RADIOECOLOGICAL SIMULATION OF THE <sup>131</sup>I ACTIVITY DYNAMICS IN DIFFERENT TYPES OF GRASS VEGETATION IN THE CHERNOBYL ACCIDENT YEAR
The dynamics of the grass fodder and food crop crude biomass in Mazovia in the year of the Chernobyl disaster has been caLcuLated. Densities of the <sup>137</sup>Cs и <sup>131</sup>I fallout on soil and grass have been studied as a function of rainfall and biomass density as of the time most of the fallout took place. A method is described to convert the instrumental data for the radionuclide activity dynamics in vegetation of one type to vegetation of other types. The results of such data conversion from lawn grass to other types of food and fodder grass vegetation are presented. A method is described for adjusting the dynamics of the radionuclide transport through the food chain components (pasture grass, green meat - milk - human body) by normalizing successively the estimated data in every next component for the average value of the instrumental data ratio to the estimated data in the previous component. The proposed methods are intended to form a mutually consistent base of estimated and reconstructed instrumentaL data: <sup>137</sup>Cs and <sup>131</sup>I activity in the atmosphere - rainfall - <sup>137</sup>Cs fallout density on terrain - specific activity of <sup>131</sup>I in vegetation. Such radioecological database will provide for a longer reliability of the estimated <sup>131</sup>I specific activity dynamics in milk and in human body and, in the long run, in estimating the thyroid internal exposure doses.