Stability of immobilized 2,4,6-trinitrotoluene metabolites in soil under long-term leaching conditions

Abstract

2,4,6-Trinitrotoluene (TNT)-contaminated soil was remediated by an anaerobic/aerobic slurry process. Prior to treatment, the soil was spiked with [14C]-TNT. Leaching experiments were carried out with the decontaminated soil to determine the degree of binding of the radiolabel under a variety of conditions. To simulate natural degradation processes of soil organic matter, each of three columns was subjected to a different treatment known to enhance biological transformation over a 92-week period. Only minor amounts of radioactivity (1.0% of the bound radioactivity) were released from treated soil incubated in the presence of the lignin-degrading fungus Phanerochaete chrysosporium. Simulation of seasonal variation in temperature, including freezing of the soil, did not cause a significant release of radioactivity (1.4%). Growth and flowering of the bush bean Phaseolus vulgaris only released 0.8% of the bound radioactivity to the eluate; however, during the decomposition phase, an additional 7.7% of the bound radioactivity was released. We propose that this radioactivity was bound to soluble humic material that was mobilized due to a pH shift during the decomposition of the plant organic matter. This is supported by the observation that neither free TNT nor its metabolites were present in the eluate. During the different incubation experiments, 3.9 to 8.5% of the bound radioactivity was found as 14CO2. The results indicate a slow turnover of even strongly bound immobilized metabolites of TNT.