DEPOSITION AND CLEARANCE OF PARTICLES INHALED BY BEAGLE DOGS PREVIOUSLY EXPOSED TO SO2

The effect of preexisting pulmonary disease on the deposition and retention of inhaled relatively insoluble radiolabeled particles was studied. Two dogs were exposed to 500 ppm sulfur dioxide 2 h/day, 5 days/week for 16 weeks and two dogs were sham-exposed to filtered air for the same period. Dogs exposed to sulfur dioxide developed chronic bronchitis during this exposure period. After the bronchitis had beene stablished for 10 weeks, all 4 dogs were exposed by inhalation to 1.7 .mu. aerodynamic diameter 134Cs-labeled fused aluminosilicate particles (FAP) and the exposures to SO2 were discontinued. The bronchitis resolved within 4 weeks after SO2 was discontinued. Dogs were periodically whole-body counted and excreta were periodically collected and counted over a 385-day period following the 134Cs exposure. Deposition of the [134Cs]FAP in the pulmonary region averaged 42% for control dogs and 16% for dogs exposed to SO2, deposition in extrapulmonary regions of the respiratory tract average 58% for control dogs and 84% for dogs exposed to SO2. Although deposition patterns were different, early and long-term clearance pathways and rates were the same for all dogs, as indicated by analysis of whole body, excreta, and tissues for their burdens of 134Cs.