Effect of chronic inhalation of sulfuric acid mist upon mucociliary clearance from the lungs of donkeys.

The effect of chronic inhalation exposures to sulfuric acid mist upon mucociliary clearance from the lungs was studied, using the donkey as an analogue for man. Four animals were exposed 1 hr/day, 5 days/week, for 6 months. The mean mass concentration of acid mist was 102 microgram/m3 for two animals, and 106 microgram/m3 for the other two. The mass median aerodynamic diameter was approximately 0.5 micrometer. Clearance was monitored by serial, external in vivo measurements of the retention of an insoluble, radioactively tagged ferric oxide aerosol which was inhaled following exposure to the acid mist. Bronchial clearance became erratic within the first week of exposure; rates were significantly different, usually slower than control on many test days, although the degree of response varied among the four animals. Two animals exhibited a sustained impairment of clearance towards the end of the 6-month exposure period and continued to have erratic clearance during a 3-month follow-up period. No changes in the regional deposition of the ferric oxide occurred during the course of the study in any of the animals. It is proposed that alterations in bronchial mucociliary clearance may be an early, if not the first, physiologic effect resulting from the inhalation of sulfuric acid mist, and this may be a factor in the pathogenesis of chronic bronchitis in populations exposed to the sulfur oxide-particulate-complex in the ambient air, which often includes sulfuric acid.