Adsorption and attenuation behavior of 3-nitro-1,2,4-triazol-5-one (NTO) in eleven soils

Heavy metal immobilization and radish growth improvement using Ca(OH)2-treated cypress biochar in contaminated soil

Heavy metal contamination poses a significant threat to soil quality, plant growth, and food safety, and directly affects multiple UN SDGs. Addressing this issue and offering a remediation solution are vital for human health. One effective approach for immobilizing heavy metals involves impregnating cypress chips with calcium hydroxide (Ca(OH)2) to enhance the chemical adsorption capacity of the resulting woody charcoal. In the present study, un-treated cypress biochar (UCBC) and calcium-treated cypress biochar (TCBC), were introduced into pristine and contaminated soil, at rates of 3, 6, and 9% (w/w). Both BCs were alkaline (UCBC pH: 8.9, TCBC pH: 9.7) with high specific surface area, which improved the soil properties (pH, EC, and OM). Radish (Raphanus sativus) cultivated in pots revealed that both UCBC and TCBC demonstrated significant improvements in growth attributes and heavy metal immobilization compared to the control, with TCBC exhibiting superior effects. The TCBC surface showed highly active nanosized precipitated calcium carbonate particles that were active in immobilizing heavy metals. The application of TCBC at a rate of 9% resulted in a substantial reduction in Zn and Cu uptake by radish roots and shoots. In contaminated soil, Zn uptake by radish roots decreased by 55% (68.3-31.0 mg kg-1), and shoots by 37% (49.3-31.0 mg kg-1); Cu uptake decreased by 40% (38.6-23.2 mg kg-1) in roots and 39% (58.2-35.2 mg kg-1) in shoots. Uptake of Pb was undetectable after TCBC application. Principal component analysis (PCA) highlighted the potential of TCBC over UCBC in reducing heavy metal concentrations and promoting radish growth. Future research should consider the long-term effects and microbial interactions of TCBC application.

Investigating residue dissolution of insensitive high explosives in two sandy soil types: A predictive modelling approach

The demand for munitions that are less likely to detonate accidentally has led to an increased use of Insensitive High Explosives (IHE), which contain substances like 2,4-dinitroanisole (DNAN) and 5-nitro-1,2,4-triazol-3-one (NTO). These substances have different properties compared to traditional explosives, and their potential environmental impact is not well understood. When these explosives are used in live-fire training exercises, their residues end up in the soil. It is important to determine how these residues dissolve and enter the soil. This study aimed to experimentally measure the rate at which an IHE formulation dissolves when exposed to rainwater with pH levels of 5.0 and 6.5, and to simulate how these residues dissolve and move through two different soil types. The dissolution rates were determined by conducting experiments in which IHE particles (30-60 mg) were exposed to water with varying pH levels and temperatures. The results showed that the dissolution rate of NTO did not vary with pH, while the dissolution rate of DNAN and RDX decreased with decreasing pH. Specifically, the dissolution rate of DNAN decreased from 18 ± 40 μg min-1 at pH 6.5 to 6 ± 4 μg min-1 at pH 5.0, while the dissolution rate of RDX decreased from 8 ± 4 to 3 ± 1 μg min-1. These findings were used to develop a stochastic model that successfully simulated the concentration of IHE in the leachate from soil columns over time. A sensitivity analysis revealed that while dissolution rates determined the amount of mass entering the soil, they did not significantly regulate the amount of mass that migrated through the soil and leached out of the soil columns.

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 6 months (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 1 M 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.

Evaluating the effect of insensitive high explosive residues on soil using an environmental quality index (EQI) approach

The environmental impact of Insensitive High Explosive (IHE) detonation residues to soil quality was assessed using a series of outdoor soil mesocosms. Two different soils were used including a pristine sandy soil and a land-degraded soil collected from a training range. Both soils were spiked with an IHE mixture comprised of 53 % NTO, 32 % DNAN and 15 % RDX at three different concentrations 15, 146 and 367 mg/kg respectively. The concentration levels were derived from approximate residues from 100 detonations over a 2 week training period. A set of five physico-chemical and biological indicators representative of the two soils were selected to develop environmental quality indexes (EQI). It was found that none of the concentrations tested for the pristine soil affected the chemical, biological and physical indicators, suggesting no decrease in soil quality. In contrast, the EQI for the degraded soil was reduced by 24 %, mainly due to a decrease in the chemical and biological components of the soil. Therefore, it is concluded that depending on the soil health status, IHE residues can have minor or severe consequences on soil health. Further studies are needed to determine the environmental impact of IHE on soil and water especially in the case where a larger number of detonations are more likely to be carried out on a training range.

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.

Photolysis of 3-Nitro-1,2,4-triazol-5-one: Mechanisms and Products

Insensitive munitions formulations that include 3-nitro-1,2,4-triazol-5-one (NTO) are replacing traditional explosive compounds. While these new formulations have superior safety characteristics, the compounds have greater environmental mobility, raising concern over potential contamination and cleanup of training and manufacturing facilities. Here, we examine the mechanisms and products of NTO photolysis in simulated sunlight to further inform NTO degradation in sunlit surface waters. We demonstrate that NTO produces singlet oxygen and that dissolved oxygen increases the NTO photolysis rate in deionized water. The rate of NTO photolysis is independent of concentration and decreases slightly in the presence of Suwannee River Natural Organic Matter. The apparent quantum yield of NTO generally decreases as pH increases, ranging from 2.0 × 10-5 at pH 12 to 1.3 × 10-3 at pH 2. Bimolecular reaction rate constants for NTO with singlet oxygen and hydroxyl radical were measured to be (1.95 ± 0.15) × 106 and (3.28 ± 0.23) × 1010 M-1 s-1, respectively. Major photolysis reaction products were ammonium, nitrite, and nitrate, with nitrite produced in nearly stoichiometric yield upon the reaction of NTO with singlet oxygen. Environmental half-lives are predicted to span from 1.1 to 5.7 days. Taken together, these data enhance our understanding of NTO photolysis under environmentally relevant conditions.

Adsorption and Removal Kinetics of 2,4-Dinitroanisole and Nitrotriazolone in Contrasting Freshwater Sediments: Batch Study

Environmental release of 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) is of great concern due to high migration potential in the environment. In the present study we evaluated the adsorption and microbially-mediated removal kinetics of dissolved DNAN and NTO in contrasting freshwater sediments with different total organic carbon (TOC) content. River sand (low TOC), pond silt (high TOC), clay-rich lake sediment (low TOC), wetland silt (high TOC), carbonate sand (low TOC), and iron-rich clay (low TOC) were evaluated. Separate abiotic and biotic bench-top sediment slurry incubations were carried out at 23, 15, and 4 °C for DNAN and NTO. Experiments were conducted over 3 weeks. Time series aqueous samples and sediment samples collected at the end of the experiment were analyzed for DNAN and NTO concentrations. The DNAN compound equilibrated with sediment within the first 2 h after addition whereas NTO showed no adsorption. 2,4-Dinitroanisole adsorbed more onto fine-grained organic-rich sediments (K_d  = 2-40 L kg^-1  sed^-1 ) than coarse-grained organic-poor sediments (K_d  = 0.2-0.6 L kg^-1  sed^-1 ), and the TOC content and cation exchange capacity of sediment were reliable predictors for abiotic DNAN adsorption. Adsorption rate constants and equilibrium partitioning constants for DNAN were inversely proportional to temperature in all sediment types. The biotic removal half-life of DNAN was faster (t_1/2  = 0.1-58 h) than that of NTO (t_1/2  = 5-347 h) in all sediment slurries. Biotic removal rates (t_1/2  = 0.1-58 h) were higher than abiotic rates (t_1/2  = 0.3-107 h) for DNAN at 23 °C. Smaller grain size coupled with higher TOC content enhanced biotic NTO and DNAN removal in freshwater environments. Environ Toxicol Chem 2023;42:46-59. © 2022 SETAC.

A laboratory rill study of IMX-104 transport in overland flow

The deposition of explosive contaminants in particulate form onto the soil surface during low-order detonations can lead to ground and surface water contamination. The vertical fate and transport of insensitive munitions formulation IMX-104 through soil has been thoroughly studied, however the lateral transport of explosive particles on the surface is less known. The objective of this research was to understand the impact of overland flow on the transport of IMX-104 constituent compounds 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The effect of overland flow was examined in a rill flume using several flow rates (165-, 265-, and 300-mL min^-1) and IMX-104 particle sizes (4.75-9.51 mm, 2.83-4.75 mm, 2-2.83 mm, and <2 mm). We found that the smaller particles were transported more in solution and with the sediment compared to the larger particles, which had a higher percent mass remaining on the surface. As flow rate increased, there was an increase in the percent mass found in solution and sediment and a decrease in the percent mass remaining on the surface. NTO fate was dominated by transport in solution, while DNAN, RDX and HMX were predominantly transported with the sediment. This research provides evidence of the role of overland flow in the fate of energetic compounds.

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.

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.

Improved corrosion resistance and thermal stability of insensitive NTO explosives by MXene modification in the presence of non-covalent bonds

Strong corrosiveness to metals is the main factor restricting the widespread application of the insensitive explosive 3-nitro-1,2,4-triazole-5-one (NTO).

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS)

3-Nitro-1,2,4-triazol-5-one (NTO) is a major and the most water-soluble constituent in the insensitive munition formulations IMX-101 and IMX-104. While NTO is known to undergo redox reactions in soils, its reaction with soil humic acid has not been evaluated. We studied NTO reduction by anthraquinone-2,6-disulfonate (AQDS) and Leonardite humic acid (LHA) reduced with dithionite. Both LHA and AQDS reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO), stoichiometrically at alkaline pH and partially (50-60%) at pH ≤ 6.5. Due to NTO and hydroquinone speciation, the pseudo-first-order rate constants (k_Obs) varied by 3 orders of magnitude from pH 1.5 to 12.5 but remained constant from pH 4 to 10. This distinct pH dependency of k_Obs suggests that NTO reactivity decreases upon deprotonation and offsets the increasing AQDS reactivity with pH. The reduction of NTO by LHA deviated continuously from first-order behavior for >600 h. The extent of reduction increased with pH and LHA electron content, likely due to greater reactivity of and/or accessibility to hydroquinone groups. Only a fraction of the electrons stored in LHA was utilized for NTO reduction. Electron balance analysis and LHA redox potential profile suggest that the physical conformation of LHA kinetically limited NTO access to hydroquinone groups. This study demonstrates the importance of carbonaceous materials in controlling the environmental fate of NTO.

Outdoor dissolution and photodegradation of insensitive munitions formulations IMX-101 and IMX-104: Photolytic transformation pathway and mechanism study

New munition compounds have been developed to replace traditional explosives to prevent unintended detonations. However, insensitive munitions (IM) can leave large proportion of unexploded charge in the field, where it is subjected to photodegradation and dissolution in precipitation. The photolytic reactions occurring on the surfaces of IMX-101 and IMX-104 formulations and the subsequent fate of photolytic products in the environment were thoroughly investigated. The constituents of IMX-101 and IMX-104 formulations dissolve sequentially under rainfall in the order of aqueous solubility: 3-nitro-1,2,4-triazol-5-one (NTO) > nitroguanidine (NQ) > 2,4-dinitroanisole (DNAN) > 1,3,5-hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). A linear relationship between DNAN dissolution and rainwater volume was observed (r²: 0.86-0.99). It was estimated that it would take 16-228 years to completely dissolve these formulation particles under natural environmental conditions in Oracle, AZ. We used LC/MS/MS and GC/MS to examine the dissolution samples from IMX-101 and 104 particles exposed to rainfall and sunlight and found six DNAN photo-transformation products including 2-methoxy-5-nitrophenol, 4-methoxy-3-nitrophenol, 4-methoxy-3-nitroaniline, 2-methoxy-5-nitroaniline, 2,4-dinitrophenol, and methoxy-dinitrophenol, which are in good agreement with computational modeling results of bond strengths. The main DNAN photodegradation pathways are therefore proposed. Predicted eco-toxicity values suggested that the parent compound DNAN, methoxy-nitrophenols, methoxy-nitroanilines and the other two products (2,4-dinitrophenol and methoxy-dinitrophenol) would be harmful to fish and daphnid. Our study provides improved insight about the rain dissolution and photochemical behavior of IM formulations under natural conditions, which helps to form target-oriented strategies to mitigate explosive contamination in military training sites.

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.

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.

Adsorption behaviour of 1,3,5-trinitroperhydro-1,3,5-triazine, 2,4-dinitroanisole and 3-nitro-1,2,4-triazol-5-one on commercial activated carbons

Insensitive high explosives are increasingly being used to replace more sensitive formulations, however large quantities of environmentally hazardous wastewater are generated from loading, assembling and packing processes. Currently, there is limited literature regarding the treatment of wastewater contaminated with these hazardous insensitive high explosive materials such as 1,3,5-trinitroperhydro- 1,3,5-triazine (RDX), 2,4-dinitoranisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO). The preferred method of explosive wastewater treatment is adsorption by activated carbon, usually through treatment columns or fluidised beds that are simple to operate and cost effective. The aim of this research was to assess whether commercially available activated carbons would be suitable and economically viable to treat explosive wastewater containing RDX, DNAN and NTO. Bottle point tests were used to determine adsorption capacity and adsorption kinetics for the individual insensitive high explosives with three different activated carbons. Equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherms to determine the mechanisms of adsorption. Six hour bottle point tests for a mixture of the three insensitive high explosive constituents were used to consider possible preferential adsorption. As expected, RDX and DNAN were adsorbed at concentrations up to 40 mg.L-1 and 150 mg.L-1 respectively by the activated carbons tested, demonstrating the viability of treatment by adsorption. However, at the high concentrations of NTO expected in wastewater (1400 mg.L-1) activated carbons were rapidly saturated, suggesting that treatment of NTO contaminated wastewater would require prohibitively large quantities of activated carbon compared to RDX and DNAN.

Flexible porous aerogels decorated with Ag nanoparticles as an effective SERS substrate for label-free trace explosives detection

Sensitive and reliable methods for explosives detection are of significance in homeland security due to the serious threats of explosives in terrorist attack events. However, such suitable sensors are still rare. Herein, porous silica aerogels decorated with silver nanoparticles (SiO2-Ag hybrids) were prepared and applied as a flexible SERS substrate for ultrasensitive explosives detection. It is worth noting that the silica aerogel we prepared had good flexibility compared with traditional silica aerogels, which effectively avoided structural damage during sample collection. Also, because of excellent adsorption performance provided by the silica aerogel, trace explosive 3-nitro-1,2,4-triazol-5-one (NTO) could be enriched and realized by label-free detection. Combined with the plasma enhancement provided by Ag NPs decorated around these porous aerogels, the limit of detection for explosive NTO was as low as 7.94 × 10-10 M. As far as we know, this SiO2-Ag hybrid SERS substrate was firstly used for the detection of explosives. It presented good sensitivity and reproducibility for analyte sensing. Most importantly, this is a label-free method for trace explosives detection and has a good application prospect in homeland security.

Chronic oral toxicity of 3-nitro-1,2,4-triazol-5-one (NTO) in rats

To evaluate the effects of chronic exposure to 3-nitro-1,2,4-triazol-5-one (nitrotriazolone, NTO), male and female rats were given ad libitum access to NTO in drinking water at concentrations of 0, 36, 110, 360, 1100, and 3600 mg/L for one year. NTO did not affect body weight, body weight gain, or food consumption in either sex. No treatment-related effects were observed in clinical chemistry and hematology parameters at the 6 month or one year sampling. At both the interim and final sampling, males and females from the 3600 mg/L group produced smaller volumes of urine that was darker, more concentrated, and contained more bilirubin than the controls. Total and motile sperm counts were not affected by NTO treatment. Absolute and relative organ weights did not differ between control and NTO treated groups for either sex. Spontaneous age-related neoplasms occurred in controls and NTO groups at rates consistent with published historic controls. NTO was generally non-toxic in females at the doses tested. Toxicity in males was limited to testicular toxicity as demonstrated in previous studies. Chronic exposure did not result in testicular toxicity at lower doses and the toxicity observed only in the high dose group in this study is less severe than that observed in shorter exposures of previous studies, suggesting differences may be associated with influences of study design on kinetics. A Benchmark Dose (BMD) of 1604 mg/L (76 mg/kg-day) and a Benchmark Dose Lower Bound (BMDL₁₀) of 921 mg/L (44 mg/kg-day) were determined for chronic effects of NTO in male rats.

The effect of soil type on the extraction of insensitive high explosive constituents using four conventional methods

Explosive contamination is commonly found at military and manufacturing sites (Hewitt et al., 2005; Clausen et al., 2004; Walsh et al., 2013). Under current environmental legislation the extent of the contamination must be characterized by soil sampling and subsequent separation of the explosive contaminants from the soil matrix by extraction to enable chemical analysis and quantification (Dean, 2009). It is essential that the extraction method can consistently recover explosive residue from a variety of soil types i.e. all materials that have not degraded or irreversibly bound to the matrix, so that any resultant risk is not underestimated. In this study, five different soil types with a range of organic content, particle size and pH, were spiked with a mixture of RDX, DNAN, NQ and NTO at 50 mg/kg and were extracted using one of four one-step extraction methods: stirring, shaking, sonication, and accelerated solvent extraction (ASE). Analysis of the extraction efficiencies of the four methods found that they were broadly successful for the extraction of all IHE constituents from all five soils (an average of 84% ± 14% recovery across 80 extractions). However, soils with high organic content (Total Organic Content (TOC) ≥ 2%) were found to significantly affect extraction efficiency and reproducibility. NTO and DNAN were the least consistent in extraction efficiency with poorest recovery of NTO as low as 37% ± 2%. Of the four tested methods shaking was found to be the most reproducible, though less efficient than stirring (64%-91%). ASE was found to have the most variable results for extraction of IHE constituents suggesting that ASE was the most affected by the different soil types. Therefore, it is recommended that the efficiency and reproducibility of the selected extraction method should be validated by extracting known concentrations of the IHE from the soil of interest and that any required correction factors are reported.

Adsorption and oxidation of 3-nitro-1,2,4-triazole-5-one (NTO) and its transformation product (3-amino-1,2,4-triazole-5-one, ATO) at ferrihydrite and birnessite surfaces

The emerging insensitive munitions compound (IMC) 3-nitro-1,2,4-triazole-5-one (NTO) is currently being used to replace conventional explosives such as 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), but the environmental fate of this increasingly widespread IMC remains poorly understood. Upon release from unexploded solid phase ordinances, NTO exhibits high aqueous solubility and, hence, potential mobilization to groundwater. Adsorption and abiotic transformation at metal oxide surfaces are possible mechanisms for natural attenuation. Here, the reactions at ferrihydrite and birnessite surfaces of NTO and its biotransformation product, 3-amino-1, 2, 4-triazol-5-one (ATO), were studied in stirred batch reactor systems at controlled pH (7.0). The study was carried out at metal oxide solid to solution ratios (SSR) of 0.15, 1.5 and 15 g kg^-1. The samples were collected at various time intervals up to 3 h after reaction initiation, and analyzed using HPLC with photodiode array and mass spectrometric detection. We found no detectable adsorption or transformation of NTO upon reaction with birnessite, whereas ATO was highly susceptible to oxidation by the same mineral, showing nearly complete transformation within 5 min at 15 g kg^-1 SSR to urea, CO_2(g) and N_2(g). The mean surface-area-normalized pseudo-first order rate constant (k) for ATO oxidation by birnessite across all SSRs was 0.05 ± 0.022 h^-1 m^-2, and oxidation kinetics were independent of dissolved O₂ concentration. Both NTO and ATO were resistant to oxidation by ferrihydrite. However, NTO showed partial removal from solution upon reaction with ferrihydrite at 0.15 and 1.5 g kg^-1 SSR and complete loss at 15 g kg^-1 SSR due to strong adsorption. Conversely, ATO adsorption to ferrihydrite was much weaker than that measured for NTO.

Investigation into the environmental fate of the combined Insensitive High Explosive constituents 2,4-dinitroanisole (DNAN), 1-nitroguanidine (NQ) and nitrotriazolone (NTO) in soil

Contamination of military ranges by the use of explosives can lead to irreversible environmental damage, specifically to soil and groundwater. The fate and effects of traditional explosive residues are well understood, while less is known about the impact of Insensitive High Explosives (IHEs) that are currently being brought into military service. Current research has focussed on the investigation of individual constituents of IHE formulations, which may not be representative of real-world scenarios when explosive residues will be deposited together. Therefore, this study investigated the fate and transport of the combined IHE constituents 2,4-dinitroanisole (DNAN), 1-nitroguanidine (NQ) and 3-nitro-1,2,4-triazol-5-one (NTO) in two UK soil types. Static experiments ran for 9weeks to determine the fate of the combined explosive constituents in soil by monitoring the rate of degradation. Transport was examined by running soil column experiments for 5weeks, with a watering regime equivalent to the average yearly UK rainfall. Both static and soil column experiments confirmed that DNAN and NTO started to degrade within twenty-four hours in soil with high organic content, and were both completely degraded within sixty days. NQ was more stable, with 80% of the original material recovered after sixty days. The major degradation product of DNAN in the test soils was 2-amino-4-nitroanisole (2-ANAN), with trace amounts of 4-amino-2-nitroanisole. NTO was rapidly degraded in soil with high organic content, although no degradation products were identified. Results supported work from literature on the individual constituents DNAN, NQ and NTO suggesting that the three explosives in combination did not interact with each other when in soil. This study should provide a useful insight into the behaviour of three combined Insensitive High Explosive constituents for the predication of soil and water contamination during military training.

Dissolution and transport of insensitive munitions formulations IMX-101 and IMX-104 in saturated soil columns

Military training exercises can result in deposition of energetic residues on range soils, which ultimately can contaminate groundwater with munitions constituents. Column experiments followed by HYDRUS-1D modeling were conducted to evaluate dissolution and transport of energetic constituents from the new insensitive munitions (IM) formulations IMX-101, a mixture of 3-nitro-1,2,4-triazol-5-one (NTO), nitroguanidine (NQ), and 2, 4-dinitroanisole (DNAN), and IMX-104, a mixture of NTO, 1,3,5-hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and DNAN. NTO and DNAN are emerging contaminants associated with the development of insensitive munitions as replacements for traditional munitions. Flow interruption experiments were performed to investigate dissolution kinetics and sorption non-equilibrium between soil and solution phases. The results indicated that insensitive munitions compounds dissolved in order of their aqueous solubility, consistent with prior dissolution studies conducted in the absence of soil. Initial elution of the high concentration pulse of highly soluble NTO and NQ was followed by lower concentrations, while DNAN had generally lower and more constant concentrations in leachate. The sorption of NTO and NQ was low, while RDX, 1,3,5,7-octahydro-1,3,5,7-tetranitrotetrazocine (HMX, an impurity in technical grade RDX), and DNAN all exhibited appreciable sorption. DNAN transformation was observed, with formation of amino-reduction products 2-ANAN (2-amino-4-nitroanisole) and 4-ANAN (4-amino-2-nitroanisole). HYDRUS-1D model, incorporating one-dimensional advective-dispersive transport with particle dissolution and first-order solute transformation was used to simulate the measured breakthrough curves. Optimized dissolution parameters varied widely but were correlated between compounds in the same formulation. Determined adsorption coefficients generally agreed with values determined from batch and column studies conducted with pure NTO and DNAN, while mass-loss rate coefficients were in better agreement with ones from batch than column studies possibly due to suppression of microbial transformation during elution of high concentrations of explosives. Even in the low organic matter soils selected in this study DNAN experienced significant retardation and transformation, indicating potential for its natural attenuation.

Biodegradation of insensitive munition formulations IMX101 and IMX104 in surface soils

The biodegradation potential of insensitive munition melt cast formulations IMX101 and IMX104 was investigated in two unamended training range soils under aerobic and anaerobic growth conditions. Changes in community profiles in soil microcosms were monitored via high-throughput 16S rRNA sequencing over the course of the experiments to infer key microbial phylotypes that may be linked to IMX degradation. Complete anaerobic biotransformation occurred for IMX101 and IMX104 constituents 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one during the 30-day incubation period with Camp Shelby (CS) soil. By comparison, soil from Umatilla chemical depot demonstrated incomplete DNAN degradation with reduced transformation rates for both IMX101 and IMX104. Aerobic soil microcosms for both soils demonstrated reduced transformation rates compared to anaerobic degradation for all IMX constituents with DNAN the most susceptible to biotransformation by CS soil. Overall, IMX constituents hexahydro-1,3,5-trinitro-1,3,5-triazine and 1-nitroguanidine did not undergo significant transformation. In CS soil, organisms that have been associated with explosives degradation, namely members of the Burkholderiaceae, Bacillaceae, and Paenibacillaceae phylotypes increased significantly in anaerobic treatments whereas Sphingomonadaceae increased significantly in aerobic treatments. Collectively, these data may be used to populate fate and transport models to provide more accurate estimates for assessing environmental costs associated with release of IMX101 and IMX104.

Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

The explosive 2,4,6-trinitrotoluene (TNT) is currently a main ingredient in munitions; however the compound has failed to meet the new sensitivity requirements. The replacement compound being tested is 2,4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and human exposure potential. The objective of this study was to investigate the environmental fate and transport of DNAN in soil, with specific focus on sorption processes. Batch and column experiments were conducted using soils collected from military installations located across the United States. The soils were characterized for pH, electrical conductivity, specific surface area, cation exchange capacity, and organic carbon content. In the batch rate studies, change in DNAN concentration with time was evaluated using the first order equation, while adsorption isotherms were fitted using linear and Freundlich equations. Solution mass-loss rate coefficients ranged between 0.0002h^-1 and 0.0068h^-1. DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3Lg^-1, and Freundlich coefficients between 1.3 and 34mg^1-nLⁿkg^-1. Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil, indicating that similar to TNT, organic matter and clay minerals may influence adsorption of DNAN. The results of the miscible-displacement column experiments confirmed the impact of sorption on retardation of DNAN during transport. It was also shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-ANAN and 4-ANAN. The magnitudes of retardation and transformation observed in this study result in significant attenuation potential for DNAN, which would be anticipated to contribute to a reduced risk for contamination of ground water from soil residues.

Column transport studies of 3-nitro-1,2,4-triazol-5-one (NTO) in soils

Development of the new, insensitive, energetic compound, NTO (3-nitro-1,2,4-triazol-5-one), creates need for the data on NTO's fate and transport to predict its behavior in the environment and potential for groundwater contamination. To measure the transport of NTO in soils, we conducted miscible-displacement experiments under steady state and interrupted flow conditions using eight soils having varying physical and geochemical properties. The breakthrough curve (BTC) data were analyzed using temporal moment analysis and simulated using HYDRUS-1D to determine transport parameters and better understand the mechanisms of sorption and transformation. Parameters determined from the miscible-displacement study were compared to results obtained from batch experiments conducted for the same soils, and examined in relation to soil properties. Column NTO linear adsorption coefficients (K_d) were low and correlated well (P = 0.000049) with measurements from the batch studies. NTO transformation rate constants increased and NTO recovery decreased with increase in soil organic carbon (OC) content. Autoclaved soils had slower transformation rates and greater NTO recoveries indicating that microorganisms play a role in NTO transformation. In addition, the transformation rate increased with time in soils with higher OC. Monod-type kinetics was implemented in HYDRUS-1D to simulate the observed increase in transformation rate with time. We think this phenomenon is due to bacterial growth. Results indicate very low adsorption of NTO in a range of soils, but natural attenuation through transformation that, depending on soil OC content and hydraulic residence time, could result in complete removal of NTO.

Study on a novel high energetic and insensitive munitions formulation: TKX-50 based melt cast high explosive

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a promising candidate to replace traditional explosives, HMX and RDX, used in insensitive munitions, which is currently being explored to achieve shock insensitive melt cast formulations.

Sequential anaerobic-aerobic biodegradation of emerging insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO)

Insensitive munitions, such as 3-nitro-1,2,4-triazol-5-one (NTO), are being considered by the U.S. Army as replacements for conventional explosives. Environmental emissions of NTO are expected to increase as its use becomes widespread; but only a few studies have considered the remediation of NTO-contaminated sites. In this study, sequential anaerobic-aerobic biodegradation of NTO was investigated in bioreactors using soil as inoculum. Batch bioassays confirmed microbial reduction of NTO under anaerobic conditions to 3-amino-1,2,4-triazol-5-one (ATO) using pyruvate as electron-donating cosubstrate. However, ATO biodegradation was only observed after the redox condition was switched to aerobic. This study also demonstrated that the high-rate removal of NTO in contaminated water can be attained in a continuous-flow aerated bioreactor. The reactor was first fed ATO as sole energy and nitrogen source prior to NTO addition. After few days, ATO was removed in a sustained fashion by 100%. When NTO was introduced together with electron-donor (pyruvate), NTO degradation increased progressively, reaching a removal efficiency of 93.5%. Mineralization of NTO was evidenced by the partial release of inorganic nitrogen species in the effluent, and lack of ATO accumulation. A plausible hypothesis for these findings is that NTO reduction occurred in anaerobic zones of the biofilm whereas ATO was mineralized in the bulk aerobic zones of the reactor.

A two-stage extraction procedure for insensitive munition (IM) explosive compounds in soils

The Department of Defense (DoD) is developing a new category of insensitive munitions (IMs) that are more resistant to detonation or promulgation from external stimuli than traditional munition formulations. The new explosive constituent compounds are 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), and nitrotriazolone (NTO). The production and use of IM formulations may result in interaction of IM component compounds with soil. The chemical properties of these IM compounds present unique challenges for extraction from environmental matrices such as soil. A two-stage extraction procedure was developed and tested using several soil types amended with known concentrations of IM compounds. This procedure incorporates both an acidified phase and an organic phase to account for the chemical properties of the IM compounds. The method detection limits (MDLs) for all IM compounds in all soil types were <5 mg/kg and met non-regulatory risk-based Regional Screening Level (RSL) criteria for soil proposed by the U.S. Army Public Health Center. At defined environmentally relevant concentrations, the average recovery of each IM compound in each soil type was consistent and greater than 85%. The two-stage extraction method decreased the influence of soil composition on IM compound recovery. UV analysis of NTO established an isosbestic point based on varied pH at a detection wavelength of 341 nm. The two-stage soil extraction method is equally effective for traditional munition compounds, a potentially important point when examining soils exposed to both traditional and insensitive munitions.