Despite four decades since the Chоrnobyl disaster, stagnant water bodies in the Chornobyl Exclusion Zone (CEZ) remain highly contaminated with radionuclides. Moreover, ichthyofauna species are among the most radiation-sensitive components of freshwater biota. The leukocyte and erythrocyte fractions of the hematopoietic system were studied in four fish species from water bodies in the CEZ across a gradient of absorbed dose rate of radiation exposure ranging from 5.1 to 84.5 µGy/h. In control water bodies, the exposure doses did not exceed 0.07 µGy/h. A threshold level of dose rate was established, up to which an increase in the absolute number of leukocytes in the peripheral blood occurs, indicating the activation of compensatory processes in the fish organism. For roach (Rutilus rutilus), rudd (Scardinius erythrophthalmus), and Prussian carp (Carassius gibelio), this level was within 30-40 µGy/h, and for European perch (Perca fluviatilis), it was about 15 µGy/h of current exposure dose. Under the influence of a higher dose rate, the number of leukocytes in the fish blood decreased, and for some species, reached a level 12-18% lower than the control sample values, indicating an impairment of hematopoietic processes. Qualitative analysis of erythrocytes in the blood of CEZ fish revealed numerous structural cell disorders, as well as disorders associated with mitotic division pathology. The total number of morphological abnormalities in red blood cells at maximum dose rates exceeded the control indicators by 12.1 times for roach, 12.4 times for perch, 14.2 times for Prussian carp, and 38.3 times for common rudd. Among the erythrocyte abnormalities, cells with nuclear deformation, vacuolated cytoplasm, chromatinolysis, and cytolysis prevailed. It is assumed that the blood system of the studied species responds to long-term chronic irradiation by activating compensatory-adaptive processes, which are manifested by a change in the number of leukocytes and a redistribution of individual cell types in the leukogram. The radiation exposure, the effect of which exceeds the acceptable capabilities of the organism, causes a significant reduction in the absolute number of leukocytes, leading to a deterioration of the organism's immune status and, consequently, increasing the risk of helminthization, as well as bacterial and viral diseases in fish.

Chronic ionizing radiation causes elevated levels of DNA damage and reactive oxygen species in plants. Aquatic ecosystems in Chornobyl zone, a major radiological disaster site, are contaminated by harmful radionuclides. We focused on explaining the biochemical mechanisms responsible for the susceptibility of a wild aquatic plant (common reed, Phragmites australis) grown in Chornobyl zone to biotic stress. The fungal infection assay indicated that life in a radionuclide-contaminated environment might compromise plant immunity. Proteome profiling identified 1,867 proteins and we selected several dozen proteins with consistently higher and lower abundance in the samples from the littoral of contaminated lakes by hierarchical clustering. Discordant expression of coding genes pointed to posttranscriptional regulation. Proteins that accumulated in reed upon chronic irradiation suggested a biochemically stable phenotype with effective protection against reactive carbonyls. Simultaneously, proteins that depleted in plants collected from the littoral of radiologically contaminated lakes indicated worse stress resilience and enhanced susceptibility to biotic agents. Furthermore, the quantification of antioxidant enzyme activities and carbonylated proteins rebutted the idea about substantial oxidative stress in chronically irradiated plants. We advocate the necessity to consider increased pathogen sensitivity while developing policies for the management of radionuclide-contaminated areas.

The peculiarities of accumulation of artificial radionuclides by higher aquatic plants and fish of water bodies of the Chernobyl exclusion zone and the territories of the western and southern traces of the Chernobyl accident release were analyzed and compared. In 2020-2021, 90Sr activity concentration in higher aquatic plants of the cooling pond of the Chernobyl Nuclear Power Station, Lake Daleke, and the Yanivsky backwater accounted for 10-46 kBq/kg, 137Cs - 5.4-47.0 kBq/kg, whereas in the Azbuchyn, Vershyna, and Glyboke lakes - respectively 64-419 kBq/kg and 9.3-63.4 kBq/kg. The activity concentration of 90Sr in fish of the cooling pond of the Chernobyl NPS, Lake Daleke, and the Yanivsky backwater was 1.4-8.6 kBq/kg and 137Cs -2.3-3.2 kBq/kg, whereas in the Azbuchyn, Vershyna, and Glyboke lakes - respectively 21-213 kBq/kg and 4.2-6.2 kBq/kg. In 2020-2021 in many studied water bodies located outside the Chernobyl exclusion zone, the levels of 90Sr accumulation in helophytes did not differ reliably and accounted for about 10 Bq/kg. In helophytes of Lake Lisove, 90Sr activity concentration attained 181 Bq/kg. The maximum activity concentration of 137Cs in helophytes of the Kaniv Reservoir and the Irsha River was not more than 30 Bq/kg and in Lake Lisove it accounted for 16 920 Bq/kg, whereas in other water bodies located outside the Chernobyl exclusion zone - 65- 515 Bq/kg. The maximum activity concentration of 137Cs in hydatophytes of the Bile, Luky, and Lisove lakes accounted for respectively 639, 1066, and 6417 Bq/kg and in other water bodies it was not more than 150 Bq/kg. The activity concentration of 90Sr in fish organism of Lake Lisove attained 23 Bq/kg, whereas in other water bodies it was not more than 11.3 Bq/kg. The maximum activity concentration of 137Cs in fish of Lake Lisove and Lake Bile accounted for respectively 1400 and 314 Bq/kg, in the Povchanske and Kyiv reservoirs - 154 and 124 Bq/kg, whereas in other water bodies it was not more than 38 Bq/kg.

During the acute phase of the Chornobyl accident the biota of the contaminated area was exposed to high doses of ionising radiation. Although these doses decreased significantly over the years, the exposure persisted over a prolonged period. This long-term exposure can be considered as a direct cause of genetic modifications occurring in organisms, and the search for correlative changes in the state of biota under the impact of radioactive contamination is an extremely urgent task. The aquatic macrophyte Glyceria maxima is the most common coenosis-forming plant of the littoral vegetation of the floodplain water bodies in the Chornobyl Exclusion Zone, and is capable of concentrating radionuclides in significant quantities. In this study, we aim to determine whether long-term radiation exposure has affected organs of reproductive structure (flower, pollen, seed) and, consequently, the viability of local populations of this species. All the traits analysed showed an inverse relationship with the absorbed dose rate of the maternal plants. It was determined that with an increase in the absorbed dose rate, the pollen size decreases, and the range of individual grains in the sample begins to vary more: small, heterogeneous in shape and size pollen grains are formed. Additionally, a decrease in pollen grain size correlates with a decrease in the proportion of fertile pollen. Pollen grains viability (fertility) decreases by 20-40% with increasing radiation dose rate. The response of reproductive structures to radiation exposure is non-linear: already at low doses (>2 mu Gy/h), negative changes in functional and morphological traits are observed, while at higher doses (9-13 mu Gy/h), the changes slow down. It is assumed that the radiation exposure mainly affects the early reproductive stages (pollen grains and partially flowers), while the main nutrients in water, that determine the trophic status of the reservoir, affects the late stages (seeds).

The limits of the average value of the average annual external radiation dose rate of fishes from four lakes (with different degrees of radionuclide pollution of ichthyofauna representatives) of the Chornobyl Exclusion Zone as of 2021 are given, namely: Azbuchyn Lake (4 - 33 μGy/h), Vershyna Lake (3 - 26 μGy/h), Glyboke Lake (2 - 15 μGy/h) and Plyutovyshche Lake (0.02 - 0.16 μGy/h). Bottom-dwelling fish species such as tench and Prussian carp receive the highest external radiation dose, and rudd and surface fish species receive the lowest. It has been proven that the radionuclide 137Cs forms from 62.8 to 98.7 % of the absorbed dose of external irradiation of fishes from the studied water bodies. It is clearly shown that the current levels of the average annual absorbed external dose rate for many of the studied fishes of the lakes exceed the screening dose of 2 μGy/h and in 6 cases out of 22 exceed the safe level of 10 μGy/h recommended by the European Commission project “PROTECT”.

The 1986 Chornobyl Nuclear Power Plant accident caused radioactive contamination of water bodies within the Pripyat River floodplain, resulting in the accumulation of radionuclides by macrophytes, which are fundamental species in water ecosystems. Yellow water lily Nuphar lutea (L.) Smith., a macrophyte playing a significant role in the formation of vegetation cover in aquatic ecosystems, is commonly considered as a bioindicator of water pollution. In this study, we investigate the potential of N. lutea as an indicator of radionuclide contamination in water bodies, particularly through changes in its reproductive structures, such as pollen viability, morphology of pollen grains, seeds, and fruits. Our findings reveal that pollen viability remains stable at total absorbed dose rates below 14.4 mu Gy/h, with only 1-4% of sterile grains. However, beyond this threshold the percentage of sterile grains increases nearly fivefold, pointing to high internal plant exposure to 90Sr. A similar trend was observed in the allometry and size of pollen grains, where small and flattened grains are formed in the reservoir with the highest external radiation dose rate (>= 14.4 mu Gy/h). On the other hand, while morphometric parameters of fruits are influenced by radiation, their variation appears to be the result of a combination of physicochemical factors and the trophic status of a water body. Our research highlights the adverse impact of long-term radiation exposure on the male reproductive system of N. lutea and shows the potential of using the pollen grains sterility as an indicators of heavily radionuclide-contaminated water bodies. Additionally, we observed gradual changes in a pollen allometric length-to-width coefficient as the radiation dose level increases.

The structural indices of the communities of benthic and phytophilous invertebrates were studied in water bodies differing in the levels of external radiation dose rate within the Chornobyl exclusion zone. The macrofauna of invertebrates of all studied water bodies was characterized by low species richness, numbers, and biomass. The obtained results suggest that the benthic and phytophilous invertebrate fauna of the cooling pond of the Chornobyl Nuclear Power Plant differs in its structure from the fauna of other water bodies of the Chornobyl exclusion zone more significantly than these water bodies differ from each other in terms of dose load levels on the biota. We consider the main reason for these differences to be the succession processes in the ecosystem caused by the transformation of the cooling pond of the Chornobyl Nuclear Power Plant. There is no reason to claim that the influence of external ionizing radiation determines the change in the structural indices of the communities of benthic and phytophilous invertebrates in water bodies of the Chornobyl exclusion zone.

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

The paper deals with analysis of hematological parameters of the common rudd (Scardinius erythrophthalmus L.) and Prussian carp (Carassius gibelio Bloch) from the most radionuclide-contaminated water bodies of the Chernobyl Exclusion Zone. Data on absolute and relative leukocyte composition and morphological disorders of erythrocytes in peripheral blood were obtained. The leukocyte fraction of both fish species similarly responded to the absorbed dose rate. In the doses' range of 5.1-54.1 μGy/h, reactive changes of the compensatory nature were recorded with increase of the leukocytes content at the expense of lymphocyte and granulocyte fractions. Under the higher doses (up to 84.5 μGy/h), hematopoiesis was damaged with sharp decrease of the leukocytes' content and significant changes in leukograms, which was also confirmed by the hematological indices' values. The morphological disorders in erythrocytes increased along with absorbed dose rate.

This study deals with an assessment of radiation dose dynamics to fish and higher aquatic plants (helophytes) in Glyboke Lake (10-km exclusion zone) during the early phase of the Chernobyl accident. Models of radioactive contamination of water and sediment and models of radioactive contamination and radiation dose to fish and aquatic plants were developed. It was found that, in 1986, the total dose rate to fish reached 0.25 Gy d-1. Within 6 months after the accident, the dose rate due to 90Sr, 134Cs and 137Cs had increased. The absorbed dose to prey fish of Glyboke Lake for this period was estimated as being 27???81 Gy of which 4???40 Gy was formed by 131I exposure. The radiation dose rate due to 90Sr, 106Ru, 134+137Cs and 144Ce to aquatic plants reached its quasiequilibrium values approximately 50 days after the accident and remained virtually unchanged until the end of the 1986 growing season. The highest levels of 89Sr, 91Y, 95Zr, 103Ru, 141Ce exposure were observed between 30 and 50 days with a decrease by 2???3 times at the end of the growing season. Radiation exposure of the shortlived 131I, 140Ba, 140La, 239Np reached its maximum within 5???15 days after the accident. The absorbed dose rate to aquatic plants reached 0.69 Gy d-1, while the contribution of cerium radionuclides to the total dose rate formed 50% in the initial period and reached 90% at the end of the growing season. The magnitude of the radiation dose rate to plant roots was 2.4 times higher than aboveground organs, and that of rhizomes was 1.6 times higher. During the growing season of 1986 the total dose of exposure of plants in Glyboke Lake was about 78 Gy. The results of this study emphasise the necessity to consider the history of exposure of past generation of living organisms as part of the assessment of current radiation effects.

The study is based on long-term observations (1998-2021) over the species richness and cenotic activity of macrophytes of floodplain water bodies of the Chornobyl exclusion zone. During this period, the species composition of macrophytes of the studied water bodies remained almost unchanged. The lists of species found in 1998 differ from those registered in 2021 only by three species, including Nymphaea alba, Trapa natans (registered only since 2007), and Utricularia minor (found only in 1998, whereas in subsequent years was not observed at all). In the studied water bodies, macrophytes are not diverse in their species composition; their cenotic structure is simple, whereas overgrowing intensity of water surface is high. The presence of rare species of the boreal complex, including primarily Hottonia palustris, Potamogeton acutifolius, and Callitriche cophocarpa, makes these water bodies objects of protection and research. In 1998, a common feature of the vegetation cover of all studied floodplain water bodies was a predominance of macrophyte communities, in which the species of river and lake ecosystems, as well as indicator species of increased water logging processes, were registered. At the present time, natural structure of macrophyte communities of floodplain water bodies of the Prypyat River, which was deteriorated as a result of the construction of flood-protection hydraulic structures, is gradually recovered. The peculiarities of the distribution of macrophytes at the present time are indicative of the improvement of water exchange in floodplain water bodies. The chronic ionizing radiation influencing the biota of the studied water bodies for more than 30 years did not result in significant changes in the floristic and cenotic composition of macrophytes. Certain changes are conditioned by changes in hydrological and hydrochemical regime of the floodplain of the Prypyat River.

During the accident in April 1986, the Cooling Pond (CP) of the Chornobyl Nuclear Power Plant (ChNPP) was heavily contaminated by fuel particles and radionuclides of cesium-137 (137Cs) and strontium-90 (90Sr). Starting from the end of 2014, a gradual decrease of the CP water level began leading to the transformation of the whole reservoir into eight separate sectors and raising the concern of the fate of 137Cs and 90Sr in the future. In this study, two mathematical models were applied to reproduce radioactive contamination of the CP from 1986 to 2021 and to provide a forecast of 137Cs and 90Sr concentrations in the CP water from 2022 to 2030. The hydrodynamic model THREETOX provided three-dimensional (3D) currents in the CP corresponding to hydrological conditions before and after water level drawdown, and these currents were used in the box model POSEIDON-F for the long-term simulations of the changes in 137Cs and 90Sr concentrations in water, bottom sediments, and biota. Seasonal changes in the distribution coefficient (Kd) describing the partition of 137Cs between water and sediments were considered in the box model, which allowed us to reproduce the observed variations of concentration. Calculated concentrations of 137Cs and 90Sr in water and freshwater fish occupying different trophic levels agreed well with measurements for the entire post-accident period. After the water level drawdown, concentrations of 137Cs in the CP water slightly increased in all eight sectors, while 90Sr concentrations significantly increased in sectors close to ChNPP, which was explained by an additional 90Sr source when comparing the simulation results and measurement data. Using the model forecast from 2022 to 2030, we predict that the concentration of both radionuclides will gradually decrease in new water bodies of the Cooling Pond except in the northern sectors, where the suggested additional source of 90Sr will lead to a stabilization of 90Sr concentrations.

Skeletal abnormalities in juveniles of common roach ( Rutilus rutilus ) and common rudd ( Scardinius erythrophthalmus ) from the cooling pond of the Chornobyl NPP were studied. We observed abnormalities and structural disorders of the caudal and abdominal segments. Abnormalities such as additional processes of neural and haemal spines, partial or total vertebral fusions, deformation of the last vertebra of the caudal section, deformation of spine and deformation of the ribs were found. Abnormalities in the common roach also included significant curvatures of the ribs. Quantitatively, both populations showed significant numbers of rib deformations (Pidbirna Lake, control water body—93%; Chornobyl NPP cooling pond—95% of the total individuals), but qualitatively, the deformations of the ribs in fish from the Chornobyl NPP cooling pond were much more pronounced. We found 13 types of abnormalities localized in two main parts of the skeleton. It was determined that the number of observed abnormalities depended on the level of radioactive contamination of water bodies and absorbed dose rate for fish. The individual spectrum of abnormalities for the control populations did not exceed five abnormalities per individual, while in the Chornobyl NPP cooling pond populations, up to 29 abnormalities per individual were observed with some individuals showing multiple vertebral abnormalities. Overall, these findings suggest very strong effects of radioactive contaminants on fish growth and development.

Changes in the absorbed dose rate of external and internal exposure of the representatives of fish fauna of the cooling pond of the Chornobyl NPS and Lake Azbuchyn after the interruption of water supply into the cooling pond at the end of 2014 were investigated in 2014-2021. Changes in hydrological regime resulted in the decrease in water level in the cooling pond by 6.5-7.0 m, whereas in Lake Azbuchyn - by 2.5-3.0 m. In this case, 90Sr concentration activity in the water and biota increased. It has been found that in 2021 dose load from the incorporated 90Sr on fish of the cooling pond increased on the average by a factor of 4.5, whereas in Lake Azbuchyn - by a factor of 7.5 as compared to previous period (prior to a decrease in water level). The external dose rate for fish of the cooling pond remained almost unchanged, whereas in Lake Azbuchyn it increased as a result of replacing littoral and sub-littoral zones of the lake with the sections of the bottom characterized by an essentially higher level of radio-nuclide contamination.

I arrived on May 28 th by train in Gatersleben

Monitoring and characterizing species biodiversity is essential for germplasm preservation, academic studies, and various practical applications. Duckweeds represent a group of tiny aquatic plants that include 36 species divided into 5 genera within the Lemnaceae family. They are an important part of aquatic ecosystems worldwide, often covering large portions of the water reservoirs they inhabit, and have many potential applications, including in bioremediation, biofuels, and biomanufacturing. Here, we evaluated the biodiversity of duckweeds in Ukraine and Eastern China by characterizing specimens using the two-barcode protocol with the chloroplast atpH–atpF and psbK–psbI spacer sequences. In total, 69 Chinese and Ukrainian duckweed specimens were sequenced. The sequences were compared against sequences in the NCBI database using BLAST. We identified six species from China (Spirodela polyrhiza, Landoltia punctata, Lemna aequinoctialis, Lemna minor, Lemna turionifera, and Wolffia globosa) and six from Ukraine (S. polyrhiza, Lemna gibba, Lemna minor, Lemna trisulca, Lemna turionifera, and Wolffia arrhiza). The most common duckweed species in the samples from Ukraine were Le. minor and S. polyrhiza, accounting for 17 and 15 out of 40 specimens, respectively. The most common duckweed species in the samples from China was S. polyrhiza, accounting for 15 out of 29 specimens. La. punctata and Le. aequinoctialis were also common in China, accounting for five and four specimens, respectively. According to both atpH–atpF and psbK–psbI barcode analyses, the species identified as Le. aequinoctialis does not form a uniform taxon similar to other duckweed species, and therefore the phylogenetic status of this species requires further clarification. By monitoring duckweeds using chloroplast DNA sequencing, we not only precisely identified local species and ecotypes, but also provided background for further exploration of native varieties with diverse genetic backgrounds. These data could be useful for future conservation, breeding, and biotechnological applications.

The chemical and radiation stability of titanium dioxide with surface arsenate groups during 90Sr adsorption has been studied. The oxalate technique has been used to obtain a solution containing 90Sr from the objects of the aquatic environment of the Chornobyl Exclusion Zone. The dependence of the strontium adsorption on the acidity of the solution and the initial activity of the solution (Bq per mL) has been shown. SEM, XRF, and EDS spectroscopy confirm the chemical resistance of 4As-TiO2 during regeneration. According to the study with 90Sr, the decrease in the adsorption capacity of 4As-TiO2 during regeneration is associated with incomplete leaching of strontium from 4As-TiO2 micropores.Using an electron accelerator, the radiation resistance of titanium dioxide with surface arsenate groups to beta--particles with an energy of 1 MeV has been studied. The invariability of the elemental composition and adsorption properties of 4As-TiO2 at irradiation doses of 5.107Sv testifies to the high radiation resistance of 4As-TiO2. The result obtained indicates the promise of 4As-TiO2 for improving radiochemical methods.

The levels of specific activity of 90Sr and 137Cs in fish of one of the most polluted reservoirs of the Chornobyl Exclusion Zone (ChEZ) - Vershyna Lake. During the research period from 2011 to 2021 for all studied fish of the lake. The peak ranges of the specific activity of radionuclides are noted at the level of 32960-213300 (average value 67832-22936) Bq/kg for 90Sr and 838-25907 (4811-569) Bq/kg for 137Cs. It is shown that at the current stage, the specific activity of 90Sr in the ichthyofauna of the lake exceeds the permissible levels, which are accepted in Ukraine for fish products in more than 942-6094, and 137Cs - in 6-173 times. The 90Sr/137Cs ratio in lake fish is in the range of 3-108. The distribution of radionuclides in the organs and tissues of silver crucian carp is given. Estimated dose rate of fish irradiation of the Vershyna Lake. As shown by the results of studies of the ichthyofauna of Vershyna Lake , the maximum average dose rate irradiation was noted in representatives of bentophagous Prussian carp (149,5-12,1 ?Gy/h), the minimum - in the pelagic Sunbleak (56,2-5,1 ?Gy/h). It was noted, that 90Sr is the dominant radionuclide in the formation of the total radiation dose of fish from Vershyna Lake (in contrast to all other investigated reservoirs of the ChEZ).

There are two partially linked risks to the Kyiv city associated with the Dnieper river: (A) risk of the inundation of the urban coastal areas during the extremely high floods or due to the break of the Hydropower Plant dam located upstream Kyiv, and, (B) risk of the secondary radioactive contamination of the Dnieper waters due to the intensification of the dynamics of "Chornobyl" radionuclides during high floods and man-made impacts - dredging in Kyiv Reservoirs for navigation routes and other purposes. The Chornobyl Nuclear Power Plant has located 130 km from Kyiv at the bank of Pripyat river, which is 20 km downstream from ChNPP inflows into the Kyiv reservoir of the Dnieper River. After the Chornobyl accident, about 5.4×1013 Bq of 137Cs and 1013 Bq of 90Sr were deposited in the bottom sediments of the Kyiv Reservoir. Nowadays, 35 years after the Chornobyl accident, the population of Kyiv still is very sensitive to the risks of secondary environmental contaminations by the “Chornobyl radionuclides”. Therefore even low levels of such risks should be carefully assessed by well-grounded methods. The main goals of our multidisciplinary study are: * to develop a model/data based Decision Support System (DSS) for the assessment of both kind of the described above risks A) and B), * to analyze the influence of the natural hazard – extremely high river floods on the resuspension of contaminated sediments and environmental risks due to the man-made impacts – dredging, dam breaks, and others. The components of these research and development activities are following: * field and laboratory studies of the contemporary contamination of the bottom sediments and biota in the Kyiv reservoir to receive the input data for the model calibration and improvement of the model structure; * customization for the Kyiv Reservoir and the Dnieper river at Kyiv of the 2D COASTOX model which the hydrodynamic module is based on the nonlinear shallow water equations, and the sediment/radionuclide transport model using the advection-diffusion equations with specific sink/source terms for radionuclides; * customization for the Kyiv Reservoir of the hydro-ecological POSEIDON model that simulates the influence of resuspension of radioactive sediments on the contamination of fishes and other hydrobionts; * improvement of methods for the numerical solution of model equations and algorithms based on finite volume methods for their parallelization using multiprocessor systems and graphics cards to speed up computations; * to create high-performance DSS with a user-friendly interface that can use GPUs to quickly predict the radiation status of surface waters and inundation of river banks in emergencies. The DSS is installed in the Department of Hydrological Forecasting of the Ukrainian Hydrometeorological Center and is used for the quantification of the risk scenarios and analyses of the links of both risks. Due to the high computational performance, the DSS can be used for the real-time numerical predictions with the zoning of the flood risks in a case of emergency.

The results of the assessment of levels of radionuclide contamination of fish during 2013 - 2019 in the reservoirs of the Chornobyl Exclusion Zone (lakes Azbuchyn, Vershyna, Hlyboke, Daleke, Yanivsky Backwater, Chornobyl NPP cooling pond) are presented. It was found that the concentration of 137Cs in representatives of ichthyofauna of water bodies during the study period continued to decrease, while the concentration of 90Sr, with some exceptions, remained unchanged or increased. The concentration of radionuclides in fish of the studied reservoirs was about 60 - 5000 times for 90Sr and in 3 - 200 times for 137Cs higher than the permissible levels for fish products accepted in Ukraine.