Dmitry Valentinovich Monakhov

The possibility of using algorithm VERT_MIG the simulations of vertical migration of radionuclides in the soil are discussed. The algorithm was successfully used to develop models of migration 137Cs and 90Sr in radioactive contamination of different soils as a result of accidents at Chernobyl and Fukushima-1. The results of modeling are presented. The prospects for further use of this algorithm and some aspects of the use of simulation in this area are discussed.

The ²²⁶Ra, ²³²Th, ⁴⁰K vertical profiles were studied in relation with the soil properties: pH_H2O, the sum of exchangeable Ca²⁺ and Mg²⁺, the degree of saturation with bases, the content of humus, mobile forms of phosphorus and potassium. An increase in the specific activity of ²²⁶Ra, ²³²Th, ⁴⁰K associated with the accumulation of humus and the biogenic accumulation of mobile forms of potassium and phosphorus in the upper 0-10 cm layer of horizon A in the soil of the oak forest was detected. The removal of ²²⁶Ra from the middle part of the profile of dark gray forest deep-carbonate soil was recorded. A positive correlation between the specific activity of ²²⁶Ra and the sum of the exchange bases Ca²⁺ and Mg²⁺ indicating the conjugate behavior of these elements-analogues in the horizons A, A(AE), AB and the lower horizons B1, B2, B3 was revealed. Removal of ²³²Th from horizon A(AE) and accumulation in horizon AB under conditions of local podzolization of dark gray forest soil in birch forest was observed.

Speciation of ²²⁶Ra and ²³²Th in sod-podzolic-gley concretionary soil are studied. It has been shown that with periodic overmoistening by surface waters and alternation of reducing and oxidizing conditions, the mobility and availability to plants of ²²⁶Ra is substantially higher than ²³²Th. The sum of fractions available to plants (water-soluble and exchangeable) and mobile (water-soluble, exchangeable and mobile) of ²²⁶Ra is 2-10 times higher than ²³²Th. Segregated ferruginous nodules formed in the eluvial horizons of this soil have a weak effect on the mobility of ²²⁶Ra, but significantly reduce the mobility of ²³²Th, much of which is substantially fixed inside the crystal lattices of newly formed minerals.

Some aspects of application of simulation modeling of radionuclide behavior in food chains of terrestrial ecosystems are discussed. The model of behavior of ¹³⁷Cs in the system of type soil-vegetation-herbivores-predators is described. The results of modeling, including the calculation of the dynamics of dose load on animals, are presented. It is shown that in the simplified “Chernobyl” scenario of the radiological situation, dose loads on herbivores are significantly lower than on predators. In general, in animals in the first 10 years, the main contribution to the dose load is made by external irradiation. Then the external and internal dose loads become approximately equal.

The simulation model of seasonal dynamics of ¹³⁷Cs in the components of the snytevoy oak forest ecosystem EcoradOak_CS_FW was further developed, which now includes first- and second-order consumers. The radiocesium redistribution in a full-scale food web of   a forest ecosystem of the type “soil—vegetation cover—herbivores—predators” is modeled. The algorithm used in the model allows us to take into account the influence of soil, meteorological, phenological and physiological factors on the behavior of radionuclide in the food web and predict radiological situations under various conditions of radioactive fallout. Data   on the contamination of animals with radiocesium obtained using the model are used to calculate the dynamics of the internal dose. The results of modeling can be used in the rationing of forest products of deciduous forests. The model is also applicable to the study of potassium redistribution in the trophic chain of a deciduous forest ecosystem.

The aim of the work is to summarize the data available in the scientific literature on the values of the ¹³⁷Cs/¹³³Cs isotope ratio in soils and vegetation cover of forest ecosystems in radioactively contaminated and background territories. The values of the specific activity of ¹³⁷Cs and the concentration of ¹³³Cs presented in radioecological studies are unified by calculating the molar ratio of these isotopes. Based on the generalized literature data, it is shown that the values of ¹³⁷Cs/¹³³Cs in soils, forest litter and vegetation increase in radioactively contaminated areas. In background regions exposed only to global radioactive fallout, the isotopic ratio of ¹³⁷Cs/¹³³Cs is about 0,1–1,0 (× 10^-8), whereas in the Chernobyl fallout zone it increases by 1000–100 000 times. The isotopic ratio of ¹³⁷Cs/¹³³Cs decreases down the soil profiles in various forest ecosystems. Spatial variation of the ¹³⁷Cs/¹³³Cs ratio in litter is associated with the diversity of ecotopes in forest biogeocenoses. The alignment of the values of the ¹³⁷Cs/¹³³Cs ratio in the vegetation cover and upper soil horizons indicates the achieved equilibrium of technogenic ¹³⁷Cs with natural stable ¹³³Cs in the biogeochemical cycle of this element. A comparative study revealed that the isotopic ratio of ¹³⁷Cs/¹³³Cs increases in the following range of plant cover representatives: Bryophyta < Sorbus aucuparia < Lichenes < Russula vesca < Frangula alnus < Polypodiophyta. For fungi, interspecific differences were noted in the following increasing series in the isotopic ratio ¹³⁷Cs/¹³³Cs: Lactarius deliciosus < Sarcodon scabrosus < Suillus bovinus < Tricholoma saponaceum < Lepista nuda < Russula delica < Macrolepiota excoriata. For the reference species of coniferous trees — Pinus sylvestris - the isotopic ratio of ¹³⁷Cs/¹³³Cs in the forest area of the Bryansk region polluted by Chernobyl fallout increases in the following number of components: roots < large branches < trunk wood < needles < small branches < cones.

From 1978 to 2021, the migration parameters and dynamics of the distribution of ¹³⁷Cs in arable and virgin soils of the Tula region were studied. Identical patterns of distribution of ¹³⁷Cs from global and Chernobyl fallout in the soil profile of leached chernozems were revealed. On arable land, agrotechnical measures contribute to the uniform distribution of ¹³⁷Cs in the arable soil layer. In virgin soil horizons of chernozem soils of meadow phytocenoses, the processes of redistribution of radionuclides in the surface layers were most active in the first 10-year period after the fallout, which this contributed to the equalization of ¹³⁷Cs content in layers 0–2 and 2–5 cm and its increase in the 5–10 cm layer to more than 30% by the beginning of 2000. Nowadays, more than 75% of the ¹³⁷Cs content in virgin chernozem soils of the Tula region is concentrated in the upper 15 cm layer, and the penetration depth of radionuclides reaches 40–45 cm.

The article deals with issues related to the development of radioecology as an independent scientific discipline. The achievements of the past years, the studies that are currently being carried out, as well as promising areas of development in this area are analyzed. A corrected periodization of the stages of development of radioecology is proposed, taking into account the experience accumulated to date in the field of this discipline. At the initial stage (1895–1929:), empirical material was collected; at the first stage (1930–1960), the theoretical foundation was laid and radioecology was formed as an independent discipline; at the second stage (1961–1990), intensive development of radioecology was noted, and at the third stage (1991–2010) — progressive development of radioecology; the forth modern stage of radioecology development falls at the beginning of the twentieth century (2011 — present). For each stage the main scientific achievements and evolution of ideas in the field of radioecology are considered. It is postulated that at present the development of this discipline is associated with the further improvement of world nuclear technologies, the elimination of the consequences of a number of radiation incidents (the accident at the Fukushima nuclear power plant, 2011), the revision of the concept of radiation protection of the environment and a number of other provisions. Particular attention is paid to forest radioecology, one of the most important main directions of this science.

We studied morphological properties, pH, organic carbon content, and specific activity of ¹³⁷Cs and natural radionuclides (⁴⁰K, ²²⁶Ra, ²³²Th) in the upper horizons of soils in deactivated and slightly damaged areas of the city. The studies were carried out in the urban ecosystems of the city of Elektrostal (Moscow region) in 2019, i.e. 6 years after local precipitation of ¹³⁷Cs due to a radiation incident. Morphological features of the upper horizons of urban soils were: brownish-gray color, light-loamy composition, small-lumpy and lumpy structure, inclusions of construction and household waste. In the upper horizons of urbiquasizems and urban soils, a low carbon content (less than 1%) with high coefficients of variation - were detected. In the studied urban soils, a wide range of water pH values was noted: from acidic (4,6–5,5) to highly alkaline (>8,0) reaction. Correlation analysis showed that in the upper horizons of UR, the content of organic carbon was reduced and alkalinization of the soil environment was observed. The accumulative type of distribution of ¹³⁷Cs was recorded for soil profiles of polluted urban ecosystems in which decontamination measures were not carried out. The profiles of urban soils that were subjected to decontamination revealed low values of the specific activity of ¹³⁷Cs in surface bulk layers and maxima in buried contaminated horizons. In the bulk horizons of UR, which include a large amount of crushed stone, there is an increase in the specific activity of ²²⁶Ra. Some technogenic horizons UR and TCH, consisting mainly of quartz sand, are characterized by very low values of specific activities ²²⁶Ra and ⁴⁰K. Correlations of chemical and radiation indicators in the profiles of urban soils reflect the different composition and properties of upper horizons formed as a result of excavation and decontamination work.