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4
Red Phosphorus Smoke

BACKGROUND INFORMATION

The military application of phosphorus smokes for environmental screening can contain either white phosphorus or red phosphorus in various matrices (e.g., felt, butyl rubber, or polymer epoxy binders). The compositions of the various phosphorus smokes are similar, being composed primarily of polyphosphoric acids with less than 1% trace levels of organic compounds. This chapter provides an evaluation of the health effects of red phosphorus (RP) in combination with butyl rubber (BR).

Military Applications

Red phosphorus is not manufactured by the U.S. Army and is obtained from sources outside the United States (e.g., People's Republic of China) and shipped to Pine Bluff Arsenal in Arkansas for blending and filling operations for certain munitions and testing (Mitchell and Burrows 1990). In Army field use, red phosphorus smoke is deployed explosively from grenades and mortar shells.



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4 Red Phosphorus Smoke BACKGROUND INFORMATION The military application of phosphorus smokes for environmental screening can contain either white phosphorus or red phosphorus in various matrices (e.g., felt, butyl rubber, or polymer epoxy binders). The compositions of the various phosphorus smokes are similar, being composed primarily of polyphosphoric acids with less than 1% trace levels of organic compounds. This chapter provides an evaluation of the health effects of red phosphorus (RP) in combination with butyl rubber (BR). Military Applications Red phosphorus is not manufactured by the U.S. Army and is obtained from sources outside the United States (e.g., People's Republic of China) and shipped to Pine Bluff Arsenal in Arkansas for blending and filling operations for certain munitions and testing (Mitchell and Burrows 1990). In Army field use, red phosphorus smoke is deployed explosively from grenades and mortar shells.

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The obscurant portion of the grenades consists of a 95:5 mixture of red phosphorus and styrene-butadiene rubber (butyl rubber) in the presence of methylene chloride, which is later removed by low temperature drying (Lundy and Eaton 1994). Analysis of samples for methylene chloride found none present (Brazell et al. 1984). The purpose of the butyl rubber is to reduce the cloud-pillar effect found with pure red phosphorus. This mixture of red phosphorus and butyl rubber (RP-BR) also contains two other compounds. The red phosphorus is coated with about 1.25% (by weight) of insulating oil, and approximately 1% talc or silica is added to break up and improve uniformity of the pattern. Red phosphorus is also the major ingredient in mortar rounds used to generate smoke. In that use, it is combined with sodium nitrate and an epoxy binder in a ratio of 80:14:6 parts by weight, respectively. Physical and Chemical Properties The red allotropic form of elemental phosphorus is intermediate to the black and white varieties in reactivity. Red phosphorus reacts slowly with oxygen and water vapor and can evolve phosphine gas, which is highly toxic. The reaction is extremely slow at normal temperatures and humidities and is not considered to be a factor in the deployment of phosphorus munitions in military operations. However, this reaction can be catalyzed by metal ions (e.g., iron and copper), which can markedly increase the oxidation rate. The physical and chemical properties of red phosphorus are listed below: Formula: Polymeric (P4)n CAS no.: 7723-14-0 Molecular weight: 123.9n Density: 2.34 g/cm3 Melting point: Sublimes at 416°C

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Heat of sublimation: 19.7 kcal/mol Ignition temperature: 280°C in air Solubility: Insoluble in organic solvents, negligible in water Occurrence and Use Phosphorus is the 11th most abundant element in the earth's crust. It commonly occurs in the lithosphere in igneous, sedimentary, and metamorphic rock. Depending upon the nature of interatomic bonds established during its formation, solid elemental phosphorus can occur in three allotropic forms: black, white, or red. In the biosphere, phosphorus is an essential nutrient in the formation of structural biomolecules, such as membrane phospholipids; functional macromolecules, such as nucleic acids and adenosine triphosphate; and metabolic intermediates, such as sugar phosphates. Human activities, such as the manufacture and use of detergents, fertilizers, and water softeners, contribute to phosphorus in the environment. Combustion Products The combustion products associated with RP-BR have been chemically and physically characterized by the U.S. Army. Table 4-1 summarizes the composition of phosphoric acids in RP-BR smoke. The combustion products of RP-BR and white phosphorus impregnated in felt, also used by the Army to generate an obscuring smoke, are similar under the same burn conditions (Ramsey et al. 1985). The particles are composed primarily of various phosphoric acids present as a complex mixture of polymeric forms with organic compounds and inorganic gases only at trace levels. Phosphorus trioxide is particularly likely to be formed, which is of interest because it reacts with water to form phosphoric

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TABLE 4-1 Composition of the Phosphoric Acids in RP-BR Smoke from Static Burn Component Composition % Orthophosphate 22.8 Pyrophosphate 19.6 Tripolyphosphate 13.3 Tetrapolyphosphate 11.5 P5-P13 32.8 Higher polyphosphates Low   Source: Brazell et al. (1984). acid and phosphine (Ballou 1981). The relative proportion of the different acids of phosphorus in RP-BR smoke changes with time after it is generated, but the predominate component of the smoke remains phosphoric acid (orthophosphate) (Ballou 1981; Mitchell and Burrows 1990). Only trace amounts of phosphine have been measured in some cases (Ballou 1981). Measurement of the mass median aerodynamic diameter (MMAD) of RP-BR aerosol particles generated to test the toxicity of the smoke in animals have ranged from 0.4 to 1.6 µm, and geometric standard deviations ranged from 1.5 to 1.9 (Aranyi 1984, Aranyi et al. 1988b; Ballou 1981). All measurements of RP-BR smoke reported or recommended in this chapter are referred to in milligrams of total particulates per cubic meter. TOXICOKINETICS No studies were available on the toxicokinetics of RP-BR smoke or its components. TOXICITY SUMMARY: ELEMENTAL RED PHOSPHORUS Red phosphorus is a relatively inactive allotrope of phosphorus. Little, if any, significant toxicity appears to be associated with

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elemental red phosphorus unless it is contaminated with white phosphorus (Mitchel and Burrows 1990; Lundy and Eaton 1994). No dermal irritation was noted when red phosphorus was applied to the skin of rabbits at doses of 0.5 g per site. Similarly, dermal application of the element to guinea pigs resulted in no skin irritation or sensitization. Interdermal injection resulted in only slight irritation. Doses of 100 mg did not result in rabbit eye irritation. In Fischer 344 rats, the oral LD50 was reported to be greater than 10 g/kg (Mitchell and Burrows 1990). TOXICITY SUMMARY: RED PHOSPHORUS-BUTYL RUBBER Effects in Humans No studies have been conducted on the effects of RP-BR smoke in humans. However, Mitchell and Burrows (1990) estimated that human exposure to RP-BR at concentrations of about 2,000 mg/m3 for longer than 15 min might result in death. They suggested further that acute exposure at concentrations of 1,000 mg/m3 should be considered intolerable and that 700 mg/m3 is the highest tolerable concentration; above that, masks must be worn (Mitchell and Burrows 1990). Others have reported that concentrations exceeding 100 mg/m3 were unendurable for all workers except the ''inured" worker (ACGIH 1991). Effects in Animals Dermal Exposures When air samples of combusted RP-BR were collected using an electrostatic precipitator and the residue (0.1 mL) was instilled in the eyes of rabbits, severe irritation and corneal ulceration were evident. When this same material was administered to the intact

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or abraded skin of rabbits clipped free of hair, severe irritation was produced (Weimer et al. 1977). Inhalation Exposures One-Time Exposures Lethality. The concentration lethal to 50% (LC50) of Sprague-Dawley rats that were exposed to RP-BR smoke for 1 hr on 5 consecutive days was estimated to be 2,320 mg/m3 (Aranyi et al. 1988a). In contrast, daily 4-hr exposures for 5 days at lower concentrations (i.e., W 1,000 mg/m3) did not produce significant mortality (Aranyi et al. 1988a). Other reports estimated that a single 1-hr LC50 for rats was approximately 4,000 mg/m3 (Ballou 1981; Shinn et al. 1985). The presence of butyl rubber in the smoke was assumed to be toxicologically insignificant. In both reports, the animals continued to die during the 14-day observation period following exposure, indicating that both acute and delayed effects resulted from these 1-hr exposures. Twenty percent died after a 1-hr exposure at 3,100 mg/m3, and eight of nine died within 2 days of a 1-hr exposure at 8,460 mg/m3 (Ballou 1981). Lethal effects were accompanied by symptoms of respiratory distress, including pulmonary edema, congestion, and atelectasis. Ballou (1981) found that the application of Haber's law (i.e., effects are proportional to the exposure concentration (C) multiplied by the duration (or time, T) of the exposure, or the CT product) predicted lethality of such smokes with a 65% error. Several studies indicate that exposure concentration, instead of the CT product, is the major determinant of lethality over relatively short exposures (Shinn et al. 1985; Aranyi et al. 1988a; Lundy and Eaton 1994). Weimer et al. (1977) studied the acute effects of a single exposure to RP-BR smoke with a wide range of exposure CT values in three species of animals. For rats, average exposure concentrations ranged from 1,128 to 1,882 mg/m3, and exposure durations

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ranged from 60 to 240 min, producing CT values of 67,685 to 451,680 mg·min/m3. For guinea pigs, exposure concentrations ranged from 120 to 2,277 mg/m3, and exposure durations ranged from 5 to 150 min, producing CTs from 45,570 to 451,680 mg•min/m3. For dogs, exposure concentrations ranged from 1,212 to 1,882 mg/m3, and exposure durations ranged from 30 to 240 min, producing CTs from 45,570 to 451,680 mg•min/m3. Weimer et al. (1977) found the CT products lethal to 50% (LCT50) of rats, guinea pigs, and dogs tested were 222,700, 4,040, and more than 451,700 mg·min/m3, respectively. The exposure time in these studies varied from 5 min to 240 min. No rats died following exposure at 1,128 mg/m3 for 60 min, and 4 of 10 died after exposure at 1,676 mg/m3 for 120 min. For the guinea pig, 4 of 10 died from a 10-min exposure at 352 mg/m3; whereas none died from a 5-min exposure at 120 mg/m3. No deaths occurred among dogs exposed to the highest dose studied (1,882 mg/ for 240 min). These studies indicate that RP-BR smoke is only slightly toxic to the rat and dog, but that the guinea pig is more sensitive. Table 4-2 summarizes the acute lethality data. Skin and Eye Irritation. Weimer et al. (1977) reported conjunctivitis in rats exposed at 1,813 mg/m3 for 180 min and in dogs exposed at 1,882 mg/m3 for 240 min. No conjunctivitis was apparent 3 days after exposure ended. In the rat, however, that exposure concentration resulted in 9 of 10 deaths over a 6-day period after exposure (Weimer et al. 1977). Pulmonary Effects. Ballou (1981) found that gross pathology in rats following exposure to high concentrations of airborne RP-BR smoke varied somewhat with concentration, but the pathology consistently involved the laryngeal and proximal tracheal regions. As indicated in Table 4-2, at the highest exposure concentration tested (8,460 mg/m3 for 1 hr), eight of nine animals died within 2 days. Seven of those had significant laryngeal and tracheal lesions that consisted of a fine fibrinlike coat on the laryngeal and proximal tracheal mucosa. Pulmonary edema and hemorrhage were

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TABLE 4-2 Acute Lethality of Red Phosphorus-Butyl Rubber Smoke Species Exposure Duration Exposure Concentration (mg/m3) End Points and Comments Reference Rat 1 hr/d, 5 d 2,320 LC50 Aranyi et al. 1988a Rat 4 hr/d, 5 d W 1,000 No significant mortality Aranyi et al. 1988a Rat 1 hr 4,000 LC50 Ballou 1981; Shinn et al. 1985 Rat 1 hr 8,460 8/9 died with 2 d Ballou 1981 Rat 1 hr 3,100 20% lethality Ballou 1981 Rat 60 min 1,128 No deaths Weimer et al. 1977   120 min 1,676 4/10 died     150 min 1,625 5/10 died     180 min 1,572 8/10 died   Guinea pig 5 min 120 No deaths Weimer et al. 1977   10 min 352 4/10 died     15 min 484 7/10 died     10 min 797 9/10 died   Dog ≤ 240 min ≤ 1,882 No deaths Weimer et al. 1977 prominent. The only rat that survived the exposure had laryngeal edema, small fibrin tags in the central larynx, and essentially no epiglottis. All the other concentrations tested (5,360, 4,330, and 3,150 mg/m3 for 1 hr and 1,530 mg/m3 for 4 hr) also resulted in some lethality in the exposed groups. At all these concentrations, the animals showed marked laryngeal and epiglottal erosion, hemorrhage, ulceration with fibrin deposition, enlarged lymph nodes, edema with pulmonary congestion, and mucus accumulation in the trachea. In the series of experiments conducted to estimate LCT50 values

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for rats, guinea pigs, and dogs, Weimer et al. (1977) stated that the animals were not visible for observation during exposure. Following exposure, however, all animals displayed signs of respiratory distress at all exposure concentrations. The lowest exposure concentrations tested for the rat, guinea pig, and dog were 1,128 mg/m3 for 60 min, 120 mg/m3 for 5 min, and 1,519 mg/m3 for 30 min, respectively. Animals were hypoactive and salivating. As the CT values increased, distress became more marked. Those effects persisted for up to 2 days after exposure. Following a one-time 3.5-hr exposure of rats at 1,000 mg/m3, Aranyi et al. (1988b) observed a large reduction in pulmonary bacteriocidal activity, from 80% activity in the controls to 35% activity in the exposed group. Other Effects. Weimer et al. (1977) also reported some extrapulmonary effects following inhalation of RP-BR. Male rats exposed at 1,676 mg/m3 for 120 min had kidney weights that were significantly less than control weights. Also, body weights were significantly lower after exposure at 1,625 mg/m3 for 150 min. Both of those concentrations also produced significant mortality. The authors stated that the gross pathology and histopathological evaluations of the rats, guinea pigs, and dogs failed to show any lesions that could be attributed to the smoke inhalation. No significant changes in blood hematology or chemistry developed in dogs, guinea pigs, or rats that could be agent-related. Repeated Exposures Skin and Eye Irritation. Weimer et al. (1980) reported transient ocular irritation in rats exposed to RP-BR smoke concentrations of 0 (control), approximately 22 mg/m3, and approximately 165 mg/m3 for 8 min per day, 5 days per week, for 12 weeks (60 rats per group). During the eighth week, a reddening and swelling of the eyelids was noted in rats at both concentrations. Those effects subsided by the end of the exposure. Several control rats also

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displayed similar reddened eyelids. The number of animals with eye irritation exposed to the control, low, and high concentrations of RP-BR smoke was 3, 8, and 14, respectively. Although no statistical analyses were performed, the dose-response relation suggests that this effect was attributable to the RP-BR exposure. Pulmonary Effects. Weimer et al. (1980) also examined the pulmonary effects of repeated exposures to two concentrations of RP-BR. Two strains of rats (Sprague-Dawley and Fischer 344), two strains of mice (Swiss and A-strain), guinea pigs, and rabbits were used. The test animals were exposed for 5 days per week over 12 weeks. The low exposure concentration resulted in a cumulative CT of 10,705 mg•min/m3 and a mean daily exposure CT of 178 mg•min/m3. The mean daily exposure time was about 8 min. At the high exposure concentration, the cumulative CT was 81,691 mg•min/m3; the mean daily exposure CT was 1,319 mg•min/m3, and the mean daily exposure duration was 8 min. The daily exposure concentrations ranged from 8 to 43 mg/m3 (average 22 mg/m3) for the low exposure concentration. For the high exposure concentration, RP-BR concentrations were between 80 and 288 mg/m3 daily (average 165 mg/m3). During the first 3 days of exposure, both strains of rats displayed an increase in breathing rates following exposure to either concentration. Although histological changes were observed in the lungs, trachea, upper respiratory tract, and other organs in both rats and mice, Weimer et al. (1980) stated that these changes were not unlike those observed in the controls. Moreover, the changes were sporadic, and the incidence or severity of the changes was not related to the exposure concentration. The authors concluded that the pathological changes identified could not be attributed to exposure to the smoke. Some of the animals were held for 24 months in clean air after the exposure. No evidence of latent toxic effect or exposure-related tumor formation was found that could be agent-related. However, no long-term cancer bioassays have been conducted on RP-BR smoke aerosol. At both concentrations, the rabbits and guinea pigs exposed

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to RP-BR had a number of morphological lesions in the lung, trachea, nasal turbinates, liver, kidney, heart, testes, ovaries, urinary bladder, and other organs, but these changes also were seen in the controls. Weimer et al. (1980) stated that these changes could not be attributed to the test substance. The high incidence of pathology in the control animals might have resulted from one or more of several factors, including disease, age or source of the animals, or animal housing conditions. Pulmonary function tests performed on exposed guinea pigs indicated that after 3 weeks of exposure, pulmonary resistance decreased at the high and low exposure concentrations, but only in male guinea pigs. This effect was not present following 6, 9, or 12 weeks of exposure. Weimer et al. (1980) concluded that animals exposed repeatedly to RP-BR did not experience short-term or cumulative toxic effects. Thus, the high exposure concentration, 165 mg/m3, could be considered a no-observed-adverse-effect level (NOAEL) for all strains and species of animals tested. In another set of studies, male and female Sprague-Dawley rats were exposed to RP-BR aerosols ranging in concentrations from 400 to 1,200 mg/m3 for 2.25 hr per day, 4 days per week, for 4 weeks (Aranyi 1983, 1984; Lundy and Eaton 1994). During the exposure, wheezing and labored breathing were observed in the male rats exposed at the high dose. Decreased body weights and reduced food consumption were seen in the male rats during the 4-week exposure, but those conditions returned to normal during the 14-day recovery period. These authors also examined pulmonary free cells collected by lung lavage and found a slight, but not statistically significant, increase in total number of free cells immediately following exposures at 750 mg/m3 (Aranyi 1983, 1984; Aranyi et al. 1988b). After a 14-day recovery period, the count returned to normal. A significant increase in the protein level in the pulmonary lavage fluid of rats of both sexes after exposure to more than 1,000 mg/m3 indicated pulmonary edema, which was resolved during the recovery period (Aranyi 1984). The primary lesion of the respiratory tract was terminal

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Category and Species Exposure Frequency and Duration NOAEL (mg/m3) LOAEL (mg/m3) End Point and Comments Reference Rabbit 8 min/d, 5 d/wk, 12 wk 165 – No effects Weimer et al. 1980 Rat 3.5 hr, 4 d – 400 Terminal bronchiolar fibrosis Aranyi 1983 Rat 2.25 hr/d, 4 d/wk, 4 wk ♀ : 750 ♂ : 1,000 ♀ : 1,000 ♂ : 1,200 Increased protein in lavage fluid Aranyi 1984 Rat 2.25 hr/d, 4 d/wk, 4 wk 400 750 Terminal bronchiolar fibrosis Aranyi 1984 Rat 2.25 hr/d, 4 d/wk, 13 wk – 300 Decreased total cells in pulmonary lavage fluid; reversible in clean air Aranyi et al. 1988b Rat 2.25 hr/d, 4 d/wk, 13 wk 180 300 Reduced bactericidal activity; reversible in clean air Aranyi et al. 1988a,b Rat 2.25 hr/d, 4 d/wk, 13 wk 50 180 Terminal bronchiolar fibrosis Aranyi 1986; Aranyi et al. 1988a Biochemical Effects Rat 2.25 hr/d, 4 d/wk, 4 wk – ♀: 400 ♂: 750 Decrease in cholesterol and BUN levels Aranyi 1984 Immunological Effects Rat 2.25 hr/d, 4 d/wk, 4 wk 400 750 Decreased white-blood-cell count Aranyi 1984

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Rat 2.25 hr/d, 4 d/wk, 4 wk – ♀: 400 ♂: 750 Increased cellular ATP levels Aranyi 1984 Rat 2.25 hr/d, 4 d/wk, 4 wk – 750 Decreased activity of 5'-nucleotidase Aranyi 1984; Aranyi et al. 1988b Rat 2.25 hr/d, 4 d/wk, 13 wk – 300 Increased cellular ATP levels Aranyi et al. 1988b Rat 2.25 hr/d, 4 d/wk, 13 wk 300 750 Decreased activity of 5'-nucleotidase Aranyi et al. 1988b Behavioral Effects Rat 2.25 hr/d, 5 d/wk, 4 wk – 400 Increased motor activity; incomplete recovery after 2 wk in clean air Aranyi 1983, 1984 Reproductive and Developmental Effects Rat 8 min/d, 5 d/wk, 10 wk 132 1,186 Decreased birth weight (reproductive end points not fully evaluated) Weimer et al. 1980; Lundy and Eaton 1994 Mutagenic Effects Rat 2.25 hr/d, 4 d/wk, 2 wk – 1,000 Clastogenic response Aranyi 1984 Abbreviations: hr, hour(s); min, minute(s); d, day(s); wk, week(s); ♂, male; ♀, female. Notes: Aranyi (1984) used exposure concentrations of 400, 750, and 1,000 mg/m3 for females and 750, 1,000, and 1,200 mg/m3 for males. Thus, if an effect was observed at all concentrations tested, the LOAEL (without a NOAEL) would be 400 mg/m3 for females and 750 mg/m3 for males. Aranyi (1983, 1984) and Aranyi et al. (1988a,b) found no differences in responses between male and female rats exposed for 2.25 hr/d, 4 d/wk for 4 wk; therefore, only male rats were used in the 13-wk exposure experiments.

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A major health concern for repeated inhalation exposures to RP-BR smoke aerosol is development of terminal bronchiolar fibrosis. That condition is irreversible. The induction of fibrosis appears to be influenced by both concentration and duration of exposure. After 2 weeks of exposure, 50% of male rats exposed at 750 mg/m3 had minimal fibrosis, and all the test animals exposed at 1,200 mg/m3 had minimal-to-mild fibrosis. After 4 weeks of exposure, all rats exposed at 750 and 1,200 mg/m3 exhibited fibrosis. After 13 weeks of exposure, 100% of the rats exposed at 750 mg/m3 or more and 30% of the rats exposed at 300 mg/m3 had terminal bronchiolar fibrosis, and 100% of the rats exposed at 180 mg/m3 exhibited minimal fibrosis. At 50 mg/m3, the lowest concentration tested, no changes were found. Based on these studies, the NOAEL for terminal bronchiolar fibrosis in rats was 50 mg/ and the LOAEL was 180 mg/m3. Carcinogenicity There is no evidence of carcinogenicity or mutagenicity of RP-BR smoke; however, few tests have been conducted to examine these end points. EXISTING RECOMMENDED EXPOSURE LIMITS The American Conference of Governmental Industrial Hygienists (ACGIH 1991) Threshold Limit Values (TLVs), both time-weighted-average (TWA) values (for 8 hr per day, 5 days per week, for 40 years) and short-term exposure limits (STELs), for various components of RP-BR smokes are listed in Table 4-4. ACGIH (1991) recommended the TLV-TWA for phosphoric acid by analogy to comparable experience and data for sulfuric acid. ACGIH (1991) observed that the TLV-TWA is below the concentration that causes throat irritation among unacclimated workers

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TABLE 4-4 ACGIH Recommended Exposure Limits RP-BR Smoke Component TLV-TWA TLV-STEL Phosphine 0.3 ppm (0.42 mg/m3) 1.0 ppm (1.4 mg/m3) Phosphoric acid 1.0 mg/m3 3.0 mg/m3 Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; TLV, Threshold Limit Value; TWA, time-weighted average; STEL, short-term exposure limit. and is well below the concentration that is well tolerated by acclimated workers. SUBCOMMITTEE EVALUATION AND RECOMMENDATIONS Using the toxicity information described above, the subcommittee developed exposure guidance levels for military personnel exposed during an emergency release and during regular training exercises and for consideration at military-training-facility boundaries to protect nearby communities from emergency or repeated releases of RP-BR smoke. Military Exposures Emergency Exposure Guidance Level (EEGL)1 The EEGLs are based on the subcommittee's interpretation of available information in the context of an emergency, when some risk of reversible health effects and discomfort are considered acceptable. 1   Guidance for a rare, emergency situation resulting in exposure of military personnel.

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The major toxic end points associated with such short-term exposures would be lethality, respiratory distress and irritation, and pulmonary lesions. All the other effects documented for RP-BR smoke were from studies using longer-term exposures, and extrapolation from those to a 15-min, 1-hr, or 6-hr EEGL would be inappropriate. The most sensitive response to short-term exposures to RP-BR aerosols is respiratory distress. Data from humans indicate that concentrations as low as 100 mg/m3 can be considered intolerable (Table 4-3). Given the lack of documentation by ACGIH (1991) on how the human LOAEL of 100 mg/m3 was determined, the subcommittee used the animal data to estimate EEGLs. Because the guinea pig might be uniquely sensitive to respiratory irritants, results from this species were not used. Data from the rat and dog indicate a LOAEL for respiratory distress at an exposure concentration of approximately 1,200 mg/m3 for 1 to 1.5 hr (Table 4-3). Using an uncertainty factor of 10 to extrapolate from a LOAEL to a NOAEL and an additional uncertainty factor of 10 to extrapolate from animals to humans, the subcommittee developed a 1-hr EEGL of 10 mg/m3 (i.e., 12 rounded to one significant digit). Assuming that Haber's law applies over relatively short exposure durations (i.e., 15 min to 6 hr), the corresponding 15-min and 6-hr EEGLs (rounded to one significant digit) are 40 and 2 mg/m3, respectively. Therefore, the subcommittee recommends 40, 10, and 2 mg/m3 for 15 min, 1 hr, and 6 hr, respectively, for the EEGLs based on the animal data. To check their recommendations against the available human information, the subcommittee also estimated an EEGL based on the ACGIH (1991) report. Using a divisor of 10 to extrapolate from a LOAEL of 100 mg/m3 in humans to a NOAEL and assuming the concentration is "intolerable" in an exposure of approximately 1 hr, a 1-hr EEGL is 10 mg/m3. Again applying Haber's law, the corresponding 15-min and 6-hr EEGLs are 40 and 2 mg/m3, respectively. Thus, the EEGLs that the subcommittee developed on the basis of the animal studies are consistent with the human information.

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The maximum anticipated total dose for field exposures (i.e., the peak concentration of a single volley of L8A1 grenades) has been estimated to be about 500 mg/m3, and such a cloud would be expected to persist for 1 to 3 min (Weimer et al. 1980). Irritation might be expected following exposure to phosphorus smoke condensates because of the high phosphoric acid content. Permissible Exposure Guidance Levels (PEGL)2 The PEGL should be similar to the ACGIH TLV-TWA, which appears to protect the worker from occupational exposure. The PEGL is designed to protect specific populations (i.e., military personnel and munitions workers). The combustion products associated with exposure to RP-BR smoke exposure have been characterized chemically. Because the product of concern is primarily phosphoric acid, the existing TLV-TWA for phosphoric acid exposure seems appropriate for military personnel as well. Therefore, establishing another set of exposure limits is not necessary. The PEGL for an exposure of 8 hr per day for 5 days per week (i.e., 40 hr per week) is 1.0 mg/m3. Public Exposures Short-Term Public Emergency Guidance Level (SPEGL)3 Assuming that the general population comprises a wide variety of possibly sensitive individuals, an additional uncertainty factor of 10 is appropriate to extrapolate from an EEGL to a level 2   Guidance for repeated exposure of military personnel during training exercises. 3   Guidance for a rare, emergency situation potentially resulting in an exposure of the public to a military-training smoke.

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protective of the general public. Thus, the SPEGLs for a single emergency exposure for RP-BR smoke are 4.0, 1.0, and 0.2 mg/m3 for exposure durations of 15 min, 1 hr, and 6 hr, respectively (i.e., the corresponding EEGL values divided by 10). Permissible Public Exposure Guidance Level (PPEGL)4 The possibility of repeated contamination of the air during military operations creates the need for establishing some guidance level for the communities in close proximity to Army operations. The Army has estimated that nearby community exposures to smokes and obscurant exposures might be as long as 8 hr per day, perhaps for a lifetime. The TLV-TWA that has been set for phosphoric acid provides an acceptable concentration to which nearly all workers might be repeatedly exposed, day after day, without adverse effects during their working lifetime. To extend this exposure level to the general population requires the incorporation of an additional uncertainty factor of 10, because the general population might include individuals who are more sensitive to such exposures than are healthy workers. Dividing the existing TLV-TWA for phosphoric acid of 1.0 mg/m3 by a factor of 10 (for sensitive subpopulations), the PPEGL would be 0.1 mg/m3. Summary of Subcommittee Recommendations The subcommittee's recommendations for exposure limits for RP-BR smoke for military personnel are summarized in Table 4-5. The recommendations for RP-BR-smoke concentrations at the boundaries of military-training facilities are summarized in Table 4-6. 4   Guidance for repeated exposures of public communities near military-training facilities.

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TABLE 4-5 EEGLs and PEGL for RP-BR Smoke for Military Personnel Exposure Guideline Exposure Duration Guidance Level (mg/m3) EEGL 15 min 40   1 hr 10   6 hr 2 PEGL 8 hr/d, 5 d/wk 1 TABLE 4-6 SPEGLs and PPEGL for RP-BR Smoke at the Boundaries of Military-Training Facilities Exposure Guideline Exposure Duration Guidance Level (mg/m3) SPEGL 15 min 4   1 hr 1   6 hr 0.2 PPEGL 8 hr/d, 5 d/wk 0.1 RESEARCH NEEDS The subcommittee recognizes the need for further research to better understand the potential toxicity of RP-BR. Research in the following areas will provide better insight into possible health effects of inhalation of RP-BR and help to determine with greater confidence a guidance level that is not overly conservative but is scientifically defensible. Short-term (e.g., 10 min to 8 hr) inhalation studies are needed to evaluate the degree to which Haber's law applies to RP-BR smoke. Research should be undertaken to determine possible reproductive and developmental toxicity in mammals. Studies should be conducted to determine and to identify possible sensitive populations.

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Performance studies for military personnel operating in a smoke environment could determine if significantly impaired performance could occur. Documentation of the effects of exposure on humans should be developed to the extent possible. Pharmacokinetic and metabolism studies should be conducted to understand the mechanism of toxicity of RP-BR smokes. Further studies on possible mutagenic effects of RP-BR would be appropriate and would aid in clarifying whether this substance is a possible clastogen. Finally, the subcommittee notes that Army personnel who work with this smoke, trainers in particular, are potentially a rich source of information on the health effects of the smoke. The subcommittee recommends that the Army conduct a prospective study with appropriate controls in which pulmonary-function tests and routine chemistry tests (panel 20 plus Mg and thyroid tests as a minimum requirement) are performed on personnel who are exposed repeatedly to the smoke. REFERENCES ACGIH (American Conference of Governmental Industrial Hygienists). 1991. Documentation of the Threshold Limit Values and Biological Exposure Indices, 6th Ed. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio. Aranyi, C. 1983. Research and Development on Inhalation Toxicologic Evaluation of Red Phosphorus/Butyl Rubber Combustion Products, Phase 2 Report . AD-A158323. IIT Research Institute, Chicago. Aranyi, C. 1984. Research and Development on Inhalation Toxicologic Evaluation of Red Phosphorus/Butyl Rubber Combustion Products, Phase 3 Report. AD-A173549. IIT Research Institute, Chicago. Aranyi, C. 1986. Research and Development on Inhalation Toxicologic Evaluation of Red Phosphorus/Butyl Rubber Combustion Products,

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and Dogs. Tech. Rep. ARCSL-TR-77052. Chemical Systems Laboratory, U.S. Army Armament, Munitions and Chemical Command, Aberdeen Proving Ground, Edgewood, Md. Weimer, J.T., G.E. Affleck, R.L. Farrand, F.K. Lee, and R.J. Pellerin. 1980. The Acute and Chronic Effects of Repeated Exposure to United Kingdom Red Phosphorus Screening Smokes in Rats, Mice, Guinea Pigs, and Rabbits. Tech. Rep. ARCSL-TR-79053. Chemical Systems Laboratory, U.S. Army Armament, Munitions and Chemical Command, Aberdeen Proving Ground, Edgewood, Md.