Toxicity of 144Ce inhaled in a relatively insoluble form by aged Beagle dogs. VIII

The toxicity of relatively insoluble 144Ce inhaled by 8- to 10.5-year-old dogs is being investigated to provide information on age-related differences in the response of dogs to lung burdens of this fission product. These data on aged dogs will be compared to the results of similar studies of dogs exposed at approximately 3 months or 12 to 14 months of age. Forty-two dogs were exposed, nose only, to aerosols of 144Ce in fused aluminosilicate particles to yield initial lung burdens of 2.2 to 75 μCi/kg body weight and 12 control dogs were exposed to nonradioactive fused aluminosilicate particles. To date, 37 dogs have died or were euthanized 197 to 2375 days after inhalation of 144Ce. The prominent findings were radiation pneumonitis in 19 dogs that died at early times with cumulative doses to lung of 20 000 to 74 000 rads and neoplastic disease in six of 14 dogs that died 943 days after exposure or later. Pulmonary tumors were found in four of these dogs. However, only one of these tumors killed the dog. No hemangiosarcomas have been observed in this study. This result is in contrast to the results with immature or young adult dogs exposed to 144Ce. The difference may be a dose-related phenomenon since dogs which developed hemangiosarconomas had greater initial lung burdens of 144Ce. Aged dogs with similar burdens died at earlier times with radiation pneumonitis. Observations are continuing on the five surviving 144Ce-exposed and four control dogs