Bioavailability of⁹⁹Tc to a macrophyte of the Yenisei River

Abstract

Abstract.The experiments on accumulation of 99 Tc by Elodea biomass showed that 99 Tc activity concentration can reach 120 ± 6 Bq/g, with the concentration factor for 99 Tc 2700 ± 500 L/kg. In experiments on 99 Tc release, over 504 h about 82% of the total 99 Tc activity was released into the water from plant biomass; most of 99 Tc was released within the first 192 h. Results of chemical fractionation of the biomass show that 99 Tc contained in biomass was mainly concentrated in the exchangeable and the adsorbed fractions (83%). Thus, the data obtained using chemical fractionation of biomass confirmed the experimental data on 99 Tc release, which suggested that most of the biomass-bound 99 Tc was adsorbed on the biomass surface. 99 Tc tightly bound to Elodea biomass (fractions of organics and mineral residue) constituted just 17% of the total 99 Tc activity. Decreased illumination of Elodea shoots during the experiment did not cause any reduction in 99 Tc activity concentration or concentration factor. Results of chemical fractionation of the biomass grown under lower illumination conditions show that the percentage of 99 Tc tightly bound to Elodea biomass (fractions of organics and mineral residue) decreased while the 99 Tc of the adsorbed fractions decreased. Our results and data reported by other authors suggest that some part of 99 Tc activity can be bioavailable to living organisms and that the portion of bioavailable 99 Tc can be determined by a number of factors.