Plutonium in Bone: A High Resolution Autoradiographic Study Using Plutonium-241

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Abstract
Plutonium-241 citrate solution at pH 6·5 was injected intravenously into hamsters and an adult rabbit at a dose of 10 kBq g−1 (260 nCi g−1). The hamsters were killed serially at 15 min, 2 hours, 1 day, 10 days, 1 month and 6 months after injection and the rabbit at 1 week. Their knee-joints of femora were examined for plutonium-241 by autoradiography. Few differences were found between the pattern of plutonium distribution in the hamsters and the rabbit. The results showed that although plutonium is initially distributed on bone surfaces, at long periods after injection it becomes deposited throughout the bone matrix. Plutonium uptake by cells in resorbing areas of periosteum, in active osteoblasts, and in chondrocytes in regions of cartilage mineralization was rapid. Plutonium concentrated more slowly on the resting bone surfaces and at sites of low metabolic activity. In addition, some unlabelled sections of skeletal tissues were immersed in a plutonium-241 citrate solution. When autoradiographed, it was found that plutonium was bound by cell nuclei, tooth enamel matrix, dentine, predentine and bone matrix. Plutonium binding to cartilage matrix was weak. The results are discussed with reference to the literature, and a model is proposed to explain the distribution pattern and fate of plutonium deposits in bone.