Retention of monodisperse or polydisperse aluminosilicate particles inhaled by dogs, rats, and mice

Abstract

This study compared long-term retention of 134Cs-labeled fused aluminosilicate particles inhaled by three animal species. Dogs, rats, and mice were briefly exposed to 0.7-, 1.5-, or 2.8-micron activity median aerodynamic diameter (AMAD) monodisperse particles or a polydisperse aerosol with 1.5 to 2.0 micron AMAD and geometric standard deviation of 1.5 to 2.0. Tissues and excreta were collected for up to 850 days after exposure to determine retention and clearance patterns of the inhaled particles. Simulation models were developed for each animal species and aerosol. Solubilization was the dominant factor in long-term lung clearance for most of the particles inhaled by dogs; mechanical clearance was dominant in rats and mice. After accounting for solubility, physical clearance from the lung to the gastrointestinal tract and to lung-associated lymph nodes (LALNs) was independent of particle size within the size range investigated. Rats and mice demonstrated a rapid clearance from the pulmonary region, with most of the mechanically cleared particles going to the gastrointestinal tract; significant translocation to the LALNs occurred for only a few days. The dogs cleared deposited particles at a slower rate, with most of the long-term clearance going to LALNs. A small portion of the initial deposit was retained in the upper respiratory tract of all three species. Results from the data for dogs were used to make long-term predictions for chronic inhalation of particles by humans.