После Чернобыльской аварии один из наиболее загрязненных радионуклидами (прежде всего, 137Cs) участков черноземов сформировался в Плавском районе Тульской области в пределах полузасушливой лесостепной зоны Среднерусской возвышенности. Цель исследования: выявить современный уровень загрязнения почв Плавского радиоактивного пятна и определить соответствие стандартам качества картофеля, возделываемого на этой территории, по содержанию 137Cs. Исследования выполняли в центральной части Плавского района Тульской области. Работы проводили с 2014 по 2022 год с учетом изменений в структуре посевных площадей хозяйства. Отбор проб для настоящего исследования проводили в 2017–2018 году. Непосредственными объектами исследований послужили почвы обследуемой территории и растения картофеля. Пробы отбирали в конце августа в период полной спелости. На участке производили пробоотбор монолитов почв ненарушенного сложения с помощью кольцевого пробоотборника ПГ-450 с площади 300 см2, послойно с шагом по 10 см до глубины 30 см в трехкратной повторности с расстоянием между точками 15–20 м. Надземную часть растительности отбирали методом сплошного укоса с площади 2500 см2. Пробоотбор подземной части растительности исследуемых площадок производили с такой же площади и до глубины 30 см. Плотность радиоактивного загрязнения почв 137Cs в профиле черноземов (кБк/м2) рассчитывали с учетом удельной активности радионуклида, толщины слоя почвы и плотности сложения (с учетом фиксированной площади пробоотборника). Спустя 30 лет после аварии на Чернобыльской АЭС черноземы Плавского радиоактивного пятна все еще загрязнены техногенным 137Cs со значительным превышением допустимых уровней его накопления в почве. Однако перенос 137Cs из черноземов в клубни картофеля и другие компоненты урожая не является интенсивным, а современные уровни накопления радионуклида в клубнях значительно ниже заявленных требований санитарно-гигиенической безопасности продуктов питания человека. After the Chernobyl accident, one of the most contaminated with radionuclides (primarily 137Cs) areas of chernozems was formed in the Plavsky district of the Tula region within the semi-arid forest-steppe zone of the Central Russian Upland. The purpose of the study: to identify the current level of soil contamination of the Plavsky radioactive spot and to determine compliance with the quality standards of potatoes cultivated in this area, according to the content of 137Cs. The research was carried out in the central part of the Plavsky district of the Tula region. The work was carried out from 2014 to 2022, taking into account changes in the structure of the acreage of the farm. Sampling for this study was carried out in 2017–2018. The immediate objects of research were the soils of the surveyed territory and potato plants. Sampling was carried out at the end of August during the period of full ripeness. At the site, monoliths of undisturbed soils were sampled using a PG-450 annular sampler, from an area of 300 cm2, in layers in increments of 10 cm to a depth of 30 cm in triple repetition with a distance between points of 15–20 m. The aboveground part of the vegetation was selected by the method of continuous mowing from an area of 2500 cm2. Sampling of the underground part of the vegetation of the studied sites was carried out from the same area and up to a depth of 30 cm. The density of radioactive contamination of 137Cs soils in the profile of chernozems (kBq/m2) was calculated taking into account the specific activity of the radionuclide, the thickness of the soil layer and the density of addition (taking into account the fixed area of the sampler). 30 years after the Chernobyl accident, the chernozems of the Plavsky radioactive spot are still contaminated with technogenic 137Cs with a significant excess of permissible levels of its accumulation in the soil. However, the transfer of 137Cs from chernozems to potato tubers and other crop components is not intensive, and the current levels of radionuclide accumulation in tubers are significantly lower than the stated requirements for sanitary and hygienic safety of human food.

The behavior of 137Cs and K in the soil–plant system of the Chernozemic Zone long after the Chernobyl accident was studied. Experimental plots were laid in the central part of Plavsk radioactive hotspot of Tula oblast in wheat, soybean, buckwheat, rapeseed, sunflower, and grass–legume agrocenoses and in natural biogeocenoses of a dry meadow. The mean soil contamination with 137Cs was 171 ± 26 kBq/m2 (498 ± 100 Bq/kg), and the mean content of total K in soils was 2.0 ± 0 1

On the territory of the Plavsky radioactive hotspot of the Tula region of Russia, formed as a result of the accident at the Chernobyl nuclear power plant in 1986, an assessment of the radiation safety of growing carrots and beets was carried out in 2019. It has been established that at present the content of 137Cs in arable leached chernozems of the surveyed lands is 90–170 kBq/m2 , which is 2.5–4.5 times higher than the permissible level of density of surface radioactive contamination of soils. However, the specific activity of the radionuclide in carrot and beetroot crops does not exceed 5 Bq/kg, which is significantly less than the maximum permissible level of 137Cs accumulation in vegetables (600 Bq/kg for absolutely dry weight). The accumulation coefficients of 137Cs in the total biomass of carrots and beets are 2.0·10−2 and 7.5·10−2, and in eaten root crops – 1.1·10−2 and 2.0·10−2, respectively, which is in good agreement with the IAEA estimate for the intensity of the transition 137Cs in the production of vegetable roots from loamy and clayey soils.

To assess the transfer of macro (K, P, S, Mg, Ca, as well as Si, Na, Fe, Al, Mn and Ti) and microelements (Zn, Ba, Cu, Sr, Mo, as well as As, Zr, Pb, Co, Ni, V and Cr) from Luvic Chernozems (Aric, Loamic, Pachic) into agricultural plants, we studied the inventories of chemical elements in three agrocenoses (wheat, soybean, Galega orientalis Lam. and Bromopsis inermis Leyss grass mixtures) from the Plavsk upland (Tula Region). This territory is subjected to intensive industrial and agricultural impacts: it is 40 km away from the town of Shchekino with a nitrogen fertilizer plant and a thermal power plant, 60 km away from Tula with large metallurgical enterprises, 70 km away from the town of Novomoskovsk with several chemical enterprises and state district power plant. In soils, the total content of elements was determined by the X-ray fluorescence spectrometry. The elemental composition of plants after autoclave decomposition with a mixture of concentrated nitric acid and hydrogen peroxide and the content of the bioavailable fraction (extracted by an ammonium acetate buffer with pH 4.8) of elements in soil were estimated by the atomic emission spectrometry with inductively coupled plasma. In topsoil (a 10-cm layer), maximal inventories are typical for total Si (40 ± 4 kg/m2), Al (7.0 ± 0.8 kg/m2) and Fe (3.4 ± 0.3 kg/m2) and for bioavailable Ca (570 ± 48 g/m2), Mg (43 ± 4 g/m2), K (22 ± 6 g/m2). In plants, the main inventories (g/m2) of K, P, S, Mg, Si, Mn, Zn, Ba, Cu, Mo occur in the above ground phytomass. The most effectively plants assimilate bioavailable fractions of K, P, Ti, Mo, As, Zr, V. Based on the resource method for soil quality assessment, the studied Chernozems are characterized by a low level of Ni contamination, a moderate supply of bioavailable K with a lack of bioavailable P.

Anna A. Oleshkevich, Specific features of change in enzymate activity in

Agricultural land use in the area of the post-Chernobyl Playsk radioactive hotspot (Tula region, Central Russia) has raised a problem of radioecological safety of obtained plant foodstuff. Verification of Cs-137 activities and inventories in components of "soil-plant" systems of the territory has been conducted in 2014-2017 in 10 agrosystems and 2 semi-natural meadows. It was revealed that density of Cs-137 contamination of arable chernozems and alluvial calcareous soils nowadays varies in a range 140-220 kBq/m(2) and exceeds radiation safety standard by(similar to)3.5-6 times. Deep plowing of the arable soils up to 30-cm in 1986-1987 resulted in decreasing of Cs-137 inventories in rooting zone by approximate to 70% for crops cultivated with shallow disk plowing (wheat, barley), and by approximate to 35% for crops cultivated with middle plowing (buckwheat, amaranth, white mustard). The investigated plants and their compartments can be grouped on the basis of transfer factor values as follows: maize (stems and leaves) > amaranth > brome-grass > vegetation of dry meadow, galega, sunflower (seeds), vegetation of wet meadow > maize (grain), soybean (pods), barley (grain), buckwheat (grain), potatoes (tubers) > white mustard (seeds), wheat (grain). It is noticeable that generative plant compartments are characterized by less Cs-137 activities in comparison with stems and leaves; and that Cs-137 root uptake is not coincide with total flux of mineral nutrients in "soil-plant" systems. In sum, Cs-137 soil-to-plant transfer in the area of the Plavsk radioactive hotspot is characterized by considerable discrimination, so Cs-137 activities in plants are completely in accordance with national standards. (C) 2019 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and Hosting by Elsevier B.V.

Vertical distribution of Cs-137 in cultivated chernozems of the Plavsk radioactive hotspot has been investigated, with the emphasis on the plough horizon.It is shown that the commonly expected complete homogeneity of the isotope vertical distribution within the plough and old-plough horizons of cultivated chernozems is not always achieved.Incomplete homogeneity can be explained by the application of different cultivation techniques for various crops within the crop rotation system employed.Important observation is that in cases of relatively shallow cultivation (such as disking to 12-15 cm depth) the largest root biomass content remains within the upper 10 cm layer, while maximum Cs-137 content is shifted downwards to underplough layer at 10-20 cm depths.At the same time, traditional cultivation with plough layer rotation and mixing to the 20-25 cm depth results in more uniform Cs-137 distribution through the plough layer, while layer of active root uptake of mineral matter for row crops shifts from the soil surface downward.Therefore, it can be recommended that the systematic monitoring of cultivated topsoil conditions based on preliminary assessment of Cs-137 vertical profile distribution, taking into account agrotechnical specifics of different crops within the crop rotation, must be carried out in order to obtain the reliable assessment of the soil radioecological status.

(1) Moscow Lomonosov State University, Soil Science Faculty, Radioecology & Ecotoxicology Department, Moscow, Russian Federation (tparamonova@soil.msu.ru), (2) Moscow Lomonosov State University, Geography Faculty, Laboratory of soil erosion & fluvial processes, Moscow, Russian Federation (vladimir.r.belyaev@gmail.com) , (3) Moscow Lomonosov State University, Faculty of Chemistry, Radiochemistry Department, Moscow, Russian Federation (kuzmenkova213@gmail.com)