Acute Toxicity of Beta-Emitting Radionuclides That May Be Released in a Reactor Accident and Ingested

Suckling, weanling, and adult rats received ^{106}{\rm Ru}-{}^{106}{\rm Rh}$ by gavage and adult beagle dogs ingested ^{106}{\rm Ru}-{}^{106}{\rm Rh}$ to determine the toxicity of this high-energy (1.4 MeV av) β-emitting nuclide pair. The LD50' s for suckling, weanling, and adult rats were 1.5, 18, and 9.0 mCi/kg, respectively. Adult rats were given ^{147}{\rm Pm}$ by gavage to determine if a low-energy (0.06 MeV av) β emitter could also cause death by damaging the bowel. The LD50 of ^{147}{\rm Pm}$ in rats was about 5 Ci/kg. The calculated radiation doses absorbed in the "target cells" at the LD50 level were approximately the same for the two radionuclides (3500 rad), although the doses at the mucosal surface differed widely. The LD50 for ^{106}{\rm Ru}-{}^{106}{\rm Rh}$ in dogs was about 3.5 mCi/kg. Dosimeters placed beneath the mucosa in dogs indicated that the radiation dose to the "target cells" that caused death from ^{106}{\rm Ru}-{}^{106}{\rm Rh}$ was about the same as it was for rats. The signs of intestinal injury, their duration, and the probabilities of tissue repair were much different in the dog than in the rat. The midcolon and lower colon of dogs were usually denuded at focal sites after ingestion of 2.5 to 4.0 mCi/kg, and frequently that damage was irreversible. The fatal consequence of severe mucosal damage was averted in two dogs by colectomy and an ileorectal anastomosis.