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

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 (NH4+). 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.

Iron and Electron Shuttle Mediated (Bio)degradation of 2,4-Dinitroanisole (DNAN).

The Department of Defense has developed explosives with the insensitive munition 2,4-dinitroanisole (DNAN), to prevent accidental detonations during training and operations. Understanding the fate and transport of DNAN is necessary to assess the risk it may represent to groundwater once the new ordnance is routinely produced and used. Experiments with ferrous iron or anthrahydroquinone-2,6-disulfonate (AH2QDS) were conducted from pH 6.0 to 9.0 with initial DNAN concentrations of 100 µM. DNAN was degraded by 1.2 mM Fe(II) at pH 7, 8, and 9, and rates increased with increasing pH. Greater than 90% of the initial 100 µM DNAN was reduced within 10 min at pH 9, and all DNAN was reduced within 1 h. AH2QDS reduced DNAN at all pH values tested. Cells of Geobacter metallireducens were added in the presence and absence of Fe(III) and/or anthraquinone-2,6-disulfonate (AQDS), and DNAN was also reduced in all cell suspensions. Cells reduced the compound directly, but both AQDS and Fe(III) increased the reaction rate, via the production of AH2QDS and/or Fe(II). DNAN was degraded via two intermediates: 2-methoxy-5-nitroaniline and 4-methoxy-3-nitroaniline, to the amine product 2,4-diaminoanisole. These data suggest that an effective strategy can be developed for DNAN attenuation based on combined biological-abiotic reactions mediated by Fe(III)-reducing microorganisms.