Bioaccumulation and chemical modification of Tc by soil bacteria.
Bioaccumulation and chemical modification of pertechnetate (TcO4-) by aerobically and anaerobically grown soil bacteria and by pure cultures of sulfate-reducing bacteria (Desulfovibrio sp.) were studied to gain insight on the possible mechanisms by which bacteria can affect the solubility of Tc in soil. Aerobically grown bacteria had no apparent effect on TcO4-; they did not accumulate Tc nor modify its chemical form. Anaerobically grown bacteria exhibited high bioaccumulation and reduced TcO4-, enabling its association with organics of the growth medium. Reduction was a metabolic process and not merely the result of reducing conditions in the growth medium. Association of Tc with bacterial polysaccharides was observed only in cultures of anaerobic bacteria. Sulfate-reducing bacteria efficiently removed Tc from solution and promoted its association with organics. Up to 70% of the total Tc in the growth medium was bioaccumulated and/or precipitated. The remaining Tc in soluble form was entirely associated with organics. Pertechnetate was not reduced by the same mechanism as dissimilatory sulfate reduction, but rather by some reducing agent released in the growth medium. A calculation of the amount of Tc that could be associated with the bacterial biomass present in soil demonstrates that high concentration ratios in cultures do not necessarily imply that bioaccumulation is an important mechanism for long-term retention of Tc in soil.
Henrot
J
J
Graduate Program in Ecology, University of Tennessee, Knoxville.
D001419:Bacteria / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D013670:Sodium Pertechnetate Tc 99m / Q000378:metabolism; D012988:Soil Microbiology; D012989:Soil Pollutants; D012990:Soil Pollutants, Radioactive; D012995:Solubility
D011135:Polysaccharides, Bacterial; D012989:Soil Pollutants; D012990:Soil Pollutants, Radioactive; D013670:Sodium Pertechnetate Tc 99m