Munitions Constituents

Munitions Constituents (EM) are chemicals used in formulations as propellants, pyrotechnics, and explosives in weapon systems, munitions, and blasting agents. This article introduces these materials, major physical and chemical properties, and fate in the environment. Important chemical groups include nitroaromatics (e.g. 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (2,4-DNT), nitramines (e.g. hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetreazocine (HMX)), nitrate esters (e.g. nitroglycerin (NG), pentaerythritol tetranitrate (PETN)), and nitrocellulose (NC). Ammonium perchlorate (AP) is commonly used as a propellant in solid rock fuel and is addressed in a separate article on perchlorate. Insensitive munitions (IM) are energetics in newer military explosives and are generally considered more stable than traditional explosives.

Related Article(s):

• Munitions Constituents - Deposition
• Munitions Constituents - Dissolution
• Munitions Constituents - Sorption
• Munitions Constituents - IM Toxicology
• Munitions Constituents- TREECS™ Fate and Risk Modeling

CONTRIBUTOR(S): Dr. Kevin Finneran and Dr. Robert Borden, P.E.

Key Resource(s):

• EPA Federal Facilities Forum Issue Paper: Site Characterization for Munitions Constituents, EPA/505/S-11/001, 2012.

Explosives and Propellants

Table 1. Common US military explosives, propellants, and IM formulations.

Explosive materials are commonly classified according to the speed of the chemical reaction wave that propagates through the material. If the wave velocity is greater than the speed of sound (supersonic), the material is said to undergo detonation and is considered an explosive. If the wave propagation velocity is less than the speed of sound, the material is considered to undergo deflagration (rapid burning) and is often used as a propellant.

Common military explosives are mixtures consisting of one or more explosive compounds including trinitrotoluene (TNT), 1,3,5-hexahydro-1,3,5-trinitrotriazine or Research Development Explosive (RDX), octrahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine or High Melting Explosive (HMX), and 2,4,6- trinitro-phenylmethylnitramine (tetryl) and ammonium picrate. However, the US military is replacing many of these materials with insensitive munitions (IM) to reduce risks of accidental detonation. IM materials will burn, rather than explode, when subjected to fast or slow heating, bullets, shrapnel, shaped charges, or the detonation of another nearby munition. Important components of IM include 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), 3-nitro-1,2,4-triazol-5-one (NTO) and other traditional munitions components (RDX, HMX). We highlight common military explosives, propellants, and IM formulations in Table 1.

Propellant formulations often contain several components. The primary component is often nitrocellulose (NC), which is combined with other EM compounds including nitroglycerin (NG), NQ, DNT, HMX, burn rate modifiers, binders or plasticizers, and stabilizers. Gun propellants usually are single component based (e.g., NC), double based (e.g., NC and NG), or triple based (e.g., NC, NG, and NQ).

Physical and Chemical Properties

The structure (e.g., Fig. 1), as well as physical and chemical properties of explosive materials control their fate and transport in the environment (Table 2).

With the exception of NG, the major EM are solids at ambient temperatures (Table 2). Table 2 provides the molecular mass, aqueous solubility, Log octanol-water partition coefficient (Log K_ow), and vapor pressure of common explosive materials. Although NG is a liquid, it is commonly used as a component of double- and triple-base propellants, with the solid polymeric NC. Aqueous solubility of EM varies dramatically between the different materials and can have an important influence on their mobility in the environment. Organic compounds with a high K_ow are more likely to sorb to organic carbon in soil or bioaccumulate; however, EM tend to be high in nitrogen, and by definition, are strong oxidizing agents. EM materials tend to form crystals. The vapor pressure of these materials is relatively low, so volatilization is not an important removal mechanism for most EM.

Explosive	CAS	Formula	Molecular Weight [g/mol]	Aqueous Solubility at 25°C [mg/L]	Log Kow	Vapor Pressure at 20°C [mm Hg]
TNT	118-96-7	C7H5N3O6	227.13c	130c	1.60c	1.99 E-4c
RDX	121-82-4	C3H6N6O6	222.26d	56.4i	0.87d	1 to 4 E-9d
HMX	2691-41-0	C4H8N8O8	296.16a	4.5i	0.165i	3.3E-14a
Tetryl	479-45-8	C7H5N5O8	287.14a	80a		5.7E-9 (25°C)a
2,4-DNT	121-14-2	C7H6N2O4	182.15a	300 (22°C) f	1.98f	1.47E-4f
2,6-DNT	606-20-2	C7H6N2O4	182.15a	180 (22°C)f	1.72 or 2.10f	5.67E-4f
2-ADNT	35572-78-2	C7H7N3O4	197.17a	2800a		4.0E-5a
4-ADNT	19406-51-0	C7H7N3O4	197.17a	2800a		2.0E-5a
NTO	932-64-9	C2H2N4O3	130.08	2000m	0.858m
DNAN	119-27-7	C7H6N2O5	198.13j	213o, p	1.58o, p	1.E-4 (25°C)j
NQ	556-88-7	CH4N4O2	104.07	4,400n	-0.89j 0.21l	1.00E-9 (est)j
a = Thiboutout et al. (2002), b = Pennington et al. (2006) Final Report, c = EPA Technical Fact Sheet for TNT, d = EPA Technical Fact Sheet for RDX, f = EPA Technical Fact Sheet for DNT, g = EPA Technical Fact Sheet for Perchlorate, h = McGrath (1995), i = Monteil-Rivera et al. (2004), j = DNAN WEEL FINAL, l = DRDC 2011, m = NTO WEEL FINAL, n = van der Schalie (1985), o = Hawari (2014), p = Hawari et al. (2015). Table 2. Physical and chemical properties of important explosives and propellants.

Health and Environmental Impacts

Exposure of humans to EM compounds can result in significant health issues. High oral or dermal exposures to TNT can cause liver and blood damage, anorexia, and anemia. High oral exposures to RDX can cause neurological affects such as convulsions. Some EM can bioaccumulate in crop plants (e.g. RDX), leading to potential exposure by eating or direct contact. TNT and 2,4-DNT are classified as possible human carcinogens by the U.S. EPA. In contrast, HMX is not currently classified as a human carcinogen, but has been shown to have adverse impacts on the liver and nervous system in some laboratory animals. The US military is replacing many of traditional explosives with IMs to reduce risks of accidental detonation. Since IM materials including DNAN, NTO, and NQ have not been in common use, considerable effort has been focused on understanding the toxicity of these materials (see Munitions Constituents - IM Toxicology).

There are currently no federal maximum contaminant levels (MCLs) for TNT, RDX, and HMX. Life-time health advisory levels in drinking water vary from 400 µg/L for HMX, to 2 µg/L for RDX, and 2 µg/L for TNT.

Fate and Transport in the Environment

Much of the early work on environmental issues related to EM focused on concentrated sources including manufacturing facilities and locations where off-specification, unserviceable, and obsolete munitions were destroyed . More recently, attention has focused on potential contamination from military training when partial detonations deposit EM particles on range soils (see Munitions Constituents - Deposition). Once deposited on a range, the EM dissolves over time, a process thought to be the rate-limiting step for aqueous transport of these compounds to soil and groundwater. The mass of EM dissolved is a function of the aqueous solubility of the compound, the mass of explosive residues deposited on the soil, the size of individual residues, and the three-dimensional (3D) structure of formulations that have multiple constituents (see Munitions Constituents - Dissolution). During transport through the subsurface, EM migration is influenced by sorption to the solid phase (see Munitions Constituents - Sorption), as well as chemical transformation and biodegradation.

However, the Department of Defense (DoD) has invested considerable resources to understand how these factors can be influenced, or how they operate in natural settings, to limit transport of EM in surface or groundwater. In addition, a number of remediation strategies have been developed that address EM, and applied both in situ and ex situ at DoD facilities.

See Also

• Natural Attenuation of Explosives in Soil and Water Systems at DoD Sites
• A Predictive Capability for the Source Terms of Residual Munitions Constituents from Burning and/or Detonation Activities
• In-Situ Remediation of Explosives Contaminated Groundwater with Sequential Reactive Treatment Zones
• Bacterial Degradation of DNT and TNT Mixtures
• Microbial Degradation of RDX and HMX
• Novel Pathways of Nitroaromatic Metabolism: Hydroxylamine Formation, Reactivity and Potential for Ring Fission for Destruction of TNT
• Fe0-Based Bioremediation of RDX-Contaminated Groundwater
• Remediation of Explosives Contaminated Groundwater with Zero-Valent Iron
• Environmental Fate and Transport of a New Energetic Material, CL-20
• Environmental Fate and Transport of a New Energetic Material, CL-20
• Integrated Automated Analyzer for Monitoring of Explosives in Groundwater
• Long-Term Monitoring for Explosives-Contaminated Groundwater
• Enhancement of In Situ Bioremediation of Energetic Compounds by Coupled Abiotic/Biotic Processes
• Biodegradation of Nitroaromatic Compounds by Stimulating Humic Substance- and Fe(III)-Reduction
• Groundwater Chemistry and Microbial Ecology Effects on Explosives Biodegradation
• Development of Biomarkers for Assessing In Situ RDX Biodegradation Potential
• New Approaches to Evaluate the Biological Degradation of RDX in Groundwater
• Identification of Microbial Gene Biomarkers for In Situ RDX Biodegradation
• Monitored Natural Attenuation of Explosives in Groundwater
• Phytoremediation of Explosives-Contaminated Groundwater in Constructed Wetlands
• Portable SERS Instrument for Explosives Monitoring
• Biologically Active Zone Enhancement (BAZE) for In Situ RDX Degradation in Ground Water
• Electrically Induced Redox Barriers for In Situ Treatment of Groundwater
• Remediation of TNT and RDX in Groundwater Using Zero-Valent Iron Permeable Reactive Barriers and Zero-Valent Iron In Situ Treatment Wells
• In Situ Bioremediation of Energetic Compounds in Groundwater
• Treatment of RDX and HMX Plumes Using Mulch Biowalls
• Field Demonstration/Validation of Electrolytic Barriers for Energetic Compounds at Pueblo Chemical Depot
• Bioaugmentation for Aerobic Bioremediation of RDX-Contaminated Groundwater