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<br />''NTO''
 
<br />''NTO''
  
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Aqueous NTO formed [[wikipedia:Ammonium|ammonium]], [[Https://en.wikipedia.org/wiki/Nitrate|nitrate]], [[wikipedia:Nitrite|nitrite]], and a urazole intermediate when irradiated with [[wikipedia:Ultraviolet|UV]] light<ref name=":12" /><ref name=":14">Moores, L.C., Kennedy, A.J., May, L., Jordan, S.M., Bednar A. J., Jones S.J., Henderson D.L., Gurtowski L., and Gust, K.A., 2020. Identifying degradation products responsible for increased toxicity of UV-degraded insensitive munitions. Chemosphere, 240, 124958. [https://doi.org/10.1016/j.chemosphere.2019.124958. doi: 10.1016/j.chemosphere.2019.124958]</ref>. A significant amount of the original NTO mass was not recovered. This may be due, in part, to the volatilization of gaseous species since bubbles formed in the irradiated solutions. A proposed pathway for NTO photolysis is shown in Figure 9<ref name=":12" />. The first step is the breaking of the C-NO<sub>2</sub> bond, which has the lowest bond energy (Figure 4). This forms a nitro radical and a triazolone radical. The nitro radical can then form [[wikipedia:Nitrite|nitrite]] and [[wikipedia:Nitrate|nitrate]], and the triazolone radical can form urazole upon reaction with water. Urazole and/or NTO may undergo [[wikipedia:Hydrolysis|hydrolysis]] that breaks open the [[wikipedia:Heterocyclic_compound|heterocyclic ring]] and ultimately forms degradation products such as [[wikipedia:Ammonium|ammonium]] and carbon dioxide gas. In aquatic toxicity studies, UV-irradiated NTO was found to be up to 100 times more toxic than non-irradiated NTO<ref name=":13" /><ref name=":14" />. The specific photolysis products responsible for this increase in toxicity are still being investigated.
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Aqueous NTO formed [[wikipedia:Ammonium|ammonium]], [[wikipedia:Nitrate|nitrate]], [[wikipedia:Nitrite|nitrite]], and a urazole intermediate when irradiated with [[wikipedia:Ultraviolet|UV]] light<ref name=":12" /><ref name=":14">Moores, L.C., Kennedy, A.J., May, L., Jordan, S.M., Bednar A. J., Jones S.J., Henderson D.L., Gurtowski L., and Gust, K.A., 2020. Identifying degradation products responsible for increased toxicity of UV-degraded insensitive munitions. Chemosphere, 240, 124958. [https://doi.org/10.1016/j.chemosphere.2019.124958. doi: 10.1016/j.chemosphere.2019.124958]</ref>. A significant amount of the original NTO mass was not recovered. This may be due, in part, to the volatilization of gaseous species since bubbles formed in the irradiated solutions. A proposed pathway for NTO photolysis is shown in Figure 9<ref name=":12" />. The first step is the breaking of the C-NO<sub>2</sub> bond, which has the lowest bond energy (Figure 4). This forms a nitro radical and a triazolone radical. The nitro radical can then form [[wikipedia:Nitrite|nitrite]] and [[wikipedia:Nitrate|nitrate]], and the triazolone radical can form urazole upon reaction with water. Urazole and/or NTO may undergo [[wikipedia:Hydrolysis|hydrolysis]] that breaks open the [[wikipedia:Heterocyclic_compound|heterocyclic ring]] and ultimately forms degradation products such as [[wikipedia:Ammonium|ammonium]] and carbon dioxide gas. In aquatic toxicity studies, UV-irradiated NTO was found to be up to 100 times more toxic than non-irradiated NTO<ref name=":13" /><ref name=":14" />. The specific photolysis products responsible for this increase in toxicity are still being investigated.
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[[File: PhotolysisFig9.png | thumb | 650px | left | Figure 9. Proposed phototransformation pathways for NTO. Redrawn from Becher et al. (2019)<ref name=":12" />.]]
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''[[wikipedia:Nitroguanidine|NQ]]''
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The major products formed from [[wikipedia:Nitroguanidine|NQ]] photolysis are [[wikipedia:Nitrate|nitrate]], [[wikipedia:Nitrite|nitrite]], [[wikipedia:Guanidine|guanidine]], and [[wikipedia:Urea|urea]]. Minor products include [[wikipedia:Cyanamide|cyanamide]], [[wikipedia:2-Cyanoguanidine|cyanoguanidine]], [[wikipedia:Ammonium|ammonium]], [[wikipedia:Melamine|melamine]], [[wikipedia:Ammeline|ammeline]], and [[wikipedia:Cyanide|cyanide]]<ref name=":12" /><ref name=":14" /><sup>,29, 30, 31</sup>. [[wikipedia:Methylnitronitrosoguanidine|Nitrosoguanidine]] and hydroxyguanidine were identified as intermediates that were further phototransformed<sup>30,31</sup>. A proposed pathway for NQ photolysis is shown in Figure 10<ref name=":12" />. The weakest bond is the N-NO<sub>2</sub> bond (Figure 4), and when it is cleaved, it forms nitro and [[wikipedia:Guanidine|guanidine]] radicals. The nitro radical can form [[wikipedia:Nitrite|nitrite]] and [[wikipedia:Nitrate|nitrate]]. The [[wikipedia:Guanidine|guanidine]] radical, upon reaction with a hydrogen ion or a water molecule, can form [[wikipedia:Guanidine|guanidine]] or hydroxyguanidine, respectively. [[wikipedia:Ammonia|Ammonia]] and [[wikipedia:Cyanamide|cyanamide]] can also form from the breakdown of the [[wikipedia:Guanidine|guanidine]] radical. [[wikipedia:Cyanamide|Cyanamide]] can then undergo either [[wikipedia:Dimer_(chemistry)|dimerization]] to form [[wikipedia:2-Cyanoguanidine|cyanoguanidin]]<nowiki/>e or hydrolysis to form [[wikipedia:Urea|urea]]. [[wikipedia:Melamine|Melamine]] is a trimer of [[wikipedia:Cyanamide|cyanamide]] and [[wikipedia:Ammeline|ammeline]] is a [[wikipedia:Hydrolysis|hydrolysis]] product of [[wikipedia:Melamine|melamine]]. [[wikipedia:Cyanide|Cyanide]] may be formed from [[wikipedia:2-Cyanoguanidine|cyanoguanidine]] under acidic conditions<ref name=":13" />.
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UV-irradiated [[wikipedia:Nitroguanidine|NQ]] was found to be orders of magnitude more toxic to aquatic organisms than [[wikipedia:Nitroguanidine|NQ]] that was not irradiated<ref name=":13" /><ref name=":14" /><sup>32,33</sup>. Furthermore, it was responsible for most of the toxicity of irradiated [[wikipedia:IMX-101|IMX-101]]. Moores et al. (2020) found that [[wikipedia:Guanidine|guanidine]], [[wikipedia:Nitrite|nitrite]], [[wikipedia:Ammonia|ammonia]], [[wikipedia:Methylnitronitrosoguanidine|nitrosoguanidine]], and [[wikipedia:Cyanide|cyanide]] produced from [[wikipedia:Nitroguanidine|NQ]] photolysis were each more toxic to ''Daphnia pulex'' than [[wikipedia:Nitroguanidine|NQ]], with [[wikipedia:Nitrite|nitrite]] and [[wikipedia:Cyanide|cyanide]] contributing the most to the toxicity<ref name=":14" />. When adding up the individual toxicities caused by these photolysis products, only 25% of the overall toxicity caused by exposure to irradiated [[wikipedia:Nitroguanidine|NQ]] was accounted for. This implied that additional, unidentified products with greater toxicity to ''D. pulex'' formed and/or that exposure to all the products at once created a synergistic toxic effect. [[File: PhotolysisFig9.png | thumb | 650px | left | Figure 9. Proposed phototransformation pathways for NTO. Redrawn from Becher et al. (2019)<ref name=":12" />.]]
  
 
   
 
   
  
 
<br /><references />
 
<br /><references />

Revision as of 20:25, 15 December 2021

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Munitions Constituents – Photolysis

Munitions compounds (MCs), including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ), absorb light in the UV range and are therefore susceptible to photolysis on soil surfaces and in surface water. Photochemical reactions are important to consider when assessing the environmental impact of MCs since they can yield products that differ from their parent compounds in both toxicity and transport behavior. Quantum yield calculations can aid in predicting the photolysis rates and half-lives of MCs. The photolysis of MCs may be enhanced or inhibited in the presence of compounds that are also excited by UV irradiation.


Related Article(s):


Contributor(s): Dr. Warren Kadoya


Key Resource(s):

Introduction

Insensitive munitions, including IMX-101 and IMX-104, are replacing traditional explosives because they are less prone to accidental detonation and therefore safer for military personnel to handle. IMX-101, composed of 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ), will replace 2,4,6-trinitrotoluene (TNT) in artillery; IMX-104, composed of DNAN, NTO, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), will replace Composition B (Comp B) in mortars[6]. As both traditional munitions compounds and these insensitive munitions compounds (collectively referred to as MCs) may be deposited onto firing ranges via incomplete detonation, understanding their environmental fate is of concern[7]. Phototransformation due to sunlight exposure is an important fate-controlling parameter for MCs and can occur on the surfaces of solid explosive particles, as shown in Figure 1, as well as in the aqueous phase following MC dissolution by rainwater. Furthermore, MC photolysis can be affected by the presence of natural organic matter and other compounds that are excited by sunlight.

Figure 1. Color change over time as particles of IMX-101 and IMX-104 were exposed to sunlight and rainfall, suggesting phototransformation. Image courtesy of the U.S. Army Engineer Research and Development Center[8].

Direct photolysis

Compounds that absorb ultraviolet (UV, 100-400 nm) and/or visible (Vis, 400-800 nm) light can undergo direct photolysis from sunlight. Light is absorbed in discrete units, or photons, and the energy of these photons is indirectly proportional to the wavelength of the light. When a chemical molecule absorbs a photon, its ground state electrons may become excited. As the excited electrons return to the ground state, they may undergo a chemical reaction that results in transformation. Figure 2 shows that the UV range is further divided into UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm). Because most of UV-C is filtered out by the Earth’s atmosphere, direct photolysis of compounds at the surface primarily involves UV-A and UV-B[9].

Figure 2. The ultraviolet and visible spectrum of sunlight measured at noon in midsummer in Cleveland, Ohio in June 1986. Reproduced with permission from Q-Lab Corporation[9].

The MCs TNT, RDX, DNAN, NTO, and NQ may undergo direct photolysis since they all absorb light in the UV-Vis range (Figure 3). These graphs convey the probability that the compounds will absorb light at a given wavelength. The absorption maxima correspond to one or more electrons transitioning to an excited state.

Figure 3. UV-Vis absorbance spectra for munitions compounds. Spectra over the wavelength range of 200-800 nm were obtained using a Jasco V-630 UV-Vis Spectrophotometer and quartz cuvettes, UV transparent to 200 nm (YeHui Instruments). Adapted from Taylor et al. (2017)[10].

For a chemical bond to break via direct photolysis, a molecule must absorb a photon with higher energy than the energy of the bond. The energy of photons in the UV-Vis range is similar to the bond energies of several single covalent bonds found in organic molecules[1]. Therefore, many of the bonds in TNT, DNAN, NTO, and NQ are susceptible to photolysis from sunlight exposure (Figure 4).

Figure 4. Calculated bond energies (black) and corresponding photon wavelengths (blue, determined from Planck’s equation[1]) required to break the bonds in TNT, DNAN, NTO, and NQ (calculations by Dr. Diego Troya[11]). Energies for bonds in the aromatic and heterocyclic rings are not shown because they exceed the maximum energy of the photons in sunlight reaching the Earth’s surface (500 kJ/mol or 239 nm).

Photolysis products and pathways

The products of the direct photolysis of MCs have been studied in depth, both in photoreactors using UV bulbs emitting light at a given wavelength (Figure 5) or wavelength ranges (including simulated sunlight) and outdoors in natural sunlight. The photolysis of MCs can form mineral products as well as transformation products that may be more toxic than the original compounds.

Figure 5. Example of a UV photoreactor (A) with slots for UV bulbs (B) and a rotating carousel to hold samples (C). Reproduced with permission from The Southern New England Ultraviolet Company.

TNT

The formation of pink and red wastewater released by some ammunition plants led to investigations into the photolysis products of TNT starting in the 1970s. Laboratory experiments observed rapid phototransformation from sunlight in natural waters, some with half-lives less than an hour[12]. Numerous photolysis products of TNT have been reported and include, but are not limited to, 2-amino-4,6-dinitrobenzoic acid, 2,4,6-trinitrobenzaldehyde, 4,6-dinitroanthranil, 2,4,6-trinitrobenzonitrile, 2,4,6-trinitrobenzoic acid, 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitrobenzyl alcohol, and an array of azo and azoxy compounds[2][13][14][15][16].

The mechanism of TNT photolysis is not completely understood as numerous products are formed, many of which are not readily synthesized or purchased[16]. However, evidence suggests that TNT is initially excited to a triplet state by UV light[12]. Figure 6 shows a proposed environmental reaction pathway for TNT that combines photo- and biological reactions based on studies in waste disposal lagoons[15].

Figure 6. Proposed environmental transformation pathway for TNT, including phototransformation and biotransformation reactions. Image courtesy of the U.S. Army Engineer Research and Development Center[15][17].

The aquatic toxicity of phototransformed TNT solutions and ammunition wastewaters was not found to be significantly different from that of untransformed TNT[18][19]. Although TNT phototransformation products tend to be more toxic than TNT, the relatively low product formation coupled with the disappearance of TNT may explain these results.

RDX

RDX photolysis products detected in aqueous systems include nitrite, nitrate, ammonia, formaldehyde, formic acid, formamide, nitrous oxide, and 4-nitro-2,4-diazabutanal[20][21][22][23]. Stable phototransformation products also detected include nitroso compounds MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine), DNX (hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine), and TNX (hexahydro-1,3,5-trinitroso-1,3,5-triazine), which contain one, two, and three nitroso groups each, respectively, in place of the nitro groups. The formation of unsaturated MUX (1,3-dinitro-1,2,3,4-tetrahydro-1,3,5-triazine) was also reported (Figure 7)[3].

Figure 7. Proposed phototransformation mechanism for RDX. Image courtesy of the U.S. Army Engineer Research and Development Center[3].

Peyton et al. (1999) compiled experimental results for RDX photolysis in a proposed reaction mechanism (Figure 7)[3]. The most common first step is the breaking of an N-N bond between a nitro group and a nitrogen atom in the heterocyclic ring, resulting in two radical species (structure (R) in the center and an NO2 radical). They hypothesize that the NO2 radical can become an NO radical that may then recombine with structure (R), giving nitroso product MNX. This process can be repeated to form products DNX and TNX (i.e., via cleavage of the other N-N bonds, as shown in the formation of structure [R2]). The formation of MUX, containing an unsaturation (C=N double bond in the ring) was likely due to the loss of HNO2 from RDX. Other products could include a combination of nitroso groups and unsaturations. The unsaturated compounds, including MUX, are expected to undergo hydrolysis, forming many smaller products (e.g., nitrite and formaldehyde)[3][23]. One of the major products of RDX photolysis is nitrate, a common groundwater pollutant of concern, despite being much less toxic than RDX[21]. The risk posed by the other toxic products should be evaluated, though they are formed in smaller quantities.

DNAN

The products formed from DNAN photolysis include nitrate, nitrite, 2,4-dinitrophenol (DNP), 2-methoxy-5-nitrophenol, 4-methoxy-3-nitrophenol, [[1]], formaldehyde, and formic acid[4][24][25].Rao et al. (2013) proposed a pathway for DNAN photolysis with photooxidation as the primary mechanism (Figure 8)[4]. According to the computational modeling of DNAN bond energies, the C-N bonds and the C-O bond of the methoxy group are most susceptible to photolysis (Figure 4)[26]. This is in agreement with the transformation products formed. Once DNAN is excited to a photo-activated triplet state, OH- in solution can displace either of its nitro groups via an SN2 reaction to form a methoxynitrophenol. This releases nitrite, which can then form nitrate through further photooxidation. DNP could form via O-demethylation of DNAN, which could occur by hydroxylation of the methyl group and the release of formaldehyde[27]. Formaldehyde or formic acid may react with NH2 groups in methoxynitroanilines or aminonitrophenols to produce formamide derivatives[25].

Figure 8. Proposed phototransformation pathways for DNAN. Redrawn from Rao et al. (2013)[4].

Ecotoxicity estimates predict that DNAN phototransformation products are less toxic than DNAN, except for DNP, which is more toxic and known to uncouple oxidative phosphorylation[4][26]. However, upon further photolysis, DNP was shown to degrade into nitrocatechol and nitrite[4][25].


NTO

Aqueous NTO formed ammonium, nitrate, nitrite, and a urazole intermediate when irradiated with UV light[5][28]. A significant amount of the original NTO mass was not recovered. This may be due, in part, to the volatilization of gaseous species since bubbles formed in the irradiated solutions. A proposed pathway for NTO photolysis is shown in Figure 9[5]. The first step is the breaking of the C-NO2 bond, which has the lowest bond energy (Figure 4). This forms a nitro radical and a triazolone radical. The nitro radical can then form nitrite and nitrate, and the triazolone radical can form urazole upon reaction with water. Urazole and/or NTO may undergo hydrolysis that breaks open the heterocyclic ring and ultimately forms degradation products such as ammonium and carbon dioxide gas. In aquatic toxicity studies, UV-irradiated NTO was found to be up to 100 times more toxic than non-irradiated NTO[19][28]. The specific photolysis products responsible for this increase in toxicity are still being investigated.

NQ

The major products formed from NQ photolysis are nitrate, nitrite, guanidine, and urea. Minor products include cyanamide, cyanoguanidine, ammonium, melamine, ammeline, and cyanide[5][28],29, 30, 31. Nitrosoguanidine and hydroxyguanidine were identified as intermediates that were further phototransformed30,31. A proposed pathway for NQ photolysis is shown in Figure 10[5]. The weakest bond is the N-NO2 bond (Figure 4), and when it is cleaved, it forms nitro and guanidine radicals. The nitro radical can form nitrite and nitrate. The guanidine radical, upon reaction with a hydrogen ion or a water molecule, can form guanidine or hydroxyguanidine, respectively. Ammonia and cyanamide can also form from the breakdown of the guanidine radical. Cyanamide can then undergo either dimerization to form cyanoguanidine or hydrolysis to form urea. Melamine is a trimer of cyanamide and ammeline is a hydrolysis product of melamine. Cyanide may be formed from cyanoguanidine under acidic conditions[19].

UV-irradiated NQ was found to be orders of magnitude more toxic to aquatic organisms than NQ that was not irradiated[19][28]32,33. Furthermore, it was responsible for most of the toxicity of irradiated IMX-101. Moores et al. (2020) found that guanidine, nitrite, ammonia, nitrosoguanidine, and cyanide produced from NQ photolysis were each more toxic to Daphnia pulex than NQ, with nitrite and cyanide contributing the most to the toxicity[28]. When adding up the individual toxicities caused by these photolysis products, only 25% of the overall toxicity caused by exposure to irradiated NQ was accounted for. This implied that additional, unidentified products with greater toxicity to D. pulex formed and/or that exposure to all the products at once created a synergistic toxic effect.

Figure 9. Proposed phototransformation pathways for NTO. Redrawn from Becher et al. (2019)[5].



  1. ^ 1.0 1.1 1.2 Schwarzenbach, R.P., Gschwend, P.M., and Imboden, D.M., 2002. Chapter 15, Direct Photolysis. In: Schwarzenbach, R.P., Gschwend, P.M., and Imboden, D.M. (eds). Environmental Organic Chemistry. 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc, pp. 611-654. doi:10.1002/0471649643.ch15
  2. ^ 2.0 2.1 Pennington, J.C., Thorn, K.A., Co, L.G., MacMillan, D.K., Yost, S., and Laubscher, R.D., 2007. Photochemical Degradation of Composition B and Its Components. U.S. Army Engineer Research and Development Center (ERDC)/ Environmental Laboratory (EL) TR-07-16. Report pdf
  3. ^ 3.0 3.1 3.2 3.3 3.4 Peyton, G.R., LeFaivre, M.H., and Maloney, S.W., 1999. Verification of RDX photolysis mechanism. U.S. Army Engineer Research and Development Center (ERDC)/ Construction Engineering Research Laboratory (CERL) TR 99/93. Report pdf
  4. ^ 4.0 4.1 4.2 4.3 4.4 4.5 Rao, B., Wang, W., Cai, Q., Anderson, T., and Gu, B., 2013. Photochemical Transformation of The Insensitive Munitions Compound 2,4-Dinitroanisole. Science of The Total Environment, 443, pp. 692-699. doi: 10.1016/j.scitotenv.2012.11.033
  5. ^ 5.0 5.1 5.2 5.3 5.4 5.5 Becher, J.B., Beal, S.A., Taylor, S., Dontsova, K., Wilcox, D.E., 2019. Photo-transformation of aqueous nitroguanidine and 3-nitro-1,2,4-triazol-5-one: Emerging munitions compounds. Chemosphere, 228, pp. 418-426. doi:10.1016/j.chemosphere.2019.04.131
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  11. ^ Dontsova, K., Taylor, S., Brusseau, M. L., Simunek, J., and Hunt, E., 2017. Influence of climate on dissolution and phototransformation of NTO and DNAN from insensitive munitions and their fate in soils. In: Poster, the SERDP-ESTCP symposium, Washington, D.C., November 28-30, 2017. The Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP).
  12. ^ 12.0 12.1 Mabey, W.R., Tse, D., Baraze, A., and Mill, T., 1983. Photolysis of nitroaromatics in aquatic systems. I. 2,4,6-trinitrotoluene. Chemosphere, 12(1), pp. 3-16. doi: 10.1016/0045-6535(83)90174-1
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  19. ^ 19.0 19.1 19.2 19.3 Kennedy, A.J., Poda, A.R., Melby, N.L., Moores, L.C., Jordan, S.M., Gust, K.A., and Bednar, A.J., 2017. Aquatic toxicity of photo-degraded insensitive munition 101 (IMX-101) constituents. Environmental Toxicology and Chemistry, 36(8), pp.2050-2057. doi: 10.1002/etc.3732
  20. ^ Just, C.L., and Schnoor, J.L., 2004. Phytophotolysis of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in Leaves of Reed Canary Grass. Environmental Science and Technology, 38(1), pp. 290-295. doi: 10.1021/es034744z
  21. ^ 21.0 21.1 Bordeleau, G., Martel, R., Ampleman, G., and Thiboutot, S., 2013. Photolysis of RDX and nitroglycerin in the context of military training ranges. Chemosphere, 93(1), pp. 14-19. doi: 10.1016/j.chemosphere.2013.04.048
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  24. ^ Taylor, S., Walsh, M.E., Becher, J.B., Ringelberg, D.B., Mannes, P.Z., and Gribble, G.W., 2016. Photo-degradation of 2,4-dinitroanisole (DNAN): An emerging munitions compound. Chemosphere, 167, pp.193-203. doi:10.1016/j.chemosphere.2016.09.142
  25. ^ 25.0 25.1 25.2 Hawari, J., Monteil-Rivera, F., Perreault, N., Halasz, A., Paquet, L., Radovic-Hrapovic, Z., Deschamps, S., Thiboutot, S., Ampleman, G., 2015. Environmental fate of 2, 4-dinitroanisole (DNAN) and its reduced products. Chemosphere, 119, pp.16-23. doi: 10.1016/j.chemosphere.2014.05.047
  26. ^ 26.0 26.1 Qin, C., Abrell, L., Troya, D., Hunt, E., Taylor, S., and Dontsova, K., 2021. Outdoor dissolution and photodegradation of insensitive munitions formulations IMX-101 and IMX-104: Photolytic transformation pathway and mechanism study. Chemosphere, 280, 130672. doi: 10.1016/j.chemosphere.2021.130672
  27. ^ Studziński. W., Gackowska, A., Przybyłek, M., Gaca, J., 2017. Studies on the formation of formaldehyde during 2-ethylhexyl 4-(dimethylamino)benzoate demethylation in the presence of reactive oxygen and chlorine species. Environmental Science and Pollution Research, 24(9), pp. 8049-8061. doi:10.1007/s11356-017-8477-8 Article pdf
  28. ^ 28.0 28.1 28.2 28.3 28.4 Moores, L.C., Kennedy, A.J., May, L., Jordan, S.M., Bednar A. J., Jones S.J., Henderson D.L., Gurtowski L., and Gust, K.A., 2020. Identifying degradation products responsible for increased toxicity of UV-degraded insensitive munitions. Chemosphere, 240, 124958. doi: 10.1016/j.chemosphere.2019.124958
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