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

A VARIETY of Smokes and obscurants have been developed and used to screen armed forces from view, signal friendly forces, and mark positions. Smokes are produced by burning or vaporizing particular products. Obscurants are anthropogenic or naturally occurring particles suspended in the air. They block or weaken transmission of particular parts of the electromagnetic spectrum, such as visible and infrared radiation or microwaves. Fog, mist, and dust are examples of natural obscurants. White phosphorus and hexachloroethane smokes are examples of anthropogenic obscurants.

The U.S. Army seeks to reduce the likelihood that exposure to smokes and obscurants during training would have adverse health effects on military personnel or civilians. To protect the health of exposed individuals, the Office of the Army Surgeon General requested that the National Research Council (NRC) independently review data on the toxicity of smokes and obscurants and recommend exposure guidance levels for military personnel in training and for the general public residing or working near military-training facilities.

The Army requested recommendations for four types of exposure guidance levels: (1) emergency exposure guidance levels (EEGLs) for a rare, emergency situation resulting in exposure of military personnel for less than 24 hr; (2) repeated exposure guidance levels (REGLs) for repeated exposure of military personnel during training exercises (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 exposure of the public to military-training smoke; and (4) repeated public exposure guidance levels (RPEGLs) for repeated exposures of the public residing or working near military-training facilities (referred to permissible public exposure guidance levels in Volume 1).

The NRC assigned this project to the Committee on Toxicology (COT), which convened the Subcommittee on Military Smokes and Obscurants. The subcommittee conducted a detailed evaluation of data on the toxicity of eight obscuring smokes and seven colored smokes. The results are published in three volumes. This volume, Volume 3, reviews the potential toxicity of seven colored smokes used for signaling, marking, and, in some cases, simulating exposure to chemical-warfare agents in military training. Toxicity data and exposure guidance levels for eight obscuring smokes were addressed in previous volumes: diesel fuel, fog oil, red phosphorus, and hexachloroethane were presented in Volume 1; white phosphorus, brass, titanium dioxide, and graphite were presented in Volume 2.

Colored smokes are generated by deploying an M18 grenade or 40-mm cartridge containing a pyrotechnic mixture of fuel and dye. The dye mixtures originally formulated by the Army were yellow, green, red, and violet. Because of the potential health hazards of the smoke formulations and the combustion products, the Army developed new formulations for the same colors. However, grenades and cartridges containing the old smoke formulations are still in inventory. Therefore, the Army requested that the NRC evaluate the toxicity of both the old and the new smoke formulations, with the exception of the new violet-smoke formulation, which was removed from the inventory due to its acute toxicity.

Using the NRC guidelines published in 1986 and 1992 for recommending exposure guidance levels, the subcommittee evaluated the toxicity data on each of the old and new smoke formulations, the combustion products (smoke), and the individual dye components. The old smoke formulations are listed below with their dye components:

The new smoke formulations are listed below with their dye components:

No studies have been conducted in animals or humans on the toxicity of the old yellow-smoke formulation or its combustion products. In one study, rats, mice, and guinea pigs were exposed to a smoke containing benzanthrone, one of the old yellow-smoke components, and a blue dye not present in the Army's old yellow-smoke formulation. Animals exposed at concentrations of 0.9 to 13.4 grams per cubic meter (g/m³) for 1 hr exhibited injury characterized by lung necrosis, sloughing of the mucosa, edema in the alveolar space, and necrosis in the tracheobronchial tree.

No studies have been conducted on the toxicity of the old green-smoke formulation or its combustion products. In two studies rats, mice, and guinea pigs were exposed to smokes containing solvent green 3, one of the dye components of the old formulation. The smokes used in those studies also contained dye components not present in the Army's old green smoke. In one study, animals exposed to smoke containing solvent green 3 and auramine hydrochloride at concentrations of 0.6 to 12.1 g/m³ for 1 hr exhibited injury characterized by lung necrosis, sloughing of the mucosa, and edema in the alveolar space. In the other study, animals were exposed to a smoke composed of solvent yellow 33, disperse red 9, and solvent green 3 at concentrations of 0.1 to 1.0 g/m³ for 1 hr per day, 5 days per week for 100 days. The dye was retained in the lungs of all animals. Histological examination revealed pulmonary congestion, alveolitis, chronic pneumonia, and lung inflammation.

Old red smoke was evaluated for acute toxic effects in several animal species. Rats, rabbits, guinea pigs, dogs, swine, and goats were exposed to old red smoke at concentrations of 1.5 to 18 g/m³ for 10 to 240 min.

All animals showed signs of upper-respiratory-tract irritation and salivation immediately after exposure, and all had labored breathing for 7 days after the exposure. The study reported the combined mortality of the total number of animals of all the species exposed to the smoke. Only general information can be obtained from this study, because the mortality results in individual species were not given.

The toxicity of old violet smoke was evaluated in a study using rats, rabbits, guinea pigs, dogs, swine, and goats. Animals were exposed at concentrations of 1.3 to 7.8 g/m³ for 8 to 142 min. All animals showed upper-respiratory-tract irritation and salivation. As in the study of old red smoke, only general information can be obtained from this study because the results were reported as the combined mortality of the total number of animals of all the species exposed to the smoke. The old violet-smoke formulation was tested for mutagenicity and found to be positive in the Ames assay.

No studies have been conducted in animals or humans on the toxicity of the new yellow-smoke formulation or its combustion products. However, two studies evaluated the toxicity of smokes containing solvent yellow 33, the major component of the new yellow-smoke formulation. The smokes used in both studies also contained dyes not present in the Army's new formulation. One study used a smoke containing solvent yellow 33, solvent green 3, and disperse red 9. In that study, histological examination of rats, mice, and guinea pigs exposed to the smoke at concentrations of 0.1 to 1.0 g/m³ for 1 hr per day, 5 days per week for 100 days revealed pulmonary congestion, alveolitis, chronic pneumonia, and lung inflammation. The other study evaluated the toxicity of a smoke containing solvent yellow 33 and disperse orange 11. Mice, rats, and guinea pigs were exposed at 0.11 to 1.0 g/m³ for 1 hr per day, 5 days per week for 200 days. Toxic effects appeared to be confined to the respiratory tract. Lymphocyte infiltration in the larynx and trachea of mice and guinea pigs and dilated mucous glands in the trachea of mice and rats were reported.

The only data on the toxicity of the new green-smoke formulation are from an inhalation study on a mixture of solvent yellow 33 and solvent green 3 aerosols. The mixture was not acutely toxic; however, mild

pulmonary inflammation was observed and was attributed to solvent green 3. No-observed-adverse-effect levels for the aerosolized mixture were 50 milligrams (mg)/m³ for a 4-week exposure and 10 mg/m³ for a 13-week exposure. Two other studies might have some relevance in assessing the potential toxicity of new green smoke, although the smoke formulation did not have the same composition as the Army's. One study evaluated the toxicity of a smoke containing solvent yellow 33, solvent green 3, and disperse red 9. Histological examination of rats, mice, and guinea pigs exposed to the smoke at concentrations of 0.1 to 1.0 g/m³ for 1 hr per day, 5 days per week for 100 days revealed pulmonary congestion, alveolitis, chronic pneumonia, and lung inflammation. Another study evaluated the toxicity of a smoke composed of solvent yellow 33 and disperse orange 11. Mice, rats, and guinea pigs were exposed at 0.11 to 1.0 g/m³ for 1 hr per day, 5 days per week for 200 days. Toxic effects appeared to be confined to the respiratory tract; lymphocyte infiltration in the larynx and trachea of mice and guinea pigs and dilated mucous glands in the trachea of mice and rats were reported.

No studies have been conducted using new red smoke. Data are available on the toxicity of an aerosolized mixture containing solvent red 1 and disperse red 11. Inhalation exposure of rats and rabbits to the aerosolized mixture resulted in nasal and lung lesions. Only minimal details of the study are available; therefore, the study's scientific merits cannot be evaluated adequately, and the information cannot be used to recommend exposure guidance levels.

In addition to evaluating the toxicity data on the smoke formulations and the combustion products, the subcommittee reviewed toxicity data on the individual dyes used in the smoke formulations. Toxicity data for nine dyes were reviewed and summarized. Concern about the toxicity of several of them is substantial. For example, four dyes that have been demonstrated to be dermal sensitizers in humans and laboratory animals are benzanthrone, a component of the old yellow-and old green-smoke formulations; solvent yellow 33, a component of the new yellow-and new green-smoke formulations; solvent red 1, a component of the new red-smoke formulation; and disperse red 9, a component of the old red-and violet-smoke formulations. Additionally, their potential for pulmo-

nary sensitization after inhalation of the smokes has not been addressed adequately and remains a source of uncertainty. Because each of the seven smokes evaluated contains one of the four dyes identified as sensitizing agents, that uncertainty applies to all smokes under consideration.

The subcommittee concludes that the available toxicity data base for the combustion products of the old and new smoke formulations is inadequate for use in assessing the potential health risk of exposure to these smokes and in recommending exposure guidance levels. Review of the data identified sufficient evidence of toxicity for smoke formulations and combustion products to raise concern, particularly with regard to dermal and respiratory-tract sensitization. However, the data are too sparse to permit well-informed recommendations for exposure guidance levels. Stringent guidance levels could be arbitrarily set to protect personnel; however, the Army's current policy states that troops without protective clothing must avoid entering the smoke cloud during training. That policy should serve to protect troops until further research can be performed to provide more information for recommending exposure guidance levels.

The primary reason for the subcommittee's concern about the potential toxicity of the colored smokes is the demonstration of contact allergic dermatitis in humans and laboratory animals exposed to several of the dyes that are components of the old and new smokes. On the basis of its review and evaluation, the subcommittee concludes that additional research must be conducted on the toxicity of the colored smokes before well-informed recommendations for exposure guidance levels can be made. The subcommittee recommends that, at a minimum, acute inhalation studies be conducted in experimental animals to test the toxicity of the colored smokes. Acute toxicity studies would be most relevant for recommending emergency guidance levels such as the EEGLs and SPEGLs. Such exposures might occur during training exercises in which military personnel might be exposed for several minutes, twice per day, two to four times per year. Some military personnel, particularly instructors involved in training exercises, might be repea2:27 PM 12/31/03tedly exposed to the smokes over several years, as might a community living near a military-

training facility. For those exposure scenarios, the REGL and RPEGL are the most appropriate guidance levels, and studies assessing the potential toxicity of the smokes following repeated exposure would provide the most appropriate data for setting those exposure guidance levels. Thus, the Army should also consider conducting subchronic inhalation studies in experimental animals to test the toxicity of the smokes under conditions of repeated exposure.

Both acute and repeated inhalation studies should be carried out using combusted smokes, and the particle size and combustion products should be representative of the smokes used by the Army. Toxicity testing of other smoke formulations or of individual dyes might not provide results similar to those obtained with the combusted smokes. For example, particle size, surface area, and surface characteristics of the smokes might be important determinants of toxicity. Thus, the use of smokes with surface properties different from those of the smokes used by the Army would be difficult to interpret within the context of potential exposure of military personnel.

Finally, there is concern that potential sensitization resulting from exposure to several of the dyes used in the smoke formulations might cause allergic dermatitis and respiratory-tract hypersensitivity. The subcommittee recommends that studies be conducted in animal models appropriate for assessing the sensitivity potential from dermal and inhalation exposures. Those studies should also be conducted using the combusted smokes. To ensure that such studies are designed correctly, the Army should consult with an expert panel before conducting them.

Until adequate data are available for determining exposure guidance levels, the subcommittee recommends that the Army follow its current policy on protecting military personnel from the respiratory and dermal effects of the colored smokes. In addition, the subcommittee recommends that these smokes be used only for signaling and marking and not for obscuring (the Army has developed other smokes for obscuring purposes). Because the potential toxicity of colored smokes is unknown, the subcommittee recommends that the Army avoid exposing the general public to the colored smokes.