Microbial degradation of explosives: biotransformation versus mineralization

Abstract

The nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is a reactive molecule that biotransforms readily under both aerobic and anaerobic conditions to give aminodinitrotoluenes. The resulting amines biotransform to give several other products, including azo, azoxy, acetyl and phenolic derivatives, leaving the aromatic ring intact. Although some Meisenheimer complexes, initiated by hydride ion attack on the ring, can be formed during TNT biodegradation, little or no mineralization is encountered during bacterial treatment. Also, although the ligninolytic physiological phase and manganese peroxidase system of fungi can cause some TNT mineralization in liquid cultures, little to no mineralization is observed in soil. Therefore, despite more than two decades of intensive research to biodegrade TNT, no biomineralization-based technologies have been successful to date. The non-aromatic cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) lack the electronic stability enjoyed by TNT or its transformed products. Predictably, a successful enzymatic change on one of the N-NO2 or C-H bonds of the cyclic nitramine would lead to a ring cleavage because the inner C-N bonds in RDX become very weak (<2 kcal/mol). Recently this hypothesis was tested and proved feasible, when RDX produced high amounts of carbon dioxide and nitrous oxide following its treatment with either municipal anaerobic sludge or the fungus Phanaerocheate chrysosporium. Research aimed at the discovery of new microorganisms and enzymes capable of mineralizing energetic chemicals and/or enhancing irreversible binding (immobilization) of their products to soil is presently receiving considerable attention from the scientific community.

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

“…It has been proposed that nitroso intermediates may be formed as a result of both aerobic and anaerobic HMX degradation. Hawari et al [64] proposed an alternative pathway for HMX degradation involving ring oxidation, which results in the transient production of methylenedinitramine and bis(hydroxymethyl)nitramine. These products may be further transformed to nitrous oxide and formaldehyde, which then may be converted to nitrogen, carbon dioxide, and methane via denitrification or methanogenesis.…”

UV–VIS spectroscopy of 2,4,6-trinitrotoluene-hydroxide reaction

“…TNT has been listed as a priority pollutant, a Class C carcinogen, and has adverse effects on humans, plants, and animals (Rosenblatt et al 1991;Smith 1991;Won, DiSalvo, and Ng 1976;Palazzo and Leggett 1986;Simini et al 1995). TNT remediation methods, such as incineration, composting, bioremediation, and photolysis, have been used with mixed success (Bruns-Nagel et al 1998;Dillert et al 1995;Lang et al 1998;Haselhorst 1999;Hawari et al 2000). Existing technologies are hindered by problems such as high energy costs, costly equipment, extensive soil excavation, very slow degradation rates, or incomplete degradation of the explosive contaminants.…”

TNT biotransformation potential of the clinical isolate of Salmonella typhimurium - potential ecological implications

“…Several researchers have reported TNT degradation by aerobic bacteria, which use denitration pathway [2,4,20,21] and showed that TNT denitration is profitable to bacteria. [22,23] The level of denitration was substantially higher in static cultures than in orbital shaken cultures (data not shown).…”