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.
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