Microbial role in immobilization of technetium in soil under waterlogged conditions

Technetium behaviour in soil depends upon its chemical forms. The nuclide is expected to be in a soluble form of pertechnetate (TcO4−) under an aerobic condition, however, this changes through a combination of factors such as a redox condition and microbial activity. In this study, a radiotracer experiment was carried out to clarify the influence of microbial activity on plant available Tc under waterlogged condition. Air-dried soil with 0, 0.05, 0.5% glucose contents and sterile soil were used to compare the effect of microbial activity. The soils were waterlogged with 95mTc or 95mTc solution and kept at room temperature. Relative activities of the bottom solutions which had collected 1 hour after waterlogging indicated high correlations with the amounts of total-C, total-N, active-Al. Relative activities of Tc in the surface solutions of the air-dried soils decreased with increasing glucose concentration, however, those of sterile soils were almost constant during the experiment. Our results showed Tc adsorption onto the soil is influenced by the activity of microorganisms, that is, the redox potential of the soil is lowered by their activity. Most of the Tc in the surface solution is sorbed on the surface soil strongly and this can be a cause of reduced Tc availability to rice plants during the waterlogged period.