Degradation Of Explosives Research Articles

The stability of TNT, RDX and PETN in simulated post-explosion soils: Implications of sample preparation for analysis

Explosives residues in soils may be a useful source of evidence following the detonation of an improvised explosive device (IED), such as a vehicle-borne IED. Soil samples collected from the vicinity of an explosion scene will often be stored for some time prior to analysis, yet explosives residues in soil samples are susceptible to rapid degradation or transformation. Although some research has assessed the use of different storage temperatures with a view to reducing explosives’ degradation over time, further research examining the degradation of explosives in soil when stored under a variety of storage conditions is crucial to determine the optimal sample collection and storage procedures for soil containing explosives residues. In this work, three different soils were spiked with solutions of TNT, RDX and PETN and stored either at room temperature, refrigerated or frozen. Samples were extracted over 6 weeks, with additional samples gamma-irradiated or nitrogen purged prior to storage. Experimental results indicate that TNT underwent very rapid degradation at room temperature, attributed to microbial action, whereas PETN and RDX proved to be more stable. Gamma irradiation and nitrogen purging proved of some benefit for mitigating TNT degradation, with lower storage temperatures ultimately proving the most effective method of mitigating degradation.

Reduction and persulfate oxidation of nitro explosives in contaminated soils using Fe-bearing materials.

The oxidative and reductive transformation of nitro explosives in contaminated soils with Fe-bearing materials and persulfate (S2O8(2-)) was examined via batch experiments. Zero-valent cast iron [Fe(0)], steel dust from a steel manufacturing plant, and FeS rapidly reduced 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in soil under anaerobic conditions as long as a sufficient amount of water was present. The Fe-bearing materials also effectively activated persulfate to enhance the oxidative transformation of TNT and RDX in soil-water systems. Kinetically, reductive and oxidative transformations removed more than 90% of the explosives from a soil-water system within 5 h under the given conditions. Pseudo-first-order rates in the range of 0.7-23.4 h(-1) were observed. By increasing the concentration of persulfate or Fe-bearing materials, the oxidative transformation could be promoted. Treated soils via redox reactions using the Fe-bearing materials did not show significant toxicity, except for the case of TNT-contaminated soils oxidized by FeS-assisted persulfate. Considering the kinetics of explosive degradation and the toxicity of treated wastewaters and soils, Fe(0) or steel dust-assisted persulfate oxidation may be a safe option as an ex situ remediation process for the treatment of explosive-contaminated soils.

Improved TNT detoxification by starch addition in a nitrogen-fixing Methylophilus-dominant aerobic microbial consortium

In this study, a novel aerobic microbial consortium for the complete detoxification of 2,4,6-trinitrotoluene (TNT) was developed using starch as a slow-releasing carbon source under nitrogen-fixing conditions. Aerobic TNT biodegradation coupled with microbial growth was effectively stimulated by the co-addition of starch and TNT under nitrogen-fixing conditions. The addition of starch with TNT led to TNT mineralization via ring cleavage without accumulation of any toxic by-products, indicating improved TNT detoxification by the co-addition of starch and TNT. Pyrosequencing targeting the bacterial 16S rRNA gene suggested that Methylophilus and Pseudoxanthomonas population were significantly stimulated by the co-addition of starch and TNT and that the Methylophilus population became predominant in the consortium. Together with our previous study regarding starch-stimulated RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) degradation (Khan et al., J. Hazard. Mater. 287 (2015) 243–251), this work suggests that the co-addition of starch with a target explosive is an effective way to stimulate aerobic explosive degradation under nitrogen-fixing conditions for enhancing explosive detoxification.

Evaluation of remediation processes for explosive‐contaminated soils: kinetics and Microtox® bioassay

AbstractBACKGROUNDSoils and sediments near military sites where training regularly occurs are vulnerable to contamination from toxic nitro explosives such as 2,4,6‐trinitrotoluene (TNT) and hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX). In order to clean up the explosive‐contaminated soils, several options have been investigated and evaluated as ex situ remediation processes, including alkaline hydrolysis, subcritical water degradation, zero‐valent iron (Fe(0)) reduction, and Fe(0)‐assisted Fenton oxidation. The kinetics of the remediation processes were evaluated and the toxicity of treated solutions determined using the Microtox® bioassay.RESULTSKinetically, using four remediation methods, explosives were rapidly degraded in contaminated soils. Under optimal conditions, more than 99% of explosives were destroyed. However, the Microtox® bioassay showed that after degradation of explosives by alkaline hydrolysis, treated solutions did not show any decrease in toxicity, suggesting that hydrolytic products may still be toxic. Similarly, the Fe(0) reduction process did not significantly aid removal of toxicity due to the toxicity of reduction products. In contrast, subcritical water degradation and Fe(0)‐assisted Fenton oxidation markedly reduced the toxicity of explosives. When a toxic metal (e.g. Pb in shooting ranges) co‐existed with explosives, toxicity still remained after complete degradation of the explosives by subcritical water degradation or Fe(0)‐assisted Fenton oxidation, indicating that additional treatment may be needed.CONCLUSIONSResults suggest that, besides removal/degradation of toxic explosives, reduction of toxicity after treatment should be evaluated to select a practical option to remediate explosive‐contaminated soils. © 2015 Society of Chemical Industry

Remediation of Explosive-Contaminated Soils: Alkaline Hydrolysis and Subcritical Water Degradation

Alkaline hydrolysis and subcritical water degradation were investigated as ex-situ remediation processes to treat explosive-contaminated soils from military training sites in South Korea. The addition of NaOH solution to the contaminated soils resulted in rapid degradation of the explosives. The degradation of explosives via alkaline hydrolysis was greatly enhanced at pH ≥12. Estimated pseudo-first-order rate constants for the alkaline hydrolysis of 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil at pH 13 were (9.6 ± 0.1)×10−2, (2.2 ± 0.1)×10−1, and (1.7 ± 0.2)×10−2 min−1, respectively. In the case of subcritical water degradation, the three explosives were completely removed at 200–300°C due to oxidation at high temperatures and pressures. The degradation rate increased as temperature increased. The pseudo-first-order rate constants for DNT, TNT, and RDX at 300°C were (9.4 ± 0.8)×10−2, (22.8 ± 0.3)×10−2, and (16.4 ± 1.0)×10−2, respectively. When the soil-to-water ratio was more than 1:5, the extent of alkaline hydrolysis and subcritical water degradation was significantly inhibited.

전분 환 투입에 의한 실험실 규모 침전지 저부에서의 생화학적 환경 변화와 화약물질(TNT 및 RDX) 분해

A starch ball was devised to conveniently supply carbon source to indigenous microorganisms and to enhance biotransformation of explosive compounds(TNT and RDX) in the sediments of settling basins installed in military shooting ranges. To identify optimum dose/sediment ratio for degradation of explosives in the basin, a series of bench scale settling basin experiments were performed for 30 days while monitoring supernatant pH, DO, concentrations of nitrite, nitrate, sulfate, explosive compounds, and acute toxicity measured by bacterial luminescence. Addition of starch ball induced changes in oxidation conditions from oxic to anoxic in the benthic zone of the basin, which resulted in subsequent reductive degradation of both TNT and RDX in the liquid and solid phase of basin. However, fermentation products of excess starch, acetic acid and formic acid, caused acute toxicity in the liquid phase. The optimum ratio of starch ball/sediment for explosive compounds degradation by inducing changes in bio-geochemical environments without increase in acute toxicity, was found to be 0.009~0.017.

Fluorescent proteins as biosensors by quenching resonance energy transfer from endogenous tryptophan: Detection of nitroaromatic explosives

Ensuring domestic safety from terrorist attack is a daunting challenge because of the wide array of chemical agents that must be screened. A panel of purified fluorescent protein isoforms (FPs) was screened for the ability to detect various explosives, explosive simulants, and toxic agents. In addition to their commonly used visible excitation wavelengths, essentially all FPs can be excited by UV light at 280nm. Ultraviolet illumination excites electrons in endogenous tryptophan (W) residues, which then relax by Förster Resonance Energy Transfer (FRET) to the chromophore of the FP, and thus the FPs emit with their typical visible spectra. Taking advantage of the fact that tryptophan excitation can be quenched by numerous agents, including nitroaromatics like TNT and nitramines like RDX, it is demonstrated that quenching of visible fluorescence from UV illumination of FPs can be used as the basis for detecting these explosives and explosive degradation products. This work provides the foundation for production of an array of genetically-modified FPs for in vitro biosensors capable of rapid, simultaneous, sensitive and selective detection of a wide range of explosive or toxic agents.

The 1.5-Å Structure of XplA-heme, an Unusual Cytochrome P450 Heme Domain That Catalyzes Reductive Biotransformation of Royal Demolition Explosive

XplA is a cytochrome P450 of unique structural organization, consisting of a heme-domain that is C-terminally fused to its native flavodoxin redox partner. XplA, along with flavodoxin reductase XplB, has been shown to catalyze the breakdown of the nitramine explosive and pollutant hexahydro-1,3,5-trinitro-1,3,5-triazine (royal demolition explosive) by reductive denitration. The structure of the heme domain of XplA (XplA-heme) has been solved in two crystal forms: as a dimer in space group P2(1) to a resolution of 1.9 A and as a monomer in space group P2(1)2(1)2 to a resolution of 1.5 A, with the ligand imidazole bound at the heme iron. Although it shares the overall fold of cytochromes P450 of known structure, XplA-heme is unusual in that the kinked I-helix that traverses the distal face of the heme is broken by Met-394 and Ala-395 in place of the well conserved Asp/Glu plus Thr/Ser, important in oxidative P450s for the scission of the dioxygen bond prior to substrate oxygenation. The heme environment of XplA-heme is hydrophobic, featuring a cluster of three methionines above the heme, including Met-394. Imidazole was observed bound to the heme iron and is in close proximity to the side chain of Gln-438, which is situated over the distal face of the heme. Imidazole is also hydrogen-bonded to a water molecule that sits in place of the threonine side-chain hydroxyl exemplified by Thr-252 in Cyt-P450cam. Both Gln-438 --> Ala and Ala-395 --> Thr mutants of XplA-heme displayed markedly reduced activity compared with the wild type for royal demolition explosive degradation when combined with surrogate electron donors.

Enthalpy of Solution and Kováts Retention Indices for Nitroaromatic Compounds on Stationary Phases Using Gas Chromatography

Worldwide terrorism has recently resulted in increased efforts to detect and identify explosive residues. Availability of experimentally determined thermochemical data for explosive compounds and their degradation products is limited, however. Gas chromatography was used to determine the enthalpy of solution, ΔsolH, for a series of nitroaromatic explosives and explosive degradation products including nitrobenzene, 2-nitrotoluene, 3-nitrotoluene, 4-nitrotoluene, 1,2-dinitrobenzene, 1,3-dinitrobenzene, 1,4-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 3,4-dinitrotoluene, 3,5-dinitrotoluene, 1,3,5-trinitrobenzene, and 2,4,6-trinitrotoluene. Four polar stationary phases (by mass composition), namely, 80 % dimethyl + 20 % diphenyl polysiloxane, 14 % cyanopropylphenyl + 86 % dimethyl polysiloxane, 50 % phenyl + 50 % methyl polysiloxane, and 100 % polyethylene glycol, were evaluated with the 13 nitroaromatic compounds. Isothermal Kovats retention indices are also reported for the nitroaromatics as well...

Explosive degradation of woody biomass under the presence of metal nitrates

The influence of various metal nitrates (Fe, Ni, Cu, Zn, etc.) has been studied in the pyrolysis of woody biomass under inert atmosphere. Pyrolysis samples have been prepared by impregnation of wood with aqueous solution of the salts as well as by mechanical mixing of powders of wood and nitrates. Thermogravimetric analysis showed that the addition of nickel, copper and zinc nitrates reduced significantly the decomposition temperature of wood below 150 °C. The decomposition of wood completes explosively at the temperature. The pyrolysis products have been analysed by GC–MS and XRD methods. Preliminary result of the quantitative analysis of emitted NO x gas in the pyrolysis treatment is also presented.

Catalytic degradation of nitroaromatic explosives with Fenton's reagent

Oxidation of the nitroaromatic explosives namely, 2,4,6-trinitrophenol (PA), ammonium picrate (AP), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) by Fenton's reagent has been investigated in this study. The initial concentrations of nitroaromatics were in the range of 1.0 × 10 −5 to 3.0 × 10 −4 M. For the Fenton oxidation of the four nitroaromatics, the structural characteristic is the major factor affecting the decomposition rate rather than the interference effect coming from the oxidation intermediates. Oxidation rate of the explosives in the Fenton process were in the following sequence: DNT > PA > AP > TNT. The results were in good agreement with kinetic model, assuming the pseudo-steady-state hypothesis of hydroxyl radical formed by the Fenton reaction. Thus, a half-life prediction model was proposed and compared with the half-lives calculated from pseudo-first-order equation to prove the interference effect resulted from the oxidation intermediates.

Catalytic degradation of explosives with goethite and hydrogen peroxide

Goethite (α-FeOOH), one of soil contents, can be dissolved in acidic water to produce ferrous ions initiating Fenton reaction with hydrogen peroxide to degrade explosive. In this study, a series of catalytic degradation of nitro aromatic explosives, namely picric acid (PA) and ammonium picrate (AP) have been investigated using the FeOOH/H 2O 2 process. The controlling factors, such as adsorption of goethite dosage, hydrogen peroxide concentration and UV-light exposure on the oxidation of nitro aromatic explosives were investigated. The results showed that target compounds were adsorbed on the surface of goethite while the oxidation was proceeding. Furthermore, inhibition effect of nitro aromatic intermediates on the reaction was also discussed. A half-life kinetic model has been proposed to predict the half-lives of explosive oxidation in the goethite/H 2O 2 system.

Halide salts accelerate degradation of high explosives by zerovalent iron

Zerovalent iron (Fe 0, ZVI) has drawn great interest as an inexpensive and effective material to promote the degradation of environmental contaminants. A focus of ZVI research is to increase degradation kinetics and overcome passivation for long-term remediation. Halide ions promote corrosion, which can increase and sustain ZVI reactivity. Adding chloride or bromide salts with Fe 0 (1% w/v) greatly enhanced TNT, RDX, and HMX degradation rates in aqueous solution. Adding Cl or Br salts after 24 h also restored ZVI reactivity, resulting in complete degradation within 8 h. These observations may be attributed to removal of the passivating oxide layer and pitting corrosion of the iron. While the relative increase in degradation rate by Cl − and Br − was similar, TNT degraded faster than RDX and HMX. HMX was most difficult to remove using ZVI alone but ZVI remained effective after five HMX reseeding cycles when Br − was present in solution.

Defects of Passivation Films for Color-Filter-Based OLED Devices: Effects on Dark Spot Formation

The color filter (CF)-based organic light-emitting diode (OLED) devices suffer dark spots due to remaining moisture in the CFs. A passivation film is thus used to prevent this remaining moisture from reaching the OLED. The characteristics of defects in passivation films and their effects on dark spot formation in OLED devices were investigated. The structure of the sample devices were CF /over coat (OC) passivation film by sputtering /indium-tin-oxide (ITO) anode /OLED/Al cathode , fabricated on glass substrates. The defects of passivation films caused dark spots in the OLED devices. These defects can be classified as particulate and nonparticulate. The particulate defects can be further classified as typical pinhole defects resulting from large particles (micrometer order size) and as defects with a characteristic explosive shape resulting from small particles (submicrometer order). The explosive degradation of the films may be due to the gasification of localized moisture. Nonparticulate defects consist of microvoids formed at the OC-passivation film interface. The surface treatments, such as “light-ashing” and “ion-cleaning” done on the OC surface are largely responsible for these microvoids.

Deformation mechanism of the explosive degradation of heavy metal azides under pulsed treatments

The experimental results on the kinetics of explosive degradation of heavy metal azides by the action of nanosecond laser and electron-beam pulses and by the impact of accelerated microparticles are reported. It was found that, basically, the kinetics of the processes was qualitatively and quantitatively similar under the action of all the above factors. A local lattice deformation was the overall result of initiation by all the above factors. A theoretical analysis of the dependence of the electronic structure and electron density of a crystal on the degree of lattice deformation demonstrated that the lattice deformation resulted in a redistribution of bonds between atoms within the anion and between atoms of neighboring anions. A possible structural mechanism for the initiation of the primary reaction is discussed.

Degradation Kinetics and Mechanism of RDX and HMX in TiO2 Photocatalysis

This study was undertaken to examine the photocatalytic degradation of explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with a circular photocatalytic reactor, using a UV lamp as a light source and TiO2 as a photocatalyst. The effects of various parameters, such as the RDX or HMX concentration, the amount of TiO2, and the initial pH, on the photocatalytic degradation rates of explosives were examined. In the presence of both UV light and TiO2, RDX and HMX were more effectively degraded than with either UV or TiO2 alone. The degradation rates were found to obey pseudo-first-order kinetics represented by the Langmuir-Hinshelwood model. Increases in the RDX and HMX degradation rates were obtained with decreasing initial concentrations of the explosives. The RDX and HMX degradation rates were higher at pH 7 than at either pH 3 or pH 11. A dose of approximately 0.7 g l−1 of TiO2 degraded HMX more rapidly than did higher or lower TiO2 doses. RDX (20 mg l−1) photocatalysis resulted in an approximately 20% decrease in TOC, and HMX (5 mg l−1) photocatalysis resulted in a 60% decrease in TOC within 150 minutes. A trace amount of formate was produced as an intermediate that was further mineralized by RDX or HMX photocatalysis. The nitrogen byproducts from the photocatalysis of RDX and HMX were mainly NO3 − with NO2 − and NH4 +. The total nitrogen recovery was about 60% from RDX (20 mg l−1), and 70% from HMX (5 mg l−1), respectively. Finally, a mechanism for RDX/HMX photocatalysis was proposed, along with supporting qualitative and quantitative evidence.

Micellar electrokinetic chromatography and capillary electrochromatography of nitroaromatic explosives in seawater

The ability to separate nitroaromatic and nitramine explosives in seawater sample matrices is demonstrated using both MEKC and CEC. While several capillary-based separations exist for explosives, none address direct sampling from seawater, a sample matrix of particular interest in the detection of undersea mines. Direct comparisons are made between MEKC and CEC in terms of sensitivity and separation efficiency for the analysis of 14 explosives and explosive degradation products in seawater and diluted seawater. The use of high-salt stacking with MEKC results, on average, in a three-fold increase in the number of theoretical plates, and nearly double resolution for samples prepared in 25% seawater. By taking advantage of long injection times in conjunction with stacking, detection limits down to sub mg/L levels are attainable; however, resolution is sacrificed. CEC of explosive mixtures using sol-gels prepared from methyltrimethoxysilane does not perform as well as MEKC in terms of resolving power, but does permit extended injection times for concentrating analyte onto the head of the separation column with little or no subsequent loss in resolution. Electrokinetic injections of 8 min at high voltage allow for detection limits of explosives below 100 microg/L.

Atomic Resolution Structures and Solution Behavior of Enzyme-Substrate Complexes of Enterobacter cloacae PB2 Pentaerythritol Tetranitrate Reductase: MULTIPLE CONFORMATIONAL STATES AND IMPLICATIONS FOR THE MECHANISM OF NITROAROMATIC EXPLOSIVE DEGRADATION

The structure of pentaerythritol tetranitrate (PETN) reductase in complex with the nitroaromatic substrate picric acid determined previously at 1.55 A resolution indicated additional electron density between the indole ring of residue Trp-102 and the nitro group at C-6 of picrate. The data suggested the presence of an unusual bond between substrate and the tryptophan side chain. Herein, we have extended the resolution of the PETN reductase-picric acid complex to 0.9 A. This high-resolution analysis indicates that the active site is partially occupied with picric acid and that the anomalous density seen in the original study is attributed to the population of multiple conformational states of Trp-102 and not a formal covalent bond between the indole ring of Trp-102 and picric acid. The significance of any interaction between Trp-102 and nitroaromatic substrates was probed further in solution and crystal complexes with wild-type and mutant (W102Y and W102F) enzymes. Unlike with wild-type enzyme, in the crystalline form picric acid was bound at full occupancy in the mutant enzymes, and there was no evidence for multiple conformations of active site residues. Solution studies indicate tighter binding of picric acid in the active sites of the W102Y and W102F enzymes. Mutation of Trp-102 does not impair significantly enzyme reduction by NADPH, but the kinetics of decay of the hydride-Meisenheimer complex are accelerated in the mutant enzymes. The data reveal that decay of the hydride-Meisenheimer complex is enzyme catalyzed and that the final distribution of reaction products for the mutant enzymes is substantially different from wild-type enzyme. Implications for the mechanism of high explosive degradation by PETN reductase are discussed.

Toxicity and Degradation of Explosives

Safety regulations about handling energetic materials deal mostly with the protection of man against explosions. Explosives contain many components with toxic hazards where protection measures are necessary or a replacement by other substances should be considered. Not only the well-known toxins like aromatic nitro compounds, nitrosamines, mercury, and lead are important, but also hazardous burning and detonation products and metabolites arising in the environment need serious control. Residues of organic nitro compounds and nitrates in the environment show, influenced by the microbiology, slow degradation reactions. Recently developed compounds have to be investigated to assess toxicity risks and possible endocrine effects.

Development of a hollow fibre liquid phase microextraction method to monitor the sonochemical degradation of explosives in water

A novel method for the enrichment of nitroaromatic compounds present in water samples is presented here coupling hollow fibre liquid phase microextraction (LPME) with gas chromatography. A hydrophobic porous polypropylene hollow fibre was used as the interface between the donor water sample and microvolumes of the acceptor organic phase. Parameters such as extraction solvent, stirring rate, salt concentration and sampling time were studied and optimised. Overall, extraction of 11 nitroaromatics was achieved by exposing 3 μl of toluene for 20 min in a 5 ml stirred aqueous solution at room temperature. The developed protocol yielded a linear calibration graph in the concentration range 10–500 μg l −1 and the limits of detection were calculated to range between 0.29 and 0.87 μg l −1. Precision expressed in terms of relative standard deviation varied between 6.1 and 11.8%. The developed hollow fibre LPME method was subsequently used successfully to monitor the sonochemical degradation of an aqueous solution containing 100 μg l −1 of each target analyte at an ultrasonic frequency of 80 kHz. Ultrasonic treatment was found capable of efficiently removing the 2-, 3- and 4-nitrotoluene isomers as well as the 2- and 4-amino dinitrotoluene isomers within 300 min of irradiation. The rest of the analytes were more recalcitrant and significant removal was not observed even after prolonged times of ultrasonic irradiation.