In Vivo Deposition of Inhaled Ultrafine Particles in the Respiratory Tract of Rhesus Monkeys

Radon progeny are usually associated with ultrafine particles with diameters ranging from 0.001-0.005 μm for “unattached” progeny and from 0.005-0.2 μm for those attached to indoor aerosols. To assess the health effects of inhaling indoor radon progeny, it is necessary to study the regional deposition of these ultrafine particles when inhaled. Laboratory animals are often used in studies of the toxicity of inhaled particles and vapors. Information is available on the deposition of particles with diameters > 0.2 μm in the nasal passages of laboratory animals. However, there are very few data on the deposition of ultrafine particles < 0.2 μm in diameter, and most of the information has come from studies in nasal casts. In this article we describe in vivo deposition of inhaled ultrafine particles in the airways of rhesus monkeys. Two types of aerosols were used: 220Rn progeny and monodisperse 59Fe2O3 particles, in particle diameters ranging from 0.005-0.1 μm. Eight monkeys were exposed for 5-8 min and sacrificed immediately after exposure. The total and regional depositions were estimated from the amounts of radioactivity measured in various tissues. The results indicated that substantial nasal deposition of ultrafine particles occurs, and both total and nasal depositions increase with decreasing particle size. Peak deposition in the lung occurred between 0.005 μm and 0.1 μm. The in vivo nasal deposition data agreed well with those from the nasal cast studies.