Reductive transformation of bound trinitrophenyl residues and free TNT during a bioremediation process analyzed by immunoassay

To follow the fate of bound metabolites of TNT in soil, a synthetic trinitrophenyl residue covalently linked to humic acids was used as model compound. A selective monoclonal antibody was able to detect chemical changes of the nitro groups of the bound residues. The genera possibility of reductive transformations of nitro groups of bound molecules and the reductions rates should be determined. In comparison to the reduction of free TNT and its metabolites, the reductive transformation of the bound trinitrophenyl residue was delayed, and the transformation rate was considerably slower. Trinitrophenyl residues also could be detected by the immunoassay in humic acids extracted from TNT contaminated soil. The reductive transformation of these trinitrophenyl residues started after the reduction of free TNT. At the end of the treatment, small amounts of these residues were still detectable indicating that some of these structures were not completely reduced during the process. From present results one can conclude that the further reduction of nitro groups of bound metabolites requires a prolonged anaerobic treatment. Not only the monitoring of free nitroaromatic compounds is recommended during the bioremediation process but also the measurement of bound residues to determine the optimal conditions and duration of the treatment.