Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitroamine explosive that is a major component in many military high-explosive formulations. In this study, two aerobic bacteria that are capable of using RDX as the sole source of carbon and nitrogen to support their growth were isolated from surface soil. These bacterial strains were identified by their fatty acid profiles and 16S ribosomal gene sequences as Williamsia sp. KTR4 and Gordonia sp. KTR9. The physiology of each strain was characterized with respect to the rates of RDX degradation and [U- Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitroamine that is one of the most powerful and commonly used military explosives. RDX has contaminated soils and groundwater at army ammunition plants and other military sites through its manufacture, use on testing and firing ranges, and disposal (22). RDX is a toxic compound that affects the central nervous system of laboratory animals, causing convulsions (10, 37), and it has been proposed as a possible human carcinogen (38). Information on the environmental factors that determine the transport and fate of RDX in soils is needed to accurately assess the risk posed by RDX and to ensure the sustainability of live-fire training exercises.Anaerobic biodegradation of RDX has been extensively studied (1,6,21,23,25,26,29,(42)(43)(44)(45). McCormick et al. (29) proposed a pathway where RDX undergoes sequential reduction of the nitro groups to form hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine; hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine; and hexahydro-1,3,5-trinitroso-1,3,5-triazine. According to the proposed pathway, this transformation then produces formaldehyde, methanol, hydrazine, and dimethyl hydrazine. Hawari et al. (23) proposed another pathway where ring cleavage occurs before sequential reduction, producing the metabolites methylenedinitramine and bis(hydroxymethyl)nitramine.Although most of the initial strains isolated could only degrade RDX anaerobically (25,32,41,42), several pure strains have subsequently been isolated that aerobically degrade RDX as a nitrogen source. Binks et al. (8) isolated Stenotrophomonas maltophilia PB1 and tentatively identified an RDX metabolite as methylene-N-(hydroxymethyl)-hydroxylamine-NЈ-(hydroxymethyl)nitroamine. Rhodococcus sp. strain DN22 was isolated by Coleman et al. (12) and was found to produce nitrite as a metabolite. Fournier et al. (19) found that DN22 also produces the metabolites ammonia, nitrous oxide, formaldehyde, carbon dioxide, and a dead-end product with a molecular weight of 119 that was later identified as 4-nitro-2,4-diazabutanal by Bhushan et al. (7). Fournier et al. (19) also proposed a pathway for aerobic RDX degradation in which denitration occurs, followed by spontaneous ring cleavage. Further experiments determined that the enzyme responsible for the degradation of RDX by DN22 is a cytochrome P450 enzyme (7, 13). Rhodococcus rhodochrous strain 11Y, which was isolated by SethSmith et al. (33), was found to produce the metabol...

The caged cyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a new explosive that has the potential to replace existing military explosives, but little is known about its environmental toxicity, transport, and fate. We quantified and compared the aerobic environmental fate of CL-20 to the widely used cyclic nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in surface and subsurface soil microcosms. Soil-free controls and biologically attenuated soil controls were used to separate abiotic processes from biologically mediated processes. Both abiotic and biological processes significantly degraded CL-20 in all soils examined. Apparent abiotic, first-order degradation rates (k) for CL-20 were not significantly different between soil-free controls (0.018 < k < 0.030 d(-1)) and biologically attenuated soil controls (0.003 < k < 0.277 d(-1)). The addition of glucose to biologically active soil microcosms significantly increased CL-20 degradation rates (0.068 < k < 1.22 d(-1)). Extents of mineralization of (14)C-CL-20 to (14)CO(2) in biologically active soil microcosms were 41.1 to 55.7%, indicating that the CL-20 cage was broken, since all carbons are part of the heterocyclic cage. Under aerobic conditions, abiotic degradation rates of RDX were generally slower (0 < k < 0.032 d(-1)) than abiotic CL-20 degradation rates. In biologically active soil microcosms amended with glucose aerobic RDX degradation rates varied between 0.010 and 0.474 d(-1). Biodegradation was a key factor in determining the environmental fate of RDX, while a combination of biotic and abiotic processes was important with CL-20. Our data suggest that CL-20 should be less recalcitrant than RDX in aerobic soils.

CAS 135285-90-4 2,4-DANT 2,4-diaminonitrotoluene, TNT degradation intermediate 2,6-DANT 2,6-diaminonitrotoluene, TNT degradation intermediate di/Fe molar ratio of sodium dithionite to reducible ferrous iron in sediment dithionite is used to chemically reduce ferric iron surface phases DCB dithionite-citrate-bicarbonate soil extraction for ferric oxides DNX hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine, RDX deg. intermediate DOD U.S. Department of Defense DOE U.S. Department of Energy EPA U.S. Environmental Protection Agency EPPS N-2-hydroxyethylpiperazine propane sulfonic acid, pH buffer ERDC U.S Army Research and Development Center FRC Field Research Center at the U.S. DOE Oak Ridge Site GC gas chromatography HE high explosive HEPES 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid, pH buffer HMX 1,3,5,7-tetranitro-1,3,5,7-tetrazocane, high melting explosive, CAS 2691-41-0 HPLC-UV high performance liquid chromatography with ultraviolet detection 2-HADNT 2-hydroxyaminodinitrotoluene, TNT degradation intermediate 4-HADNT 4-hydroxyaminodinitrotoluene, TNT degradation intermediate LC/MS liquid chromatography/mass spectrometry MDNA methylene dinitramine, RDX and HMX degradation intermediate MNX hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine, RDX deg. intermediate MSM mineral salt media used for microbial experiments 4-NADB 4-nitro-2,4-diaza-butanal, RDX degradation intermediate PIPES 1,4-piperazinediethanesulfonic acid, pH buffer PLFA phospholipids fatty acids