Incorporation of 14C-labeled 2,4,6-trinitrotoluene metabolites into different soil fractions after anaerobic and anaerobic-aerobic treatment of soil/molasses mixtures

Experiments were conducted to evaluate the level of incorporation of C-14-labeled 2,4,6-trinitrotoluene (TNT) and metabolites into the organic soil matrix of anaerobic and sequential anaerobic-aerobic treated soil/molasses mixtures. After 9 weeks of anaerobic-aerobic incubation with an optimized experimental setup, we determined nearly 84% of the initially applied radioactivity immobilized in different soil fractions, whereas only 57% of the radioactivity was measured as immobilized in the soil organic matrix at the end of the anaerobic treatment (after 5 weeks). After alkaline hydrolyses of the solvent-extracted soil/molasses mixtures, small amounts of radioactivity were found in the humic acid and fulvic acid fraction, whereas the major part of radiolabel was found to be strongly bound to the humin fraction. In agreement with these findings, the amount of extractable radioactivity (water, methanol, and ethyl acetate extractions) decreased from 40% after the anaerobic phase to nearly 9% after the aerobic treatment phase. The transformation of TNT at the end of the experiments was above 95% and 97% after anaerobic and sequential anaerobic-aerobic treatment, respectively. We propose a two-step treatment process (anaerobic-aerobic bioremediation process) with some special procedures during the anaerobic and the aerobic treatment phases as the most promising method for effective, economic, and ecologically acceptable disposal of TNT from contaminated soils by means of immobilization (for example, humification) of this xenobiotic.