Early alveolar clearance of particles in rabbits undergoing acute and subchronic exposure to ozone

The concentration-response relationship for changes in early alveolar clearance resulting from O3 inhalation were investigated. Groups of five rabbits were exposed to 0.0, 0.1, 0.6, or 1.2 ppm O3, 2 hr/day X 1 day; or to 0.0, 0.1, or 0.6 ppm O3, 2 hr/day X 13 days. Following the initial O3 exposure all rabbits inhaled an aerosol of 85Sr-tagged, 3.0-micron, polystyrene latex particles and particle retention was determined daily for the following 14 days. Single exposures to O3 produced a concentration related trend from accelerated clearance at 0.1 ppm to a transient impairment of clearance at 1.2 ppm. Subchronic exposure resulted in a significant acceleration of particle clearance at both 0.1 and 0.6 ppm, with the effect more pronounced at the higher level. These results demonstrate that single or repeated exposure of rabbits to 0.1 ppm O3, a level below the current National Ambient Air Quality Standard, produces alterations in early alveolar clearance. The effects observed at higher levels of O3 appeared to depend on both the concentration and exposure regime; acute exposures produced a concentration related trend toward an initial retardation of clearance, which was followed by an acceleration in particle removal, while repeated exposures resulted in a persistent acceleration of clearance.