Uranium and uranium decay series radionuclide dynamics in bone of rats following chronic uranium ore dust inhalation

The accumulation and release of uranium and some uranium decay chain radion uclides were measured in the bones of rats that had been chronically expose d to inhaled uranium ore dust during the first half (approximately) of thei r natural adult lifespan. Endochondral bone (femur, tibia, humerus, radius, and ulna), membrane bone (skull roofing bones) and muscle of Sprague-Dawle y rats (n = 55) that died at various times up to 65 weeks after the end of chronic inhalation of uranium ore dust aerosol (4.2 h d(-1) for 65 wk) and from age matched controls (n = 10), were analyzed for uranium, Th-230, Ra-2 26, Pb-210, and Po-210. Overall, during the period of dust inhalation, the nuclides accumulated in the above order of decreasing concentration in dry bone. However, the results demonstrate that there was some differential acc umulation of uranium and uranium decay series radionuclides in muscle and t wo bone types of rats during the chronic inhalation period. The data also s how that the bone levels of some, but not all, radionuclides decreased sign ificantly with time after inhalation ceased. Lung uranium concentration at the time of death was a highly significant covariant for temporal changes i n the levels of some radionuclides in both endochondral bone and membrane b one, indicating that lung remained a major source of these isotopes for acc umulation in these bone types after ore dust inhalation had ceased. For som e isotopes, the two bone types behaved differently during the dust inhalati on period, and differently again after the dust inhalation ceased. The rela tive behavior of one bone type compared to the other for a particular isoto pe during the dust inhalation period did not predict the relative behavior after dust inhalation ceased. However, a faster accumulation of one bone ty pe compared to the other for a particular isotope during the dust inhalatio n period predicted a faster decrease after dust inhalation ended.