Behavior of technetium in soil: Sorption-desorption processes

The objectives of the first part of this thesis are to determine if soil bacteria affect TcO/sub 4//sup /minus//, and if so, by which mechanism. Bioaccumulation of Tc and chemical modification of TcO/sub 4//sup /minus// were studied in mixed cultures of aerobic and anaerobic soil bacteria, and in pure culture of sulfate-reducing bacteria. Bacteria were grown in liquid media and Tc association with organics was determined by gel permeation chromatography. Mixed aerobic bacteria had no apparent effect on TcO/sub 4//sup /minus//. Mixed anaerobic bacteria reduced TcO/sub 4//sup /minus//, enabling its association with the organics of the growth medium. The second part of the thesis has for objectives to (1) provide data on the kinetics and the extent of Tc sorption and desorption under conditions realistic for the field; (2) determine the importance of microbial activity, soil water content, Tc concentration, and organic matter on Tc sorption; and (3) describe the behavior of Tc under fluctuating water tension. Technetium sorption was studied in 2 contrasting horizons of an Ultisol: Ap horizon (2.73% organic matter, high-microbial activity) and Bt horizon (0.51% organic matter, low microbial activity). Fresh samples of the 2 horizons were incubated in the laboratory under various soil water contents more » and Tc concentrations. At time intervals, soil water was collected from the samples by centrifugation and sorption was calculated from the change of Tc concentration in the soil water. Microbial activity was reduced by gamma-irradiation of the soil. « less