Cover Image

PAPERBACK
$54.75



View/Hide Left Panel

5
Hexachloroethane Smoke

BACKGROUND INFORMATION

The toxicity of hexachloroethane (HCE) smoke (referred to as HC smoke)1 is attributed to the production of zinc chloride (ZnCl2). Karlsson et al. (1991) compared acute inhalation exposures of HC smoke generated with zinc oxide (ZnO) with those generated with titanium dioxide (TiO2). TiO2-HCE smoke proved to be far less toxic than ZnO-HCE smoke, and ZnO-HCE smoke was lethal, causing gross pathological pulmonary injuries and death due to pulmonary edema. These authors also compared exposures to titanium tetrachloride (TiCl4) gas with exposures to ZnCl2 aerosol. No animals died from exposure to TiCl4 at concentrations up to 2,900 mg/m3 for 10 min, whereas the LC50 for ZnCl2 was 2,000 mg/m3 for a 10-min exposure.

Most reports of accidental human exposures to HC smoke indicate symptoms consistent with exposures to the ZnCl2 component released when the smoke bomb is ignited. Therefore, the exposure-response assessments for HC smoke are probably most reliably interpreted, given present data, on the basis of the exposure-response data for ZnCl2.

1  

In this chapter, HCE refers to the compound hexachloroethane, and HC smoke is the term used by the military for smoke produced by combusting HCE with zinc oxide and producing zinc chloride.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 127
5 Hexachloroethane Smoke BACKGROUND INFORMATION The toxicity of hexachloroethane (HCE) smoke (referred to as HC smoke)1 is attributed to the production of zinc chloride (ZnCl2). Karlsson et al. (1991) compared acute inhalation exposures of HC smoke generated with zinc oxide (ZnO) with those generated with titanium dioxide (TiO2). TiO2-HCE smoke proved to be far less toxic than ZnO-HCE smoke, and ZnO-HCE smoke was lethal, causing gross pathological pulmonary injuries and death due to pulmonary edema. These authors also compared exposures to titanium tetrachloride (TiCl4) gas with exposures to ZnCl2 aerosol. No animals died from exposure to TiCl4 at concentrations up to 2,900 mg/m3 for 10 min, whereas the LC50 for ZnCl2 was 2,000 mg/m3 for a 10-min exposure. Most reports of accidental human exposures to HC smoke indicate symptoms consistent with exposures to the ZnCl2 component released when the smoke bomb is ignited. Therefore, the exposure-response assessments for HC smoke are probably most reliably interpreted, given present data, on the basis of the exposure-response data for ZnCl2. 1   In this chapter, HCE refers to the compound hexachloroethane, and HC smoke is the term used by the military for smoke produced by combusting HCE with zinc oxide and producing zinc chloride.

OCR for page 127
Military Applications HC smoke is used by the U.S. military in a wide variety of munitions, some of which are shown in Table 5-1. HC smoke is produced by burning a mixture containing roughly equal parts of HCE and ZnO and approximately 6% granular aluminum. Combustion Products The smoke mixture in a smoke bomb or grenade is initially ignited by a pyrotechnic starter mixture. The reaction is self-perpetuating and exothermic. The overall reaction was summarized by Cichowicz (1983): Another reaction produces carbon monoxide instead of solid carbon. ZnCl2 leaves the reaction zone as a hot vapor. On cooling below the condensation point, it nucleates to form an aerosol that rapidly absorbs water from the surrounding atmosphere. Hydrated ZnCl2 particles then scatter light, thereby obscuring vision. Because of ZnCl2's affinity for water, the aerosol likely consists of the hydrated forms of ZnCl2 under most atmospheric conditions (Katz et al. 1980). A starter mixture containing silicon, potassium nitrate, charcoal, iron oxide, granular aluminum, cellulose nitrate, and acetone, which is required to initiate the reaction, might generate very small amounts of other airborne contaminants. However, the acute toxic effects of exposure to HC smoke are considered to arise primarily from inhalation of the ZnCl2 component, which comprises almost two thirds of the total mass of HC smoke (Table 5-2). All measurements of HC smoke are expressed in this chapter as milligrams of ZnCl2, unless noted otherwise. The munitions listed in Table 5-1 all use slightly different chemical mixtures (Novak et al. 1987). An analysis of trace materials

OCR for page 127
TABLE 5-1 Characteristics of HC Smoke Munitions Smoke-Pot Munitionsa Container Size (in.) Filling Weight (lb) Ignition Method Weight (lb) (approx.) with Fuse Delay Time (sec) Burning Time (min) Smoke pot, HCE, 10-lb, M1 9 by 5.5 diameter 10 Matchhead and scratcher block or electrical 12.5 10 5-8 Smoke pot, HCE, 30-lb, ABC-M5 9.5 by 8.5 diameter 31 Matchhead and scratcher block or electrical 33 20-30 2-22 Smoke pot, floating, HCE, M4A2 13 by 12 diameter 27.5 M207A1 smoke-pot fuse 38 10-20 10-15 Smoke grenade, HCE, M8 4.75 by 2.5 diameter 1.2 M201A1 fuse 1.5 0.7-2b 1.7-2.5 Cartridge,c 105-mm, HCE, M84A1   12.3 Mechanical, time, and super-quick fuse 13.0 60-90 3 Projectile,d 155-mm, HCE, M116A1   25.8 Mechanical, time, and super-quick fuse 26.2 60-90 4 a All HC smokes are type C, which contains granular aluminum, hexachloroethane, and zinc oxide. Other types of HC smoke were used in the early years of smoke generation. b Time to functioning after release of safety lever. c No future production for the M84A1 was planned as of 1983. d M116A1 was completing its production life cycle in 1983 and would be replaced by XM 825 white phosphorus fill. Source: Cichowicz (1983).

OCR for page 127
TABLE 5-2 Approximate Composition of HC Smokea Constituent Estimated Mass Fraction, % Zinc chloride 62.5 Zinc oxide 9.6 Iron oxideb 10.7 Aluminum oxideb 5.4 Lead oxideb 1.0 Total particulate phase 89.2 Chlorinated vapors 10.8 a The analysis does not take into account any liquid water that associates with ZnCl2. b These metals were assumed to be present as the oxide for purposes of calculating the mass fraction. Source: DeVaull et al. (1989) in HC smoke mixtures found common zinc impurities (Katz et al., 1980). Arsenic ranged from 0.13 to 5.0 microgram per gram (µg/g), mercury from 0.35 to 0.60 µg/g, cadmium from 53 to 1,523 µg/g, and lead from 50 to 858 µg/g. The cadmium and lead concentrations displayed a strong negative correlation. Trace gas-phase products were measured in a field test of a standard M5-HCE 30-lb smoke pot (Katz et al. 1980). Table 5-3 shows the resulting gas-phase products at two distances from the pot. Laboratory tests showed that hydrogen chloride (HCl) vapor formation decreased with increasing relative humidity (Katz et al. 1980). Because the field test was performed at -2°C, humidity was probably low. Thus, HCl vapor concentrations shown in Table 5-3 could be much higher than those produced under more humid conditions. However, Katz et al. (1980) speculated that under humid conditions, HCl is absorbed from the vapor phase into ZnCl2 and water aerosol particles. Therefore, with increasing humidity, exposure of respiratory tissue to HCl might shift to lower portions of the lung, because small aerosol particles can penetrate to the lower lung and vapor can be removed readily from incoming air in the upper airways. During four field tests, estimated chlorine (Cl2) production ranged from 3 to 19 mg/g of mixture combusted.

OCR for page 127
Aerosol formation was studied in a chamber using scaled-down HC smoke pots (Katz et al. 1980). The mass-median and the count-mean diameters produced were approximately 0.4 µm and 0.3 µm, respectively, averaged over 29 experiments. The observed size distribution was log-normal at lower initial particle concentrations (83 × 106 particles per cubic centimeter) and multimodal at higher concentrations. Relative humidity had no consistent effect on the total particulate concentration or the particle size. As the aerosols aged over a 2-hr period, the mass-median and count-mean diameters nearly doubled as the particle concentration decreased by a factor of about 6. Laboratory-produced HC smoke consisted primarily of Zn+2 and Cl-1 (Katz et al. 1980). The aluminum content ranged from 0.49% to 4.06% of the Zn content, with a mean of 1.79%. The lead content ranged from 0.13 to 2.2 µg/mg of Zn, and the cadmium content ranged from 0.18 to 5.0 µg/mg of Zn. The ratios of both lead and cadmium to zinc were slightly higher than the ratios in the unburned mixture and were well correlated with them. Physical and Chemical Properties of Zinc Chloride CAS no.: 7646-85-7 Molecular formula: ZnCl2 Molecular weight: 136.29 Chemical name: Zinc chloride Synonyms: Butter of zinc, zinc butter, zinc Physical state: Solid Melting point: 290°C Boiling point: 732°C Density: 2.907 at 25°C Vapor pressure: 1 mm Hg at 428°C Solubility: 4.32 × 106 mg/L at 25°C 6.15 × 106 mg/L at 100°C 1 g/1.3 mL ethyl alcohol 1 g/2 mL glycerol 1 g/0.25 mL 2% hydrochloroacetic acid

OCR for page 127
TABLE 5-3 Chemical Analysis of Vapor Reaction Products from Field Test of 30-lb Military HC Smoke Pot Distance from Mount to Pot (cm) CO (ppm) HCl (ppm) COCl2 (ppm) CCl4 (ppm) C2Cl4 (ppm) C2Cl6 (ppm) C6Cl6 (ppm) ≈ 15 <1 1128 30 33 36 nd nd ≈ 15 <1 1958 16 8 9 nd nd ≈ 15 <1 5693 30 57 192 40 103 ≈ 15 <1 6822 20 36 81 40 95 ≈ 200 <1 1137 1 1 2 nd nd Abbreviation: nd, not determined. Source: Katz et al. (1980).

OCR for page 127
Occurrence and Use ZnCl2 is used in preserving wood and in the manufacture and dyeing of fabrics. In addition to its use in military obscurants, ZnCl2 is also the major ingredient in smoke from smoke bombs used for crowd dispersal and in fire-fighting exercises (by both military and civilian communities) (ASTDR 1994). ZnCl2 also has uses in dental, medical, and household applications, as well as in herbicides (ATSDR 1994). Military Exposures Inhalation is expected to be the most important route of exposure. Undoubtedly excessive exposure has occurred in the military. Hill and Wasti (1978) summarized case reports of accidental exposures, many of which were fatal. The fatal exposures resulted from the discharge of HC smoke devices in enclosed spaces. The exposures in these reported cases generally are poorly characterized and represent only the most extreme conditions. Very few data on HC smoke exposure are available for typical atmospheric conditions. Young et al. (1989) collected air samples during 1-hr demonstrations of M5 smoke pots and M8 smoke grenades at the U.S. Army Chemical School. Cadre members ignited these devices and students remained upwind. Personal and area samples were collected using mixed-cellulose-ester filters and high-flow personal-sampling pumps. Also, the particle-size distribution was characterized using cascade impactors. Zinc in the samples was measured by atomic absorption spectroscopy. Exposures to zinc for three cadre members were 0.0375, 0.0652, and 0.0776 mg/m3 , or 0.0781, 0.1358, and 0.1616 mg/m3 as ZnCl2. The mass-median diameters of the particles ranged from 0.4 to 2.8 µm. Thus, a large portion of the particulate mass was respirable. Simulated combat training during a military operation on urban terrain (MOUT) exercise indicated that trainees and instructors are exposed to ZnCl2 in concentrations ranging from 0.02 to 0.98 mg/m3 during a 225-min period. The average exposure

OCR for page 127
concentration was 0.26 mg/m3 with a standard deviation of 0.26 mg/m3 (or 59 mg•min/m3 over a 225-min exposure) (Young 1992, as cited in Lundy and Eaton 1994). The most extensive field study of HC smoke, reported by DeVaull et al. (1989), shows the average smoke composition observed over five experiments. Composition and sampling location varied from test to test. In these tests, the total weight of smoke released ranged from 218.5 to 229.3 kg for groups of 18 to 20 M5 smoke pots. The particle mass-median diameters ranged from 0.77 to 1.05 µm, with geometric standard deviations from 1.78 to 2.36. Those particle sizes generally agree with those found by Katz et al. (1980) for aged aerosol and by Young et al. (1989), confirming that the aerosol has a large respirable mass fraction. DeVaull et al. (1989) also measured four specific chlorinated organic compounds. The geometric mean ratios of tetrachloromethane, tetrachloroethylene, hexachloroethane, and hexachlorobenzene to zinc in HC smoke were found to be 0.014, 0.009, 0.010, and 0.030, respectively. A computer simulation of exposure to smoke released from 41 M5 smoke pots was carried out for a wind speed of 6 m/sec using the HAZARD2 program (Cichowicz 1983). The roughly rectangular area with exposures expected to exceed 60,000 mg•min/m3 was 1,400 m wide in the cross-wind direction and about 1,000 m downwind of the release. Donohue et al. (1992) estimated that acute exposures in excess of 50,000 mg•min/m3 can cause death or severe injury. Table 5-4 shows calculations of Cichowicz (1983), who estimated minimum downwind distances from an M5 smoke pot necessary to limit exposures to designated concentrations and concentration-time profiles under various atmospheric conditions. The minimum distances downwind from one M5 smoke pot are listed in column 4 of Table 5-4. Similarly, distances are shown that are calculated to yield the concentration × time (CT) products ranging from the STEL (2 mg/m3 × 15 min = 30 mg•min/m3 ) to the highest estimated exposure level of 4,800 mg•min/m3.

OCR for page 127
TABLE 5-4 Downward Distances from One M5 Smoke Pot (HC) Necessary to Limit Exposure to Designated ZnCl2 Concentrations and Concentration × Time Products Atmospheric Condition Wind Speed (m/sec) Plume Rise (m) Distance at Peak Concentration ≤ 2 mg/m3 (m) Distance at CT ≤ 30 mg•min/m3 (m) Distance at CT ≤ 2,000 mg•min/m3 (m) Distance at CT ≤ 4,800 mg•min/m3 (m) Night (very stable) 1 0 3,900a 3,700 190 100   3 0 2,000 1,720 80 40   1 18 3,600 3,200 – – Day (neutral stability) 1 0 1,100 950 80 50 Abbreviation: CT, concentration × time product. Source: Adapted from Cichowicz (1983).

OCR for page 127
The potential for exposure during HC smoke training was explored in a cancer risk-assessment study (Novak et al. 1987). On the basis of the Army's Training Ammunition Management Information System (TAMIS), 15 bases using HC smoke munitions for training were identified. Fort Irwin in California was believed to have the greatest potential for exposure of all the sites in the United States and thus was chosen for study. At that base, Army forces train by mock combat with a simulated opponent force (OPFOR). A typical scenario is that OPFOR attacks the friendly force under cover of obscurants, often a combination of HC smoke and fog oil. Three exposure categories were identified: smoke-generator squads, OPFOR, and friendly forces (Novak et al. 1987). The smoke-generator squads must stay 50 to 75 m directly downwind of the smoke pots. These squads were generating smoke 2 weeks per month for 10 months in 1982 and 3 weeks per month for 12 months in 1986. They have the greatest consistent exposure potential. Friendly forces rotate through this training and seldom train for more than 2 to 3 months per year. OPFOR attacks one friendly force after another over the course of a year and spends much of its training time under smoke cover; the prescribed OPFOR tactics in the 1980s called for heavy use of obscurants. Novak et al. (1987) estimated the ''worst-practical-case" long-term exposure at Fort Irwin for a soldier deploying smoke pots and standing 50 m directly downwind of the smoke pot. On the basis of usage of HC-smoke munitions in fiscal year 1982 and an assumed 2-year tour of duty, each person in the smoke-generator squad was considered exposed to emissions from 262 M5 smoke pots. Using air-dispersion modeling under very stable conditions and a wind speed of 2 m/sec, Novak et al. (1987) estimated that each member of the smoke generator squad was exposed to HC smoke at a total concentration of 9,916 mg•min/m3. Again assuming a 2-year tour of duty, exposure concentrations were estimated to range from a minimum of 52.2 to nearly 20,000

OCR for page 127
mg•min/m3 for the OPFOR, from 0.04 to 0.48 mg•min/m3 for the friendly force, and approximately 62 mg•min/m3 total HC smoke for the nearby community. In addition to exposure to the smoke itself, workers manufacturing HC smoke munitions might be exposed to toxic materials. The most significant possible exposure is to HCE. HCE is a white crystalline solid with a vapor pressure equivalent to 770 ppm at 25°C (Eaton et al. 1994). Its camphorlike odor can be detected as low as 0.15 ppm. The HCE concentration in HC-smoke munitions production areas was found to be above the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 9.7 mg/m3 (Selden et al. 1993). Workers in these areas are protected with either air-supplied hoods at fixed work stations or full-face-piece respirators with both filters and organic vapor cartridges. Nevertheless, the plasma concentrations of HCE in workers rose from 0.08 ± 0.14 µg/L to 7.30 ± 6.04 µg/L after working for more than 5 weeks in the loading and packing operations (Selden et al. 1993). TOXICOKINETICS The toxicokinetics of ingested Zn has been studied in humans and animals, but inhaled Zn has not been systematically investigated (Donohue et al. 1992; ATSDR 1994). Intestinal absorption of radiolabeled ZnCl2 increased up to 55% at low concentrations of Zn (90 µmol or less) in humans and declined with much higher concentrations of Zn (Payton et al. 1982). Uptake can be increased by dietary zinc deficiency (Istfan et al. 1983). Data on distribution and excretion of inhaled ZnCl2 are not available, but at least one report of unmasked humans who succumbed following acute exposure to a high concentration of HC smoke showed increased concentrations of Zn in the lung and striated muscle (Hjortso et al. 1988).

OCR for page 127
Assuming an inhalation rate of 0.03 /min and 100% absorption, the total absorbed dose is 1.86 mg of HC smoke (i.e., 62.3 × 0.03). The average daily dose over a 70-year lifetime for a 70-kg person is This dose is quite small compared with the dose estimated for smoke-pot operators. Estimated Cancer Risk Using the information above, the subcommittee estimated a lifetime cancer risk by multiplying the upper limit of the cancer potency of HC smoke (0.036/mg/kg per day) by the dose averaged over a lifetime. For smoke-pot operators on a 2-year tour of duty, the lifetime cancer risk for an average daily dose of 0.0049 mg/kg per day was estimated to be for a neutral atmospheric condition. For a very stable atmospheric condition, the average daily lifetime dose was estimated to be 0.0436 mg/kg per day, giving a lifetime cancer risk of If average atmospheric conditions are assumed, the estimated risks for smoke-pot operators would be lower. In the community of Baker, even using the unrealistic worst-case atmospheric conditions, the average daily lifetime dose was estimated to be 1 × 10-6 mg/kg per day, resulting in a lifetime cancer risk of less than 3.6 × 10-8 (i.e., 0.036 × 10-6) throughout the lifetime of Baker residents.

OCR for page 127
EXISTING RECOMMENDED EXPOSURE LIMITS The ACGIH (1991) proposed a TLV time-weighted average (TWA) of 1 mg/m3 for 8 hr per day, 5 days per week (or 40 hr per week) and a 15-min TLV short-term exposure limit (STEL) of 2 mg/m3 for ZnCl2. SUBCOMMITTEE EVALUATION AND RECOMMENDATIONS On the basis of the toxicity information presented for ZnCl2, the subcommittee developed exposure guidance levels for military personnel exposed during an emergency release or during regular-training exercises and for nearby communities to protect them from emergency or repeated releases of HC smoke. Military Exposures Emergency Exposure Guidance Level (EEGL)2 To define an EEGL for ZnCl2, several factors must be taken into consideration. Based on reports from acute human inhalation exposures, CT products of 160 mg•min/m3 produced slight nausea and cough, and 240 mg•min/m3 was associated with irritation of the nose, throat, and chest and with nausea and cough (Cullumbine 1957). Donohue et al. (1992) summarized these data by suggesting that the noticeable irritation range for nose, throat, and chest is 160 to 240 mg•min/m3. The NOAEL of 160 mg•min/m3 for ZnCl2 is based on short-term exposures of humans and therefore can be used for the EEGL 2   Guidance for a rare, emergency situation resulting in an exposure of military personnel.

OCR for page 127
without adjustment to account for extrapolation uncertainties (e.g., animal to human, LOAEL to NOAEL). Thus, for a 60-min exposure period, the EEGL would be 2.7 mg/m3, rounded off to 3.0 mg/m3. Similarly, for a 15-min exposure period, the EEGL would be 10 mg/m3, and for a 6-hr exposure period, the EEGL would be 0.4 mg/m3. The 15- and 60-min EEGLs exceed the current STEL value set by ACGIH (2 mg/m3) but can be justified by the fact that the EEGL is set for a one-time emergency exposure situation which is not expected to reoccur. Permissible Exposure Guidance Levels (PEGL)3 A PEGL is required because of the chronic intermittent exposures to smokes that are experienced by soldiers, which would approximate 50 8-hr exposures during a 2-year tour of duty. Virtually no human data are available upon which to base a PEGL. One repeated inhalation toxicity exposure study carried out by Marrs et al. (1988) identified a NOAEL for rodents as ZnCl2 at 26.6 mg/m3 for 1 hr per day, 5 days per week, for 20 weeks. Using that NOAEL, a divisor of 10 for uncertainties associated with sparse animal data and with the shorter daily duration of exposure (1-hr exposures for the rodent compared with 8-hr exposures for military personnel), and another divisor of 10 to extrapolate from animals to humans, the subcommittee recommends a PEGL for ZnCl2 of 0.2 mg/m3. Comparison with Other Exposure Guidance Levels The ACGIH 8-hr TLV-TWA for ZnCl2 of 1.0 mg/m3 is higher than both the 6-hr EEGL of 0.4 and the PEGL of 0.2 mg/m3 recommended above. The ACGIH TLV-TWA is based on 3   Guidance for repeated exposure of military personnel during training exercises.

OCR for page 127
unpublished reports that a 30-min exposure at 4.8 mg/m3 caused mild, transient respiratory irritation and that 0.4 mg/m3 (duration of exposure not specified) was not considered irritating. ACGIH did not indicate why Haber's law was not applied to the 30-min exposure level to extrapolate to longer exposure periods. Without evidence to the contrary, the subcommittee assumes that Haber's law is applicable and therefore recommends the lower values for the 6-hr EEGL and PEGL rather than the ACGIH recommendation for its 8-hr TLV-TWA. The actual exposures that can be experienced if cancer risks are not to exceed 1 × 10-4, for example, would require that a total dose of no more than 5,000 mg of HC smoke be experienced (i.e., the 8,800-mg HC smoke associated with a 1.8 × 10-4 cancer risk divided by 1.8 to yield a 1 × 10-4 cancer risk). Assuming 262 exposures during a 2-year tour of duty, the total dose from a single smoke pot could not exceed 19 mg (5,000 mg of HC smoke divided by 262 exposures). Assuming further an inhalation rate of 0.03/min, the exposure concentration generated by the smoke pot could not exceed 630 mg•min/m3 (i.e., 19 mg divided by 0.03 /min) or approximately 10 mg•hr/m3 (i.e., 630 mg•min/m3 divided by 60 min/hr) for a total of 262 such exposures. In the case of the training staff who endure a greater number and duration of such exposures, the values would have to be altered accordingly. Public Exposures Short-Term Public Emergency Guidance Level (SPEGL)4 In calculating the SPEGL, the EEGL is divided by an uncertainty factor of 10 to account for the susceptible subpopulations of the general public (e.g., the elderly, chronically ill, and children) that could conceivably be exposed. This calculation results in a 4   Guidance for a rare, emergency situation potentially resulting in an exposure of the public to a military-training smoke.

OCR for page 127
SPEGL, expressed as a CT product, of 16 mg•min/m3. The corresponding 15-min, 60-min, and 6-hr SPEGLs are 1, 0.3, and 0.04 mg/m3, respectively. Permissible Public Exposure Guidance Level (PPEGL)5 The general public living or working near military-training facilities could experience chronic intermittent exposures. For the PPEGL, the PEGL is divided by an uncertainty factor of 10 to account for sensitive populations (e.g., the elderly, chronically ill, and children). A PPEGL of 0.01 mg/m3 is recommended. Comparing the outcome of the example of cancer-risk estimates with the PEGL suggests that, because the cancer risks for the nearby community, as computed above, are well below the usual level of concern, the PPEGL guidelines should be used. Comparison of Recommendations with Conservative Screening Cancer-Risk Estimates Given the one finding of cancer in mice exposed to HC smoke (Marrs et al. 1988), the subcommittee estimated a conservative cancer potency factor for HC smoke (see Carcinogenic Effects) and estimated the corresponding cancer risk associated with the recommended exposure guidance levels for military personnel and the public. For a 60-min EEGL of 3 mg/m3 for ZnCl2, the total exposure of 3 mg averaged over a 75-hr lifetime for a 70-kg adult is 3 mg/m3 (75 yr × 365 days × 70 kg) = 1.6 × 10-6 mg/kg per day. The cancer risk is estimated to be below 0.086 × (1.6 × 10-6) = 1 × 10-7. For 400 hr of exposure of military personnel during a tour of duty at a PEGL of 0.1 mg/m3, the total exposure would be 40 mg 5   Guidance for repeated exposures of public communities near military-training facilities.

OCR for page 127
of ZnCl2. For this exposure, the cancer risk is estimated to be less than 2 × 10-6. For the SPEGL, the possible lifetime exposure would be 0.3 mg of ZnCl2, which would correspond to a cancer risk of less than 2 × 10-8. For 30 hr of exposure per year at a PPEGL of 0.01 mg/m3 for ZnCl2, the total annual dose would be 0.3 mg of ZnCl2, corresponding to an annual cancer-risk estimate of less than 2 × 10-8. For a 30-year period of residence in the community, the corresponding risk estimate would be less than 6 × 10-7. Thus, the subcommittee concludes that the exposure guidance levels recommended for military personnel and the public developed on the basis of noncancer end points are sufficiently low to represent a negligible (i.e., approximately 1 × 10-6 or less) cancer risk if the substance is a human carcinogen. The data available to date, however, are insufficient to conclude that ZnCl2 is a human carcinogen. Summary of Subcommittee Recommendations Table 5-8 summarizes the subcommittee's recommendations for EEGLs and the PEGL for military personnel exposed to HC smoke. Table 5-9 summarizes the subcommittee's recommendations for SPEGLs and the PPEGL for military-training facilities to ensure that nearby communities are not exposed at concentrations that might cause adverse effects. TABLE 5-8 EEGLs and PEGL for HC Smoke for Military Personnel Exposure Guideline Exposure Duration Guidance Level (mg/m3)a EEGL 15 min 10   1 hr 3   6 hr 0.4 PEGL 8 hr/d 0.2 a Expressed in milligrams of ZnCl2 per cubic meter.

OCR for page 127
TABLE 5-9 SPEGLs and PPEGL for HC Smoke at the Boundaries of Military Training Facilities Exposure Guideline Exposure Duration Guidance Level (mg/m3)a SPEGL 15 min 1   1 hr 0.3   6 hr 0.04 PPEGL 8 hr/d 0.02 a Expressed in milligrams of ZnCl2 per cubic meter. RESEARCH NEED It is clear from the data reviewed in this chapter that insufficient information is available to evaluate potential long-term toxicity of ZnCl2. As noted above, almost all studies have focused on pulmonary effects, and little information exists on potential toxicity to other systems, such as the developmental or reproductive systems or nervous system. In addition, little information exists on effects resulting from repeated exposures and on the reversibility of observed effects. If use of HC smoke devices based on reactions of HCE with ZnO continues, then additional information with respect to effects on other organs and systems is required to ensure the health of military personnel and to prevent releases beyond military facilities that might pose risks to the general public. 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. ATSDR (Agency for Toxic Substances and Disease Registry). 1994. Toxicological Profile for Zinc (Update). TR-93/15. Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services, Atlanta, Ga.

OCR for page 127
Brown, R.F.R., T.C. Marrs, P. Rice, and L.C. Masek. 1990. The histopathology of rat lung following exposure to zinc oxide/hexachloroethane smoke or instillation with zinc chloride followed by treatment with 70% oxygen. Environ. Health Perspect. 85:81-87. Cichowicz, J.J. 1983. Environmental Assessment, Programmatic Life Cycle Environmental Assessment for Smoke/Obscurants. HC Smoke, Vol. 4. ARCSL-EA-83007. Chemical Research and Development Center, U.S. Army Armament, Munitions and Chemical Command, U.S. Army Aberdeen Proving Ground, Edgewood, Md. Cullumbine, H. 1957. The toxicity of screening smokes. J. R. Army Med. Corps 103:119-122. DeVaull, G.E., W.E. Dunn, J.C. Liljegren, and A.J. Policastro. 1989. Analysis Methods and Results of Hexachloroethane Smoke Dispersion Experiments Conducted as Part of Atterbury-87 Field Studies. AD-A216048. Prepared by Argonne National Laboratory, Argonne, Ill., for the U.S. Army Medical Research and Development Command, Fort Detrick, Frederick, Md. Domingo, J.L., J.M. Llobet, J.L. Paternain, and J. Corbella. 1988. Acute zinc intoxication: Comparison of the antidotal efficacy of several chelating agents. Vet. Hum. Toxicol. 30:224-228. Donohue, J.M., L. Gordon, C. Kirman, and W.C. Roberts. 1992. Zinc Chloride Health Advisory. Interagency Agreement (IAG) 85PP5869. Office of Water, U.S. Environmental Protection Agency, Washington, D.C., and the U.S. Army Medical Research and Development Command, Fort Detrick, Frederick, Md. Eaton, J.C., R.J. LoPinto, and W.G. Palmer. 1994. Health Effects of Hexachloroethane (HC) Smoke. USABRDL-TR-9402. AD-A277 838. U.S. Army Biomedical Research and Development Laboratory, Fort Detrick, Frederick, Md. Evenson, D.P., R.J. Emerick, L.K. Jost, H. Kayongo, and S.R. Stewart. 1993. Zinc-silicon interactions influencing sperm chromatin integrity and testicular cell development in the rat as measured by flow cytometry. J. Anim. Sci. 71:955-962. Hill, H.G., and K. Wasti. 1978. A Literature Review–Problem Definition Studies on Selected Toxic Chemicals. Occupational Health and Safety and Environmental Aspects of Zinc Chloride, Vol. 5, Final Report. AD A056020. Franklin Institute Research Laboratories, Philadelphia. Hjortso, E., J. Qvist, M.I. Bud, J.L. Thomsen, J.B. Andersen, F. Wiberg-Jorgensen, N.K. Jensen, R. Jones, L.M. Reid, and W.M. Zapol.

OCR for page 127
1988. ARDS after accidental inhalation of zinc chloride. Intensive Care Med. 14:17-24. Istfan, N.W., M. Janghorbani, and V.R. Young. 1983. Absorption of stable 70Zn in healthy young men in relation to zinc intake. Am. J. Clin. Nutr. 38:187-194. Johnson, F.A., and R.B. Stonehill. 1961. Chemical pneumonitis from inhalation of zinc chloride. Dis. Chest 40:619-623. Karlsson, N., I. Fangmark, I. Haggqvist, B. Karlsson, L. Rittfeldt, and H. Marchner. 1991. Mutagenicity testing of condensates of smoke from titanium dioxide/hexachloroethane and zinc/hexachloroethane pyrotechnic mixtures. Mutat. Res. 260:39-46. Katz, S., A. Snelson, R. Farlow, R. Welker, and S. Mainer. 1980. Physical and Chemical Characterization of Fog Oil Smoke and Hexachloroethane Smoke. DAMD17-78-C-8085. AD-A080 936. IIT Research Institute, Chicago. Lundy, D., and J. Eaton. 1994. Occutational Health Hazards Posed by Inventory U.S. Army Smoke/Obscurant Munitions (Review Update). U.S. Army Medical Research Detachment, Wright-Patterson Air Force Base, Ohio. Marrs, T.C., H.F. Colgrave, J.A.G. Edginton, R.F.R. Brown, and N.L. Cross. 1988. The repeated dose toxicity of a zinc oxide/hexachloroethane smoke. Arch. Toxicol. 62:123-132. Novak, E.W., L.B. Lave, J.J. Stukel, and D.J. Schaeffer. 1987. A Revised Health Risk Assessment for the Use of Hexachloroethane Smoke on an Army Training Area. USA-CERL Tech. Rep. N-87/26. Construction Engineering Research Laboratory, U.S. Army Corps of Engineers, Champaign, Ill. Payton, K.B., P.R. Flanagan, E.A. Stinson, D.P. Chodirker, M.J. Chamberlain, and L.S. Valberg. 1982. Technique for determination of human zinc absorption from measurement of radioactivity in a fecal sample or the body. Gastroenterology 83:1264-1270. Schenker, M.B., F.E. Speizer, and J.O. Taylor. 1981. Acute upper respiratory symptoms resulting from exposure to zinc chloride aerosol. Environ. Res. 25:317-324. Seldén, A., M. Nygren, A. Kvamlöf, K. Sundell, and O. Spångberg. 1993. Biological monitoring of hexachloroethane. Int. Arch. Environ. Health 65:S111-S114. Stocum, W.E., and R.G. Hamilton. 1976. A Risk Analysis of Exposure to High Concentrations of Zinc Chloride Smoke. SAND76-0386. Sandia Laboratories, Albuquerque, N.Mex.

OCR for page 127
Young, J.Y., D.A. Smart, J.T. Allen, D.L. Parmer, A.B. Rosencrance, E.E. Brueggeman, and F.H. Broski. 1989. Field Exposure of Chemical School Students and Cadre to Fog Oil and Hexachloroethane (HC) Smokes. Tech. Rep. 8908. U.S. Army Biomedical Research and Development Laboratory, Fort Detrick, Frederick, Md. Young, J.Y. 1992. Field Exposure of Infantry Soldiers to Hexachloroethane and Colored Smoke During a ''Military Operation-Urban Terrain" Training. U.S. Army Biomedical Research and Development Laboratory, Fort Detrick, Frederick, Md. Zaporowska, H., and E. Wasilewski. 1992. Combined effect of vanadium and zinc on certain selected hematological indices in rats. Comp. Biochem. Physiol. C 103:143-147.

OCR for page 127
This page in the original is blank.