ИСТИНА

The paper presents data on the role of microbiological factors in behavior technetium in the upper aquifers (10-15 m) near the surface repository of radioactive waste (Russia, Tomsk region). Pollution of groundwater has been going on for 50 years and now, in addition to radionuclides, concentration of nitrate ions reached to 5000 mg/l. The presence of nitrate ions and a small amount of dissolved oxygen leads to high values of the redox potential, which creates the prerequisites for technetium high migration activity in higher oxidation states. In the samples of ground water, an active microbial community capable of using nitrate, pertechnetate ions for cell respiration was found. There were also found sulfatereducers capable to produce biogenic sulfides and Fe-reducers. All this bacteria are well known microorganism with significant role in Tc geochemistry [1-45. Laboratory modeling of the microbial stimulation process with organic substrates led to activation of microflora, consumption of nitrate ions to molecular nitrogen, reduction of pertechnetate to Tc(IV). The results of computer geochemical modeling have shown that the immobilization of technetium in the formation occurs mainly in the form of a tetravalent oxide and in a mixture with a biogenic sulphide. while biogenic sulfide ions can play the role of an antioxidant buffer in the event of ingress of new portions of the oxidant into the system. It is important to note that Tc reduction occurs only after nitrate consumption and Eh reduction to anaerobic zone. Thus microbial roles in Tc immobilization are: biogeochemical - Eh reduction due to oxidizer consumption (oxygen, nitrate, etc.); - mineralization by biogenic sulphide interaction and biochemical – dissimilatory Tc reduction due to oxidoreductaze enzymes.