Toxicity of 0.4- and 0.8-microm sulfuric acid aerosols in the guinea pig.

To determine mortality caused by inhaled sulfuric acid mist, groups of Hartley guinea pigs 2-3 mo old were exposed for 8 h to graded concentrations of aerosols of 0.4 or 0.8 microm mass median aerodynamic diameter. Relative humidity during exposures was maintained at 70-80%. Based on probit analysis, the concentration required to produce 50% mortality (LC50) for deaths to 21 d after exposure was 30 mg/m3 for the 0.8-microm aerosol. For the 0.4-microm aerosol, the LC50 was above 109 mg/m3, the highest concentration obtainable at that particle size. At both particle sizes, the animals either tended to develop severe dyspnea and die minutes (0.4 microm) or hours (0.8 microm) thereafter or appeared nearly unaffected. Lesions in animals that died as a results of 0.4-microm exposures were restricted to hyperinflation; animals that died as a result of 0.8-microm exposures also showed hemorrhage and transudation. No gross or histopathologic changes were observed in animals that appeared unaffected during exposure. Differences in total and/or regional respiratory tract deposition may account for the different responses to the two aerosols.