Toxicity of Military Smokes and Obscurants: Volume 3 (1999)

Ever since smokeless powder replaced black powder as the standard propellant for guns and firearms, the armed forces have sought methods to blanket battlefields by creating a haze similar to that created by black powder. A variety of smokes and obscurants has been developed and used in wartime operations for screening armed forces from view, deceiving the enemy, signaling friendly forces, and marking positions. To ensure defense preparedness, large quantities of smokes and obscurants also are used in military training. Obscurants are anthropogenic or naturally occurring particles suspended in air that block or weaken the transmission of particular parts of the electromagnetic spectrum, such as visible and infrared radiation or microwaves. Smokes are produced by burning or vaporizing some product. White and gray smokes are deployed in grenades to obscure vehicle locations or troop movement, and colored smokes are used to mark specific locations.

In order to reduce the likelihood that exposure to smokes and obscurants during combat training would have adverse health effects on military personnel and the general public residing or working near military-training facilities, the Office of the Army Surgeon General requested the National Research Council (NRC) review the data on the toxicity of

military smokes and obscurants and recommend exposure guidance levels for military personnel during combat training and for the general public residing or working near military-training facilities.

The NRC assigned this project to the Committee on Toxicology (COT), which convened the Subcommittee on Military Smokes and Obscurants. This volume, Volume 3, reviews data for the seven colored smokes used by the Army for signaling purposes. In Volume 1 of this series, the subcommittee evaluated four obscuring smokes: fog oil, diesel fuel, red phosphorus, and hexachloroethane (NRC 1997). In Volume 2, four additional obscuring smokes were reviewed: white phosphorus, brass, titanium dioxide, and graphite (NRC 1999).

The specific task of the subcommittee was to review the health effects associated with exposure to the smokes and other obscurants and, if appropriate, to recommend four exposure guidance levels: (1) emergency exposure guidance levels (EEGLs) for a rare, emergency situation resulting in an exposure of military personnel for a period of less than 24 hr; (2) repeated exposure guidance levels (REGLs) for repeated exposure of military personnel during training (referred to as permissible exposure guidance levels in Volume 1); (3) short-term public emergency guidance levels (SPEGLs) for a rare, emergency situation potentially resulting in an acute exposure of the public to a military-training smoke; and (4) repeated public exposure guidance levels (RPEGLs) for possible repeated exposures of the public residing or working near military-training facilities (referred to as permissible public exposure guidance levels in Volume 1). It was further requested that all four guidance levels take into account developmental and reproductive toxicity in men and women and that exposures of potentially susceptible subpopulations (e.g., ill or elderly persons and children) be considered in deriving the SPEGL and RPEGL.

The military uses colored smokes, disseminated via the M18 grenade or the M713, M715, or M716 40-millimeter (mm) cartridge, for signaling and marking and, in some cases, for training to simulate exposure to chemical-warfare agents (Rubin and Buchanan 1983). The colored-smoke formulations are incorporated into the M18 grenade and the 40-mm cartridge with a pyrotechnic mixture to deploy the smoke.

Four original (old) smoke formulations, which contain dyes—red,

yellow, green, and violet—are used in the M18 grenade and the 40-mm cartridge. Studies indicate that some of those dye materials are transformed during the combustion process to yield different chemical species, some of which are potentially hazardous (Rubin et al. 1982). To avoid potential health hazards, the Army developed four new formulations of the same colors. However, the new violet-smoke formulation was removed from the inventory because of its acute toxicity (Costa et al. 1990; AEHA 1992, 1993a,b; Lundy and Eaton 1994). Because quantities of grenades and cartridges still in inventory contain the old smoke formulations, the Army requested an evaluation of the toxicity of the four old and the three new formulations.

Table 1-1 lists the components of the colored-smoke M18 grenades and the 40-mm cartridges.

In the old M18 grenades, the colored dyes were mixed with sulfur, potassium chlorate, and sodium bicarbonate, with optional amounts of a mixture of pure, refined kerosene and tricalcium phosphate for control of dusting and caking, respectively (Lundy and Eaton 1994). The old smoke formulations were studied extensively by Rubin et al. (1982). The mixtures were fractionated by vacuum sublimation, differential solubility, and liquid chromatography. The major components were isolated and identified by comparison with the pure dyes using a variety of instrumental techniques. A number of contaminants at minor concentrations (less than 1%) were identified by gas chromatography-mass spectroscopy. All the smoke formulations contained relatively large quantities (10-25%) of chloroform-insoluble or nonvolatile undifferentiated carbonaceous material (Lundy and Eaton 1994).

In the new M18 grenades, sugar is used as the fuel instead of sulfur, and magnesium carbonate is used as a coolant instead of sodium bicarbonate

(Lundy and Eaton 1994). The new red grenade also contains terephthalic acid in addition to the dye and pyrotechnic ingredients.

The composition of the yellow, green, and red dyes in the new formulation was also changed (Lundy and Eaton 1994). The new yellow dye was reformulated to replace benzanthrone (BZA) and dibenzochrysenedione (DBC) with a single component: dye solvent yellow 33 (2-(2'quinolyl)-1,3-indandione (QID)). 1,4-Di-p-toluidino-9, 10-anthraquinone (PTA) is retained in the new green grenade and combined with QID instead of BZA and DBC. Thus, some of the results of chemical characterization of the smoke from the detonated old green grenades and those portions of the toxicity information obtained using the PTA fraction of the old green-smoke formulation are applicable to the new green grenade as well. The new red grenade contains solvent red 1 (α-methoxybenzenazo-1-naphthol) (MBN) and disperse red 11 (1,4-diamino-2-methoxy-anthraquinone) (DMA). The smoke formulations were studied by Buchanan and Ma (1988). All the mixtures contained small amounts (0.6% to 3.7%) of insoluble residue. The minor contaminants (less than 1% of mixture), 1-p-toluidinoanthraquinone and aminoanthraquinone were identified in the new green-and red-smoke formulations, respectively. No minor contaminant was identified in the new yellow formulation.

Signaling smokes are produced by volatilizing and condensing a mixture containing an organic dye (Owens and Ward 1974). A colored-smoke munition is composed of a pyrotechnic mixture of fuel and dye; a cooling agent is sometimes added to prevent excessive decomposition of the dye. The heat produced by the fuel volatilizes the dye, which then condenses outside the munition to form the colored smoke. The fuel is formulated as a mixture of an oxidizing agent and a combustible material. The burning time can be regulated by adjusting the proportions of oxidant and combustible material and by using coolants.

In separate studies, Rubin et al. (1982) and Buchanan and Ma (1988) characterized the components of the smoke produced by deploying the

old red and violet grenades and all four colors of the new M18 grenades, respectively. The grenades were detonated inside canvas tents, and samples of the generated vapors and particles were collected. Chin et al. (1983) (as cited in Lundy and Eaton 1994) studied the combustion products of the U.S. Navy red-, yellow-, and green-smoke formulations, which use the same dye constituents as the old Army smoke formulations. In this study, the grenade fill, including the dyes, the fuel, the oxidizer, the cooling agent and binders, was thermally vaporized, and the solids and vapors produced were collected on filters and traps, respectively, and analyzed by thin-layer chromatography, high-performance liquid chromatography, gas chromatography, gas chromatography-mass spectrometry, nuclear magnetic resonance, ultraviolet spectrometry, and electron dispersive X-ray analysis. The results of the Rubin et al. (1982) and Chin et al. (1983) studies were in agreement in the case of the red grenade fill, the only case of overlap in the three studies. The vast majority (90-95%) of the dyes in the colored-smoke grenades remain unchanged during the combustion process (Chin et al. 1983). Approximately 5-10 percent of those dyes undergo decomposition when the grenades are detonated. Combustion products include polynuclear aromatic hydrocarbons, polynuclear organic materials, carbon dioxide, carbon monoxide, hydrochloric acid, and water and are the result of uncombusted impurities, pyrosynthesis, and degradation of the component dyes. The amounts and types of the combustion products produced are affected by variables such as burn time, burn rate, and atmospheric conditions such as humidity. Tables 1-2 and 1-3 summarize the major combustion products.

Current Army policy regarding colored smokes states that during training, troops must avoid entering the smoke cloud (AEHA 1992, 1993a,b). If troops are required to enter the smoke plume, they must wear a chemical protective mask, long-sleeve shirts, head coverings, pants that cover the entire leg, and boots.

In addition, Army policy requires that personnel involved with production of the M18 colored-smoke grenades and exposed to the pure dyes or smoke formulations wear protective equipment, including coveralls, butyl rubber gloves, head coverings, and respiratory protection.

An EEGL is defined as a concentration of a substance in air (as a gas, vapor, or aerosol) that will permit continued performance of specific tasks during emergency exposures lasting up to 24 hr—an occurrence expected to be infrequent in the lifetime of a person (NRC 1986, 1992a). ''Emergency'' connotes a rare and unexpected situation with potential for significant loss of life, property, or mission accomplishment if not controlled. An EEGL, a single ceiling-exposure concentration for a specified duration, specifies and reflects the subcommittee's interpretation of available information in the context of an emergency.

An EEGL is acceptable only in an emergency, when some risks or some discomfort must be endured to prevent greater risks (such as fire, explosion, or massive release). Exposure at the EEGL might produce such effects as increased respiratory rate, headache, mild central-nervous-system effects, and respiratory-tract or eye irritation. The EEGL should prevent irreversible harm. Even though some reduction in performance is permissible, it should not prevent proper responses to the emergency (such as shutting off a valve, closing a hatch, or using a fire extinguisher). For example, in normal work situations, upper-respiratory-tract irritation or eye irritation causing discomfort would not be considered acceptable; during an emergency, it would be acceptable if it did not cause irreversible harm or seriously affect judgment or performance. The EEGL for a substance represents the subcommittee's judgment based on evaluation of experimental and epidemiological data, mechanisms of injury, and, when possible, operating conditions in which an emergency exposure might occur, as well as consideration of U.S. Department of Defense (DOD) goals and objectives. EEGLs were recommended for military use and are intended for healthy, young military personnel. Therefore, they are not directly applicable to general populations consisting of elderly, very young, and ill persons.

A SPEGL is defined as a concentration of a substance in air that is acceptable for an unpredicted, single or rare, short-term emergency exposure of the general public. The SPEGL takes into account the likely wide range of susceptibility among individuals in the general public, including potentially sensitive subgroups, such as children, the elderly, and persons with serious debilitating diseases. Effects of exposure on the developing embryo and fetus and on the reproductive capacity of men and women also are considered in setting a SPEGL.

For purposes of assessing military smokes and other obscurants for the Army, the subcommittee recommended two additional guidance levels, REGLs and RPEGLs. The subcommittee defines a REGL as the concentration of a substance in air to which healthy military personnel can be exposed repeatedly, up to a specified total exposure on a weekly basis (usually 8 hr per day, 5 days per week), for several years without experiencing adverse health effects or degradation in performance.

The subcommittee defines a RPEGL as the concentration of a substance in air to which the general public can be exposed repeatedly without experiencing adverse health effects or discomfort. RPEGLs, like SPEGLs, take into account the likely wide range of susceptibility among individuals in the general public, including potentially susceptible subpopulations (children, the elderly, and the chronically ill) and the developing embryo and fetus.

Exposure to smokes and obscurants at or below the recommended exposure guidance levels is not likely to produce adverse health effects in the general population. However, because of potential susceptibility factors including genetics, personal habits (e.g., smoking and alcohol consumption), and exposures to other chemicals, a small number of individuals might experience health effects at or below the recommended exposure guidance level.

The NRC has published guidelines for recommending EEGLs, SPEGLs, and other exposure guidance levels for continuous or repeated exposures to a variety of chemical agents (NRC 1992a,b, 1996). For purposes of assessing military smokes and other obscurants, the subcommittee recommended comparable procedures for recommending REGLs and RPEGLs. The steps in recommending exposure guidance levels are similar for EEGLs, SPEGLs, REGLs, and RPEGLs; the differences reflect attributes of the exposed populations and the duration and frequency of exposure. A detailed explanation of the approach the subcommittee used to recommend exposure guidance levels can be found in Toxicity of Military Smokes and Obscurants, Volume 1 (NRC 1997).

The general approach for recommending EEGLs is to determine a no-observed-adverse-effect level (NOAEL) directly from laboratory experi-

ments or human studies on acute (short-term) exposure or to estimate an acute-exposure NOAEL from a lowest-observed-adverse-effect level (LOAEL) with the use of a default assumption. A 15-min, 1-hr, or 6-hr EEGL is estimated from the NOAEL, depending on which exposure duration most closely matched the exposure duration associated with the NOAEL. Haber's law (the product of exposure concentration and time is a constant; C X T = k) is then used, if appropriate, to recommend EEGLs for different exposure durations.

SPEGLs are generally derived from EEGLs by applying an uncertainty factor to protect all members of the public, including susceptible subpopulations, such as the elderly, children, and the developing embryo or fetus. In the absence of specific data on variation in human susceptibility to a smoke, the subcommittee assumes that some subpopulations could be up to 10 times more susceptible than healthy military personnel. Thus, unless otherwise noted, SPEGLs are generally 10-fold lower than the EEGLs.

Data from chronic-(repeated) exposure experiments in animals or clinical observations form the basis for the REGL instead of the acute-exposure data used for the EEGL. Haber's law should not be applied to extrapolate from longer to shorter exposures.

RPEGLs for possible repeated exposures of a community near a military-training facility are calculated by dividing the REGLs recommended for military personnel by an uncertainty factor of 10 to extrapolate from healthy military personnel to a more diverse population, including potentially susceptible subpopulations.

This volume is organized into two major chapters. Chapter 2 reviews the potential toxicity of the old formulations for yellow, green, red, and violet smokes, and Chapter 3 reviews the potential toxicity of the new formulations for yellow, green, and red smokes. In each chapter, information is presented on the physical and chemical properties, toxicokinetics, and toxicity of the formulations and on the toxicity of the component dyes. Each chapter concludes with an overall evaluation of the toxicity of the formulations, reports any existing recommended exposure limits, and presents the subcommittee's recommendations for exposure guidance levels and research. Following the two major chap-

ters are nine appendixes which review the toxicity data on each of the major dye components used in the formulations.

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AEHA (U.S. Army Environmental Hygiene Agency). 1993. Health Hazard Assessment Report (RCS MED 388) on the 40 MM Colored Smoke Ground Marker. Report No. 69-37-XY57-93. U.S. Army Environmental Hygiene Agency, Aberdeen Proving Ground, Edgewood, MD.

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NRC (National Research Council). 1992a. Guidelines for Developing Community Emergency Exposure Levels for Hazardous Substances. Washington, D.C.: National Academy Press.

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