Anoxic biotransformation of 2,4-dinitrotoluene (DNT) was examined and two denitrifying enrichment cultures were developed. In one, the inoculum was acclimated to treatment of munitions wastewater that contains DNT; the other was derived from activated sludge that was not routinely exposed
to nitroaromatics. DNT was consumed readily by both cultures only when ethanol was provided as a primary substrate, with the rate of transformation twice as fast in the acclimated culture. [14C]DNT was used to track the metabolites. A negligible amount of the DNT was mineralized.
The principal initial biotransformation pathway was reduction of DNT to aminonitrotoluenes. Subsequent transformations in the acclimated culture resulted in formation of 6-nitroindazole, 2-nitrotoluene, and 4-nitrotoluene, which have not previously been reported as metabolites from DNT. Acetylation
at the para position was another important transformation pathway in the acclimated culture, resulting in accumulation of 4-acetamide-2-nitrotoluene and 4-acetamidetoluene. Reduction of aminonitrotoluenes to 2,4-diaminotoluene also occurred, followed by conversion of approximately one-third
of the 14C activity to nonfilterable material. The majority of the soluble DNT metabolites from the unacclimated culture were hydrophilic; these were characterized by gradient elution high-pressure liquid chromatography analysis and ion pairing chromatography as approximately equal
amounts of negatively charged and neutral compounds. The diversity and characteristics of these metabolites indicates that biotransformation of DNT under anoxic conditions does not necessarily eliminate the toxicological hazards associated with the parent compound. Metabolite formation should
be taken into consideration when determining discharge criteria for DNT-contaminated wastewaters exposed to denitrifying environments.
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