The results of the analysis of the 137Cs aggregated transfer factors (Tag) change in fodder of agricultural animals (hay, haylage, silage, and green fodder) in the southwestern districts of Bryansk region over the 35 years since the Chernobyl accident are presented. It is shown that the rates of Tag reduction across districts and zones of radioactive contamination varied significantly, while the dynamics of their change had an uneven character. Four time intervals are distinguished for the assessments; specifically, from 1987 to 1992, from 1993 to 2006, from 2007 to 2015, and from 2016 to 2021. The first period covered the time after the accident, when the countermeasures were carried out on a maximum scale; the second one, when the scales of remediation decreased significantly; the third period was a time (from 2006 to 2016) when the dynamics of the Tag reduction was influenced by the Federal Target Program (FTP) “Preservation and Restoration of Soil Fertility of Agricultural Lands and Agricultural Landscapes as a National Asset of Russia for 2006–2013”; and the fourth one, from 2016 to 2021, in the remote period after the accident, when the volumes of rehabilitation of agricultural lands were very low. The half-lives calculated for the period of intensive countermeasure implementation ranged from 0.73 to two years. During the next period, the 137Cs decrease in all types of forage crops strongly slowed down, and in many areas, there was a tendency toward an increase in the Tag values. During the third and fourth periods, the dynamics was of multidirectional character; namely, in the districts where the FTP activities were applied on a full scale, an essential increase in the 137Cs Tag values to fodder plants was noted; whereas a further increase in this parameter was observed in the districts with limited application of the countermeasures. The efficiency of remediation was estimated by the criterion of reduction of Tag values (reduction factor) in zones with different 137Cs deposition density on agricultural lands. It was also noted that the reduction factor across different time intervals after the accident ranged from 1.1 (silage) to 5.1 (haylage). The highest efficiency in fodder crops Tag reduction was observed both in the first period after the accident (1986–1992) and in the period of the FTP implementation. It was shown that the Tag values in the zone with a deposition density from 185 to 555 kBq/m2 did not differ significantly from those in the zone with a deposition density of 555–1480 kBq/m2.

The publication continues the series of research addressed to the dynamics of 137Cs concentrations in agricultural products after the Chernobyl accident. The purpose of the present paper was to analyze the data describing the changes of 137Cs concentrations in cow milk. The information on countermeasures in animal breeding is presented, the system of radiological monitoring of milk contamination is described. It is shown that the dynamics of 137Cs concentrations in milk was seriously affected by the implementation of agrotechnical and veterinary measures. Effective half-lives of 137Cs concentrations in milk in the first period after the accident (1987-1992) ranged from 1 to 2.0 years. In the subsequent period (1991-2015), the reduction of milk contamination slowed down and the half-lives ranged from 5 to 25 years depending on the scope of remediation works and 137Cs aging in the soil.

A review of the available data on thorium concentrations in plants and related foodstuffs is presented. It is shown that the concentration of 232Th in plants in regions with normal background radiation varies from 0.5 × 10–4 to 22.8 Bq/kg, while it reaches 0.058–80.0 Bq/kg (dry weight) in regions with elevated environmental thorium concentrations. It is also shown that the distribution of thorium among plant tissues is heterogeneous. The role of root systems as a biological barrier for thorium penetration into plants is noted.

The paper continues the cycle of publications addressed to the study of regularities of 137Cs content changes in agricultural products after the Chernobyl accident. The aim of the studies was to analyze the information describing changes in the 137Cs concentrations in agricultural animal forage: hay, haylage, silage and green fodder in the southwestern districts of the Bryansk region affected by the contamination after the ChNPP accident. The data on countermeasures in the fodder production are given and the system of radiological monitoring of fodder contamination is described. It is shown that the dynamics of changes in the 137Cs concentrations in fodder was mainly determined by the dynamics of implementation of remedial measures. The effective halflives of 137Cs concentration in forages during the first period after the accident (1987-1990) varied from 0.57 to 2.7 years. Subsequently (1991-2021) the decrease in feed contamination slowed down and the half-lives ranged from 8.0 to 50.0 years and longer depending on the scope of remediation and the characteristics of the plants used for the animal feed production.

A review of the data on thorium concentrations in the tissues of terrestrial and freshwater organisms is given. It is shown that the concentrations of 232 Th vary widely in the tissues of both animals and fish, reflecting environmental thorium concentrations. The thorium concentrations in agricultural animal tissues range from 0.9 × 10 –4 to 2.1 × 10 –2 Bq/kg in regions with a normal thorium background and from 3.1 × 10 –2 to 1.4 × 10 –1 Bq/kg fresh weight in areas with high thorium concentrations in the soil. Significantly higher values are observed in the tissues of wild animals. The highest 232 Th concentrations have been recorded in the skeleton, followed by the lungs, kidneys, liver, and, finally, muscles. It is shown that thorium accumulation tends to be higher in species occupying a higher position in trophic chains. The concentration of 232 Th in fish can reach 1.0 × 10 –1 Bq/kg (fresh weight) in areas with normal thorium background and up to 100 times higher in areas with a high thorium background. The results show the importance of studying thorium transfer along food chains and the necessity to take into account the observed patterns during assessment of the consequences of radioactive contamination of the environment.

An overview of data on thorium concentrations in terrestrial animals, as well as freshwater organisms is presented. Concentrations of 232Th in both animals and fish vary widely, reflecting environmental thorium concentrations. Thorium concentrations in the regions with a normal thorium background in animal tissues were in a range from 0.9 × 10–4 to 2.1 × 10–2 Bq/kg, and from 3.1 × 10–2 to 1.4 × 10–1 Bq/ kg in the areas with high thorium concentrations in the soil. Significantly higher values were observed in wild animals’ tissues. The highest 232Th concentrations were found to be in the skeleton, followed by lungs, kidneys, liver and finally muscles. It has been shown that thorium accumulation is higher in species occupying a higher position in the trophic chains. In areas with normal thorium background, the concentration of 232Th in fish can reach 1.0 × 10–1 Bq/kg (fresh mass), and in areas of high thorium background this value can be up to 100 times higher. The obtained results show the importance of study on the thorium transfer along the food chains and the need to consider observed regularities when assessing the consequences of radioactive contamination of the environment.

The data on the dynamics of the 137 Cs transfer coefficients ( T f ) for fodder in the long term after the Chernobyl accident (2008–2020) are presented. It is shown that the ecological half-lives of transfer coefficients varied from 7.8 to 28.9 years. The obtained estimates are consistent with the second half-life periods of transfer coefficients estimated based on data for the first eight years after the Chernobyl accident. The peculiarities of the dynamics of T f to fodder were in good agreement with the scales of remedial actions carried out in the contaminated territories.

A methodological approach to substantiating the control levels of 137 Cs in cattle feeds is presented based on the probabilistic nature of the parameters of transfer of 137 Cs to cattle feeds and cattle milk and meat. A comparative analysis of global and Russian data on the parameters of 137 Cs transfer from feed to livestock products has been made. It is shown that milk with 137 Cs remains safe when the concentration of this radionuclide in the feed is at the existing control levels; however, this does not guarantee compliance with the hygienic standards for the content of 137 Cs in meat. Based on the methodological approach, control levels are proposed for monitoring 137 Cs in the feeds of dairy and beef cattle in areas contaminated after the Chernobyl accident. The use of the proposed control levels makes it possible to optimize livestock breeding technologies in the Russian areas contaminated after the Chernobyl accident.

An international review of radioecological data derived after the accident at the Fukushima Daiichi nuclear power plant was an important component of activities in working group 4 of the IAEA Models and data for radiological impact assessment, phase II (MODARIA II) programme. Japanese and international scientists reviewed radioecological data in the terrestrial and aquatic environments in Japan reported both before and after the accident. The environmental transfer processes considered included: (a) interception and retention radionuclides by plants, (b) loss of radionuclides from plant and systemic transport of radionuclides in plants (translocation), (c) behaviour of radiocaesium in soil, (d) uptake of radionuclides from soil by agricultural crops and wild plants, (e) transfer of radionuclides from feedstuffs to domestic and wild animals, (f) behaviour of radiocaesium in forest trees and forest systems, (g) behaviour of radiocaesium in freshwater systems, coastal areas and in the ocean, (h) transport of radiocaesium from catchments through rivers, streams and lakes to the ocean, (i) uptake of radiocaesium by aquatic organisms, and (j) modification of radionuclide concentrations in food products during food processing and culinary preparation. These data were compared with relevant global data within IAEA TECDOC-1927 'Environmental transfer of radionuclides in Japan following the accident at the Fukushima Daiichi Nuclear Power Plant'. This paper summarises the outcomes of the data collation and analysis within MODARIA II work group 4 and compares the Japan-specific data with existing radioecological knowledge acquired from past and contemporary radioecological studies. The key radioecological lessons learned are outlined and discussed.

A review of the world data on the concentrations of thorium activity concentrations in soils, the atmosphere, surface waters, and bottom sediments is presented. It is shown that in the areas with normal radiation background the 232Th concentrations vary from 5 to 95 Bq/kg in the soil , from 1.0 × 10–5 to 1.0 × 10–2 Bq/L in the aquatic environment, from 4 to 100 Bq/kg in bottom sediments of surface waters, from 0.6 × 10–7 to 1.0 × 10–4 Bq/L in groundwater, and from 0.1 to 1 × 10–4 Bq/m3 in the surface air. The thorium concentrations in those environments can range from one to four orders of magnitude higher in areas with an elevated radiation background and thorium, rare earth, or tin mining areas than in areas with normal radiation background. It is also demonstrated that data on violation in the isotopic equilibrium of the thorium content in various media can be used to assess the pathways of thorium release into the environment. It is noted that the spatial patterns of thorium concentrations are rather close in the soil and bottom sediments and differ from the patterns of thorium distribution in surface waters.

The article presents methodological approaches to the organization of radioecological monitoring in the regions where nuclear power plants are located. The analysis of the monitoring results at the Beloyarsk, Kursk, Leningrad and Rostov NPPs showed that the contribution of the natural radiation background to the public exposure dose is within a narrow range from 3.13 to 4.16 mSv per year, and the dose from the existing technogenic contamination varies from 0.47 μSv (Rostov NPP) up to 150 μSv per year (Beloyarsk NPP). The variability of the exposure doses is determined by the influence of natural climatic conditions and by differences in characteristics of contamination sources, including differences in electricity generation technologies. The technogenic radiation background in the area of the Beloyarsk NPP is determined by environmental contamination as a result of previous activities, whereas in the areas of the Leningrad NPP and the Kursk NPP it is associated with Chernobyl fallout (91 and 14 μSv per year, respectively). The contribution of NPPs to the existing technogenic radiation background varies from 1% (Rostov NPP) to 10–11% (Kursk and Beloyarsk NPPs).

The paper comprehensively brings together key data on radiation effects observed in the Russian studies with an acute forest irradiation. The experiments were based on the ecosystem approach, including an assessment of the radiation impacts based on a variety of the endpoints. The effects at the cellular level were observed at the lowest doses: a double increase of the chromosome aberrations in the apical meristem of pine were found at the site with the absorbed dose of 2.5 Gy. The effects at the tissues levels and trees mortality expressed in D50 were revealed for the trees received 20-50 Gy and a double reduction in a net primary radioactivity was observed at the doses of 14-38 Gy for pine and 280-750 Gy for birch. The seasonal differences in radiosensitivity of the forest ecosystems were noted: the radiosensitivity of the irradiated trees was 3-5 fold higher after the spring irradiation than that after autumn irradiation. An importance of the ecosystem endpoints is emphasized.

A wide range of countermeasures and remedial actions has been developed and used to mitigate the consequences of the Chernobyl accident. This article summarizes the basic information on the application of countermeasures in agriculture over the 35 years after the accident and provides data on their effectiveness. The experience of using agricultural remedial measures and their influence on the radiological situation in different periods after the accident are analyzed. The most important aspects are highlighted, and the necessity of using the aftermath experience for improving emergency response systems in agriculture for potential emergencies is demonstrated.

The nuclear disaster from the FNPP accident resulted in the major contamination of forest ecosystem of Eastern Japan. Forests are the most susceptible to ionizing radiation exposure, especially conifers due to their high radiosensitivity and pollutant interception abilities. A high concentration of radionuclides in forest ecosystems caused an increase in the dose rate. Japanese cedar belongs to Japan's endemic species; therefore, the current study was aimed at the absorbed dose rate assessment of the C. japonica forest stand in the Yamakiya district. To estimate the absorbed dose rates to the Japanese cedar trees, we used the 134,137Cs concentrations in different forest ecosystems’ compartments. The calculations include data from 2011 to 2017. The dose rate assessments were performed at different heights of the forest ecosystem (canopy, trunk, understory). The average dose rates decreased from 40 µGy/day in 2011 to 13 µGy/day in 2017. The assessment results comply with the ambient dose rate measured from 2011 to 2015. The assessment showed that the water content in the litter and topsoil layers significantly influence the formation of the dose rate. Via the model, we simulated the dose rates for 20% and 80% of the litter water content. The results showed that the average measured dose rates lie within the estimated results. Due to the lack of data on litter and soil moisture during sampling, now we are trying to calculate the ground layers’ water content using the available information on precipitation rate.

The results of long-term studies of the radiobiological effects in plants and animals inhabiting territories contaminated as a result of the Chernobyl accident are summarized.