which decreased the potential migration of the radionuclide through the cores: The leaching of 99Tc in the final collectors of the R soil cores decreased from 18 to 1.7 Bq mL-1. (author)