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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 SULFURIC ACID BACKGROUND INFORMATION PHYSICAL AND CHEMICAL DATA Structural formula: H2SO4 Molecular weight: 98.08 Synonyms: Oil of vitriol CAS number: 7664–93–9 Boiling point: 290°C Density: 1.84 General characteristics: It is a clear, colorless, oily liquid. It is corrosive and in concentrated form is a strong oxidizing agent. At 340°C, it decomposes into sulfur trioxide (SO3) and water. The odor threshold for most people is 1 mg/m3 (Amdur et al., 1952). It is miscible with water and alcohol, with the generation of much heat and with contraction in volume. OCCURRENCE AND USE Sulfuric acid is prepared by the contact process or the chamber process (Duecker and West, 1959). It is widely used industrially, principally in the manufacture of fertilizers, explosives, dyestuffs, other acids, parchment paper, and glue and in the purification of petroleum and the pickling of metal (ACGIH, 1980). Dilute sulfuric acid has been used in the treatment of gastric hypoacidity (Windholz et al., 1976). SUMMARY OF TOXICITY INFORMATION A vast literature related to inhalation exposure of animals and humans to sulfuric acid (0.1–1 mg/m3) has been collected by Carson et al. (1981) in connection with the health effects of automobile exhaust under various conditions. EFFECTS ON HUMANS Accidental exposure to sulfuric acid can result during its manufacture and during the handling of concentrated and dilute solutions. H2SO4 is corrosive to all body tissues (Proctor and Hughes, 1978). The concentrated acid acts through its severe dehydrating action, whereas the dilute form is irritating due to its acid properties. Inhalation of concentrated vapor can be extremely irritating to the upper respiratory tract and may cause serious lung damage. Skin contact with concentrated acid may produce severe necrosis and frequent skin contact with dilute solutions may cause dermatitis. Eye contact with concentrated sulfuric acid can cause severe damage including glaucoma and cataracts (Grant, 1974). Fine sprays of sulfuric acid can cause stinging and burning, but the effects are generally transient.
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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 Controlled Human Exposure Amdur and associates (1952) reported results of exposure of normal unacclimated human subjects to the inhalation of sulfuric acid mist at 0.35–5 mg/m3 for 5–15 min. Concentrations below 1 mg/m3 could not be detected by odor, taste, or irritation. For two persons, the threshold was 1 mg/m3; a concentration of 3 mg/m3 was noticed by all; and 5 mg/m3 was very objectionable to some, but less so to others. A deep breath at the last concentration usually produced coughing. Pneumotachographic tracings showed respiratory changes in 15 subjects exposed to measured sulfuric acid mist concentrations. Although sulfuric acid mist, unlike pure SO2, is capable of penetrating to the deeper, more sensitive portions of the lung, 1 mg/m3 is unlikely to result in injury to the lung. Particle size of H2SO4 mist in the atmosphere plays an important role in producing toxic effects. The smaller particles (0.8 μm) are the most effective. Uncontrolled Human Exposure Premysl (1951) found the lungs of sulfuric acid plant workers less affected than those of workers exposed to dust. There was some evidence of corrosion of dental enamel. Raule (1954) stated that the maximum tolerated dose for those unaccustomed to H2SO4 was 1 mg/m3, but those used to it could tolerate three to four times as much. Chronically exposed workers may have various lesions of the skin, tracheobronchitis, stomatitis, conjunctivitis, or gastritis. Malcolm and Paul (1961) found severe erosion of the teeth in battery plant workers. Forming-room workers (sulfuric acid mist at 3–16 mg/m3) were most severely affected; charging-room workers (0.8–2.5 mg/m3) were less affected. Newhouse and associates (1978) assessed pulmonary mucociliary function after exposure at industrial TLVs to sulfur dioxide (5 ppm) and sulfuric acid mist (1 mg/m3). Bronchial clearance was measured in two sets of 10 healthy, exercising, nonsmoking adults under control and exposure conditions. A [99mTc]albumin saline aerosol (MMD, 3 μm) was inhaled as a bolus in late inspiration under controlled conditions to produce reproducible deposition in large airways. Lung retention of radioactivity was measured using a gamma camera and computer analysis. Clearance after exposure to both SO2 and H2SO4 was a significant factor (P<0.05) compared with control values. Maximal midexpiratory flow rates (MMFCs) were significantly reduced (P<0.01) after exposure to SO2 (mean decrease, 8.5%), but only slightly reduced after exposure to H2SO4 (1.4%). The speeding in clearance was probably an irritant response in both cases. For SO2, the response appeared predominantly reflex, whereas H2SO4 showed evidence of direct effect. EFFECTS ON ANIMALS Schlesinger et al. (1978) studied the effect of chronic inhalation exposure to sulfuric acid mist on mucociliary clearance from the lungs in donkeys. Four animals were exposed 1 h/d, 5 d/wk for 6 mo. The mean mass concentration of acid mist was 102–106 μg/m3. The MMD was
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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 0.5 m. Clearance was monitored by serial, external, in vivo measurements of retention of an insoluble, radioactively tagged ferric oxide aerosol, which was inhaled after exposure to the acid mist. Bronchial clearance became erratic within the first week of exposure; rates were significantly lower than control values on many test days, although the degree of response varied among the four animals. Two animals exhibited sustained impairment of clearance toward the end of the 6-mo period and continued to have erratic clearance during a 3-mo followup period. No changes in the regional deposition of the ferric oxide occurred during the course of the study in any of the animals. It was proposed that alterations in bronchial mucociliary clearance may be an early, if not the first, physiologic effect of inhalation of sulfuric acid mist, and this may be a factor in the pathogenesis of chronic bronchitis in populations exposed to the sulfur oxide-particle complex in the ambient air, which often includes sulfuric acid. Cavender et al. (1977) examined the acute pulmonary lesions caused by ozone and sulfuric acid mist in rats and guinea pigs. Rats were not affected by sulfuric acid mist at concentrations up to 100 mg/m3, except for reduced body weight at the higher concentrations. A true alveolitis developed in guinea pigs exposed to sulfuric acid mist at more than 20 mg/m3. The ozone lesion was primarily confined to the terminal bronchioles and proximal alveoli. In combination studies with ozone at up to 2 ppm and sulfuric acid mist at up to 10 mg/m3, the pulmonary lesion and lung and body-weight data were essentially the same as after exposure to ozone alone, and the number of statistically significant synergistic effects in rats and guinea pigs was about what one would expect to occur by chance alone. In another study Cavender et al. (1979) examined rats and guinea pigs exposed to ozone at 0.5 ppm, sulfuric acid mist at 10 mg/m3, or their combination 6 h/d, 5 d/wk for 6 mo. Exposure-related microscopic alterations were seen in the lungs of guinea pigs exposed to ozone alone or in combination with sulfuric acid mist. No other microscopic lesions were seen in rats or guinea pigs. No biologically relevant synergistic effects were noted in animals exposed to the combination of ozone and sulfuric acid mist. According to Yoshida et al. (1970), guinea pigs that inhaled (46 exposures twice a week for a period of 23 weeks) sulfuric acid mist alone developed breathing difficulties. The formation of lung abscesses was also observed. Inhalation of the mist remarkably reinforced experimental asthma caused by albumin sensitization. Schlesinger et al. (1978) concluded from their studies with donkeys that changes in bronchial clearance rate were observed at H2SO4 concentrations that produced no measurable effect on regional deposition, pulmonary resistance, or dynamic compliance; thus, alteration rate may be a sensitive indicator of acute response to submicrometer respiratory irritants. Fenters et al. (1979) investigated the effects of exposure of mice to sulfuric acid mist at 1.4 mg/m3, to carbon particles at 1.5 mg/m3, and to mixtures of the two at 1.5 mg/m3 3 h/d, 5 d/wk for up to 20 wk. The immunologic state of the animals was examined directly by the primary response of splenocytes after specific antigen stimulation and indirectly by infectivity studies. A measure of the effects on the immune system without the antigenic stimulation was
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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 obtained by determination of serum immunoglobulin concentrations. Significant alterations in immunoglobulin titer, decrease in primary antibody response in splenocyte antigenic stimulation, and decrease in resistance to respiratory infection (as measured by mortality, survival time, and pulmonary consolidation) after 20 wk of exposure were noted. In addition, bactericidal capacity of lungs was reduced in mice exposed to either sulfuric acid, carbon alone, or mixtures of the two. Subtle morphologic changes in the respiratory tract were detected by scanning electron microscopy. Thus, the alterations in the defense system suggest that prolonged exposure to low concentrations of sulfuric acid or to mixtures with carbon particles reduces the ability of mice to resist the secondary stress of respiratory infection. Alarie et al. (1973) exposed groups of cynomolgus monkeys to sulfuric acid mist at 0.38–4.79 mg/m3 continuously for 78 wk. Particle size varied from submicrometer to 4 m in MMD. Groups of guinea pigs were exposed at 0.10 or 0.08 mg/m3 with MMD of 2.8 and 0.8 μm, respectively, continuously for 52 wk. No deleterious effects were seen in guinea pigs. In the monkeys, concentrations of 2.43 and 4.79 mg/m3 with MMD of 3.60 and 0.73 μm, respectively, produced definite deleterious effects on pulmonary structures and deterioration in pulmonary function. At lower concentrations, these effects were less pronounced or absent. Microscopic changes consisted of focal epithelial hyperplasia and focal thickening of the bronchiolar walls. In a later study, Alarie et al. (1975) exposed groups of cynomolgus monkeys and guinea pigs to mixtures of sulfur dioxide at 0.1–5.0 ppm, fly ash at 0.5 mg/m3, and sulfuric acid mist at 0.1–1 mg/m3 for 52 wk (guinea pigs) or 78 wk (monkeys). Pulmonary function tests and serum biochemical and hematological analyses were conducted before and periodically during exposure. At the termination of exposure, the lungs were examined microscopically. Analysis of the data revealed that sulfuric acid mist was responsible for the effects observed. No synergistic action of the pollutants was detected. COMMITTEE RECOMMENDATIONS EXPOSURE LIMITS The work of Amdur et al. (1952) showed that H2SO4 at up to 5 mg/m3 was tolerated by humans for 15 min in an experimental setting. The work of Kerr et al. (1981) demonstrated that pulmonary function was not affected by exposure of humans to H2SO4 at 0.1 mg/m3 for 4 h in a chamber. Cynomolgus monkeys exposed chronically to H2SO4 up to 4.8 mg/m3 suffered changes in respiratory function and structures. The results of these investigations suggest that humans can be exposed to H2SO4 atmospheric mists at 5 mg/m3 for short periods without injury. The EELs set in 1969 are therefore still applicable: 10-min EEL: 5 mg/m3 30-min EEL: 2 mg/m3 60-min EEL: 1 mg/m3
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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 REFERENCES American Conference of Governmental Industrial Hygienists. 1980. Documentation of the Threshold Limit Values. 4th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. p. 377–378. Alarie, Y. Busey, W.M., Krumm, A.A., Ulrich, C.E. 1973. Long-term continuous exposure to sulfuric acid mist in cynomolgus monkeys and guinea pigs. Arch. Environ. Health 27:16–24. Alarie, Y.C., Krumm, A.A., Busey, W.M., Ulrich, C.E., and Kantz, R.J., II. 1975. Long-term exposure to sulfur dioxide, sulfuric acid mist, fly ash, and their mixtures: Results of studies in monkeys and guinea pigs. Arch. Environ. Health 30:254–262. Amdur, M.O., Silverman, L., and Drinker, P. 1952. Inhalation of sulfuric acid mist by human subjects. A.M.A. Arch. Ind. Hyg. Occ. Med. 6:305–313. Carson, B.L., Herndon, B.L., Ellis, H.V., III, Baker, L.H., and Horn, E. 1981. Sulfuric Acid Health Effects. Prepared for Environmental Protection Agency, Emission Control Technology Division, Ann Arbor, Michigan. EPA-460/3–81–025. Kansas City, Missouri: Midwest Research Institute. 187 p. [PB82–113, 135]. Cavender, F.L., Steinhange, W.H., Ulrich, C.E., Busey, W.M., Cockrell, B.Y., Haseman, J.K., Hogan, M.D., and Drew, R.T. 1977. Effects in rats and guinea pigs of short-term exposures to sulfuric acid mist, ozone, and their combination. J. Toxicol. Environ. Health 3:521–533. Cavender, F.K., Singh, B., and Cockrell, B.Y. 1979. The effects in rats and guinea pigs from six months exposure to sulfuric acid mist, ozone, and their combination. J. Environ. Pathol. Toxicol. 2:485–492. Duecker, W.W., and West, J.R., eds. 1959. Manufacture of Sulfuric Acid. New York: Reinhold. [475 p.] Fenters, J.D., Bradof, J.N., Aranyi, C., Ketels, K., Ehrlich, R., and Gardner, D.E. 1979. Health effects of long-term inhalation of sulfuric acid mist-carbon particle mixtures. Environ. Res. 19:244–257. Grant, W.M. 1974. Toxicology of the Eye, second edition. Springfield, IL.: Charles C.Thomas. pp. 959–960. Kerr, H.D., Kulle, T.J., Farrell, B.P., Sauder, L.R., Young, J.L., Swift, D.L., and Borushok, R.M. 1981. Effects of sulfuric acid aerosol on pulmonary function in human subjects: An environmental chamber study. Environ. Res. 26:42–50.
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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 Malcolm, D., and Paul, E. 1961. Erosion of the teeth due to sulphuric acid in the battery industry. Br. J. Ind. Med. 18:63–69. Newhouse, M.T., Dolovich, M., Obminski, G., and Wolff, R.K. 1978. Effect of TLV levels of SO2 and H2SO4 on bronchial clearance in exercising man. Arch. Environ. Health 33:24–32. Premysl, P. 1951. The influence of the work environment in the manufacture of sulfuric acid on the health of employees. Prac. Lek. 3:287 (Abstr. in A.M.A. Arch. Ind. Hyg. Occup. Med. 6:461, 1952) Proctor, N.H., and Hughes, J.P. 1978. Chemical Hazards of the Workplace. Philadelphia: J.B. Lippincott Company, pp. 452–453. Raule, A. 1954. Occupational disease casued by sulfuric acid. Med. Lav. 45:590–599 (Abstr. in Am. Ind. Hyg. Assoc., Quarterly 16:153, 1955) Schlesinger, R.B., Lippmann, M., Albert, R.E. 1978. Effects of short-term exposures to sulfuric acid and ammonium sulfate aerosols upon bronchial airway function in the donkey. Am. Ind. Hyg. Assoc. J. 39:275–286. Windholz, M., Budavari, S., Stroumtsos, L.Y., and Fertig, M.N., eds. 1976. The Merck Index: An Encyclopedia of Chemicals and Drugs. 9th ed. Rahway, NJ.: Merck & Company, p. 1163. Yoshida, K., Takatsuka, Y., Kitabatake, M., Oshima, H., and Imai, M. 1970. Guinea pig experiments in inhalation of sulfuric acid mist. Transl. of Taiki Osen Kenkyu (J. Japan Soc. of Air Pollution) 5(1):149.
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