Impact of a model soil on the biotransformation of 2,4,6-trinitrotoluene and its amine metabolites

Abstract

The end of the Cold War resulted in the closure of many sites where explosives were manufactured, processed, and stored, and packaging practices left behind highly contaminated surface waters, groundwater and soils. Chief among the explosives contaminating these sites is the xenobiotic, 2,4,6- trinitrotoluene (TNT) whose electron-withdrawing nitro-groups make this aromatic compound highly resistant to biodegradation. An alternative option to mineralization as a bioremediation strategy, however, is immobilization. TNT can be biotransformed under reducing conditions to 2,4,6-triaminotoluene (TAT), a compound that researchers are currently investigating due to its potential to become irreversibly bound to soil components. The objectives of this research were to conduct TNT biotransformation studies under planktonic conditions and compare the results to those under slurry conditions. These objectives would also contribute to the overall goals of a DEPSCoR-sponsored project entitled "Biofilm-Induced Changes in Soil Organic Matter Structure and the Resulting Impact on the Bioavailability of Sorbed 2,4,6-Trinitrotoluene and its Amine Metabolites". Three experiments were performed for this research. The first was to create a model soil that was both well-characterized yet chemically representative of real soil constituents. The second was to add TNT to actively growing Desulfovibrio sp. strain SHV and monitor TAT formation. The third was a combination of the first two experiments, adding strain SHV to the model soil to both observe TAT formation and its disappearance from solution over time. The results of the TNT biotransformation studies indicated that TNT was transformed to TAT, which became the dominant metabolite in four weeks under planktonic conditions. Under slurry conditions, TAT became the dominant metabolite in two days and disappeared from solution by day three.