Biological Effects of ⁹¹Y in Relatively Insoluble Particles Inhaled by Beagle Dogs

The toxicity of ⁹¹Y inhaled in relatively insoluble particles was investigated as part of a programme to evaluate the biological effects of inhaled beta-emitting radioriuclides. Ninety-six Beagle dogs were briefly exposed to aerosols of ⁹¹Y in fused aluminosilicate particles resulting in initial lung burdens ranging from 0.4 to 13 MBq ⁹¹Y per kg body weight and 12 dogs were exposed to stable yttrium in fused aluminosilicate particles. When inhaled in this relatively insoluble form, ⁹¹Y was retained in the lung with an effective half-life of about 50 days. Little radionuclide was translocated to other organs except the tracheobronchial lymph nodes. Thirty-two dogs that died between 1115 and 5624 days after exposure with cumulative doses to lung ranging from 31 to 250 Gy had primary pulmonary carcinomas. The absolute risk per unit dose was 60 lung tumours per 10⁴ Gy in those dogs with a total dose of less than 60 Gy.