Respiratory tract retention of relatively insoluble particles in rodents

Rats and hamsters inhaled monodisperse fused aluminosilicate particles (FAP) labelled with strontium-85 (CMD 1.25 and 1.21 μm, respectively). Respiratory tract retention was followed by external γ-ray counting and analysis of sacrificed animals for up to 15 months after exposure. Only 2% of the nasal deposit remained at an hour after administration, and less than 0.1% was retained for more than 2 days. Less than 1% of the deposit on the trachea and main bronchi was retained for more than a week. About 10% of the initial pulmonary deposit was retained at a year, far less than for FAP in man. In rats the average pulmonary clearance rate fell from 2.2 × 10^-2 per day, at 10 days after exposure to 4 × 10^-3 per day at a year following exposure, and in hamsters from 1.1 × 10^-2 per day to 5 × 10^-3 per day. The contributions of dissolution and particle transport to lymph nodes were estimated to be about 5 × 10^-4 per day and 10^-5 per day, respectively, and therefore pulmonary clearance was dominated by the transport of particles to the gastro-intestinal tract. Clearance of plutonium dioxide particles in the same rodent strains (initial pulmonary deposits approximately 1 kBq) was initially very similar, but after a few months became slower, presumably because of lung damage from the plutonium.