Uptake of technetium-99 by food crops under field conditions.

Long-term field experiments have been carried out in the Chornobyl Exclusion zone to determine parameters describing technetium (99Tc) transfer into five food plants (Lettuce, Radish, Wheat, Bean, and Potato) from four types of soil, namely Podzoluvisol, Greyzem, Phaeozem, and Chernozem. Technetium was added to the soils under field conditions in a pertechnetate form. In the first two years, soil type had little effect on Tc uptake by plants. In the first and second years after contamination, the concentration ratios (CR), defined as 99Tc activity concentration in the crop (dry weight) divided by that in the soil (dry weight), for radish roots and lettuce leaves ranged from 60 to 210. For potato tubers, the CR was d 0.4-2.3, i.e., two orders of magnitude lower than for radish and lettuce, and for summer wheat grain it was lower at 0.6 ± 0.1. After 8-9 years, root uptake of 99Tc by wheat decreased by 3-7 fold (CR from 0.016 ± 0.005 to 0.12 ± 0.034) and only 13-22 % of the total 99Tc added remained in the upper 20 cm soil layers. The time taken for half of the added 99Tc to be removed from the 20-cm arable soil layer due to vertical migration and transfer to plants was short at c. 2-3 years.

Long-term changes in 90Sr pools of Scots pine biomass in the Chornobyl Red Forest.

The trenches of the waste burial site in the Chornobyl Red Forest represent a big reservoir of radionuclides for the artificial plantation of Scots pine established in that area, but the long term dynamics of tree biomass contamination, especially with 90Sr, remains unclear. The present study was conducted between 2005 and 2018 on two groups of trees of the same age. The IN group is represented by trees growing on the trench containing highly radioactive contaminated fertile soil and organic matter, while the OUT group is located outside the trench. Within a little more than one decade, the total aboveground biomass doubled in the trees of the group OUT and increased more than four times in the group IN. In the group OUT, the concentrations of 90Sr have decreased in all biomass compartments compared to 2005, while in the group IN, the concentrations demonstrated a trend to increase. Regression analysis shows that both decrease in the compartment concentrations in the group OUT (slope coefficient 0.55) and increase in the group IN (1.58) were significant. As a result of the changes in the biomass inventories and 90Sr concentrations, in absence of changes in plantation density, the contamination of total aboveground biomass by 90Sr in the group OUT would have increased slightly in 2018 (from approximately 18 GBq ha-1 to 23 GBq ha-1) compared to 2005, while in the group IN it would have increased almost 6-fold, reaching approximately 560 GBq ha-1, or about (19 ± 9) % of the total 90Sr inventory in the trench area. Trenches of the Red Forest were shown to act as long-lasting hot spots of 90Sr bioavailability for forest trees.

Uptake from water and depuration of 137Cs and 90Sr by silver Prussian carp (Carassius gibelio).

To follow up field observations in the Chornobyl Exclusion Zone (ChEZ), a series of controlled model aquarium experiments were conducted to determine the uptake and depuration rates of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) in fresh water, varying in temperature from 5 to 27 °C, with daily feeding rates of 0-1.5 % fish weight day-1. In the present study, the 137Cs uptake rates in muscle tissues directly from water, 0.05-0.09 day-1 at temperatures of 5-27 °C, were significantly lower than previously reported for fish fed under natural conditions in contaminated lakes within the ChEZ. The rate of 90Sr uptake in bone tissues of silver Prussian carp varied from 0.055 day-1 at a water temperature of 5 °C and feeding rates ≤0.15 % fish weight day-1 to 1.5 ± 0.2 day-1 at a temperature of 27 ± 1 °Ð¡ and at the highest tested feeding rate of 1.5 % day-1. The rate of decrease of 137Cs concentration in muscle tissues was kb = 0.0028 ± 0.0004 day-1 (T1/2 = 248 ± 35 days) at the lowest water temperature tested (5 °Ð¡). At water temperatures between 13 and 26 °Ð¡ and a feeding rate of 0.15 % day-1, the rate increased to kb = 0.0071-0.0092 day-1 (T1/2 = 75-99 days). The rates of decrease of 90Sr activity concentration in bone tissues at water temperatures between 22 and 25 °Ð¡ and a feeding rate of 0.5 % day-1 were kb=0.004-0.0014 day-1, and the associated biological half-life T1/2 ranged 50-160 days, respectively. The present work supported conclusions related to the main pathways of 137Cs and 90Sr uptake by silver Prussian carp, and demonstrated the usefulness of combining field and laboratory uptake and depuration experiments.

Assessment of exposures to firefighters from wildfires in heavily contaminated areas of the Chornobyl Exclusion Zone.

The aim of this study was to assess the exposures received by firefighters engaged in extinguishing the large-scale wildfires in the most contaminated areas of the Ukrainian part of the Chornobyl Exclusion Zone in 2016 and 2020. The assessments are based on measurements of radionuclide airborne concentrations in the breathing zones of workers and at the aerosol sampling stations of the automated radiation monitoring system operated by SSE Ecocenter. During the wildfires, the radionuclide airborne concentrations increased by orders of magnitude compared to the background levels, reaching maximum values in the firefighting area of 1.20 ± 0.01 Bq m-3 for 90Sr, 0.18 ± 0.01 Bq m-3 for 137Cs, (1.8 ± 0.3) ∙10-4 Bq m-3 for 238Pu, (4.5 ± 0.7) ∙10-4 Bq m-3 for 239-240Pu, and (8.0 ± 1.3) ∙10-3 Bq m-3 for 241Pu. The internal effective doses to firefighters due to inhaled radionuclides did not exceed 2 µSv h-1 and were 3-5 times lower compared to the external dose of gamma radiation. Thus, the time of firefighting in the ChEZ will be limited by the external dose.

Dependency of radioiodine root uptake by crops on soil characteristics.

The aim of this study was to quantify the parameters of root uptake of radioiodine by agricultural crops under steady state conditions depending on the main soil characteristics. For this purpose, a long-term (483-days) pot experiment was conducted under natural conditions in the Chornobyl Exclusion Zone to grow radish in soils of four different types with added isotope 125I. The experiment demonstrated an increase in root uptake of radioiodine by radish roots in the following sequence of soil types: clay soil < loam soil â‰ª sandy soil (Chernozem ≈ Phaeozem < Greyzem â‰ª Podzoluvisol). The obtained results have been analyzed in conjunction with the results of our previous studies to identify the factors determining the parameters of root uptake of radioiodine by the studied crop species. The 125I concentration ratios (CRs) in edible parts of crop species (radish roots: from 0.003 for Chernozem to 0.02 for Podzoluvisol; lettuce leaves: 0.004-0.04; bean pods: 0.0003-0.004; wheat straw: 0.01-0.1; and wheat seeds: 0.0001-0.001) anticorrelated with the characteristics of the soils studied: the distribution coefficients Kd of 125I (from 112 L kg-1 for clay soils to 19 L kg-1 for sandy soil, R2 = 0.56-0.97) and Kd' of stable iodine (93-19 L kg-1, R2 = 0.43-0.74), stable iodine concentration in soil (6.2-0.5 mg kg-1, R2 = 0.71-0.88), and humus content (4.0-0.8%, R2 = 0.44-0.78). The obtained steady-state CR values and their dependence on the soil characteristics can be used to model the root uptake of 129I, a long-lived radiological contaminant, and to predict its accumulation in human food and animal feed.

Clean feed as countermeasure to reduce the 90Sr and 137Cs levels in fish from contaminated lakes.

Glubokoye Lake situated within the Chernobyl Exclusion Zone is highly contaminated with respect to radioactive caesium and strontium isotopes, which also is reflected in the contaminated fish. To utilize the fish resources in contaminated lakes, the present work presents for the first time the effectiveness of using clean feed to counteract contamination of radionuclides in fish. The study is based on a series of repeated experiments with Prussian carp (Carassius gibelio (Bloch, 1782)) kept in cages in the contaminated Glubokoye Lake during summer 2018-2021. By the addition of clean feed, the activity concentration of 137Cs in fish muscle tissues was lowered with a factor of 2-5 due to biodilution. Surprisingly, additional clean feed did not lead to further decrease in the uptake of 137Cs in fish. In contrast to 137Cs, the addition of clean feed increased the 90Sr activity concentration in fish by a factor of 2-4 compared to fish fed with naturally occurring feed items. Radioactive strontium accumulated mainly in the fish bones and the muscle tissue level was 2 orders of magnitude lower, similar to the distribution observed for stable Sr. By utilizing a new kinetic model describing the dynamics of strontium isotopes in bone tissues of fish, predictions fitted well with site-specific data, taking growth rates and aging into account. Results showed that clean feeding can be used to counteract high activity concentration of 137Cs in fish due to biodilution, but cannot counteract bioaccumulation of 90Sr. Findings highlighted that it is essential to understand underlying factors influencing the uptake pathways for contaminants, as access to clean feed could increase the growth and thereby reduce the body activity concentration of dietary associated radionuclides such as 137Cs (biodilution), as well as increase the transfer of dissolved compounds such as 90Sr directly from water to fish.

Seasonal changes in uptake and depuration of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) and common rudd (Scardinius erythrophthalmus).

Dynamic transfer of radionuclides to fish was studied in a series of experiments under field condition in two lakes within the Chernobyl exclusion zone during 2016-2020. "Clean" common rudd (Scardinius erythrophthalmus) and silver Prussian carp (Carassius gibelio) were transported to the contaminated Glubokoye Lake and kept in cages during several months of exposure, while contaminated Glubokoye fish were kept in cages in the "clean" Starukha Lake. Radiocaesium (137Cs) and radiostrontium (90Sr) were determined in intestine contents, muscle and bone tissues based on repeated samples during several months of exposure. During summer, the activity concentrations of 137Cs and 90Sr increased with time of exposure in clean fish caged in the contaminated lake. During autumn and winter, however, minor changes in fish uptake occurred during several weeks of exposure to the contaminated water. Furthermore, depuration in the contaminated fish was significant during summer, while insignificant during winter when exposed in the «clean¼ water. The rate constant of 137Cs uptake in muscle was between 8.0 and 22 day-1 during summer, while 0.2 to 1.0 day-1 during autumn-winter. Similarly, the rate constant of 90Sr uptake in bone was between 1.4 and 1.6 day-1, while 0.08-0.52 day-1 during autumn-winter. Biological half-lives of 137Cs in fish muscle tissue in summer were 77 ± 10 days, while exceeded 230 days during seasons at low water temperature. The results demonstrated that the transfer of 137Cs and 90Sr to fish was highly dependent upon seasons, in particular the water temperature. The transfer data obtained during low water temperature seasons deviated significantly from transfer data in literature and handbooks. Thus, seasonal changes in radionuclide transfer to fish should be taken into account when radiological impact to fish is assessed.

Wildfires in the Chornobyl exclusion zone-Risks and consequences.

Following the 1986 Chornobyl accident, an area approaching 5000 km2 surrounding the nuclear plant was abandoned, creating the Chornobyl exclusion zone (CEZ). Although this area likely contains the most radioactive terrestrial ecosystem on earth, the absence of humans and associated activities for nearly 35 years since the accident has resulted in increases in wildlife numbers. Both the Belarussian and Ukrainian components of the CEZ are now designated as nature reserves; together they form one of Europe's largest protected areas and have been described as an iconic example of rewilding. Forests and former agricultural land (now scrub) dominate the CEZ and wildfires are an annual event. In April 2020, the CEZ suffered its most widespread fires to date when greater than 800 km2 of the 2600 km2 Ukrainian portion of the CEZ was burnt. Large-scale fires in the CEZ have implications for wildlife, as they do elsewhere, but they also pose additional radioecological and radiological protection questions. We discuss the implications of wildfires in the CEZ, considering effects on wildlife and changes in radionuclide mobility. We also demonstrate that the risk to firefighters and the wider public from the inhalation of radionuclides in smoke resulting from fires in the CEZ is likely to be low. However, further experimental and modeling work to evaluate potential doses to firefighters from inhaled radioactive particles would be valuable, not least for reassurance purposes. Integr Environ Assess Manag 2021;17:1141-1150 © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Distributions of 137Cs and 90Sr activity concentrations in trunk of Scots pine (Pinus sylvestris L.) in the Chernobyl zone.

Possibility of the economical utilization of forests in the radioactive contaminated areas depends on compliance of the radionuclide activity concentrations in wood with the hygiene norms or national standards that are established by the governments or regulators. Since such regulations consider wood as a whole, development of the sampling methods for assessment of compliance of wood to the norms or standards requires the adequate addressing the issues related to heterogeneity of the radionuclide distributions within the tree trunks. In this paper we present spatial distributions of the 90Sr and 137Cs activity concentrations in the trunk wood of mature Scots pine (Pinus sylvestris L.) trees in the Chernobyl exclusion zone in the late stage (30 years) after the deposition. Four 52-53 year old model trees were sampled in the forest stand located in approximately 5 km from the accidental nuclear reactor. The radionuclide concentrations were measured in 156 wood samples collected from the wood disks cut off the tree trunks at the set of heights. To address variability of the tree sizes and radionuclide concentrations between the individual trees, we applied the corresponding relative indices enabling identification of the general patterns of the spatial distributions of 90Sr and 137Cs. We demonstrated significant differences in bioavailability and distribution trends between the studied radionuclides. 137Cs is translocated to the younger parts of the tree trunk, while the 90Sr concentrations are higher in heartwood and in senescing tissues, which is explained by the different chemical properties of Cs and Sr and by different physiological roles played in plant development by their chemical analogs and major plant nutrition elements, Ca and K respectively. In this reason, the principal distribution patterns of the studied radionuclides in the trunk wood do not significantly change with time, and the results of our study generally are in good agreement with those obtained in the earlier stage after the deposition. The above trends are clearly expressed in both radial and longitudinal directions and result in systematic deviation of the concentrations estimated based on core sampling from the average concentrations in the whole tree trunk.

A dose rate causes no fluctuating asymmetry indexes changes in silver birch (Betula pendula (L.) Roth.) leaves and Scots pine (Pinus sylvestris L.) needles in the Chernobyl Exclusion Zone.

The assessment of the fluctuating asymmetry based on measurement of the parameters of left and right parts of silver birch (Betula pendula (L.) Roth.) leaves and relative sizes of pairs of Scots pine (Pinus sylvestris L.) needles from the Chernobyl Exclusion Zone (ChEZ) was carried out. Twelve samples of both birch leaves and pairs of needles were collected from 10 trees at 5 sites in the Chernobyl Exclusion Zone and also at one control site located outside the ChEZ. Values of gamma dose rate in the air varied between the sites from 0.1 to 40 µGy h-1. Activity concentrations of 90Sr and 137Cs in the birch leaves varied over the range of 0.9÷2460 kBq kg-1 and 0.1÷339 kBq·kg-1 (DW), respectively. In addition to the above, in the Scots pine needles, these ranges were 0.7 ÷1970 kBq kg-1f for 90Sr and 0.1÷78 kBq kg-1 (DW) for 137Cs. From the values of the radionuclides activity concentrations in the plants, the internal dose rate is estimated to be in the range of 0.1 ÷ 274 µGy h-1. The main sources of the internal dose rate were radiation of 90Sr and 90Y. Indices of fluctuating asymmetry of silver birch leaves and Scots pine needles varied over the range of 0.048 ±â€¯0.007 ÷ 0.060 ±â€¯0.009 and 0.014 ±â€¯0.002 ÷ 0.018 ±â€¯0.002, respectively, and did not statistically differ for all experimental sites. The indices also did not depend on the external or internal dose rate of ionizing radiation for plants. The above findings seem to be consistent with other research effort in terms of understanding the response of organisms to chronic pollutant exposure and the long-term effects of large scale nuclear accidents.

The progeny of Chernobyl Arabidopsis thaliana plants does not exhibit changes in morphometric parameters and cellular antioxidant defence system of shoots.

Morphometric parameters and functional state of the cellular antioxidant defence system of shoots were studied in the progeny of Arabidopsis thaliana (L.) Heynh. (A. thaliana) plants, previously and chronically exposed in the Chernobyl Exclusion Zone (ChEZ). Changes in cellular antioxidant enzyme activities in the progeny of exposed plants were assumed because antioxidant status of cell may be altered by inherited epigenetic changes, resulting in changes in antioxidant-response genes expression. These changes can be inferred as induced expression of CAT and SOD genes was found previously for A. thaliana plants by another group of scientists. It is well-known that ionizing radiation may induce changes in hormonal-signalling net-work, shifting balance in growth factors that may cause changes in morphometric parameters of plants. Seeds from A. thaliana plants were collected in the ChEZ at different levels of the external dose rate from 0.28 ±â€¯0.01 to 12.93 ±â€¯0.08 µGy/h. Internal dose rate for parent plants was calculated on the basis of the activity concentration of 90Sr and 137Cs in the plants, using dose conversion coefficients for wild grass. Total dose rate, absorbed by parent plants, was calculated as the sum of the external and internal dose rate and was in a range between 2.8 ±â€¯0.2 and 99 ±â€¯8 µGy/h. Seeds were then grown in the standard laboratory conditions (nutrient-agar, light-dark cycle and appropriate temperature) to analyse morphometric parameters of seedlings and final germination percentage. No significant changes in the morphometric parameters (root length and rosette diameter of shoots) of the seedlings were observed. Changes in the final germination percentage of the studied seeds were found, but low correlation was observed between found changes and the dose rate, absorbed by parent plants. In contrast to the results obtained in A. thaliana plants directly sampled in the field, no effect on the functional state of the cellular antioxidant defence system of shoots in the progeny of Chernobyl A. thaliana plants was observed.

Environmental behaviour of radioactive particles from chernobyl.

Long-term environmental behaviour of radioactive particles released during the Chernobyl accident and deposited in sandy topsoil in Ivankiv district of Kyiv Region (Ukraine), in radioactive trench waste materials from the Red forest, and in bottom sediments from the Cooling pond has been assessed. The efficiency of the models describing the dissolution/weathering rates of U fuel particles developed 15-20 years ago was tested, and their predictions for the dynamics of remobilization, mobility and plants uptake of 90Sr were confirmed. It was found that at present in the topsoil and in radioactive trench waste material, total dissolution of fuel particles of low chemical stability (UO2+x) has occurred and about half of the non-oxidized chemically stable fuel particles (UO2) has also dissolved, indicating radiological stabilization of the environment and that the mobile fraction of radionuclides would be reduced in the future. The biological availability of 90Sr in topsoil due to fuel particles dissolution has reached maximum values and further decrease is expected. The presence of chemically extra-stable fuel particles (U-Zry-Ox) in environments should be taken into account when the total radionuclides activity concentrations are assessed during radioactive materials management. It was shown that nearly half of the 90Sr activity remained as part of the non-dissolved UO2 fuel particles at the time of the study. Taking into consideration that 31 ±â€¯4% of the radionuclide activities were still associated with non-dissolved chemically extra-stable particles (U-Zry-Ox) in radioactive trench waste materials from the Red forest, increased dissolution should not be expected in the near future. The physico-chemical form of radionuclides in air exposed sediments from the Cooling pond were determined, and results showed that about 70-80% of total 90Sr, 241Am and plutonium isotopes activity were associated with U fuel particles. The low dissolution rate of radionuclides from the pond sediments is attributed to prolonged slightly alkaline pH in the medium due to zebra mussel residues. According to new data, the emission value of 238Pu associated with fuel particles released during the Chernobyl accident amounted to 1.8 × 1013Bq (1.2% of the activity in the reactor) and 90Sr amounted to 2.6 × 1015Bq (1.5% of the activity in the reactor).

Analysis of the relationship binding in situ gamma count rates and soil sample activities: Implication on radionuclide inventory and uncertainty estimates due to spatial variability.

The paper strives to identify through geostatistical simulations the parameters which build up a correlation between radionuclide activity concentrations measured on core samples and corresponding in situ total gamma count rates measured into boreholes drilled within the contaminated soil. This numerical exercise demonstrates that a linear relationship should exist between logarithmic values of in situ count rates and logarithmic values of activity concentrations when the contamination is strongly structured through space. A sensitivity analysis to some parameters (geostatistical range of the contamination structure, core sampling method, soil water content, multiple gamma-emitter contamination, etc.) is undertaken to identify which situations may impede the use of such a correlation. Then this approach is applied on Chernobyl measurements undertaken in 2015 and compared to the co-kriging method which considers the localization of the measurements and the additional measurements. It appears that co-kriging is a better estimator than linear regression, but the latter remains an acceptable way of estimating activity from gamma emitters and presents better results than lognormal regression. Therefore, total gamma logging measurements performed into boreholes of porous media contaminated by gamma-emitting radionuclides can be used for characterizing contamination and dealing with its spatial variability with the use of co-kriging.

Soil prokaryotic communities in Chernobyl waste disposal trench T22 are modulated by organic matter and radionuclide contamination.

After the Chernobyl nuclear power plant accident in 1986, contaminated soils, vegetation from the Red Forest and other radioactive debris were buried within trenches. In this area, trench T22 has long been a pilot site for the study of radionuclide migration in soil. Here, we used 454 pyrosequencing of 16S rRNA genes to obtain a comprehensive view of the bacterial and archaeal diversity in soils collected inside and in the vicinity of the trench T22 and to investigate the impact of radioactive waste disposal on prokaryotic communities. A remarkably high abundance of Chloroflexi and AD3 was detected in all soil samples from this area. Our statistical analysis revealed profound changes in community composition at the phylum and OTUs levels and higher diversity in the trench soils as compared to the outside. Our results demonstrate that the total absorbed dose rate by cell and, to a lesser extent the organic matter content of the trench, are the principal variables influencing prokaryotic assemblages. We identified specific phylotypes affiliated to the phyla Crenarchaeota, Acidobacteria, AD3, Chloroflexi, Proteobacteria, Verrucomicrobia and WPS-2, which were unique for the trench soils.