Synergistic interaction of ozone and respirable aerosols on rat lungs. II. Synergy between ammonium sulfate aerosol and various concentrations of ozone

Pulmonary responses after continuous exposure of rats to concentrations of ozone (O₃) ranging from 0.12 to 0.64 ppm were quantified by measuring tissue collagen synthesis rate, tissue protein and DNA content, and various constituents of bronchoalveolar lavage fluid. After 7 days of exposure to 0.64 ppm of O₃, lung collagen synthesis rate and tissue content of protein and DNA were elevated. After shorter durations of exposure to 0.64 ppm of O₃, significant elevations were observed in the protein content and the activities of lactate dehydrogenase, acid phosphatase, and N-acetyl-β-d-glucosaminidase from lavage fluid. After exposure of rats to 0.20 ppm of O₃ for 7 days, changes could be detected in both lung collagen synthesis rate and tissue protein content. Total lavagable protein content, a sensitive indicator for O₃-induced effects upon the lung, was significantly elevated in lungs of rats exposed to 0.12 or 0.20 ppm of O₃. To examine whether a synergistic interaction occurred between 0.20 or 0.64 ppm of O₃ and acid aerosols, rats were continuously exposed to O₃ with and without concurrent exposure to 5 mg/m³ of ammonium sulfate. A synergistic interaction between 0.20 ppm of O₃ and ammonium sulfate aerosol was observed by measurement of total lavagable protein and of lung collagen synthesis rate. These results demonstrate that ammonium sulfate aerosol interacts synergistically with O₃ at concentrations of O₃ that approach ambient levels.