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

The metabolism, dosimetry and effects of 144Ce inhaled in fused aluminosilicate particles are being investigated in the Beagle dog to assess the biological consequences of release of 144Ce in a relatively insoluble form such as might occur in certain types of nuclear accidents. The toxicity of inhaled 144Ce is also of general interest since it is representative of intermediate-lived beta-emitting radionuclides. Two major studies with young adult dogs (12 to 14 months of age at exposure) are involved: (1) a metabolism and dosimetry study in which 24 dogs were serially sacrificed over an extended period of time, and (2) a longevity study with two series of dogs. Series I contains 15 dogs exposed to aerosols of 144Ce in fused aluminosilicate particles to yield initial lung burdens of 11 to 210 μCi/kg body weight and three control dogs exposed to nonradioactive fused aluminosilicate particles. Series II contains 96 dogs exposed to aerosols of 144Ce in fused aluminosilicate particles to yield initial lung burdens of 0.0024 to 66 μCi/kg body weight and 12 control dogs exposed to nonradioactive, fused aluminosilicate particles. To date, 51 dogs have died or were euthanized at 143 to 3280 days after inhalation of 144Ce. The prominent findings were radiation pneumonitis in 17 dogs that died or were euthanized at 750 days or later. The cumulative radiation dose to the lung at time of death has ranged from 550 to 140,000 rads. Serial observations are continuing on the 60 survivors and 15 controls