Cobalt-60 oxide aerosols: methods of production and short-term retention and distribution kinetics in the beagle dog

Cobalt-60 has been used extensively in nuclear applications and has been considered for use in nuclear auxiliary power devices. The most common chemical form used is the oxide. This study of the retention and distribution of two differnt exoides of cobalt when administered by inhalation was conducted to assess the potential inhalation hazard associated with its use. Cobaltosic oxide (Co3O4) was formed by passing a cobalt nitrate aerosol through a heating column at 8500C before delivery to the dog. Cobaltous oxide (CoO) was formed by raising the heating column temperature to 14000C. Three beagle dogs were exposed to 60Co3O4 and sacrificed singly at 8, 64 and 128 days. Three beagle dogs were exposed to 60CoO and sacrificed at 8, 16 and 64 days after exposure. Whole-body retention patterns showed that 60CoO left the body with a shorter effective half-life than 60Co3O4. The concentration of 60Co detected in the blood was at least an order of magnitude higher in the dogs exposed to 60CoO than in the dogs exposed to 60Co3O4. Cobalt-60 translocated from the lung accumulated predominantly in the kidney, liver, skeleton and cartilagenous structures such as the trachea. Higher concentrations were reached earlier in the dogs exposed to 60CoO. After early fecal excretion of material deposited in the upper respiratory tract, excretion was greatest via the urine. The higher solubility of the 60CoO formed at 14000C relative to 60Co3O4 formed at 8500C is noteworthy considering that generally aerosols formed at higher temperatures are more insoluble than aerosols formed at lower temperatures. (author)