Soil availability, plant uptake and soil to plant transfer of 99Tc -: A review

The fission yield of Tc-99 from Pu-239 and U-235 is similar to that of Cs-137 or Sr-90 and it is therefore an important component of nuclear weapons fall-out, nuclear waste and releases from nuclear facilities. There is particular current interest in Tc-99 transfer from soil to plants for: (a) environmental impact assessments for terrestrial nuclear waste repositories, and (b) assessments of the potential for phytoextraction of radionuclides from contaminated effluent and soil. Vascular plants have a high Tc-99 uptake capacity, a strong tendency to transport it to shoot material and accumulate it in vegetative rather than reproductive structures. The mechanisms that control Tc-99 entry to plants have not been identified and there has been little discussion of the potential for phytoextraction of Tc-99 contaminated effluents or soil. Here we review soil availability, plant uptake mechanisms and soil to plant transfer of Tc-99 in the light of recent advances in soil science, plant molecular biology and phytoextraction technologies. We conclude that Tc-99 might not be highly available in the long term from up to 50% of soils worldwide, and that no single mechanism that might be easily targeted by recombinant DNA technologies controls Tc-99 uptake by plants. Overall, we suggest that Tc might be less available in terrestrial ecosystems than is often assumed but that nevertheless the potential of phytoextraction as a decontamination strategy is probably greater for Tc-99 than for any other nuclide of radioecological interest. (C) 2002 Elsevier Science Ltd. All rights reserved.