Databases are being created that contain verified and updated dosimetry and worker history information for workers at the Mayak Production Association. Many workers had significant external and internal exposures, particularly during the early years (1948-1952) of operation. These dosimetric and worker history data are to be used in companion epidemiology studies of stochastic and deterministic effects. The database contains both external and internal dose information and is being constructed from other databases that include radiochemical analyses of tissues, bioassay data, air sampling data, whole body counting data, and occupational and worker histories. The procedures, models, methods, and operational uncertainties will be documented and included in the database, technical reports, and publications. The cohort of the stochastic epidemiological study is expected to include about 19,000 persons while the cohort for the deterministic epidemiological study is expected to include about 600 persons. For external dosimetry, workplace gamma, beta, and neutron doses are being reconstructed. The models used for this incorporate issues such as known isotopes, composition, shielding, further analysis of film badge sensitivities, and records of direct measurements. Organ doses from external exposures are also being calculated. Methods for calculating dose uncertainties are being developed. For internal dosimetry, the organ doses have been calculated using the established FIB-1 biokinetic model. A new biokinetic model is being developed that includes more information of the solubility and biokinetics of the different chemical forms and particulate sizes of plutonium that were in the workplace. In addition, updated worker histories will be used to estimate doses to some workers where direct measurements were not made. A rigorous quality control procedure is being implemented to ensure that the correct dosimetry data is entering the various databases being used by the epidemiologists.

Chronic inhalation of Pu particles during Mayak processing is a potential concern for workers. Of the many particle properties that affect individualised dose estimates, particle solubility in lung fluids can be most important. This study compares in vitro dissolution rates of several plutonium industrial compounds present at different stages of the Mayak processing cycle using three different solvents. The results are then used to develop values of absorption parameters for individual dose assessments. In this study, the dissolution rates of nitrate, oxide and mixed plutonium aerosols were determined using a serum ultrafiltrate stimulant (SUF), phagolysosomal simulant fluid and Ringer's solution, all using a static system. According to the results obtained with SUF, Pu nitrate is absorbed into the blood to a larger extent than predicted using model parameters currently applied for Mayak workers. Absorption into the blood of 21.5 vs. 3% of deposited nuclide as current model predicts results in underestimation of systemic burden and overestimation of the lung dose. These data are being used to provide improved retrospective dose assessments for inhaled plutonium aerosols.

This report describes a method by which potentially inhaled workplace aerosols containing plutonium compounds are classified on the basis of measured transportability in Ringer's solution. It is suggested that the criterion "transportability" be used in the ICRP respiratory tract model. Transportability is measured as the fraction of plutonium alpha activity, deposited on a collecting filter, that passes through a semi-permeable membrane in Ringer's physiological solution during two days of dialysis. First order kinetic equations are used for explanation of dialysis results. The dissolution characteristics of alpha-active aerosols are important in interpretation of their passage from the lungs after inhalation.

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.

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