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Throughout 2016 - 2021, a series of experimental studies on 137Cs uptake and excretion rate constants for the silver Prussian carp (Carassius gibelio) were conducted in the Chornobyl exclusion zone (ChEZ) under natural conditions. To confirm the metabolic parameters of 137Cs in the silver Prussian carp under strictly controlled conditions at different feed amounts real supporting laboratory experiments have been conducted. The excretion rate of the 137Cs from the silver Prussian carp increased with increasing feed amount from 0.0068 ± 0.0003 day−1 to 0.0085 ± 0.0005 day−1 at water temperatures of 26 °C. The biological half-life of 137Cs activity concentration in fish can be reduced by 2 times by increasing fish growth using clean feeding. The excretion rate of the 137Cs from the silver Prussian carp agreed with data collected in natural conditions in the ChEZ during 2016 - 2020 at different water temperatures. [ABSTRACT FROM AUTHOR]

During 2012 - 2014 sampling of soil and grain in Ivankiv district of Kyiv region at all fields adjacent to the ChNPP exclusion zone was carried out, where the cereal crops were planted. In all samples 137Cs and 90Sr activities were measured. Besides, in soil samples the exchangeable fractions of 90Sr and calcium and acidity of soil solution were determined. Dependence of 90Sr soil-grain transfer factors was specified. In conducting research works by sampling occurred 74.14-37-425:2006 SOU, SOU SOU 74.14-37-424:2006 and 01.1-37-426:2006. The activity of 90Sr was determined by standard radiochemical method. [ABSTRACT FROM AUTHOR]

Results of the study of 90Sr and 137Cs migration mobility in soils characterized with contrasting physical-chemical properties and granulometric composition has been analyzed. The mentioned radionuclides were introduced in soils in initial water-soluble form. Ecological and effective half-time of cleaning of soils 20-cm horizons (Tecol) has estimated. Mean values of Tecol 90Sr varies in limits 3.7 - 84 years. Tecol 137Cs varies in limits 61 - 265 years. Correlation of ecological half-time cleaning of soddy-podsolic soils species from radionuclide and physical-chemical properties and granulometric composition of these ones has been analyzed, strong correlation of Tecol 90Sr as well, as mean correlation of Tecol 137Cs with mentioned soils characteristics has been noted. [ABSTRACT FROM AUTHOR]

In the year 2011 sampling of soil and grain in Ivankiv district of Kyiv region at all fields adjacent to the ChNPP exclusion zone was carried out, where the cereal crops were planted. In all samples 137Cs and 90Sr activities were measured. Besides, in the soil samples the exchangeable fractions of 90Sr and calcium and acidity of the soil solution were determined. Dependence of 90Sr soil-grain transfer factors was specified. [ABSTRACT FROM AUTHOR]

Weathering of fuel particles and the subsequent leaching of radionuclides causes 90Sr mobility in Chernobyl soils to increase with time after deposition. Studies of 90Sr speciation in soils collected in 1995 and 1996 from the Chernobyl 30-km exclusion zone have been used to calculate rates of fuel particles dissolution under natural environmental conditions. Results show that the velocityof fuel particle dissolution is primarily dependent on the physico-chemical characteristics of the particles and partially dependent on soil acidity. Compared to other areas, the fuel particle dissolution rate is significantly lower in the contaminated areas to the west of the Chernobyl reactor where deposited particles were presumably not oxidized prior to release. The data have been used to derive mathematical models that describe the rate of radionuclide leaching from fuel particles in the exclusion zone and changes in soil-to-plant transfer as a function of particle type and soil pH." [ABSTRACT FROM AUTHOR]

The impact of certain types of microorganisms on 137Cs transfer from the substrate into the plant was analyzed in the experiment on artificial mediums. It was found that certain types of microorganisms could either reduce or increase the ratio of 137Cs transfer from the substrate to the plant. It is shown that this property is independent of the localization of the microorganism on the surface of the root, for all the analyzed bacteria belonging to the rhizospheric group. Azotobacter chroococcum UKM B-6003 stimulated the radionuclide transfer to plants up to 1.5 times, while the best bacteria for reducing its accumulation is Burkholderia sp IMER-B1 -53 - 1.3 times in comparison with the control. It was shown that the strain Bacillus megaterium UKM B-5724 from the collection of the Institute of Microbiology and Virology of NASU has a high ability to accumulate radionuclides.

The specific activity of 90Sr in milk and vegetables for the last 15 years does not exceed the permissible level in Ukraine outside the Chernobyl exclusion zone. Exceeding the acceptable level of 90Sr is registered only in food grain. Specific activity of 90Sr in grain, which is produced in the high contaminated areas of the Kiev region, nowadays may reach 60-70 Bq/kg, which exceeds the permissible level of 20 Bq/kg for bread-grain. The part of 90Sr activity in the biologically available form has reached its maximum values for the post-accidental period due to the fuel particle dissolution. Contamination of grain with this radionuclide has slowly decreased in recent years. Values of concentration ratios and aggregated transfer factors of 90Sr from soil to rye, oat and winter wheat grain are inversely proportional to the exchangeable calcium content in soil. The transfer factors and dependences are in good accordance with those that have been obtained in our previous works and with generalized data of the IAEA for sandy soils. Application in Ukraine of such countermeasures as liming, fertilizing and manuring makes it possible nowadays to produce grain that meets the requirements of hygienic regulations on the 90Sr content in bread-grain.

The quantitative "dose rate-effect" dependences are presented for the cytogenetic damages in the seedlings and apical meristem of Scots pine growing in the Chernobyl zone. The specific patterns of dynamics of formation of the morphological effects in the studied species are considered for the conditions of the internal and external chronic irradiation. The correlation dependencies are established for the irradiation effects appearing at the morphological and cell level. The assumption concerning the mechanism of the morphological changes formation is done.

Controlled burning of experimental plots of forest or grassland in the Chernobyl exclusion zone has been carried out in order to estimate the parameters of radionuclide resuspension, transport and deposition during forest and grassland fires and to evaluate the working conditions of firemen. An increase of several orders of magnitude of the airborne radionuclide concentration was observed in the territory near the fire area. The resuspension factor for (137)Cs and (90)Sr was determined to range from 10(-6) to 10(-5) m(-1), and for the plutonium radionuclides from 10(-7) to 10(-6) m(-1) (related to the nuclides in the combustible biomass). These values are 2 orders of magnitude lower if they are calculated relatively to the total contamination density (including the nuclides in the soil). The radionuclide fallout along the plume axis is negligible in comparison to the existing contamination. However, the additional inhalation dose for firemen exposed in the affected area can reach the level of the additional external irradiation in the period of their mission. The plutonium nuclides constitute the dominating contribution to the inhalation dose.

To predict parameters of radionuclide resuspension, transport and deposition during forest and grassland fires, several model modules were developed and adapted. Experimental data of controlled burning of prepared experimental plots in the Chernobyl exclusion zone have been used to evaluate the prognostic power of the models. The predicted trajectories and elevations of the plume match with those visually observed during the fire experiments in the grassland and forest sites. Experimentally determined parameters could be successfully used for the calculation of the initial plume parameters which provide the tools for the description of various fire scenarios and enable prognostic calculations. In summary, the model predicts a release of some per thousand from the radionuclide inventory of the fuel material by the grassland fires. During the forest fire, up to 4% of (137)Cs and (90)Sr and up to 1% of the Pu isotopes can be released from the forest litter according to the model calculations. However, these results depend on the parameters of the fire events. In general, the modeling results are in good accordance with the experimental data. Therefore, the considered models were successfully validated and can be recommended for the assessment of the resuspension and redistribution of radionuclides during grassland and forest fires in contaminated territories.

The data obtained through a series of experiments were used to specify the correlation of activities of the fuel component radionuclides of Chernobyl fallout and to create the maps of the 30-km Chernobyl zone terrestrial density of contamination with 154Eu, 238Pu, 239+240Pu and 241Am (on 01.01.2000). In the year 2000, total inventories of the fuel component radionuclides in the upper 30-cm soil layer of the 30-km Chernobyl zone in Ukraine (outside the ChNPP industrial site, excluding the activity located in the radioactive waste storages and in the cooling pond) were estimated as: 90Sr--7.7 x 10(14) Bq; 137Cs--2.8 x 10(15) Bq; 154Eu--1.4 x 10(13) Bq; 238Pu--7.2 x 10(12) Bq; 239+240Pu--1.5 x 10(13) Bq; 241Am--1.8 x 10(13) Bq. These values correspond to 0.4-0.5% of their amounts in the ChNPP unit 4 at the moment of the accident. The current estimate is 3 times lower than the previous widely-cited estimates. Inventories of the fuel component radionuclides were also estimated in other objects within the 30-km zone and outside it. This allowed more accurate data to be obtained on the magnitude of a relative release of radionuclides in the fuel particles (FP) matrix during the Chernobyl accident outside the ChNPP industrial site. It amounts to 1.5+/-0.5% of these radionuclides in the reactor, which is 2 times lower than the previous estimates. Two-thirds of the radionuclides release in the FP was deposited on the territory of Ukraine.

Retransfer of radionuclides on the condensation trails of Chernobyl radioactive fallouts during forest fires has been experimentally evaluated and their mathematical transfer model verified. It has been shown that radionuclide retransfer will make no great impact on additional pollution of an area even under the most unfavourable conditions. The contribution of convective and non-convective components of transfer to the formation of a radioactive aerosol concentration field has been assessed. Time course of changes in the concentration of radioactive aerosol and its dispersive composition are shown in different phases of fire and at different distance from its source.

Representative large-scale soil sampling on a regular grid of step width about 1 km was carried out for the first time in the near zone of the Chernobyl accident (radius 36 km). An integrated map of terrestrial 90Sr contamination density in the 30 km exclusion zone (scale 1:200,000) has been created from the analysed samples. Maps of the main agrochemical characteristics of the soils, which determine the fuel particle dissolution rates and the contamination of vegetation, were produced. The total contents of 90Sr on the ground surface of the 30 km zone in Ukraine (without the reactor site and the radioactive waste storages) was about 810 TBq (8.1 x 10(+14) Bq) in 1997, which corresponds to 0.4-0.5% of the Chernobyl reactor inventory at the time of the accident. This assessment is 3-4 times lower than previous estimates.

The two-component convective-diffusional model was used for determination of vertical migration parameters of 90Sr [correction of 90Cs] and 137Cs in meadow ecosystems and dependence from meadow type and soil properties was shown. The migration coefficients decrease in the order: peat land, lowland meadows, flood-plain meadows, dry meadows. The ecological half-life in the root zone ranges from 55 to 143 y for dry meadows and from 15 to 21 y for peat lands. Analogous parameters for 90Sr was 30-96 and 13-18 y, respectively. Since 1987 to 1994 the ecological half-life of 137Cs increased by a factor of 1.7-6.0.