Stability of Immobilized TNT Derivatives in Soil as a Function of Nitro Group Reduction

Abstract

The stability of soil bound metabolites of 2,4,6-trinitrotoluene (TNT) was investigated. Highly TNT-contaminated soil from a former production site was spiked with [ring-UL- 14 C]TNT. An anaerobic short-term treatment (8 days) was carried out and compared with a previously described long-term anaerobic (51 day) treatment. In the short-term experiment the anaerobic treatment was stopped to examine the early-stage effects of the reduction process on the stability of TNT derivatives in soil at the time of the maximum accumulation of aminodinitrotoluenes, whereas the long-term anaerobic treatment was continued until the formation of triaminotoluene. In contrast to the soil from long-term anaerobic treatment, no significant reduction of aminodinitrotoluenes to diaminonitrotoluenes was observed after short-term anaerobic treatment, and the binding of reduced metabolites to the soil was incomplete. In both experiments the anaerobic phase was followed by an aerobic treatment. After the short-term anaerobic/aerobic treatment only 40% of the initial radioactivity was bound to the soil compared to 98% after the extended anaerobic incubation. A significant amount of this bound radioactivity could be released into organic solvents by silylation. The silylation extracts were analyzed by thin-layer chromatography and radiocounting. The released radioactivity from silylation after the long-term treatment was attributed to polar compounds cross-linked with humic material. For the silylated extracts after short-term anaerobic treatment conditions, a significant amount of released radioactivity (28%) found in fractions was attributed to TNT and aminodinitrotoluenes. This study indicates that with a shorter duration of the anaerobic phase in the overall treatment, physically entrapped (sequestered) metabolites remain in the soil. To eliminate physical entrapment, TNT derivatives should be completely reduced by a sufficiently extended anaerobic treatment.