Munitions Constituents Research Articles

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4−, NO3−). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L−1 concentrations of TNT, DNAN, ClO4− and NO3− under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L−1 concentrations of RDX and HMX to <20 μg L−1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L−1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L−1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Thermodynamic Two-Site Surface Reaction Model for Predicting Munition Constituent Reduction Kinetics with Iron (Oxyhydr)oxides.

Iron (oxyhydr)oxides comprise a significant portion of the redox-active fraction of soils and are key reductants for remediation of sites contaminated with munition constituents (MCs). Previous studies of MC reduction kinetics with iron oxides have focused on the concentration of sorbed Fe(II) as a key parameter. To build a reaction kinetic model, it is necessary to predict the concentration of sorbed Fe(II) as a function of system conditions and the redox state. A thermodynamic framework is formulated that includes a generalized double-layer model that utilizes surface acidity and surface complexation reactions to predict sorbed Fe(II) concentrations that are used for fitting MC reduction kinetics. Monodentate- and bidentate Fe(II)-binding sites are used with individual oxide sorption characteristics determined through data fitting. Results with four oxides (goethite, hematite, lepidocrocite, and ferrihydrite) and four nitro compounds (NB, CN-NB, Cl-NB, and NTO) from six separate studies have shown good agreement when comparing observed and predicted surface area-normalized rate constants. While both site types are required to reproduce the experimental redox titration, only the monodentate site concentration controls the MC reaction kinetics. This model represents a significant step toward predicting the timescales of MC degradation in the subsurface.

Electron Transfer Energy and Hydrogen Atom Transfer Energy-Based Linear Free Energy Relationships for Predicting the Rate Constants of Munition Constituent Reduction by Hydroquinones.

No single linear free energy relationship (LFER) exists that can predict reduction rate constants of all munition constituents (MCs). To address this knowledge gap, we measured the reduction rates of MCs and their surrogates including nitroaromatics [NACs; 2,4,6-trinitrotoluene (TNT), 2,4-dinitroanisole (DNAN), 2-amino-4,6-dinitrotoluene (2-A-DNT), 4-amino-2,6-dinitrotoluene (4-A-DNT), and 2,4-dinitrotoluene (DNT)], nitramines [hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and nitroguanidine (NQ)], and azoles [3-nitro-1,2,4-triazol-5-one (NTO) and 3,4-dinitropyrazole (DNP)] by three dithionite-reduced quinones (lawsone, AQDS, and AQS). All MCs/NACs were reduced by the hydroquinones except NQ. Hydroquinone and MC speciations were varied by controlling pH, permitting the application of a speciation model to determine second-order rate constants (k) from observed pseudo-first-order rate constants. The intrinsic reactivity of MCs (oxidants) decreased upon deprotonation, while the opposite was true for hydroquinones (reductants). The rate constants spanned ∼6 orders of magnitude in the order NTO ≈ TNT > DNP > DNT ≈ DNAN ≈ 2-A-DNT > DNP- > 4-A-DNT > NTO- > RDX. LFERs developed using density functional theory-calculated electron transfer and hydrogen atom transfer energies and reported one-electron reduction potentials successfully predicted k, suggesting that these structurally diverse MCs/NACs are all reduced by hydroquinones through the same mechanism and rate-limiting step. These results increase the applicability of LFER models for predicting the fate and half-lives of MCs and related nitro compounds in reducing environments.

Transport of insensitive munitions constituents, NTO, DNAN, RDX, and HMX in runoff and sediment under simulated rainfall

Insensitive munition constituents derived from residues of low order detonations and deposited on military training grounds present environmental risks. A series of rainfall simulation experiments on small soil plots examined the effect of precipitation, soil properties, and particle size on transport of IMX-104 munition components: NTO (3-nitro-1,2,4-triazol-5-one), DNAN (2,4-dinitroanisole), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7- tertranitro-1,3,5,7-tetrazocine). The primary pathways for rainfall driven transport were subsurface infiltration, off-site transport in solution, and transport in solid form including re-adsorption onto soil particles. The transport was solubility dependent with NTO moving mostly in solution, which was dominated by either runoff or infiltration depending on soil. DNAN, RDX, and HMX, were transported primarily in particulate form. The fine energetic fraction (<2 mm) showed the highest mobility, while the coarsest fraction (>4.75 mm) remained in-situ after rainfall. A simple linear model relating energetics transport with sediment yield and energetics particle size and was proposed. These findings provide the first comprehensive mass balance of munition constituents as affected by overland flow under rainfall. They improve our understanding of environmental fate of munitions, can further be used for predictive modelling, developing mitigation strategies, and regulatory compliance.

Modeling the Reduction Kinetics of Munition Compounds by Humic Acids.

Dissolved organic matter (DOM) comprises a sizeable portion of the redox-active constituents in the environment and is an important reductant for the abiotic transformation of nitroaromatic compounds and munition constituents (NACs/MCs). Building a predictive kinetic model for these reactions would require the energies associated with both the reduction of the NACs/MCs and the oxidation of the DOM. The heterogeneous and unknown structure of DOM, however, has prohibited reliable determination of its oxidation energies. To overcome this limitation, humic acids (HAs) were used as model DOM, and their redox moieties were modeled as a collection of quinones of different redox potentials. The reduction and oxidation energies of the NACs/MCs and hydroquinones, respectively, via hydrogen atom transfer (HAT) reactions were then calculated quantum chemically. HAT energies have been used successfully in a linear free energy relationship (LFER) to predict second-order rate constants for NAC reduction by hydroquinones. Furthermore, a linear relationship between the HAT energies and the reduction potentials of quinones was established, which allows estimation of hydroquinone reactivity (i.e., rate constants) from HA redox titration data. A training set of three HAs and two NACs/MCs was used to generate a mean HA redox profile that successfully predicted reduction kinetics in multiple HA/MC systems.

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity.

The environmental fate of 3-nitro-1,2,4-triazol-5-one (NTO) and other insensitive munitions constituents (MCs) is of significant concern due to their high water solubility and mobility relative to legacy MCs. Plant-based biochars have been shown to possess a considerable electron storage capacity (ESC), which enables them to undergo reversible electron transfer reactions. We hypothesized biochar can act as a rechargeable electron donor to effect abiotic reduction of MCs repeatedly through its ESC. To test this hypothesis, MC reduction experiments were performed using wood-derived biochars that were oxidized with dissolved oxygen or reduced with dithionite. Removal of aqueous NTO, an anion at circumneutral pH, by oxidized biochar was minimal and occurred through reversible adsorption. In contrast, NTO removal by reduced biochar was much more pronounced and occurred predominantly through reduction, with concomitant formation of 3-amino-1,2,4-triazol-5-one (ATO). Mass balance and electron recovery with ferricyanide further showed that (1) the amount of NTO reduced to ATO was relatively constant (85-100 μmol per gram of biochar) at pH 6-10; (2) the fraction of biochar ESC reactive toward NTO was ca. 30% of that toward ferricyanide; (3) the NTO-reactive fraction of the ESC was regenerable over multiple redox cycles. We also evaluated biochar transformation of other MCs, including nitroguanidine (NQ), 2,4-dinitroanisole (DNAN), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). While mass and electron balances could not be established due to sorption, DNAN and RDX reduction by reduced biochar was confirmed via detection of multiple reduction products. In contrast, NQ was not reduced under any of the conditions tested. This study is the first demonstration of organic contaminant degradation through biochar's rechargeable ESC. Our results indicate biochar is a regenerable electron storage medium and sorbent that can remove MCs from water through concurrent reduction and sorption, and is thus potentially useful for pollution control and remediation at military facilities.

Transport of Insensitive Munitions Constituents, NTO, DNAN, RDX, and HMX in Runoff and Sediment Under Simulated Rainfall

Transport of Insensitive Munitions Constituents, NTO, DNAN, RDX, and HMX in Runoff and Sediment Under Simulated Rainfall

Removal of munition constituents in stormwater runoff: Screening of native and cationized cellulosic sorbents for removal of insensitive munition constituents NTO, DNAN, and NQ, and legacy munition constituents HMX, RDX, TNT, and perchlorate.

Technologies are needed to address contamination with energetic compounds at military installations. This research developed and evaluated novel and sustainable materials that can be used to remove munition constituents (MC) from stormwater runoff. Initial work focused on 3-nitro-1,2,4-triazol-5-one (NTO), as it is both highly soluble and ionized at environmentally relevant pH values. Screening cellulosic materials indicated that cationized (CAT) versions of pine shavings (pine, henceforth) and burlap (jute) demonstrated >70% removal of NTO from artificial surface runoff. CAT materials also demonstrated >90% removal of the anionic propellant perchlorate. NTO removal (~80%) by CAT pine was similar across initial pH values from 4 to 8.5 S.U. An inverse relationship was observed between NTO removal and the concentration of the major anions chloride, nitrate, and sulfate due to competition for anion binding sites. Sorption isotherms were performed using a mixture of the three primary legacy explosives (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-s-triazine (RDX), 2,4,6-trinitrotoluene (TNT)), the three insensitive MC (nitroguanidine (NQ), NTO, 2,4-dinitroanisole (DNAN)), and perchlorate. Isotherm results indicated that effective removal of both legacy and insensitive MC would best be achieved using a mixture of peat moss plus one or more of the cationized cellulosic materials.

Environmental Characterization of Underwater Munitions Constituents at a Former Military Training Range.

As a result of military activities, unexploded ordnance and discarded military munitions are present in underwater environments, which has resulted in the release of munitions constituents including the high explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), along with their primary degradation products, to the water column and adjacent sediments. The present study focused on the characterization of underwater exposure and concentrations of energetics such as TNT and RDX at the former Vieques Naval Training Range at Bahia Salina del Sur (Vieques, Puerto Rico, USA), a bay with documented high incidence of munitions. In situ passive sampling using polar organic chemical integrative samplers (POCIS) was used for the detection and quantification of constituents in water at target locations approximately 15 to 30 cm from 15 individual potentially leaking munitions, and also at 15 unbiased locations approximately evenly spaced across the Bay. For comparison with POCIS-derived concentrations, grab samples were taken at the POCIS target locations. The POCIS-derived and averaged grab samples agreed within a factor of 3. When detected, munitions constituent concentrations (primarily TNT and RDX) were observed at ultratrace concentrations (as low as 4 ng/L for RDX), except 30 cm from one General Purpose bomb where the TNT concentration was 5.3 µg/L, indicating that low-level contamination exists at Bahia Salina del Sur on a very localized scale despite the relatively high density of munitions, similar to previously reported results for other munitions sites around the world. Sediment and porewater sampled at 4 stations where munitions constituents were detected in the water column had concentrations below detection (approximately 5 µg/kg and 5 ng/L, respectively), suggesting that the sediment was not a sink for these constituents at those locations. Environ Toxicol Chem 2022;41:275-286. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Physicochemical Parameters of Insensitive Munition Constituent Methylnitroguanidine (MeNQ) of Importance to Environmental Fate and Transport

Abstract1‐methyl‐3‐nitroguandine (MeNQ) is being pursued as an insensitive munition to replace legacy munitions such as TNT and RDX. This study was intended to determine the basic physicochemical properties of MeNQ as well as potential environmental fate pathways. The solubility of MeNQ was determined to be 12.92±0.52 g/L and aqueous photolysis was found to efficiently degrade the munition, where its quantum yield and half‐life were found to be 0.009 and 0.59 days, respectively. Hydrolysis was an insignificant degradation pathway resulting in 8.1 % degradation at pH 4, 2.6 % at pH 7, and 6.2 % at pH 9 after five days at an elevated temperature. Volatilization at environmentally relevant conditions was found to be insignificant as the molecule thermally degrades, leading to an inability to calculate Henry's Constant for volatilization from water. Spectroscopic (UV‐vis, FTIR, NMR) and analytical (HPLC) studies were undertaken and are shown alongside the parent molecule, NQ, for comparison to characterize the emerging munition.

Alkaline Hydrolysis Application Procedures for Munitions Constituents Management Practices

Abstract Department of defense (DoD) hand grenade training ranges have implemented alkaline hydrolysis, which is the practice of applying hydrated lime [Ca(OH)2] to range soil, to manage the deposi...

Development of health-based environmental screening levels for insensitive munitions constituents

Dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ) are constituents of insensitive munitions being developed to minimize the acute hazards associated with non-intentional detonation of warheads. Although a reference dose (RfD) has been established for NQ and occupational exposure levels have been developed for all three compounds, current state-of-the science methods were not used. Here we present the latest toxicity data and interpretations for NTO, DNAN, and NQ and use Bayesian Benchmark Dose modeling and a Bayesian approach to applying uncertainty factors to derive tolerable daily intake (TDI) values. A TDI of 0.02 mg/kg-d was calculated for DNAN based on extramedullary hematopoiesis in female rats. A TDI of 2.4 mg/kg-d was derived for NTO based on testicular toxicity in male rats. A TDI of 4.0 mg/kg-d was derived for NQ based on increased fetal resorptions in rabbits. These TDIs are generally an order of magnitude higher than previously developed reference values. These values can be used to inform public health, occupational safety, and product acquisition and stewardship decisions. Drinking water, soil, and tap water screening levels were derived for residential and worker exposure scenarios to help inform risk assessment decisions.

Biotransformation of the insensitive munition constituents 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) by aerobic methane-oxidizing consortia and pure cultures.

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.

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.

Release of Munitions Constituents in Aquatic Environments Under Realistic Scenarios and Validation of Polar Organic Chemical Integrative Samplers for Monitoring.

Munitions constituents (MC) may be released into aquatic environments as a result of underwater military munitions (UWMM) corrosion and breach. The present study investigated the release of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from Composition B fragments under 2 realistic exposure scenarios in a large flume with flow set at 15 cm/s: the first represented the release of MC from fully exposed Composition B, and the second represented release through a small hole, simulating a breached munition. Release of MC through a small hole was approximately 10 times lower than from exposed Composition B, demonstrating the strong influence of exposure to flow on release. The rate of release of MC into the flume was similar to that previously reported in a related field experiment, but a similar mass loss resulted in MC concentration in the field >300 times lower, likely by the dilution effect of hydrodynamic transport. The present study corroborates previous findings of release of MC at UWMM sites resulting in concentrations below the toxicity threshold to most species. In the flume water, MC was quantified using frequent grab sampling and polar organic chemical integrative samplers (POCIS). For TNT, POCIS-estimated time-weighted average concentrations were up to 40% higher than those derived from grab samples, whereas for RDX differences were 6% or less, demonstrating that POCIS provide reliable temporal integration of changing environmental concentrations for common MC. Environ Toxicol Chem 2019;38:2383-2391. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Photo degradation kinetics of insensitive munitions constituents nitroguanidine, nitrotriazolone, and dinitroanisole in natural waters

Herein the matrix effects on the kinetics of aqueous photolysis for the individual munitions constituents of IMX-101: nitroguanidine (NQ), dinitroanisole (DNAN), and nitrotriazolone (NTO) are reported along with the environmentally relevant kinetics and quantum yields. Photolysis potentially represents a major degradation pathway for these munitions in the environment and further understanding the complex matrices effects on photolytic kinetics was needed. Aqueous systems are of particular interest due to the high solubility of NQ (3,800 ppm) and NTO (16,642 ppm) compared to the traditional munitions trinitrotoluene (TNT, 100.5 ppm) and 1,3,5-trinitro-1,3,5-triazine (RDX, 59.9 ppm). Environmental half-lives (and quantum yields) were found to be 0.44 days (1.0×10-2), 0.83 days (3.2×10-4), and 4.4 days (5.9×10-5) for NQ, DNAN, and NTO, respectively, under natural sunlight. In laboratory experiments using nominally 300 nm bulbs in a merry-go-round style reactor in DI water the relative rate of photolysis for the three munitions constituents followed the same order NQ > DNAN > NTO, where DNAN and NTO reacted 57 and 115 times more slowly, respectively, than NQ. In the various environmentally relevant matrices tested in the laboratory experiments NQ was not significantly affected, DNAN showed a faster degradation with increasing ionic strength, and NTO showed a modest salinity and pH dependence on its rate of photolysis.

Ecotoxicity of 2,4-dinitrotoluene to cold tolerant plant species in a sub-Arctic soil

Decades of live-fire training exercises have left millions of acres of military training lands contaminated with various munitions constituents such as dinitrotoluene. Those that pose a threat to higher organisms due to their toxicity and mobility in the soil are of particular concern. Plants aid in the biodegradation and phytoextraction of contaminants, and site-specific ecotoxicity determinations are critical to inform effective remediation strategy. These ecotoxicity determinations are lacking in cold-adapted plants and would be very informative for contaminated training lands in cold regions. Therefore, we conducted a phytotoxicity study to determine the median effective concentration (EC50) of 2,4-dinitrotoluene (2,4-DNT) to four native Alaskan plant species in a sub-Arctic soil at two different temperatures. Plant species investigated were white spruce (Picea glauca), field locoweed (Oxytropis campestris), bluejoint grass (Calamagrostis canadensis), and Jacob’s ladder (Polemonium pulcherrimum). Seedling emergence, fresh plant mass, and dry plant mass were used to model plant response to 2,4-DNT contamination. White spruce was most tolerant to 2,4-DNT contamination (EC50 = 130.8 mg kg−1) and field locoweed was least tolerant (EC50 = 0.38 mg kg−1). In general, Arctic plant species were more vulnerable to 2,4-DNT when compared to plant types native to temperate or tropical regions.

Comparative toxicogenomics of three insensitive munitions constituents 2,4-dinitroanisole, nitroguanidine and nitrotriazolone in the soil nematode Caenorhabditis elegans

BackgroundEcotoxicological studies on the insensitive munitions formulation IMX-101 and its components 2,4-dinitroanisole (DNAN), nitroguanidine (NQ) and nitrotriazolone (NTO) in various organisms showed that DNAN was the main contributor to the overall toxicity of IMX-101 and suggested that the three compounds acted independently. These results motivated this toxicogenomics study to discern toxicological mechanisms for these compounds at the molecular level.MethodsHere we used the soil nematode Caenorhabditis elegans, a well-characterized genomics model, as the test organism and a species-specific, transcriptome-wide 44 K-oligo probe microarray for gene expression analysis. In addition to the control treatment, C. elegans were exposed for 24 h to 6 concentrations of DNAN (1.95–62.5 ppm) or NQ (83–2667 ppm) or 5 concentrations of NTO (187–3000 ppm) with ten replicates per treatment. The nematodes were transferred to a clean environment after exposure. Reproduction endpoints (egg and larvae counts) were measured at three time points (i.e., 24-, 48- and 72-h). Gene expression profiling was performed immediately after 24-h exposure to each chemical at the lowest, medium and highest concentrations plus the control with four replicates per treatment.ResultsStatistical analyses indicated that chemical treatment did not significantly affect nematode reproduction but did induce 2175, 378, and 118 differentially expressed genes (DEGs) in NQ-, DNAN-, and NTO-treated nematodes, respectively. Bioinformatic analysis indicated that the three compounds shared both DEGs and DEG-mapped Reactome pathways. Gene set enrichment analysis further demonstrated that DNAN and NTO significantly altered 12 and 6 KEGG pathways, separately, with three pathways in common. NTO mainly affected carbohydrate, amino acid and xenobiotics metabolism while DNAN disrupted protein processing, ABC transporters and several signal transduction pathways. NQ-induced DEGs were mapped to a wide variety of metabolism, cell cycle, immune system and extracellular matrix organization pathways.ConclusionDespite the absence of significant effects on apical reproduction endpoints, DNAN, NTO and NQ caused significant alterations in gene expression and pathways at 1.95 ppm, 187 ppm and 83 ppm, respectively. This study provided supporting evidence that the three chemicals may exert independent toxicity by acting on distinct molecular targets and pathways.

Photoperiod and Soil Munition Constituent Effects on Phytoaccumulation and Rhizosphere Interactions in Boreal Vegetation

Permafrost thaw is expected to alter biogeochemistry and hydrology, potentially increasing the mobility of soil constituents. Northern latitude boreal forests where permafrost thaw is occurring also experience extreme changes in day length during the growing season. As the effects of photoperiod on plant uptake of soil constituents or interactions with the rhizosphere are unknown, our objective was to determine these interactions with three plant species from different functional groups. A tree, forb, and grass common to military training ranges in this region were grown in soil spiked with or without lead, antimony, or 2,4-dinitrotoluene and grown under 16, 20, or 24 h of light. Plant biomass, soil constituent uptake, and rhizosphere bacterial communities were compared between treatments. Photoperiod had no effect on plant uptake of any soil constituent or on rhizosphere community, indicating that plants and their associated microbial communities adapted to this environment are resilient to extremes in photoperiod. Lead uptake was not significant in any plant species and had no effect on the rhizosphere. Antimony increased the percentage composition of Saprospirales in the rhizospheres of two of the three plants, indicating an interaction between this bacterial order and antimony. Antimony uptake by white spruce (Picea glauca) was considerable, with a mean concentration of 1731 mg kg−1 in roots, while mean shoot concentration was only 155 mg kg−1, indicating its potential to phytostabilize this heavy metal. Although antimony had the strongest impact on the rhizosphere bacterial community, it was also readily accumulated by the grass and tree.

Tracing the cycling and fate of the munition, Hexahydro-1,3,5-trinitro-1,3,5-triazine in a simulated sandy coastal marine habitat with a stable isotopic tracer, 15N-[RDX

Coastal marine habitats become contaminated with the munitions constituent, Hexahydro-1,3,5-trinitro-1,3,5-trazine (RDX), via military training, weapon testing and leakage of unexploded ordnance. This study used 15N labeled RDX in simulated aquarium-scale coastal marine habitat containing seawater, sediment, and biota to track removal pathways from surface water including sorption onto particulates, degradation to nitroso-triazines and mineralization to dissolved inorganic nitrogen (DIN). The two aquaria received continuous RDX inputs to maintain a steady state concentration (0.4 mg L−1) over 21 days. Time series RDX and nitroso-triazine concentrations in dissolved (surface and porewater) and sorbed phases (sediment and suspended particulates) were analyzed. Distributions of DIN species (ammonium, nitrate + nitrite and dissolved N2) in sediments and overlying water were also measured along with geochemical variables in the aquaria. Partitioning of RDX and RDX-derived breakdown products onto surface sediment represented 13% of the total added 15N as RDX (15N-[RDX]) equivalents after 21 days. Measured nitroso-triazines in the aquaria accounted for 6–13% of total added 15N-[RDX]. 15N-labeled DIN was found both in the oxic surface water and hypoxic porewaters, showing that RDX mineralization accounted for 34% of the 15N-[RDX] added to the aquaria over 21 days. Labeled ammonium (15NH4+, found in sediment and overlying water) and nitrate + nitrite (15NOX, found in overlying water only) together represented 10% of the total added 15N-[RDX]. The production of 15N labeled N2 (15N2), accounted for the largest individual sink during the transformation of the total added 15N-[RDX] (25%). Hypoxic sediment was the most favorable zone for production of N2, most of which diffused through porous sediments into the water column and escaped to the atmosphere.