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New insights into the photochemical degradation of the insensitive munition formulation IMX101 in water Annamaria Halasz, Jalal Hawari, and Nancy N. Perreault Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04878 • Publication Date (Web): 15 Dec 2017 Downloaded from http://pubs.acs.org on December 16, 2017
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Environmental Science & Technology
New insights into the photochemical degradation of the insensitive munition formulation IMX-101 in water Manuscript ID: es-2017-04878w
Annamaria Halasz,1 Jalal Hawari,2 and Nancy N. Perreault1* 1
National Research Council Canada, 6100 Royalmount Ave, Montreal, Quebec, H4P 2R2, Canada 2
Ecole Polytechnique de Montréal, Department of Civil, Geological and Mining
Engineering, Montreal, Quebec, H3C 3A7, Canada (
[email protected])
*Corresponding author: National Research Council Canada 6100 Royalmount Ave. Montreal, Quebec H4P 2R2, Canada E-mail:
[email protected] Telephone: (514) 496-6279; Fax: (514) 496-6265
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ABSTRACT
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This study describes photolysis of the insensitive munition formulation IMX-101 [2,4-
3
dinitroanisole (DNAN), NQ (nitroguanidine) and 3-nitro-1,2,4-triazol-5-one (NTO)] in
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aqueous solutions using a solar simulating photoreactor. Due to a large variance in the
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water solubility of the three constituents DNAN (276 mg L-1), NQ (5,000 mg L-1) and
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NTO (16,642 mg L-1), two solutions of IMX-101 were prepared: one with low
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concentration (109.3 mg L-1) and another with high concentration (2831 mg L-1). The
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degradation rate constants of DNAN, NQ and NTO (0.137, 0.075 and 0.202 d-1,
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respectively) in the low concentration solution were lower than those of the individually
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photolyzed components (0.262, 1.181 and 0.349 d-1, respectively). In the high
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concentration solution, the molar loss of NTO was 4.3 times higher than that of NQ after
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7 days of irradiation, although NQ was 2 times more concentrated and that NQ alone
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degraded faster than NTO. In addition to the known degradation products, DNAN
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removal in IMX-101 was accompanied by multiple productions of methoxy-
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dinitrophenols, which were not observed during photolysis of DNAN alone. One route
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for the formation of methoxy-dinitrophenols was suggested to involve photo-nitration of
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the DNAN photo-product methoxy-nitrophenol, during simultaneous photo-denitration of
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NQ and NTO in IMX-101. Indeed, when DNAN was photolyzed in the presence of
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15
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1 mass unit, indicating that denitration of DNAN and renitration of products
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simultaneously occurred. As the case with DNAN, we found that guanidine, a primary
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degradation product of NQ, also underwent renitration in the presence of NTO and the
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photocatalyst TiO2. We concluded that the three constituents of IMX-101 can be
NO2-labeled explosive CL-20, we detected methoxy-dinitrophenols with an increase of
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photodegraded in surface water and that fate and primary degradation products of IMX-
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101 can be influenced by the interactions between the formulation ingredients and their
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degradation products.
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Keywords: photolysis, IMX-101, 2,4-dinitroanisole, 3-nitro-1,2,4-triazol-5-one,
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nitroguanidine, insensitive munition
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INTRODUCTION
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The defense industry is currently seeking to replace traditional explosives by
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insensitive munitions (IM) that are less likely to detonate unintentionally. The U.S. Army
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already approved the IM formulation IMX-101 as a safer, and yet equally effective,
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replacement to 2,4,6-trinitrotoluene (TNT).1 2,4-Dinitroanisole (DNAN) and 3-nitro-1,2,4-
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triazol-5-one (NTO) are key components in emerging IM formulations such as IMX-101,
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IMX-104 and PAX-48. Additionally, IMX-101 contains nitroguanidine (NQ) (Table 1) and
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IMX-104 contains hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) commonly used in
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explosive compositions, e.g. Composition B (RDX, TNT and wax).2 While exhibiting
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comparable performance and processability, IMX-101 and IMX-104 are significantly less
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sensitive than TNT and Composition B, making the weapon systems they support safer
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to manufacture, transport and handle. Recent studies show that the insensitive nature of
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the explosive formulation leads to less efficient detonation in some detonation scenarios
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at the detonation point, which drives the need for better studying their fate in natural
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environment.3,4 The superior performance of IMX-101 can be explained by a series of
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complex chemical interactions between the ingredients when the formulation is
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subjected to a well-controlled thermal environment.5 The thermal stability of DNAN was
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found to be lower in IMX-101 than when examined alone, and this was attributed to
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interactions between the ingredients and their degradation products.6
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Table 1. Structure, distribution and water solubility of the IMX-101 constituents Name
Structure
Distribution
Water solubility*
% (w/w)
(mg L-1)
40-45
276
35-40
5,000
18-23
16,642
O NO 2
DNAN
NO 2 NH2
NQ
NTO
O2 N
N
NH 2 H N
O2N
N
O
NH
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*From references Hawari et al., 2015 (DNAN)7; Morris, 2002 (NQ)8; Dontsova et al.,
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2014 (NTO)9
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In nature, unexploded residues of munitions are bound to undergo some sort of biotic or
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abiotic degradation caused by soil microorganisms and plants or hydrolysis and
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photolysis. Biodegradation of IMX-101 in soil, compost and sludge10 and in surface
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soils11 was studied and phytoremediation to treat contaminated soil was reported.12
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Biodegradability of the IMX-101 constituents was also investigated under aerobic and
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anaerobic conditions.13-20 The main biodegradation products were dinitro-phenols15 and
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the amino- and diamino-derivatives from DNAN13,14 and 3-amino-1,2,4-triazol-5-one19
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from NTO.
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Photolysis is one of the major abiotic processes affecting the transformation of
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energetic compounds in waste streams and surface water bodies21 and near the soil
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surface.22 Photolytic transformation can affect the persistence and toxicity of
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contaminants. Photodegradation of individual munition constituents including NTO,
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DNAN, NQ and RDX was previously studied and showed that photodegradation is
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governed by the initial denitration of the nitro-compounds.23-28 On the other hand, little
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information is available on the photodegradation of explosive formulations in water,
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although explosives generally enter the environment as mixtures. Taylor et al.
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investigated photodegradation of DNAN as part of the IM formulations IMX-101, IMX-
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104 and PAX-21 during outdoor dissolution experiments.29 After the rapid dissolution of
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the most soluble NQ and NTO by precipitation, the remaining DNAN was
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photodegraded. The main DNAN degradation products identified in the effluent samples
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were methoxy-nitrophenols and methoxy-nitroanilines. An unknown compound, which
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also appeared during storage of samples in the dark, was suggested to be 2-nitroso-4-
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nitro-methoxybenzene.29 Photodegradation of the other two constituents NQ and NTO
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was not addressed based on the assumption that both can migrate rapidly through
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subsurface soil. A study of the aquatic toxicity of IMX-101 and its constituents, irradiated
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with 350-nm UV light, demonstrated that some photodegradation products were more
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toxic than the parent compounds, e.g., dinitrophenol (from DNAN), guanidine (from NQ)
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and 1,2,4-triazol-3,5-dione (from NTO).30
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While extensive work has been published on products distribution of DNAN under
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various conditions including photolysis, microbial degradation, treatment with ZVI, and
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alkaline hydrolysis, degradation products coming of IMX-101, where DNAN, NTO and
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NQ are present, have not been investigated to the authors’ knowledge. The aim of this
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work was to provide data on the photolysis of IMX-101 in water, at low and high
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concentrations, to address a range of possible environmental scenarios, using artificial
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sunlight generated from a SolSim solar simulating photoreactor. UV-B irradiation in a
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Rayonet photoreactor was also used to accelerate photodegradation and to facilitate
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products identification for determining the effect of interactions among the IMX-101
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ingredients and the fate of the formulation in the aqueous environment.
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MATERIALS AND METHODS
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Chemicals IMX-101, a yellow formulation composed of DNAN (40-45% w/w), NQ
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(35-40% w/w), and NTO (18-23% w/w) was provided by Defense Research and
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Development Canada (DRDC) - Valcartier. NTO (white powder) and DNAN (98.4%,
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yellow powder) were also provided by DRDC-Valcartier. NQ was purchased from
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Aldrich Chemical Co. (Milwaukee, WI) and contained 25% water as a stabilizer. NQ was
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air-dried for 72 h under fume hood prior to use. Stock solution of uniformly nitro-group-
101
labeled
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99.4% purity), purchased from ATK Thiokol Propulsion (Brigham City, UT, USA), was
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prepared in acetonitrile to be used as a source of
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explosive degrades at 300 nm via N-NO2 cleavage to produce 4 moles of NO2¯ and
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NO3¯ for each mole of disappearing CL-20.31 Titanium(IV) oxide (rutile nanopowder;
[15NO2]CL-20
(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane,
15
NO2 during photolysis. This
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