Deposition of sulfuric acid mist in the respiratory tracts of guinea pigs and rats.

Radiolabeled sulfuric acid mists in the size range of 0.4-1.2 micron mass median aerodynamic diameter (MMAD) were generated at 20 and 80% relative humidity at concentrations from 1.3 to 20 micrograms/l. Guinea pigs and rats were exposed to these aerosols by the nose-only route for short periods (30 s) and were quickly sacrificed and dissected. The regional respiratory-tract deposition patterns were measured. The results indicate that regional deposition fraction is positively correlated with droplet size of the sulfuric acid but is not correlated with atmospheric concentration or relative humidity over the ranges of the parameters studied. A comparison of the data obtained in these studies with those from earlier studies indicates that the deposition of sulfuric acid in the respiratory tract of rats is greater than for nonhygroscopic aerosols having similar MMADs. This may be due to the growth of the droplets in the high humidity of the respiratory tract.