Mobilization of Bi, Cd, Pb, Th, and U Ions from Contaminated Soil and the Influence of Bacteria on the Process

Sterile or nonsterile soil experimentally contaminated with bismuth, cadmium, lead, thorium, and uranium as uranyl then incubated with sterile water showed negligible release of metals from either sample. 10 mM cysteine solution mixed with metal-amended soil under each condition: (a) nonsterile; (b) sterile; (c) sterile then inoculated with pure cultures of soil bacterial isolates; indicated that 90.5% Bi, 4.3% Cd, and 25.9% Pb were released from the nonsterile mix within 24 hours. With uranium, 57.9% was released gradually over eight days. The same pattern was observed with sterile soil, but in smaller amounts, 30.6%, 2.6%, 5.2% and 28.3% respectively. Sterile soil containing cysteine then reinoculated with any of four bacteria isolated from the original soil resulted in release of metal greater than from sterile soil. Nonsterile soil released more Bi and U than any of the sterilized reinoculated soils tested. In the case of Cd and Pb some sterilized reinoculated soils released more Cd and Pb than the nonsterile soil while others released less. In all cases extraction of Th was negligible. The results indicated that (a) active microorganisms influence the ability of soil to retain or release metals and (b) cysteine is an effective agent for the release of some metals from soil. 10 mM glycine removed 40.7% and 5.1% of U from nonsterile and sterile soil, respectively. Commercially prepared thioglycollate culture medium resulted in significant release of both Cd and Th from of nonsterile soil.