Microbial transformation of 2,4,6-trinitrotoluene and other nitroaromatic compounds

Abstract

A variety of nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT), were reduced by hydrogen in the presence of enzyme preparations from Veillonella alkalescens. Consistent with the proposed reduction pathway, R-NO2 R-NO R-NHOH H, R-NH2, 3 mol of H2 was utilized per mol of nitro group. The rates of reduction of 40 mono-, di-, and trinitroaromatic compounds by V. alkalescens extract were determined. The reactivity of the nitro groups depended on other substituents and on the position of the nitro groups relative to these substituents. In the case of the nitrotoluenes, the para-nitro group was the most readily reduced, the 4-nitro position of 2,4-dinitrotoluene being reduced first. The pattern of reduction of TNT (disappearance of TNT and reduction products formed) depended on the type of preparation (cell-free extract, resting cells, or growing culture), on the species, and on the atmosphere (air or H2). The

Holding-Time Estimates for Soils Containing Explosives Residues: Comparison of Fortification vs. Field Contamination

“…At room temperature an average of 68.4% remained after 3 d. This increased stability of 2,4-DNT relative to TNT at room temperature agrees with the results of Maskarinec et al [8]. Under refrigeration, a slow rate of loss continued throughout the study and, by day 14, peaks corresponding to the expected reduction products, 2-amino-4-nitrotoluene and 4-amino-2-nitrotoluene [27], were observed. Refrigeration was inadequate to ensure an MHT of even 7 d for 2,4-DNT in some soils.…”

“…For refrigerator storage, TNB disappearance was slower than at room temperature, but even so, an average of only 15.3% remained after 7 d. By 28 d the concentration was below its detection limit. Coincident with this disappearance was an increased level of 3,5-DNA, the expected initial "soil-stable" microbiological transformation (reduction) product [27]. These changes are summarized for all three soils at refrigerator storage in Figure 3.…”

“…The behavior of TNT paralleled that of TNB except that the rate of disappearance was reduced. The expected stable transformation products, 2-and 4-AmDNT [27], were observed to increase as TNT concentrations declined. The rate of loss of TNT varied from soil to soil in the following order: Ft. Edwards > Charlton > Windsor, the same order that was found for TNB.…”

Bioremediation of TNT-Contaminated Soil: A Laboratory Study

“…Degradation of TNT was demonstrated by mineralization of [ 14 C]TNT, metabolite formation, and the presence of [ 14 C] in the cell biomass as TCA-precipitable material. Each of the biological systems reported in the literature as acting on TNT catalyzes the reduction of at least one nitro group [13,18,19]. In the present work, the microorganisms produced amino intermediates and were also able to mineralize TNT significantly.…”

“…Because the ring carbons of TNT were uniformly labeled, conversion to [ 14 C]CO 2 clearly denotes ring cleavage. The mechanism of TNT ring cleavage is not clear; however, the first step was a reduction process with the production of amino intermediates (4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene), as reported previously by many authors [18][19][20]. Molasses acts as an essential cosubstrate to greatly increase the soil microbial population, which then produces the necessary enzymes to degrade the TNT.…”