Insensitive Munitions Compound Research Articles

Adsorption of aqueous insensitive munitions compounds by graphene nanoplatelets

Mitigation strategies for potential environmental impacts of insensitive munition (IM) compounds, including 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), nitroguanidine (NQ), and methylnitroguanidine, (MeNQ) are being considered to enhance sustainability of current or potential IM formulations. Graphene nanoplatelets (GnPs) were investigated for adsorptive removal of each compound. GnPs were characterized to determine surface areas, along with particle size and zeta potential at different pH and ionic strength conditions. Adsorption kinetics and isotherm studies were conducted, comparing results against granular activated carbon (GAC). Ionic strength, pH, and temperature were adjusted to inform impacts on adsorptive behaviors and performance. The results indicated that GnPs adsorbed IM compounds more rapidly than GAC. Additionally, GnPs removed DNAN with greater capacity compared to GAC, likely due to π-π interactions. GnPs removed other compounds via van der Waals forces, while GAC exhibited greater adsorption capacities due to higher surface area. Although negative charges associated with GnPs and dissociated NTO species hindered adsorption, pH and ionic strength did not impact other compounds. Moreover, this study reports the first environmental treatment technique for MeNQ. Overall, these findings suggest that GnPs are a promising treatment technology for IM-laden waters, particularly those with compounds like DNAN where specific interactions enhance removal efficiency.

Validation and standardization of SPE and HPLC-UV methods for simultaneous determination of legacy and insensitive munitions

There have been few attempts to consolidate legacy and insensitive munitions analyses. Furthermore, there are no standard methods for insensitive munitions (IM) in tissues, resulting in overlapping methods and supplementary analyses. The goal of the present study was to validate extraction and instrumental methods previously developed and address analytical methodology gaps (missing tissue matrices, combined legacy and IM analysis, and IM compounds). The method encompasses analytes in waters, soils, and tissues. The primary and secondary instrumental methodologies use high performance liquid chromatography-ultraviolet (HPLC-UV) and an alternate LC-mass spectrometry (MS) method, which includes 26 compounds of interest (legacy munitions, IM, IM degradation products, and other munitions compounds). The methods were formally evaluated during a series of double-blind round robin studies including a broad variety of laboratories (Government Department of Defense (DoD), Government non-DoD, ammunition manufacturing, commercial, and academic). The results of these round robin studies were gathered to generate recovery ranges for each of the 26 compounds in each of the matrices. The recovery ranges were subsequently compared with existing recovery ranges for standard explosives analysis, United States Environmental Protection Agency (USEPA) 8330B. The validation study reveals a capable method, which reduces analysis time for IM and legacy munitions analyses.

Treatment of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), in flow-through columns packed with zero-valent iron.

The need for effective technologies to remediate the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) is emerging due to the increasing use by the US Army and environmental concerns about the toxicity and aqueous mobility of NTO. Reductive treatment is essential for the complete degradation of NTO to environmentally safe products. The objective of this study is to investigate the feasibility of applying zero-valent iron (ZVI) in a continuous-flow packed bed reactor as an effective NTO remediation technology. The ZVI-packed columns treated an acidic influent (pH 3.0) or a circumneutral influent (pH 6.0) for 6months (ca. 11,000 pore volumes, PVs). Both columns effectively reduced NTO to the amine product, 3-amino-1,2,4-triazol-5-one (ATO). The column treating the pH-3.0 influent exhibited prolonged longevity in reducing NTO, treating 11-fold more PVs than the column treating pH-6.0 influent until the breakthrough point (defined as when 85% of NTO was removed). The exhausted columns (defined as when only 10% of NTO was removed) regained the NTO reducing capacity by reactivation using 1M HCl, fully removing NTO. After the experiment, solid-phase analysis of the packed-bed material showed that ZVI was oxidized to iron (oxyhydr)oxide minerals such as magnetite, lepidocrocite, and goethite during NTO treatment. This is the first report on the reduction of NTO and the concomitant oxidation of ZVI in continuous-flow column experiments. The evidence indicates that treatment in a ZVI-packed bed reactor is an effective approach for the removal of NTO.

Biodegradation of insensitive munition (IM) formulations: IMX-101 and IMX-104 using aerobic granule technology

A laboratory-scale aerobic granular sludge (AGS) sequencing batch bioreactor (SBR) was initiated in this study for the biodegradation of hazardous insensitive munition (IM) formulation constituents; 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1-nitroguanidine (NQ), and 3-nitro-1,2,4-triazol-5-one (NTO). Efficient (bio)transformation of the influent DNAN and NTO was achieved throughout reactor operation with removal efficiencies greater than 95%. An average removal efficiency of 38.4 ± 17.5% was recorded for RDX. NQ was only slightly removed (3.96 ± 4.15%) until alkalinity was provided in the influent media, which subsequently increased the NQ removal efficiency up to an average of 65.8 ± 24.4%. Batch experiments demonstrated a competitive advantage for aerobic granular biofilms over flocculated biomass for the (bio)transformation DNAN, RDX, NTO, and NQ, as aerobic granules were capable of reductively (bio)transforming each IM compound under bulk aerobic conditions while flocculated biomass could not, thus demonstrating the contribution of inner oxygen-free zones within aerobic granules. A variety of catalytic enzymes were identified in the extracellular polymeric matrix of the AGS biomass. 16 S rDNA amplicon sequencing found Proteobacteria (27.2–81.2%) to be the most abundant phyla, with many genera associated with nutrient removal as well as genera previously described in relation to the biodegradation of explosives or related compounds.

Designing bacterial consortia for the complete biodegradation of insensitive munitions compounds in waste streams.

Insensitive munitions compounds (IMCs), such as 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), are replacing conventional explosives in munitions formulations. Manufacture and use of IMCs generate waste streams in manufacturing plants and load/assemble/pack facilities. There is a lack of practical experience in executing biodegradation strategies to treat IMCs waste streams. This study establishes a proof-of-concept that bacterial consortia can be designed to mineralize IMCs and co-occurring nitroaromatics in waste streams. First, DNAN, 4-nitroanisole (4-NA), and 4-chloronitrobenzene (4-CNB) in a synthetic DNAN-manufacturing waste stream were biodegraded using an aerobic fluidized-bed reactor (FBR) inoculated with Nocardioides sp. JS 1661 (DNAN degrader), Rhodococcus sp. JS 3073 (4-NA degrader), and Comamonadaceae sp. LW1 (4-CNB degrader). No biodegradation was detected when the FBR was operated under anoxic conditions. Second, DNAN and NTO were biodegraded in a synthetic load/assemble/pack waste stream during a sequential treatment comprising: (i) aerobic DNAN biodegradation in the FBR; (ii) anaerobic NTO biotransformation to 3-amino-1,2,4-triazol-5-one (ATO) by an NTO-respiring enrichment; and (iii) aerobic ATO mineralization by an ATO-oxidizing enrichment. Complete biodegradation relied on switching redox conditions. The results provide the basis for designing consortia to treat mixtures of IMCs and related waste products by incorporating microbes with the required catabolic capabilities.

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

Insensitive munitions compounds (IMCs) are emerging nitroaromatic contaminants developed by the military as safer-to-handle alternatives to conventional explosives. Biotransformation of nitroaromatics via microbial respiration has only been reported for a limited number of substrates. Important soil microorganisms can respire natural organic matter (NOM) by reducing its quinone moieties to hydroquinones. Thus, we investigated the NOM respiration combined with the abiotic reduction of nitroaromatics by the hydroquinones formed. First, we established nitroaromatic concentration ranges that were nontoxic to the quinone respiration. Then, an enrichment culture dominated by Geobacter anodireducens could indirectly reduce a broad array of nitroaromatics by first respiring NOM components or the NOM surrogate anthraquinone-2,6-disulfonate (AQDS). Without quinones, no nitroaromatic tested was reduced except for the IMC 3-nitro-1,2,4-triazol-5-one (NTO). Thus, the quinone respiration expanded the spectrum of nitroaromatics susceptible to transformation. The system functioned with very low quinone concentrations because NOM was recycled by the nitroaromatic reduction. A metatranscriptomic analysis demonstrated that the microorganisms obtained energy from quinone or NTO reduction since respiratory genes were upregulated when AQDS or NTO was the electron acceptor. The results indicated microbial NOM respiration sustained by the nitroaromatic-dependent cycling of quinones. This process can be applied as a nitroaromatic remediation strategy, provided that a quinone pool is available for microorganisms.

A Synergistic Nano‐Zerovalent Iron‐Hydrogen Peroxide Technology for Insensitive Munitions Wastewater Treatment

AbstractThe U.S. Army is phasing out legacy munitions compounds that are prone to accidental detonation and replacing them with insensitive munitions compounds (IMCs). The major IMCs, namely 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), 2,4‐dinitroanisole (DNAN), and nitroguanidine (NQ), are not compatible with existing munitions wastewater treatment technologies such as granular activated carbon due to their high water solubilities. In this study, a two‐stage process employing nanoscale zero‐valent iron (nZVI) and hydrogen peroxide (H2O2) was evaluated as a potential technology for the destructive treatment of IMC wastewater. In the first stage, nZVI rapidly and completely degraded all three IMCs and generated dissolved Fe(II). NTO and DNAN were degraded via nitro reduction to 3‐amino‐1,2,4‐triazol‐5‐one and 2,4‐diaminoanisole, respectively. In the second stage, H2O2 was added to oxidize the IMC reduction products through Fenton reaction utilizing the dissolved Fe(II) from the first stage. nZVI‐treated NTO and DNAN samples showed 66 % and 63 % TOC removal after oxidation, respectively. In contrast, NQ reduction products exhibited negligible mineralization. The results with individual IMCs were confirmed by an experiment using synthetic wastewater containing all three IMCs. This study illustrates the potential feasibility of a synergistic and destructive nZVI−H2O2 technology for treating IMC‐laden wastewaters at military facilities.

Method for derivatization and isotopic analysis of the insensitive munition compound 3-nitro-1,2,4-triazol-5-one (NTO)

This paper describes an offline low-temperature derivatization method combined with gas chromatography-isotope ratio mass spectrometry (GC-IRMS) to enable compound-specific isotope analysis (CSIA) of C and N in the explosive compound 3-nitro-1,2,4-triazole-5-one (NTO). NTO is being used widely as a component of insensitive munition (IM) composites such as IMX-101, a formulation that is being used to replace the more shock sensitive TNT in artillery shells. The alkylation of NTO with methyl iodide (MeI) as the derivatization reagent was performed in acetone solution at room temperature using triethylamine (Et3N) as a base catalyst. The methylated product of NTO derivatization was identified as 4-methyl-3-nitro-1,2,4-triazol-5-one (MNTO). Accurate and reproducible results were achieved by systematic optimization of MeI and Et3N concentrations and reaction time. Isotopic values of MNTO obtained by GC-IRMS were normalized against those of two 2,4-dinitroanisole (DNAN) in-house reference materials that had been calibrated with isotopic standard reference materials, USGS40 and USGS41a. The resulting method detection limit for derivatization/GC-IRMS of NTO was 788ng of NTO, yielding a precision of ±0.3‰ for both δ13C and δ15N values in good agreement with δ13C and δ15N values for NTO determined by elemental analyzer-IRMS.

Iron(II) monosulfide (FeS) minerals reductively transform the insensitive munitions compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO)

As military applications of the insensitive munitions compounds (IMCs) 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) increase, there is a growing need to understand their environmental fate and to develop remediation strategies to mitigate their impacts. Iron (II) monosulfide (FeS) minerals are abundant in freshwater and marine sediments, marshes, and hydrothermal environments. This study shows that FeS solids can reduce DNAN and NTO to their corresponding amines under anoxic ambient conditions. The reactions between IMCs and the FeS minerals were surface-mediated since they did not occur when only dissolved Fe2+(aq) and S2−(aq) were present. Mackinawite, a tetragonal FeS with a layered structure, reduced DNAN mainly to 2-methoxy-5-nitroaniline (MENA), which in turn was partially reduced to 2-4-diaminoanisole (DAAN). The layered structure of mackinawite provided intercalation sites likely responsible for partial adsorption of MENA and DAAN. Mackinawite entirely reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO). The reduction of IMCs showed concurrent oxidation of mackinawite to goethite and elemental sulfur. A commercial FeS product, composed mainly of pyrrhotite and troilite, reduced DNAN to DAAN and NTO to ATO. At pH 6.5, DNAN and NTO transformation rates were 667 and 912 μmol h−1 m−2, respectively, on the mackinawite surface and 417 and 1344 μmol h−1 m−2, respectively, on the commercial FeS surface. This is the first report of the reduction of a nitro-heterocyclic compound (NTO) by FeS minerals. The evidence indicates that DNAN and NTO can be rapidly transformed to their succeeding amines in anoxic subsurface environments and aquatic sediments rich in FeS minerals.

Accumulation of Insensitive Munition Compounds in the Earthworm Eisenia andrei from Amended Soil: Methodological Considerations for Determination of Bioaccumulation Factors.

The present study investigates the bioaccumulation of the insensitive munition compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), developed for future weapons systems to replace current munitions containing sensitive explosives. The earthworm Eisenia andrei was exposed to sublethal concentrations of DNAN or NTO amended in Sassafras sandy loam. Chemical analysis indicated that 2- and 4-amino-nitroanisole (2-ANAN and 4-ANAN, respectively) were formed in DNAN-amended soils. The SumDNAN (sum of DNAN, 2-ANAN, and 4-ANAN concentrations) in soil decreased by 40% during the 14-d exposure period. The SumDNAN in the earthworm body residue increased until day 3 and decreased thereafter. Between days 3 and 14, there was a 73% decrease in tissue uptake that was greater than the 23% decrease in the soil concentration, suggesting that the bioavailable fraction may have decreased over time. By day 14, the DNAN concentration accounted for only 45% of the SumDNAN soil concentration, indicating substantial DNAN transformation in the presence of earthworms. The highest bioaccumulation factor (BAF; the tissue-to-soil concentration ratio) was 6.2 ± 1.0 kg/kg (dry wt) on day 3 and decreased to 3.8 ± 0.8 kg/kg by day 14. Kinetic studies indicated a BAF of 2.3 kg/kg, based on the earthworm DNAN uptake rate of 2.0 ± 0.24 kg/kg/d, compared with the SumDNAN elimination rate of 0.87 d-1 (half-life = 0.79 d). The compound DNAN has a similar potential to bioaccumulate from soil compared with trinitrotoluene. The NTO concentration in amended soil decreased by 57% from the initial concentration (837 mg NTO/kg dry soil) during 14 d, likely due to the formation of unknown transformation products. The bioaccumulation of NTO was negligible (BAF ≤ 0.018 kg/kg dry wt). Environ Toxicol Chem 2021;40:1713-1725. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Selecting the best electron donor and operational temperature for the rapid biotransformation of the insensitive munitions compound 2,4-dinitroanisole (DNAN) by anaerobic sludge.

2,4-Dinitroanisole (DNAN) is a toxic compound increasingly used by the military that can be released into the environment on the soil of training fields and in the wastewater of manufacturing plants. DNAN's nitro groups are anaerobically reduced to amino groups by microorganisms when electron donors are available. Using anaerobic sludge as the inoculum, we tested different electron donors for DNAN bioreduction at 20 and 30 °C: acetate, ethanol, pyruvate, hydrogen, and hydrogen + pyruvate. Biotic controls without external electron donors and abiotic controls with heat-killed sludge were also assayed. No DNAN conversion was observed in the abiotic controls. In all biotic treatments, DNAN was reduced to 2-methoxy-5-nitroaniline (MENA), which was further reduced to 2,4-diaminoanisole (DAAN). Ethanol or acetate did not increase DNAN reduction rate compared to the endogenous control. The electron donors that caused the fastest DNAN reductions were (rates at 30 °C): H2 and pyruvate combined (311.28 ± 10.02 μM·d-1·gSSV-1), followed by H2 only (207.19 ± 5.95 μM·d-1·gSSV-1), and pyruvate only (36.35 ± 2.95 μM·d-1·gSSV-1). Raising the temperature to 30 °C improved DNAN reduction rates when pyruvate, H2, or H2 + pyruvate were used as electrons donors. Our results can be applied to optimize the anaerobic treatment of DNAN-containing wastewater.

Catalytic role of solvated electron in the spontaneous degradation of insensitive munition compounds: computational chemistry investigation

The DNAN (2,4-dinitroanisole), NTO (3-nitro-1,2,4-triazol-5-one), and NQ (nitroguanidine) are important insensitive energetic materials used in military applications. They may find their way to the environment during manufacturing, transportation, storage, training, and disposal. A detailed investigation of possible mechanisms for self-degradation of radical anions formed by addition of solvated electron to DNAN, NTO, and NQ species was performed by computational study using the PCM(Pauling)/M06-2X/6-311++G(d,p) approach. Obtained results suggest that only NQ radical anion is able for self-degradation by elimination of nitrite anion. Formation of urea radical on the earlier stage of the NQ radical anion degradation was also predicted.

Computational Investigation on Interactions between Some Munition Compounds and Humic Substances.

Humic acid substances (HAs) in natural soil and sediment environments affect the retention and degradation of insensitive munition compounds and legacy high explosives (MCs): 2,4-dinitroanisole (DNAN), DNi-NH4+, N-methyl-p-nitroaniline (nMNA), 1-nitroguanidine (NQ), 3-nitro-1,2,4-triazol-5-one (NTO; neutral and anionic forms), 2,4,6-trinitrotoluene (TNT), and 1,3,5-trinitro-1,3,5-triazinane (RDX). A humic acid model compound has been considered using molecular dynamics, thermodynamic integration, and density functional theory to characterize the munition binding ability, ionization potential, and electron affinity compared to that in the water solution. Humic acids bind most compounds and act as both a sink and source for electrons. Ionization potentials suggest that HAs are more susceptible to oxidation than the MCs studied. The electron affinity of HAs is very conformation-dependent and spans the same range as the munition compounds. When HAs and MCs are complexed, the HAs tend to radicalize first, thus buffering MCs against reductive as well as oxidative attacks.

The key role of oxygen in the bioremoval of 2,4-diaminoanisole (DAAN), the biotransformation product of the insensitive munitions compound 2,4-dinitroanisole (DNAN), over other electron acceptors

Insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), are replacing conventional explosives. DNAN is anaerobically reduced to 2,4-diaminoanisole (DAAN), a toxic aromatic amine. However, the removal of DAAN under different redox conditions is yet to be elucidated. Herein, we analyzed DAAN consumption in biotic and abiotic microcosms when exposed to different redox conditions (without added electron acceptor, without added electron acceptor but with pyruvate as a co-substrate, with sulfate, with nitrate, and with oxygen), using an anaerobic sludge as inoculum. We observed that DAAN autoxidation, an abiotic reaction, was significant in microaerobic environments. DAAN also reacted abiotically with heat-killed sludge up to a saturation limit of 67.4 μmol DAAN (g VSS heat-killed sludge)−1. Oxygen caused the fastest removal of DAAN in live sludge among the conditions tested. Treatments without added electron acceptors (with or without pyruvate) presented similar DAAN removal performances, although slower than the treatment with oxygen. Sulfate did not exhibit any effect on DAAN removal compared to the treatment without added electron acceptors. Nitrate, however, inhibited the process. An enrichment culture from the microcosms exposed to oxygen could be developed using DAAN as the sole substrate in microaerobic conditions. The enrichment profoundly changed the microbial community. Unclassified microorganisms accounted for 85% of the relative abundance in the enrichment culture, suggesting that DAAN microaerobic removal might have involved organisms that were not yet described. Our results suggest that DAAN microaerobic treatment can be coupled to DNAN anaerobic reduction in sludge, improving the treatment of DNAN-containing wastewaters.

Reduction of 3-Nitro-1,2,4-Triazol-5-One (NTO) by the Hematite-Aqueous Fe(II) Redox Couple.

3-Nitro-1,2,4-triazol-5-one (NTO) is an insensitive munition compound (MC) that has replaced legacy MC. NTO can be highly mobile in soil and groundwater due to its high solubility and anionic nature, yet little is known about the processes that control its environmental fate. We studied NTO reduction by the hematite-Fe2+ redox couple to assess the importance of this process for the attenuation and remediation of NTO. Fe2+(aq) was either added (type I) or formed through hematite reduction by dithionite (type II). In the presence of both hematite and Fe2+(aq), NTO was quantitatively reduced to 3-amino-1,2,4-triazol-5-one following first-order kinetics. The surface area-normalized rate constant (kSA) showed a strong pH dependency between 5.5 and 7.0 and followed a linear free energy relationship (LFER) proposed in a previous study for nitrobenzene reduction by iron oxide-Fe2+ couples, i.e., log kSA = -(pe + pH) + constant. Sulfite, a major dithionite oxidation product, lowered kSA in type II system by ∼10-fold via at least two mechanisms: by complexing Fe2+ and thereby raising pe, and by making hematite more negatively charged and hence impeding NTO adsorption. This study demonstrates the importance of iron oxide-Fe2+ in controlling NTO transformation, presents an LFER for predicting NTO reduction rate, and illustrates how solutes can shift the LFER by interacting with either iron species.

Rapid biotransformation of the insensitive munitions compound, 3-nitro-1,2,4-triazol-5-one (NTO), by wastewater sludge.

As the use of the new insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) increases, wastewaters, runoff and groundwater containing NTO will be generated. Little is known about the fate of NTO during biological wastewater treatment. The objective of this study was to explore the ability of wastewater sludges to promote the biotransformation of NTO. Three different sludges, i.e., anaerobic granular sludge, anaerobic digested sludge, and return activated sludge, were used to study the biotransformation of NTO under anaerobic conditions. Three different electron donor amendments were compared- hydrogen, ethanol, and acetate. Mixed microbial communities in each of the three sludge sources were effective in the reductive biotransformation of NTO. 3-amino-1,2,4-triazol-5-one (ATO) was observed as the major product of NTO biotransformation. The highest maximum specific rate of NTO reduction, about 120mg NTO/g volatile suspended solids/d, was observed in anaerobic granular sludge with hydrogen or ethanol supplied as electron donors. NTO biotransformation to ATO by anaerobic digested sludge was also studied under denitrifying conditions. In this case, reduction of NTO started only after complete denitrification of added nitrate. An important implication of this paper is that sludge from wastewater treatment plants can rapidly and readily reduce NTO to ATO.

Methods for simultaneous determination of legacy and insensitive munition (IM) constituents in aqueous, soil/sediment, and tissue matrices

Currently, no standard method exists for analyzing insensitive munition (IM) compounds in environmental matrices, with or without concurrent legacy munition compounds, resulting in potentially inaccurate determinations. The primary objective of this work was to develop new methods of extraction, pre-concentration, and analytical separation/quantitation of 17 legacy munition compounds along with several additional IM compounds, IM breakdown products, and other munition compounds that are not currently included in U. S. Environmental Protection Agency (EPA) Method 8330B. The eight additional compounds included were nitroguanidine, 3-nitro-1,2,4-triazol-5-one, picric acid, 2,4-dinitroanisole, 2,4-dinitrophenol, 2-nitrophenol, 4-nitrophenol, and new surrogate ortho-nitrobenzoic acid (o-NBA). Analytical methods were developed to enable sensitive, simultaneous detection and quantitation of the 24 IM and legacy compounds, including two orthogonal high-performance liquid chromatography (HPLC) column separations with either ultraviolet (UV) or mass spectrometric (MS) detection. Procedures were developed for simultaneous extraction of all 24 analytes and two surrogates (1,2-dinitrobenzene, 1,2-DNB; o-NBA) from high- and low-level aqueous matrices and solid matrices, using acidification, solid phase extraction (SPE), or solvent extraction (SE), respectively. For low-level aqueous samples extracted by SPE, all compounds were recovered within current Department of Defense Quality Systems Manual (DoD QSM) Ver5.3 accepted limits for aqueous samples analyzed by EPA Method 8330B (57–135%), except NQ, which was consistently recovered at approximately 50%. Likewise, all compounds were recovered from six geographically/geochemically unique soil types within current QSM accepted limits for solid samples analyzed by EPA Method 8330B (64–135%). Further, the majority of compounds were recovered from four tissue types within current limits for solids, with generally low recovery only for Tetryl (from 4 to 62%). A preparatory chromatographic interference removal procedure was adapted for tissue extracts, as various analytical interferences were observed for all studied tissue types.

Alkaline hydrolysis pathway of 2,4-dinitroanisole verified by 18O tracer experiment

The environmental fate of insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), has drawn increasing attention because of their growing use in military activities. One of the main attenuation mechanisms of DNAN degradation in aqueous environments is alkaline hydrolysis. We investigated the pathway for alkaline hydrolysis of DNAN at pH 12 by a combined approach of experiment and theory. An experiment using 18O-labeled water was performed to verify the reaction pathway. Calculated free energies for two putative reaction pathways by density-functional theory optimized at the SMD(Pauling)/M06-2X/6-311++G(2d,2p) level including explicit solvation of DNAN by 10 H2O molecules and one OH− ion gave a prediction in agreement with the experimental result. The verified reaction pathway for alkaline hydrolysis of DNAN is a SN2Ar nucleophilic aromatic substitution with a methoxy leaving group (OCH3) at the C1 site.

An integrated quantum chemical and experimental approach for exploring the structures and properties of insensitive munitions interacting with ions in bulk water

Alternatives to legacy munitions and explosives, materials that feature increased stability against external stimuli without compromising their energetic yields are currently being developed. The environmental interactions of such energetic materials need to be addressed, especially as their use becomes more widespread. In order to explore such compounds with environmental influences in mind, we assess the electronic structure and properties of these insensitive munitions (IMs) compounds in modeled hard water using both theory and experiment. To model the IMs in hard water, we have used density functional theory with the M06-2X functional and the 6-311 + G(d,p) basis set with explicit water molecules to capture features like hydrogen bonding, implicit solvent to incorporate bulk water effects, and select ions that would be present in natural water. We ensured the nature of the potential energy surfaces of optimized geometries through vibrational frequency calculations under the harmonic approximation. Several electronic properties, such as oxidation and reduction potentials and electron affinity and ionization potential, for each system are presented. Additionally, cyclic voltammetry experiments were performed, and obtained results were compared with quantum chemical predictions. The experimental reduction potentials are found to be in good agreement with the predicted results. Overall, the reduction potentials predicted by density functional theory for the IM-ion-water complexes are shifted compared with the corresponding isolated munition such that reduction or oxidation would be more facile in the presence of water and ions.

Microbial Enrichment Culture Responsible for the Complete Oxidative Biodegradation of 3-Amino-1,2,4-triazol-5-one (ATO), the Reduced Daughter Product of the Insensitive Munitions Compound 3-Nitro-1,2,4-triazol-5-one (NTO).

3-Nitro-1,2,4-triazol-5-one (NTO) is one of the main ingredients of many insensitive munitions, which are being used as replacements for conventional explosives. As its use becomes widespread, more research is needed to assess its environmental fate. Previous studies have shown that NTO is biologically reduced to 3-amino-1,2,4-triazol-5-one (ATO). However, the final degradation products of ATO are still unknown. We have studied the aerobic degradation of ATO by enrichment cultures derived from the soil. After multiple transfers, ATO degradation was monitored in closed bottles through measurements of inorganic carbon and nitrogen species. The results indicate that the members of the enrichment culture utilize ATO as the sole source of carbon and nitrogen. As ATO was mineralized to CO2, N2, and NH4+, microbial growth was observed in the culture. Co-substrates addition did not increase the ATO degradation rate. Quantitative polymerase chain reaction analysis revealed that the organisms that enriched using ATO as carbon and nitrogen source were Terrimonas spp., Ramlibacter-related spp., Mesorhizobium spp., Hydrogenophaga spp., Ralstonia spp., Pseudomonas spp., Ectothiorhodospiraceae, and Sphingopyxis. This is the first study to report the complete mineralization of ATO by soil microorganisms, expanding our understanding of natural attenuation and bioremediation of the explosive NTO.