Effects of Inhaled Fine Particles and Ozone on Pulmonary Macrophages and Epithelia

Abstract

The health effects of oxidant gas mixtures containing fine particles from dilute diesel exhaust were examined using the rat as a laboratory model to determine if the presence of diesel soot particles would worsen the effects observed following exposures to oxidant gases alone. The study was designed to simulate an environmental scenario of acute and repeated exposures to polluted ambient atmospheres such as those that occur in southern California, where automotive emissions contribute to the production of oxidant gases such as ozone (O₃) and nitrogen dioxide (NO₂). Dilute diesel exhaust (scrubbed of sulfur dioxide, SO₂, and carbon monoxide, CO), containing 250 or 500 μglm³ diesel soot particles and nitric oxide (NO), was mixed with 0.4 or 0.6 ppm O₃, respectively. Chemical reactions within the mixture converted all NO to NO₂ and nitric acid (ranging from 110 to 260 uglm³). Therefore, to determine the potential health impact of the particles, the effects of the diesel soot mixture were compared with those of a mixture containing only O₃ and NO₂, at the same concentrations as those in the diesel soot mixture.

The biological responses measured included changes in lung histopathology, changes in mucosal permeability, and changes in alveolar macrophage functions. When compared to purified air-exposed groups, exposures to the diesel soot-containing mixture at high concentrations resulted in significant adverse changes in all of the responses measured after 1 day of exposure and for macrophage functions and permeability after 5 days of exposure. The group mean differences between O₃ + NO₂ and diesel soot-exposed groups were not statistically significant. Findings from histopathology and macrophage phagocytosis studies after 20 days of exposure suggested that effects of the O₃ + NO₂ mixture were worse than those of the diesel soot-containing mixture. We conclude from these results that, at the concentrations tested, diesel soot in oxidant gas mixtures was not more toxic than the oxidant gases alone.