Retrospective estimation of strontium-90 intake dynamics and doses for the population living in the territories affected by the Chernobyl accident

An attempt has been made to find parallels in 137Cs and 90Sr transfer from the fallout of these radionuclides after the accident at the Chernobyl nuclear power plant (ChNPP) into humans for the inhabitants of the contaminated territories of the Zhytomir region in Ukraine. A model of the retrospective reconstruction of 90Sr intake levels in 1986-1998 has been developed. The model's major parameters for the period 1986-1994 are: (1) 90Sr and 137Cs fallout density in the territory of the settlement; (2) the value of the 137Cs annual intake, obtained on the basis of dynamics of 137Cs intake; (3) the value of 90Sr relative accessibility coefficient; (4) the coefficient of the countermeasure efficiency. Numerical values of the parameters have been obtained. The model's major parameters for the period 1995-1998 are: (1) 90Sr and 137Cs fallout density on the territory of the settlement; (2) value of 90Sr transfer factor from soil to milk and potato; (3) diet structure for the rural population in Ukraine. Using the proposed model it has been found that the total annual 90Sr intake in 1986 constituted 37.8, 22.7 and 18.9 Bq per (kBq.m-2) for the inhabitants of the uncontrolled and controlled territories and for Naradichi residents, respectively. 90Sr intake in 1986-1994 constituted 280 and 99 Bq per (kBq.m-2) for the inhabitants of the uncontrolled and controlled territories, respectively. The average rate of the 90Sr intake for the adult inhabitants for the 1995-1998 period was 0.19 ± 0.03 Bq.day-1 per (kBq.m-2). The model verification relies on the radionuclide content examination in autopsy samples and daily urine samples taken from residents of the contaminated area. It demonstrates the adequacy of the retrospective evaluation model for 90Sr intake levels and the possibilities for its use in dose calculations. The values have been obtained with respect to radiation doses received and expected by the population residing in controlled and uncontrolled areas. The calculations showed that: (1) maximum radiation doses for controlled areas residents reach the values of 1.2 mSv, while for uncontrolled areas they were up to 1.5 mSv; (2) median doses for these categories are within the range of 0.14-0.15 mSv. The average individual committed effective dose for people of the controlled and uncontrolled territories are estimated at the level of 12.1 and 17.6 μSv per (kBq.m-2) respectively. Thus the introduction of countermeasures prevented 5.5 μSv per (kBq.m-2) in the controlled territories. (author)