The United States Transuranium and
Uranium Registries (USTUR) and the Dosimetry Registry of the Mayak Industrial Association (DRMIA) have been independently collecting tissues at autopsy of
plutonium workers in their respective countries for nearly 30 y. The tissues are analyzed radiochemically and the analytical data are used to develop, modify, or refine biokinetic models that describe the depositions and translocations of
plutonium and transplutonium elements in the human body. The purpose of this collaborative research project is to combine the unique information on humans, gathered by the two Registries, into a joint database and perform analyses of the data. A series of project tasks are directly concerned with dosimetry in Mayak workers and involve biokinetic modeling for actinide elements. Transportability coefficients derived from in-vitro solubility measurements of actinide-containing
aerosols (as measured by the DRMIA) were related to specific workplaces within Mayak facilities. The transportability coefficients of inhaled
aerosols significantly affected the translocation rates of
plutonium from the respiratory tract to the systemic circulation. Parameters for a simplified lung model, used by Branch No. 1, Federal Research Center Institute of Biophysics (FIB-1) and the Mayak Production Association for dose assessment at long times after inhalation of
plutonium-containing
aerosols, were developed on the basis of joint USTUR and DRMIA data. This model has separate sets of deposition and transfer parameters for three
aerosol transportability groups, allowing work histories of the workers to be considered in the dose-assessment process. FIB-1 biokinetic models were extended to include the distributions of actinide elements in systemic organs of workers, and a relationship between the health of individual workers and
plutonium distribution in tissues was determined. Workers who suffered from
liver diseases generally had a smaller fraction of systemic
plutonium in the liver at death and a larger fraction in the skeleton than did relatively healthy workers. Also, the fraction of total systemic
plutonium excreted per day was significantly greater for workers with
liver diseases than for relatively healthy workers. These observations could have a considerable effect on organ dosimetry in health-impaired workers whose dose assessments were based solely on urinary excretion rates. A comparison of this model to other biokinetic models, such as those published by the International Commission for Radiological Protection, is currently underway as is the documentation of uncertainty estimates associated with the model.