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.
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Acknowledoements--Preliminary reports of this study were presented at the 8th and 11 th annual conferences of the Association for Aerosol Research (Bailey et al., 1980, Bailey and Hodgson, 1984). Technical assistance was provided by Miss J. E. Hostford and Mrs A. J. Murfitt. The authors are grateful to Dr A. C. James for advice and encouragement and for providing detailed results of the mixed oxide inhalation study. The work was partially supported by the CEC under Contracts 182-BIO-UK and BIO-D-489-UK.