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2,4-Dinitroanisole (DNAN) is a main constituent in various new insensitive munition formulations. Although DNAN is susceptible to biotic and abiotic transformations, in many environmental instances, transformation mechanisms are difficult to resolve, distinguish, or apportion on the basis solely of analysis of concentrations. We used compound-specific isotope analysis (CSIA) to investigate the characteristic isotope fractionations of the biotic (by three microbial consortia and three pure cultures) and abiotic (by 9,10-anthrahydroquinone-2-sulfonic acid [AHQS]) transformations of DNAN. The correlations of isotope enrichment factors (Λ N/C ) for biotic transformations had a range of values from 4.93 ± 0.53 to 12.19 ± 1.23, which is entirely distinct from Λ N/C values reported previously for alkaline hydrolysis, enzymatic hydrolysis, reduction by Fe 2+ -bearing minerals and iron-oxide-bound Fe 2+ , and UV-driven phototransformations. The Λ N/C value associated with the abiotic reduction by AHQS was 38.76 ± 2.23, within the range of previously reported values for DNAN reduction by Fe 2+ -bearing minerals and iron-oxide-bound Fe 2+ , albeit the mean Λ N/C was lower. These results enhance the database of isotope effects accompanying DNAN transformations under environmentally relevant conditions, allowing better evaluation of the extents of biotic and abiotic transformations of DNAN that occur in soils, groundwaters, surface waters, and the marine environment.

We present the first report of biotransformation of 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN), replacements for the explosives 1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT), respectively, by methane-oxidizing cultures under aerobic conditions. Two consortia, dominated by Methylosinus spp., degraded both compounds with transient production of reduced NTO products, and non-stoichiometric production of reduced DNAN products. No release of inorganic nitrogen was observed with either compound, indicating that NTO and DNAN may be utilized as nitrogen sources by these consortia. The pure culture Methylosinus trichosporium OB3b also degraded both compounds. Degradation was observed in the presence of acetylene (a known inhibitor of methane monooxygenase; MMO) when methanol was supplied, indicating that MMO was not involved. Furthermore, studies with purified soluble MMO (sMMO) from OB3b indicated that neither compound was a substrate for sMMO. Degradation was inhibited by 2-iodosobenzoic acid, but not by dicoumarol, suggesting involvement of an oxygen- and dicoumarol-insensitive (nitro)reductase. These results indicate methanotrophs can aerobically degrade NTO and DNAN via one or more (nitro)reductases, with sMMO serving a supporting role deriving reducing equivalents from methane. This finding is important because methanotrophic bacteria are widely dispersed, and may represent a previously unrecognized route of NTO and DNAN biotransformation in aerobic environments., (Copyright © 2020 Elsevier B.V. All rights reserved.)