Bioavailability of Tc incorporated in plant material

The effective removal rate of radiopollutants from contaminated soil usually has been estimated by considering only the radioactive decay constant. This approximation, however, becomes a matter of concern when assessments are performed for long release periods, for long-lived radionuclides and for radionuclides exhibiting relatively high values of plant-to-soil concentration ratios. Previous results obtained for 99Tc showed that phenomena other than radioactive decay may be of importance in soil depletion and that uptake by plants, as well as mechanisms affecting the availability, must be taken into account. In agricultural practice, ignorance of these mechanisms may lead to inaccurate predictions of dose levels. Harvest losses have already been theoretically discussed, and removal constants of soil radioactivity from harvest and leaching have been estimated. Validation of the soil-plant model for Tc including these depletion processes is thus necessary, and minilysimeter experiments were conducted. Contaminated plant material was reincorporated into the soil and was allowed to undergo humification; plants were cultivated on these soils and their Tc uptake was studied. Results showed that an important part of the recycled, bioincorporated Tc is immediately and highly available to plants. The results are discussed within the framework of the plant-material degradation.