Effect of pH and temperature on the sorption of Np and Pa to mixed anaerobic bacteria

Biogeochemical Factors of Cs, Sr, U, Pu Immobilization in Bottom Sediments of the Upa River, Located in the Zone of Chernobyl Accident

Laboratory modeling of Cs, Sr, U, Pu immobilization by phytoplankton of the river Upa, affected after the Chernobyl accident, has been carried out. Certain conditions are selected for strong fixation of radionuclides in bottom sediments due to biogeochemical processes. The process of radionuclide removal from the water phase via precipitation was based on their accumulation by phytoplankton, stimulated by nitrogen and phosphorus sources. After eight days of stimulation, planktonic phototrophic biomass, dominated by cyanobacteria of the genus Planktothrix, appears in the water sample. The effectiveness of U, Pu and Sr purification via their transfer to bottom sediment was observed within one month. The addition of ammonium sulfate and phosphate (Ammophos) led to the activation of sulfate- and iron-reducing bacteria of the genera Desulfobacterota, Desulfotomaculum, Desulfosporomusa, Desulfosporosinus, Thermodesulfobium, Thiomonas, Thiobacillus, Sulfuritallea, Pseudomonas, which form sulphide ferrous precipitates such as pyrite, wurtzite, hydrotroillite, etc., in anaerobic bottom sediments. The biogenic mineral composition of the sediments obtained under laboratory conditions was verified via thermodynamic modeling.

Ability of anaerobic microorganisms to associate with iodine: 125I tracer experiments using laboratory strains and enriched microbial communities from subsurface formation water

Iodine-129 ((129)I) is a fission product with a half-life of 15.7 million years. Because of its long half-life, high mobility, and high affinity to the human body, (129)I is considered as one of the most problematic radionuclides in nuclear waste disposals in deep geological formation. In this study, 16 strains of anaerobic microorganisms, including nitrate-reducing bacteria, iron-reducing bacteria, sulfate-reducing bacteria, and methanogens, were cultured anaerobically with a radioiodine tracer ((125)I) to determine whether they possess the ability to associate with iodine. We evaluated it by association efficiency, that was determined by measuring the decrease in (125)I activity in the culture supernatant. It was found that the efficiency of about half of the strains was below detection limit (1.0%), and that of the remaining strains varied from 1.0% to 6.3%, although it was not statistically significant. Similar experiments were conducted by using anaerobic microbial communities inhabiting the iodine-rich subsurface formation water collected from the Minami-kanto gas field in Japan. The specific uptake of iodine by the microbial communities was estimated to be 0.71-2.0 microg g(-1) dry weight of biomass, indicating that the association ability was, if present, very limited. These results suggest that anaerobic microorganisms, in contrast with aerobic microorganisms, neither enhance nor repress the mobility of (129)I, in the case of discharge of this radionuclide from disposal facilities into the surrounding environment.