Interspecies Comparison of Lung Clearance of "Insoluble" Particles

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Abstract
Lung clearance studies after the inhalation of monodisperse, radiolabelled test particles including lung retention measurements and excretion analysis allow for estimates of the kinetics of long-term particle transport out of the thorax into the gastro-intestinal tract. Data of several interspecies comparisons using either radiolabelled fused aluminosilicate particles or 57C03O4 particles were reviewed and compared. Species included were: man, baboon, beagle dog, guinea pig, HMT rat, F-344 rat, Long-Evans rat, hamster, mouse. Particle transport M(t) after the first days after inhalation is a slow clearance mechanism which is independent of the particle material and size used (0.5 - 4 pirn geom. diameter). M(t) was reproducible in the experimental species studied. In man, baboon, and dog the initial daily fraction M0 of the contemporary lung burden transported out of the thorax is 0.001 d-1 which is an order of magnitude less than the initial rates in rodents. Particle transport rate decreases rapidly from its initial value in all species studied. The decay of particle transport varies considerably between the species and strains. The half-life of the decreasing transport rate is slower in man, dog, F-344 rat, hamster and mouse (100 - 200 days) than in baboon, HMT rat and Long-Evans rat (< 50 days). From these studies estimates of lung retention during chronic aerosol exposure showed no equilibrium value indicating that long-term particle transport is not a sufficiently effective clearance mechanism to keep the lung burden from continuousy increasing during chronic exposure.

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