Abstract
The effects of 233U, 239Pu and 241Am in male CBA/H mice have been compared after systemic administration in citrate solutions. Each nuclide was administered to three groups of animals at levels of activity which gave estimated life-time average skeletal doses of about 0.25 - 0.3 Gy, 0.5 - 1 Gy and 1-2 Gy. Statistical modelling by Cox regression showed that, considering all three nuclides together, there was a highly significant increase in hazard of death from osteosarcoma or myeloid leukaemia with increasing dose rate. For osteosarcoma, the effect was significantly greater for 239Pu than 241Am. The analysis for 233U was statistically consistent with no effect of dose rate. For example, the increase in relative hazard of death from osteosarcoma for an increase in dose rate of 1 mGy d-1 was 4.2 (2.7 - 6.5) for 239Pu, 2.3 (1.4 - 3.4) for 241 Am and 1.1 (0.4 - 3.1) for 233U. For myeloid leukaemia, there was no significant difference between 239Pu and 241Am in the effect of dose rate. The increase in relative hazard from myeloid leukaemia for an increase in dose rate of 1 mGy d-1 was 1.8 (1.1 - 2.8) for 239Pu, 2.0 (1.4 - 2.9) for 241 Am and 1.5 (0.8 - 2.7) for 233U. Significant increases in hepatic (241Am) and renal (233U) carcinoma were also recorded. Studies of the distribution of the nuclides within the skeleton showed differences in their retention in individual bones and within bone. The proportions of alpha decays occurring near to bone surfaces and in bone marrow were in the order: 239Pu>241Am>233U. For osteosarcoma, the relative effectiveness of the nuclides was consistent with the proportion of dose delivered near to endosteal surfaces. For myeloid leukaemia, the greater effectiveness of 239Pu and 241Am than 233U was consistent with their accumulation in marrow.