Abstract
A factorial design study was performed to examine the acute effects of inhaled acid particles alone and in mixtures with ozone to test the hypothesis that acid particles and ozone would act synergistically. Sprague-Dawley rats were exposed nose-only for a single 4-h period to all 9 possible combinations of purified air and 2 concentrations each of O3 (0.3 and 0.6 ppm) and submicrometer (0.3 μm mass median diameter [MMD]) sulfuric acid aerosols H2SO4 (0.5 and 1.0 mg/m3). Respiratory-tract injury and impairment of alveolar macrophage functions were evaluated. Two-way analyses of variance were used to test for significance of main effects and statistical interactions, and Tukey multiple comparison tests were used to test the significance of differences between group mean values. Addition of H2SO4 to O3-containing atmospheres resulted in significant H2SO4 concentration-dependent reductions in O3-induced inflammatory responses, and H2SO4, alone and in combination with O3, depressed some functions of innate immunity. DNA synthesis in nasal, tracheal, and lung tissue following pollutant exposure, which is an index of injury or killing of epithelial cells, was significantly increased by O3 but not by H2SO4 when administered alone, compared to purified air. When administered with O3, H2SO4 did not reduce the effects of O3 on DNA synthesis in the trachea or the lung, but did reduce the DNA synthesis response to O3 in the nose. No significant changes in antibody-directed Fc receptor (FcR) binding of sheep red blood cells by alveolar macrophages were observed, but macrophage phagocytic activity was significantly reduced by the pollutant exposures. In summary, the results of this study indicate significant interactions between O3 and H2SO4 in concurrent exposures; however, the findings do not support the hypothesis that O3 and H2SO4 act synergistically in rats after single 4-h exposures.