ИСТИНА

Of the radioactively contaminated lands of Russia there are highly fertile chernozem soils, which remained in agricultural use despite Chernobyl fallout as was the case of Plavsk radioactive hotspot (Tula region). currently Cs-137 activities in soils of the area taking into account initial level of contamination, land use and the position of relief vary from 450-700 Bq/kg (170-280 kBq/m2). The process of Cs-137 accumulation in vegetation biomass is urgent to be under radioecological control at this area. To assess parameters of Cs-137 stockpiling in agricultural grass vegetation 8 agricultural crops of field rotation from the territory of Plavsk radioactive hot spot (spring wheat, spring barley, maize, summer rape, galega, potatoes, amaranth, lucerne-grass mixture) were selected for the study. Above- and belowground parts of plant biomass were separated for the detailed examination. To avoid the difference in Cs-137 content in soils of the plots and to appreciate the biological peculiarities of individual crops the transfer factor (TF) values (the ratio of the Cs-137 activities in vegetation and in soil) were calculated. TF values in total biomass (TFtot) for all vegetation species are under 0.1 that confirms a pronounceable discrimination of Cs-137 root uptake from contaminated soils. Among the investigated agricultural crops TFtot is minimal for rape (0.01), middle – for amaranth, lucerne and galega (0.03-0.04), wheat, barley and potatoes (0.05-0.06), and maximal – for maize (0.13). Correlation analysis demonstrate that TFtot is invariant with total as well as above- or belowground biomass and the rate of plant growth, but seemly depends on root capture capacity (r=0.68). Thus, physiological features of different plant species and families affect the specific Cs-137 bioavailability. An accounting the distribution of Cs-137 among above- and belowground parts of agricultural crops on the basis of TFag and TFbg comparison also clearly shows the importance of biological characteristics of plants: wheat, barley and maize (Gramíneae family) are characterized by elevated Cs-137 activity in belowground parts (12-14 times higher than in shoots) with TFbg 0.16-0.19; rape (Brassicaceae family) and potatoes (Solanaceae family) are characterized by similar TFag and TFbg (0.01 for rape and 0.05-0.07 for patatoes); while galega, lucerne and amaranth (Fabaceae and Amaranthaceae families respectively) are characterized by higher Cs-137 activity in aboveground part (4-6 times more than in roots) with TFag 0.04-0.06. Considering vegetation biomass structure and Cs-137 activities in above- and belowground parts of agricultural crops 86-96% of the radionuclide inventory is associated with belowground biomass in cereals communities, while in agrosystems of legumes or amaranth 87-93% of Cs-137 inventories are deposited in green aboveground parts of vegetation. Study was conducted with the support from the Russian Foundation for Basic Research (№– 14-05-00903).