Reductive Transformation of Bound Trinitrophenyl Residues and Free TNT during a Bioremediation Process Analyzed by Immunoassay

Abstract

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 general 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.

Enzymatic Transformation and Binding of Labeled 2,4,6‐Trinitrotoluene to Humic Substances during an Anaerobic/Aerobic Incubation

“…It has been shown that intestinal microorganisms are effective in reducing TNT through an oxygen‐insensitive NAD(P)H nitroreductase (Bryant and DeLuca, 1991). After incubation in the presence of anaerobic microorganisms, 4ADNT was the major nitroaromatic compound identified by HPLC which corresponded to results from Achtnich et al (1999b) and Bruns‐Nagel et al (2000) However, when catechol was added as a model humic substance in the presence or absence of laccase, the portion of reduced nitroaromatics was considerably lower (Table 1). During the anaerobic phase, the vast majority of the nitroaromatics resided in the solution and were completely extractable.…”

A Study of the Use of Alfalfa (Medicago sativa L.) for the Phytoremediation of Organic Contaminants in Soil

“…The observed unavailability of TNT in the high organic matter soil could be due to an irreversible binding (chemisorption) of TNT and its metabolites to the humic fraction of the soil organic matter (Daun et al, 1998). As found in a previous study performed by Achtnich et al (1999), it is also possible that covalent binding of partially reduced TNT metabolites to the soil organic matter is an important immobilization mechanism. Furthermore, Daun et al (1998) indicated that the soil organic matter (humic acids) has greater specific binding capacity for TNT and its metabolites than the clay fraction of the soil.…”

Effects of electrolytes on the reduction of 2,4‐dinitrotoluene by zero‐valent iron

“…The electron withdrawing properties of nitro groups on DNTs makes them resistant to chemical or biological oxidation and to hydrolysis 3. Consequently, DNTs are environmentally persistent and make remediation of waste streams and contaminated ground water difficult.…”