Validation of Biokinetic Models for Strontium: Analysis of the Techa River and Chernobyl Data

INTRODUCTION The ICRP models used in radiation protection to estimate doses resulting from internal irradiation are based on biokinetic models for different radionuclides. As a rule, a biokinetic model is based on some combination of observations of the behavior of the element in human subjects, of the same element in other mammalian species, chemically similar elements in human subjects and in other mammalian species (1). Relatively plentiful human data exist for strontium, but the heterogeneity of these data complicates the interpretation and modeling process. The human experimental data from controlled studies are most important for model parameter estimation. Data bases on public exposure are necessary to estimate the reliability of model predictions. Large data bases related to the transfer of Sr from food and milk to the human skeleton were developed in the 1950s and 1960s. They reflect the results of Sr measurements in biological samples contaminated due to nuclear test fallout. Interpretation of these environmental data is complicated by the fact that measured skeleton burdens were accumulated over an extended period and Sr intake function is not well established. However it is precisely the results of these researches that were used (along with controlled studies and animal data) for development and validation of the ICRP strontium biokinetic model (2,3). Strontium-90 was one of the main sources of environmental contamination due to the releases of the Mayak plutonium production complex (Southern Urals, 1949-1956) and the Chernobyl accident (1986). Over 800 measurements of bone samples from autopsy cases, and 31,000 whole body counter (WBC) Sr measurements for Techa River population were made at URCRM (Chelyabinsk) (4). However, for a long time these results could not be published in the open literature and were not used at full extent in validation of biokinetic models. Measurements of Sr contents in bone samples (more than 450 samples) were performed for residents of the area contaminated due to Chernobyl accident (RPI, Kiev). URCRM strontium biokinetic model was elaborated for the dose estimation for residents of the Techa River settlements. Age-dependent retention function was fitted to WBC measurements for 1976, but the subsequent WBC measurements have not been used for modeling. The URCRM model validation was olso made for adult persons in 1998 (4) using the data on radiochemical measurements of bone samples and WBC measurements for the period 1974-1993. The present paper is devoted to the validation of the ICRP67 and URCRM Sr biokinetic models by the results of the measurements of Sr body burden for the residents of the Techa Riverside and the areas contaminated as a result of the Chernobyl accident.