Metabolic fate of inhaled Co aerosols in beagle dogs.

Lung retention of 57Co in dogs after the inhalation of physically and chemically uniform particles of Co compounds was similar, indicating little biological variability. The retention of Co oxide particles ranging from 0.3 micron to 2.7 micron geometric diameter, however, depended markedly on their physicochemical parameters. Measuring the retention by a gamma camera, and analyzing excreta and blood samples enabled the distinction of different clearance pathways from the lungs particularly with the use of results of some metabolic studies. Particle dissolution was the predominant clearance pathway. Particle dissolution half-times ranged from 6 to 80 d proportional to the size of the particles. Organ analysis yielded information on the fate of the long-term burden of Co in the lungs and other organs. A fraction less than 10% of the initial lung burden was retained in the lungs of all dogs with a biological half-time of 400 d presumably after being transformed into a nonparticulate state. There were cellular structures in the tracheobronchial tree which accumulated Co significantly. These studies on dogs suggest the dose after human exposure to well-defined Co aerosols can be accurately estimated. Whereas risk assessment after the exposure to undefined aerosols containing radionuclides of Co will mostly be impossible because retention varies widely with the varying physicochemical properties of the aerosol particles.