CHRONIC EXPOSURE OF RATS TO OZONE AND SULFURIC-ACID AEROSOL - BIOCHEMICAL AND STRUCTURAL RESPONSES

Groups of rats were exposed to either 0.12 or 0.20 ppm of ozone, 20, 1 00, or 150 ppm of sulfuric acid aerosol (0.4-0.8 mu m diameter), or th eir mixtures in whole body exposure chambers for up to 90 days. Matche d control animals were exposed to filtered air in comparable chambers. The rats were examined biochemically and morphometrically for centria cinar fibrosis or other indicators of pollutant-induced changes in the terminal bronchiole-alveolar duct junction region of the lung at the end of the exposures. By evaluating different markers of lung injury, we had previously demonstrated a synergistic interaction between ozone and sulfuric acid aerosol after acute exposures to these same concent rations of the pollutants. The present experiments were designed to an swer the question of whether there was any interaction between ozone a nd respirable sized aerosols of sulfuric acid, synergistic or antagoni stic, after chronic exposures. Exposure of rats to 0.12 or 0.20 ppm of ozone elicited tissue and cellular changes at the bronchiole-alveolar duct junction. Concurrent exposure to sulfuric acid aerosol did not a ffect the extent or magnitude of these changes. Intermittent exposure (12 h per day) to ozone, with or without the acid aerosol, elicited a greater response than did continuous exposure (24 h per day). No consi stent effects of exposure to sulfuric acid aerosol alone were observed , either morphometrically or biochemically. The biochemical data were consistent with the morphometric analyses, showing trends towards or s ignificantly increased lung 4-hydroxyproline content in the rats expos ed to ozone, with or without sulfuric acid aerosol, in the intermitten t exposure experiment, but not after continuous exposure. No interacti ve effects between ozone and sulfuric acid aerosol were observed with any of the biochemical parameters examined. We conclude that ozone and sulfuric acid aerosols do not exhibit synergistic interactions after chronic exposures (90 days) of rats to the concentrations tested in th is study, which correspond to concentrations showing synergistic inter actions in previously performed acute studies. We also observed that e xposure of rats to ozone for 12 h per day elicited greater lung change s, which we interpret to indicate a mild fibrotic response, than did e xposure of rats for 24 h per day, whether or not there was accompanyin g exposure to the acid aerosol. Copyright (C) 1997 Elsevier Science Ir eland Ltd.