Retention Modeling of Diesel Exhaust Particles in Rats and Humans

摘要

The objective was to predict the lung burden in rats and humans of diesel exhaustparticles using a mathematical model. To study clearance, the authors used a compartmental model consisting of the nasopharyngeal, tracheobronchial, alveolar, and lung-associated lymph node compartments. The authors assumed a particle model made up of material components according to the characteristics of clearance: (1) a carbonaceous core or soot (80 percent of particle mass), (2) slowly cleared organics (10 percent of particle mass), and (3) fast-cleared organics (10 percent of particle mass). Kinetic equations of the retention model were first developed for rats. The lung burden calculations showed that although the organics were cleared at nearly constant rates, the alveolar clearance rate of soot decreased with increasing lung burden. At low lung burdens, the alveolar clearance rate was controlled by macrophage migration to the mucociliary escalator, whereas at high lung burdens, the clearance rate was determined principally by transport to the lymphatics. The retention model for rats was extrapolated to humans of different age groups. The reduction in the mechanical clearance in adult humans caused by exposure to high concentrations of diesel exhaust was much less than that observed in rats. The reduction in children was greater than that in adults. The authors combined the retention and deposition models to compute the accumulated mass of diesel soot and associated organics in various compartments of the human lung under different exposure conditions. The lung burdens of both soot and the associated organics were much higher in humans than in rats for the same period of exposure. Reductions in clearance caused by excessive lung burdens would not occur in humans if the exposure concentration were below 0.05 mg/cu m.