Irreversible binding of biologically reduced 2,4,6-trinitrotoluene to soil

To analyze the fate of 2,4,6-trinitrotoluene (TNT) and its reduction products, a TNT-contaminated soil (350 mg TNT/ kg dry soil) was spiked with [ring-UL-14.C]TNT and treated in a laboratory slurry reactor. During an anaerobic/aerobic treatment, the total radioactivity measured in the supernatant and methanolic soil extracts decreased to 2 per cent. The decrease corresponded to an increase of strongly bound radioactivity to the soil. Throughout the whole treatment process, mineralization of TNT was not observed. During the reductive process, unidentified polar substances increased to a maximum amount of 23.2 per cent of the total radioactivity on the day after the start of the experiment. After the end of the anaerobic phase, still 9.7 per cent of the radioactivity was found in this fraction. Only during the aerobic phase did the polar substances disappear completely. The irreversible character of the binding of the reduced metabolites of TNT to the soil was indicated by the failure of desorption even under rigorous and longterm extraction conditions. A significant release of radioactivity could be measured only by using high concentrations of HCl (5.N) or EDTA (12.5 per cent and 5.9 per cent, respectively). However, in none of the extracts were TNT or any reduced metabolites detected by HPLC and 14.C-radiocounting. Size-exclusion chromatography of humic acids extracted from the treated soil indicated that the metabolites of TNT were evenly bound to the complete range of molecular size of the humic acids.