Mineralization of 2,4- and 2,6-Dinitrotoluene in Soil Slurries

DNT-degrading bacteria can completely degrade mixtures of DNT in liquid cultures without the production of aminonitrotoluenes. We determined whether specific DNT-degrading isolates could also degrade DNT from contaminated soil in the presence of indigenous microbial communities. When 2,4-DNT- and 2,6-DNT-degrading strains were added to a mixture of 2,4-DNT and 2,6-DNT in a soil slurry, disappearance of DNT was accompanied by 14CO2 release and stoichiometric appearance of nitrite. When soil historically contaminated with mixed DNT isomers was used in slurries, the combination of DNT-degrading strains removed all of the DNT from the aqueous phase and over 99% of the initial DNT. Traces of extractable DNT remained associated with the soil; however, the toxicity of the treated soil was low. After an extended acclimation period, the 2,4-DNT, and, much later, the 2,6-DNT, was degraded in the uninoculated control. The results show that aged DNT contamination can be removed effectively from soil. The addition of specific DNT-mineralizing bacteria dramatically enhances the mineralization of DNT in soil slurries. Native bacteria do not convert DNT to aminonitrotoluenes during the short incubation times required for mineralization of DNT.