Deposition of Sulfate Acid Aerosols in the Developing Human Lung

Computations of aerosol deposition as affected by (1) aerosol hygroscopicity, (2) human age, and (3) respiratory intensity are accomplished using a validated mathematical model. The interactive effects are very complicated but systematic. Few general observations can be made; rather, the findings presented within should be addressed on a case-by-case basis. The behavior of inhaled H2SO4 particles subsequent to water vapor uptake significantly influences their total deposition values and relative spatial distribution patterns within tracheobronchial and pulmonary airways. These results must be accounted for in risk assessment protocols, since compartments of the lung have different clearance processes and sensitivities to toxic materials. There is a critical size in the 0.2–0.4 μm range: For larger particles the influence of hygroscopicity is to increase total deposition, whereas for smaller particles the opposite occurs. The magnitudes of hygroscopic effects can be pronounced; for example, the deposition of 1-μm particles increases from ∼0.1 to ∼0.5 in the adult lung for resting conditions. Calculations also establish that subject age and physical activity are critical variables to be incorporated into health effects studies. These are of particular importance since children are a sensitive subpopulation in risk assessment protocols and adult work/exercise levels must be integrated with inhalation exposures. The dosimetric model was developed to provide a scientific basis for extrapolation modeling of factors (1), (2), and (3) in the hazard evaluation of airborne contaminants.