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).

During 1998-2014 the rate of chromosomal aberrations in embryo tissues of the pond snail (Lymnaea stagnalis) and root meristems of higher aquatic plants, and also hematologic indexes of mantle liquid of the adult snails and peripheral blood of fishes in water bodies within the Chernobyl exclusion zone (EZ) was studied. The absorbed dose rate for hydrobionts from water bodies of the EZ registered in a range from 0.25 to 420 mu Gy h(-1) and in the reference ones - up to 0.09 mu Gy h(-1). The level of chromosomal aberrations in the molluscs from the most contaminated water bodies of the EZ was registered within range of 18-27% and for the molluscs from the reference lakes this index was on the average 1.5% with the maximal values 23%. The rate of chromosomal aberrations in root meristematic cells of higher aquatic plants from the contaminated lakes of the EZ was in range of 7-17% and in the plants from reference water bodies was not exceed 2.1%. The positive correlation between chromosomal aberration rate and absorbed dose rate in the pond snail's embryos and root meristems of higher aquatic plants in water bodies of the EZ was registered. Analysis of hemolymph structure of snails from the most contaminated water bodies showed a high rate of dead and phagocytic cells as well as decrease of the young amoebocytes quantity. Hematologic research of fish allows to determine on the one hand an insignificant changes of leukogram structure, and from the other hand a high level of red cells with different abnormalities in the peripheral blood of fishes from the water bodies with high levels of radioactive contamination. It is suppose that qualitative indexes of red cells in peripheral blood of fish are more sensitive to long-term radiation impact in comparison with elements of white blood, which can be used for conducting of the hematologic monitoring of radioactive contaminated water bodies. (C) 2015 Elsevier Ltd. All rights reserved.

The dynamics of the main contaminating radionuclides in the components of aquatic ecosystems within the Chernobyl APP exclusion zone is considered. The possible causes are analyzed for the marked increase in the specific activity of 90Sr in water and hydrobionts of the lakes at the dammed left bank of river Pripyat. Notable is the elevated frequency of chromosomal aberrations in the root meristems of aquatic higher plants (up to 17%) and in the embryonal tissues of gastropod mollusks (up to 27%), alterations in the hematological indices for gastropods, and high infestation of aquatic higher plants by parasitic fungi and gall arthropods in the most radiocontaminated reservoirs.

Presented studies were carried out during 1997–2007 within Krasnensky flood-lands on the left bank of the Pripyat River, which is the most contaminated region of the Chernobyl accident exclusion zone and where the complex of hydraulic engineering structures as flood protection dams was constructed, which preventing washing away of radioactive substances from soils and changing a hydrological mode of floodplain flows during a high water. In its turn it was by the reason of strengthening of over-moistening and swamping processes within embankment territories. As a result – on a background of the common tendencies of increase of the mobile forms of 90Sr in soils of catchment territories and bottom sediments of the exclusion zone, there is an increase of humic acids concentrations in waterlogged soils of Krasnensky flood-lands. It is also raises the content of the water-soluble forms of 90Sr forming with acids the soluble complexes. Thus the increase of concentrations of the mobile radionuclide forms and their inclusion into biotic circulation of aquatic ecosystems is observed. Such dynamics of 90Sr and 137Cs contents is significantly reflected on dose rate for hydrobionts due to incorporated radionuclides.

The review presents results of original in situ investigations of the transformation of physical and chemical forms of radionuclide contaminations, their transfer, distribution and migration in aquatic ecosystems. The radiation doses and disturbances caused by them in aquatic organisms under conditions of intense radioactive contamination are considered. The efficiency of water-protective hydroengineering measures and natural deactivation processes in aquatic ecosystems are estimated.

The distribution of 90Sr, 137Cs, 238Pu, 239+240Pu, and 241Am in the main components of the lakes of the Krasnenskaya floodplain of the Pripyat river, including Lake Glubokoye and Lake Dalekoye-1 located within the exclusion zone of the Chernobyl NPS, was investigated in 1998-2003. Data on the content of radionuclides in the water, bottom sediments, seston, macrozoobenthos (including Bivalvia), Gastropoda, higher aquatic plants, and fishes are presented.

A degree of radioactive contamination of the water was assessed in the water bodies of the exclusion zone of the Chernobyl NPS. They included Lake Glubokoye, Lake Dalekoye, the Krasnenskaya old riverbed of the Pripyat river, the cooling pond of the Chernobyl NPS, and the Pripyat river within the town of Chernobyl. Dynamics of 90Sr and 137Cs content in the water of the above mentioned water bodies were determined in 1989−2003.

Authors propose for the discussion the results of ten year long studies on changes in concentrations of Cs radionuclides and Sr-90 in components of the Dnieper water reservoirs (water reservoirs of the Dnieper cascade is more than 1000 km long), Prypyat' river (chernobyl'), plain water bodies of the Chernobyl NPP (ChNPP) 30-km exclusion zone. The materials include dynamics on caesium radionuclides and Sr-90 contents in water, suspensions and water plants. Interrelations between water-soluble forms of caesium radionuclides and Sr-90 and their suspensions-adsorbed ones are discussed.