Respiratory deposition and inhalability of monodisperse aerosols in Long-Evans rats

Because of limitations on conducting exposure experiments using human subjects to evaluate adverse health effects, the deposition and fate of airborne particles in animals are often studied. The results of such studies are extrapolated to humans to estimate equivalent dose and subsequent response. In this article, particle inhalability and respiratory deposition of micron-size particles are determined for female Long-Evans rats. Monodisperse aerosols were generated from a solution of radiolabeled iron chloride ((FeCl3)-Fe-59). Long-Evans rats were exposed to the radiolabeled particles in a Cannon nose-only exposure tower to determine head, lung lobar, and total lung deposition fractions. Particle deposition fractions in a hypothetical situation, when all particles are inhalable, were found from an experimentally validated deposition model. Particle inhalability in a Cannon nose-only exposure scenario was obtained by comparing the measured deposition fractions with the predicted values for the case of 100% inhalability. Particle deposition fraction and inhalability were compared with data available in the literature. For large particles, the measured deposition fraction was lower than the literature values. Consequently, our inhalability estimates were found to be lower than previously published values. The findings here will directly affect health risk assessments in humans from exposure to airborne particles. The deposition results will improve the database on particle deposition in the lung airways of rats, and inhalability information will improve the accuracy of rat-to-human data extrapolation.