Combined Biotic–Abiotic 2,4-Dinitroanisole Degradation in the Presence of Hexahydro-1,3,5-trinitro-1,3,5-triazine

Abstract

The Department of Defense has developed new explosive formulations in which traditionally used cyclic nitramines such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) have been updated with the insensitive munition (IM) 2,4-dinitroanisole (DNAN). Understanding combined degradation of both compounds at explosive-contaminated sites will allow remediation approaches that simultaneously target both contaminants. DNAN reduction in the presence of RDX was evaluated in abiotic experiments using substoichiometric, stoichiometric, and superstoichiometric concentrations of ferrous iron and anthrahydroquinone disulfonate within a pH range from 7.0 to 9.0. Biological degradation was investigated in resting cell suspensions of Geobacter metallireducens strain GS-15, a model Fe(III)-reducing Bacteria. Cells were amended into anoxic tubes buffered at pH 7.0, with initial 100 μM DNAN and 40−50 μM RDX. In both abiotic and biological experiments, the DNAN was reduced through the intermediate 2-methoxy-5-nitroaniline or 4-methoxy-3-nitroaniline to 2,4-diaminoanisole. In biological experiments, the RDX was reduced to form methylenedinitramine, formaldehyde (HCHO), and ammonium (NH 4 + ). Cells were able to reduce both DNAN and RDX most readily in the presence of extracellular electron shuttles and/or Fe(III). DNAN degradation (abiotic and biotic) was faster than degradation of RDX, suggesting that the reduction of IMs will not be inhibited by cyclic nitramines, but degradation dynamics did change in mixtures when compared to singular compounds.

Enhanced bioremediation of RDX and Co-Contaminants perchlorate and nitrate using an anaerobic dehalogenating consortium in a fractured rock aquifer

“…Although microbial community analyses could not be conducted in this study to determine specific microbes involved in the degradation reactions, WBC-2 characterization has shown a wide variety of microorganisms (Jones et al, 2006;Lorah et al, 2008a;Molenda et al, 2016). Microbial groups in WBC-2; span many of the groups identified as containing RDX-degraders, including Pseudomonas, Clostridia, and Geobacteraceae (Kwon and Finneran, 2006;Cho et al, 2013Cho et al, , 2015Cho et al, , 2016Wang et al, 2017;Niedźwiecka et al, 2020). Another study showed that anaerobic cultures developed to degrade chlorinated ethenes (predominantly trichloroethene), similar to WBC-2, could also degrade RDX (Young et al, 2006).…”

Quinone Moieties Link the Microbial Respiration of Natural Organic Matter to the Chemical Reduction of Diverse Nitroaromatic Compounds

“…30,63 Additionally, the microbial nitroaromatic compound reduction using synthetic quinones as electron shuttles has also been demonstrated. 22,23 However, to the best of our knowledge, this is the first study showing that the regeneration of the quinone moieties of NOM via chemical reactions with nitroaromatic compounds allows the cells to produce energy, even when only very low concentrations of quinones are present. By demonstrating the cycle using real humic acids, the results also validate previous studies that applied AQDS as an electron shuttle.…”

“…NOM components such as ESHA, PPHA, Leonardite humic acid, and Suwannee River humic and fulvic acids have been previously shown to be possible final electron acceptors for anaerobic microbial respiration. , Additionally, the microbial nitroaromatic compound reduction using synthetic quinones as electron shuttles has also been demonstrated. , However, to the best of our knowledge, this is the first study showing that the regeneration of the quinone moieties of NOM via chemical reactions with nitroaromatic compounds allows the cells to produce energy, even when only very low concentrations of quinones are present. By demonstrating the cycle using real humic acids, the results also validate previous studies that applied AQDS as an electron shuttle. , Furthermore, the process was studied for a culture composed mostly of Geobacter , a model soil microorganism, and using NOM, which is ubiquitous in many environmental matrices. Thus, the results have important implications on the mechanisms by which microbes can obtain energy from the reduction of nitroaromatic contaminants in nature and establish that the nitroaromatic reduction can occur wherever NOM respiration exists.…”

“…By demonstrating the cycle using real humic acids, the results also validate previous studies that applied AQDS as an electron shuttle. 22,23 Furthermore, the process was studied for a culture composed mostly of Geobacter, a model soil microorganism, and using NOM, which is ubiquitous in many environmental matrices. Thus, the results have important implications on the mechanisms by which microbes can obtain energy from the reduction of nitroaromatic contaminants in nature and establish that the nitroaromatic reduction can occur wherever NOM respiration exists.…”

“…As an alternative to biotic pathways, the abiotic reduction of nitroaromatic compounds can be carried out by bulk reducing agents, such as reactive minerals, , hydroquinones, − or reduced natural organic matter (NOM). , Due to its reversible electron transfer and storage capacity, NOM is a crucial participant in several biogeochemical processes, comprising nitroaromatic transformation. ,,, NOM’s redox reactivity has been demonstrated to occur due to the presence of quinone moieties as a major source of reversible reducing groups in NOM. For instance, electron paramagnetic resonance (EPR) detection of semiquinone radicals in NOM indicates that semiquinones were derived from one-electron redox transformations of quinone or hydroquinone moieties .…”