An interspecies comparison of the translocation of material from lung to blood

Preliminary results are reported of measurements on baboons, dogs, guinea pigs, rats, hamsters and mice which inhaled 0.8 or 1.7 μm geometric diameter monodisperse⁵⁷Co-labelled cobalt oxide particles. Lung retention at three months ranged from < 30% in rats to > 50% in baboons. Most of the cobalt which cleared from the lung was rapidly excreted. At 6-13 weeks after inhalation of 1.7 μm particles, the fraction of the remaining activity excreted per day in urine ranged from 0.0014 in baboons to 0.008 in dogs, and was approximately twice as high for 0.8 μm particles. Faecal excretion rates were similar for the two sizes, and average rates 6-13 weeks after inhalation ranged from < 0.001 per day in dogs, to > 0.01 per day in the small rodents. Measurements will continue to at least six months after exposure and the study extended to include man. The results, with those of metabolic studies on intravenously injected cobalt, and on ingested cobalt oxide, will be used to derive cobalt translocation rates from the particles in the lung to the blood, and the particle clearance rates to the GI tract for each species.