Stability of immobilized TNT derivatives in soil as a function of nitro group reduction

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 longterm 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 longterm 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.