Migration of <sup>137</sup>Cs and <sup>90</sup>Sr from black soil into vegetable of the Central part of the Forest-steppe zone of Ukraine
Regardless of the time after the Chernobyl disaster, the problem of radioactive contamination is very urgent. At present, 6.7 million hectares of our country remain contaminated, of which 1.2 million hectares of land are contaminated with 137Cs with a density of 42 to 589 kBq/m2 (1-15 Ci/km2). There are 2,161 settlements in the radioactively contaminated territories, where there are about 3 million inhabitants. For the inhabitants of rural areas of these settlements, the main part of food products belongs to the products obtained from the land, so the definition of plant contamination by artificial radionuclides 137Cs and 90Sr on the lands affected by radioactive contamination. The Chernobyl accident is relevant, since the internal dose of radiation is formed due to consumed products, grown in private plots. Reducing the transition of radionuclides 137Cs and 90Sr from soil to crop production is one of the main tasks of agricultural production on contaminated radionuclide lands. The realization of these researchers will clarify the current state of migration of data of radionuclides in the soil-vegetation link in the agro eco systems of the Central Forest-steppe of Ukraine. From the moment of the Chernobyl accident, leading scientists conducted a sufficiently large number of scientific studies on the migration of 137Cs and 90Sr in agricultural production facilities, their accumulation in food products and the assessment of human exposure doses. The focus of the scholars focused on the territory of Polissya. Preferably migration of 137Cs and 90Sr in separate links and systems of the trophic chain. In addition, somewhat more attention is paid to 137Cs, which is the main dose-forming radionuclide. In addition, in forest-steppe areas that are radioactively contaminated, a significant proportion of pollution occurs at 90Sr, whose migration rate, according to scientists, will gradually increase. All these data led to the need for a detailed study of the state of migration of 137Cs and 90Sr in the soil-vegetation chain of agro eco systems of agricultural enterprises and private parts of the central forest-steppe affected by radioactive contamination because of the Chornobyl accident in the remote period. The purpose of these studies was to study the migration of 137Cs and 90Sr in the chain of soil plants in the villages Yosypivka and Tarasivka of the Kyiv region of the central forest-steppe of Ukraine, as well as the determination of the coefficients of transition of 137Cs and 90Sr from typical black soil to vegetable products for the next prognostication. The investigated areas of the Bila Tserkva district are located in the north-eastern part of the right-bank forest-steppe region of Ukraine and are represented mainly by typical low-humus black soil in the forests within the boundary plains. In order to achieve this goal, selection of samples of crop production and soil was carried out on private plots of peasants of Yosypivska and Tarasivska villages of the Bila Tserkva district of Kyiv region according to generally accepted methods. The territory of these settlements fell into the zone of the "southern trace of radioactive contamination" and is associated with the third and fourth zones of radioactive contamination. After preparation of samples, the activity of 137Cs and 90Sr was determined in the life safety department of the Bila Tserkva National Agrarian University at the USK Gamma Plus spectrometric complex according to the methodology for this device. To determine 90Sr, selective radiochemical separation was performed by precipitation of oxalates. The 90Sr determination was performed on the USC Gamma Plus beta spectrometric path. These studies were processed using the statistical method using the Microsoft Excel program. The main vegetable crops grown on private plots were carrots, cucumbers, potatoes, cabbage, tomatoes, zucchini, onions, peppers and radish. These studies were conducted during 2016-2018. From the data of the research it is clear that the least activity of 137Cs was in potatoes, onions and cucumbers. In zucchini and pepper, it appeared twice, carrots and tomatoes - almost four times, beets and radish - almost in 8, and beans - 11 times higher. Our studies show that there is a direct proportional relationship between the activity of 137Cs and 90Sr in the yield of vegetable crops and the level of the soil contamination. The research results make it possible, on the basis of the explained coefficient of transfer of 137Cs and 90Sr, to predict the contamination by plant radionuclides that will be grown in radioactive contaminated territories of the Central Forest-steppe of Ukraine. The coefficients of transition of 137Cs from soil (typical black soil) to vegetable crops grown in the III zone of radioactive contamination accumulate from 0.01 to 0.09 and 90Sr - from 0.01 to 0.30. The lowest coefficient of transition of 137Cs in potatoes, onions and cucumbers (0.01). In cabbage, squash and pepper, the transition factor is twice as high (0.03), and in carrots and tomatoes it is three times higher (0.04), in beets - 5 times, radish - 6 and beans - in 9 times higher. The lowest transfer coefficient of 90Sr in onions (0.01), in tomatoes and cucumbers it is 2 times higher (0.02), in pepper - 4 times higher (0.04), potatoes and cabbage - nine times higher (0.09), and in beets, radishes, carrots and beans in 27-30 times higher. The research conducted by us proves that the studied vegetable production, obtained in the settlements of Yosypivka and Tarasivka, does not exceed DR-2006, that is, it is quite suitable for use. The coefficients of the transition of radionuclides 137Cs and 90Sr from the soil (in this case, this typical black soil) to crop production grown on peasants’ plots have been determined, which will allow to predict in the future the contamination of 137Cs and 90Sr of vegetable products on the radically contaminated territories of the Central Forest-Steppe data. The content of radionuclide contamination of vegetable products after 33 years of the Chernobyl disaster proves that the problem of monitoring, studying and forecasting of products is still very relevant.