DYNAMICS OF CS-137 CONCENTRATION IN AGRICULTURAL PRODUCTS IN AREAS OF RUSSIA CONTAMINATED AS A RESULT OF THE ACCIDENT AT THE CHERNOBYL NUCLEAR-POWER-PLANT

The dynamics of Cs-137 concentration in the main types of agricultural products obtained in regions of Russia contaminated as a result of the Chernobyl Nuclear Power Plant (NPP) accident, in 1986, have been analysed. The rate of decline of Cs-137 contamination in agricultural products during the period under study (1987-1992) was not uniform. Reductions of the Cs-137 content of produce was most rapid during the early years after the accident, as a consequence of the intensive application of countermeasures at that time. Half-life periods for Cs-137 content in milk (the basic dose-forming product) and the decrease in products for areas in Russia subjected to the most intensive contamination amounted to 1.6 to 4.8 years, depending on the scale of countermeasures carried out. Half-life periods of decrease of Cs-137 content in other types of agricultural products (grain, potato) were within the range of 2 to 7 years. Based on the comparison of the dynamics of Cs-137 levels in agricultural products of the regions where the countermeasures scales differed, the contribution of countermeasures and of natural biogeochemical processes to the decrease of Cs-137 contamination levels of the main types of agricultural products that determine the dose from internal irradiation of local population has been estimated.