Bioavailability of ⁹⁹Tc to a macrophyte of the Yenisei River

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