Mass transfer rates of polycyclic aromatic hydrocarbons between micron-size particles and their environment--theoretical estimates.

This paper presents a mathematical model of how rapidly polycyclic aromatic hydrocarbons (PAHs) adsorb onto initially clean micron-size particles in the ambient air and how fast these substances are likely to be desorbed from the particles after deposition on the surface lining layer of the lung. Results show that, on the one hand, the very low gas-phase concentrations of PAHs in the ambient air should result in a comparatively slow transfer of such compounds to micron-size particles, a process that may last from minutes to hours. On the other hand, the comparatively high solubilities of PAHs in the lining layer of the lung should promote an almost instantaneous release of PAHs onto nonporous particles, and a release within a matter of minutes of most PAHs reversibly adsorbed onto the interior surfaces of porous particles. Two important conclusions can be drawn from this. First, the PAHs in tobacco smoke do not have time enough to interact in the gas phase with other airborne particles before these agents are inhaled into the smoker's lungs. Therefore, adsorption in the gas phase of PAHs onto asbestos fibers can hardly be a characteristic parameter in the mechanism behind the synergistic effect between tobacco smoking and asbestos exposure for the induction of bronchial cancer. Second, the release rate of reversibly adsorbed PAHs from their carrier particles in the lung seems to be so fast that this cannot be a parameter of importance in directly influencing the residence times of such substances in the lung.