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Some of the highest 90Sr activity concentrations recorded beyond the Chornobyl Exclusion Zone occur in the Ivankiv district of Ukraine, located approximately 50 km south of the power ...plant, an area which nonetheless remains important for agricultural production. Although characterized by soils with low exchangeable calcium values, which can enhance the bioavailability of certain radionuclides, information on the transfer of 90Sr to food crops and trees in the region has remained limited to date. Analysis of 116 grain samples (wheat, rye, oat, barley or Triticale) collected from fields in 13 settlements in the region between 2011 and 2019 revealed 90Sr and 137Cs activity concentrations above Ukrainian limits in almost half of those samples, with annual averages exceeding this limit in four of those nine years (most recently in 2018) and with no clear evidence for a declining trend over time. Analysis of paired sandy soil samples from the same fields yielded concentration ratios for transfer of 90Sr from soils to grains that were on average 3 times higher than that specified by the IAEA. In addition, three quarters of wood samples collected from the trunks of trees (primarily pines) from 12 locations in the same district between 2015 and 2019 contained 90Sr activity concentrations in excess of the Ukrainian limits for firewood (60 Bq/kg), with levels more than four times that limit at one location and again no evidence for decline over time. A single sample of ash collected from a domestic wood-burning oven in the district contained 90Sr at a level 25 times higher than in the most contaminated wood sample collected in this study. Overall these results reveal additional facets of the ongoing legacy of Chornobyl contamination within the Ivankiv district, and the diversity of pathways by which local residents may be exposed to radionuclides. They also highlight the dangers associated with the current lack of routine and comprehensive environmental and food monitoring programs within the region, especially at a time in which the use of locally-sourced wood for biomass energy generation is set to expand markedly.
The novel approach for optimising soil sampling strategies in areas affected by radionuclides is suggested. Major factors influencing the efficiency of soil sampling strategies, including (number of ...samples, sampling area size, sampling depth and spatial resolution of the sample sites are examined to provide optimisation of the soil sampling plan. The experimental field studies to validate the suggested approach were performed in 25 sampling units ranging from 1.2 × 1.2 m to 60 × 60 m size. The sampling units were selected on arable farmlands, natural meadow and former agricultural land), as well as coniferous and deciduous forests with contamination density of 137Cs ranging from 2.8 kBq·m−2 to 24.5 MBq·m−2. The studied areas were contaminated by both the global fallout and the Chernobyl radioactive particles of different types. To determine the values of standard deviation of the log of the soil contamination density of 137Cs, 25 to 256 soil samples were collected with an increment of 0.07–10 m within each sampling unit. It was found that the values of standard deviation of the log of the soil contamination density of 137Cs were not dependent on the mean contamination density, the type of radioactive deposition and the landscape features. The mean value of standard deviation calculated for all sites studied was estimated as 0.44 ± 0.15 and 0.30 ± 0.10 for the sampling area 0.001 m2 (∅37 mm) and 0.005 m2 (∅80 mm) at the relative measurement uncertainties lower than 10% (CI = 95%). Concentrations of 137Cs in the soil samples were statistically independent when sampling points were situated at a distance larger than 1 m one from each other. A simple method was developed for assessing minimum sample sizes required for estimation of the median or the geometric mean of radionuclide soil contamination with a relative uncertainty set by the user. The approach was also suggested for estimation of the uncertainty of soil contamination for the case of composite samples. The approach was implemented in the Ukrainian national requirements for assessment of quality of the soil.
•The novel approach for optimising soil sampling strategies in areas affected by radionuclides is suggested.•Variability of the terrestrial density of contamination with 137Cs did not depend on the mean contamination density, the type of radioactive deposition and the landscape features.•Value of 137Cs activity concentrations in the soil samples were statistically independent when sampling points were situated at a distance larger than 1 m one from each other.•The mean value of standard deviation calculated for all sites studied was estimated.•A simple method was developed for assessing minimum sample sizes required for estimation of the median or the geometric mean of radionuclide soil contamination with a relative uncertainty set by the user.
Activity concentrations of 90Sr in fish in lakes located within the Chornobyl Exclusion Zone (ChEZ) reach 100 kBq kg−1, which is several thousand times higher than the permissible level in Ukraine ...(35 Bq kg−1). This study was conducted in the natural conditions of the ChEZ to determine the effectiveness of keeping radioactively contaminated fish in “clean” water to reduce the 90Sr content of their muscle tissue, as previously shown in short-term laboratory experiments. It was found that transferring tench (Tinca tinca (Linnaeus, 1758)) from Lake Glubokoye one of the most contaminated lakes in the ChEZ, to a cage in the “clean” Lake Starukha for 45 days did not lead to a significant decrease in 90Sr content in both bone and muscle tissues.
Establishing permissible levels of 90Sr concentration only in fish fillet, and not in the whole fish body (with bone tissue), is appropriate for human radiation protection, since the retention factors of 90Sr treatment for boiled bone tissue of crucian carp from the Chornobyl exclusion zone are less than 0.01, and up to 97% of strontium is contained in bone tissue.
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•No reduce of 90Sr content in contaminated fish when kept in “clean” water for 45 days.•Less than 1% of 90Sr is transferred to broth during boiling of fish bone tissue.•Current Ukrainian permissible levels of 90Sr in fish products need to be revised.•Long-term experiments are needed to study ways to remove 90Sr from fish tissues.
The lessons learned from the plant sampling campaigns implemented in the most Chernobyl affected countries are described. The variability of 137Cs activity concentrations in plants taken from a ...variety of sampling sites, as well as the uncertainties around the aggregated transfer factors (Tag) from soil to plants were estimated. The sampling sites covered both agricultural and natural lands in different landscapes: floodplain, plains, and watershed meadows. To determine parameters of the lognormal distribution of the 137Cs activity concentration in plants and the values of corresponding aggregated transfer factor (Tag) values, from 25 to 49 plant and soil samples were collected at each sampling site with the grid increment that varied from 1 to 10 m. The gradients of deposition i.e. monotonic changes (trends) of the contamination density conditioned by the global (in respect to study area) gradient of fallout were not observed in any of the study sites. Therefore, the variability of radionuclide contamination density (and activity concentrations in the soil) within the study sites were determined by only random factors such as microheterogeneity of radioactive deposition in a sampling point. The mean standard deviation of the logarithms of 137Cs activity concentrations in plants sampled in all such sites and the corresponding transfer factors were similar for all sites studied and were not dependent on the mean soil contamination density at the site, the type of radioactive fallout and the vegetation type. The values of the average standard deviation of the 137Cs activity concentration logarithms in plants and the corresponding transfer factors for the vegetation sampling area ≥1 m2 and the relative activity measurement uncertainties ≤10% were estimated as 0.4 ± 0.1 and 0.5 ± 0.1, respectively. A new simple method for optimization of the number of linked (conjugated) plant and soil samples as well as estimates of the activity concentration and transfer factor uncertainties when measuring composite samples were proposed. Based on the results of these studies, the recommendations were made to the sampling of plants for radionuclides.
•New approach for optimal plant sampling planning is suggested.•The variability of 137Cs activity concentrations in plants is estimated.•The variability of the activities concentrations does not depend on the mean contamination density, the type of radioactive deposition and the vegetation type.•The simple methods of the plant sampling optimization are proposed.
The effects of radiation on radial growth of Scots pine (Pinus sylvestris L.) affected by the Chernobyl accident were studied at five sites with different deposition levels. The study sites were ...chosen along a high gradient of depositions at the distance of a few hundred meters in the forests with similar forest characteristics. Air dose rates varied at the sites from the background values up to 30 μGy h−1 as of December 1, 2016. Scots pine trees exposed to sub-lethal doses of 8.6–13.2 Gy at the “Red Forest” site did not demonstrate deviations in formation of annual rings 30 years after the Chernobyl accident compared to trees with lower doses and control trees. Variation with time in annual rings thickness did reveal that the effect of radiation in trees growing at the sites with different contamination not detectable in 1986 and 1987. Conversely, the effects were clear observed in a later period in 1989–1991, i.e. 3–5 years after the accident. Until 2000, there were statistically significant differences in the annual rings growth rates of Scots pine trees exposed to external absorbed dose rates of 4.4–6.7 mGy h−1 as estimated for June 1, 1986 (or 19.5–30.0 μGy h−1 as of December 1, 2016) compared with the trees of the other sites studied. The results comply with the conclusions from research with acute pine exposure conducted in the Kyshtym area in 1975–1984.
•Effects on radial growth of highly exposed trees were observed 3–5 years after the accident.•The survived pine forest was recovered 30 years after the Chernobyl accident.•Data on growth of annual tree rings can be used as an integral indicator of the tree exposure.•Effects of annual rings tree growth comply with those observed in the Kyshtym experiments.
This study reports for the first time temporal trends for the period of 2011–2016 in 137Cs content in cow's milk originating from private farms and households of 14 settlements located in the ...territories of the Rivne region, Ukraine. These areas are still radioactively contaminated as a result of the accident at the Chernobyl Nuclear Power Plant (ChNPP) in 1986. In 2016, the average 137Cs activity concentration in milk exceeded the Ukrainian Permissible Level (PL) for adults of 100 Bq/l in samples from 6 settlements and the PL for children of 40 Bq/l in 8 settlements, reaching activity concentration of around 500 Bq/l in some samples. Estimated annual effective doses calculated utilizing two different methodologies were in the range of 1.4–2.6 mSv/year and 1.2–1.8 mSv/year, respectively. The estimated effective period of milk semi-purification (T1/2_eff) from 137Cs in these settlements was in the range from 8 to 17 years. The estimated ecological period of milk semi-purification (T1/2_eco) from 137Cs was in the range from 11 to 36 years. The optimization of the remedial actions strategy for investigated settlements exposed to an effective dose above 1 mSv/year (as estimated in 2016) has shown that a diversity of measures can decrease effective dose for a representative person to below 1 mSv/year. Such measures include application of Ferrocyn to cows, mineral fertilization of potato fields, information campaigns on consumption of wild mushrooms and other forestry products, and feeding pigs with uncontaminated fodder. The total costs of such measures are estimated to be about 71,000 Euro per year for the combined population (8336 inhabitants) of the six villages investigated in this study that showed the highest median residual 137Cs activity concentrations in milk, with a subsequent decrease in cost in the future. This would result in an averted collective dose of 11 man-Sv, at an average cost of 6.5 kEuro/man-Sv averted. In the absence of governmental programs for implementation of necessary protective measures to reduce radiological risks to impacted populations, the exceedance of PL for the activity concentration of 137Cs in cow's milk for adults of 100 Bq/l in the Chernobyl-affected areas of Ukraine could persist for many more years – until at least 2040.
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•First report on dynamics of 137Cs content in cow's milk from Chernobyl affected areas in Ukraine.•Key factors responsible for milk contamination by 137Cs have been identified.•Average 137Cs activity concentrations in milk still exceed Ukrainian PL in several settlements.•Exceedance of PL for 137Cs in cow's milk may persist until 2040 without remedial actions.•Mitigation measures can decrease an effective dose to below the limit of 1 mSv/year.
The main techniques of animal product sampling used in different time periods after the Chernobyl accident are summarised and lessons learned from this analysis are presented. It was shown that ...simple instruments for measurement γ-radiation in the environment can also be effectively implemented for measurement of γ-emitters in animal products even though these were not originally developed to measure radioactivity in food. The lessons learned related to the major tasks of the monitoring such “what to sample”, “where to sample” and “when to sample”. The role and example of application of supplementary data on radionuclide of concern properties for sampling planning are also discussed. Based on the statistical analysis of the data obtained in the affected settlement it was shown that radionuclide concentration in the animal products can be fitted by the log-normal distributions whilst the dispersion of the logarithms of the activity 137Cs concentrations in milk is not dependent on the local settlement specific factors. Based on these findings the novel approach for justification of the number of samples that should to be taken to obtain the GM estimate with predefined precision for given variability of the data is suggested.
•Experience in monitoring of animal products the Chernobyl affected areas is discussed.•Sampling methods of different animal products in case of a nuclear accident are summarised.•A method for estimating required number of samples for optimizing animal sampling plans is suggested.
Fish in lakes situated within the Chornobyl exclusion zone have been highly contaminated since the accident and have not been utilized as food for humans. In the present study, field experiments with ...less-contaminated silver Prussian carp (Carassius gibelio (Bloch, 1782)) caged in contaminated lake within the Chornobyl exclusion zone was performed from June to October 2021 to investigate the effectiveness of clean feed containing potassium ferric hexacyanoferrate (KFCF) KFeFe(CN)6, a kind of Prussian Blue as a countermeasure to reduce 137Cs accumulation in fish. The addition of clean feed containing 0.1% or 1% KFCF resulted respectively in 2.4 ± 0.4 or 4.2 ± 0.7 times lower activity concentration of 137Cs in muscle tissue of the carp compared to control fish with clean feed without KFCF and in 7-16 or 12-27 times lower activities compared to fish without additional clean feeding. After 18 weeks exposure, 137Cs levels in all the caged fish except for the control group were below the European permissible level (600 Bq kg-1) for consumption. In contrast, KFCF did not affect the intake of 90Sr in fish, although additional feed increased the growth rate and thereby accumulation in bone tissues. Hence, the use of clean feed containing KFCF is judged to be an effective and inexpensive countermeasure to reduce the 137Cs contamination of edible fish muscles.
In view of the problem complexity, numerical methods, mainly finite and boundary element methods, are fairly widely used in the calculation of the static deformation of composite shells. The paper ...presents a new approach to the calculation of the static deformation of composite cylindrical shells using potential theory methods, which made it possible to obtain a solution to the set problem in the closed analytical form. Longitudinally infinite cylindrical shells, which are sequentially rigidly joined together (by clamping the outer edges of the formed composite structure), are considered. Orthogonal curvilinear coordinates in the middle of each of the cylindrical shells have been chosen. The problem has been solved in displacements. The system of differential equations of the static deformation of each of the cylindrical shells being part of the compound body was written according to the Vlasov shallow shell theory. The composite structure was under the action of a normal surface load. The expressions for internal forces and moments are given in terms of the components of the vector of displacements and the corresponding derivatives of them. For the system of differential equations, an exact solution has been found. The problem was solved by the method of variation of arbitrary constants. To determine the integration constants, the rigid joint conditions of cylindrical shells (from physical considerations) and the generally known conditions of rigid clamping of the edges of a compound body have been formulated. A system of linear algebraic equations for the desired constants has been derived. As a result of solving the system and substituting the found constants into the expressions for displacement vectors, the final solution of the problem in the form of potential images has been obtained with the aid of constructed Green matrices for this problem. The calculation method is illustrated by some numerical results, which describe the stress state of the object under investigation, composed of two in-series connected sections, as a function of the wavelength of the cylindrical shells. Analysis of the stress state characteristics shows that both bending moment and transverse force increase with decreasing wavelength of the cylindrical sections. This can be accounted for by the way of joining the cylindrical shells in the composite structure. Deformation schemes of composite cylindrical shells (under unilateral normal load) are presented with a purely illustrative purpose as evidence of the capabilities of the proposed method.
This study analyzes the variability of 137Cs and 90Sr concentrations in wood and their radial distributions in the trunks of Scots pine and Silver birch trees in the small uniformly contaminated ...forest stands in the Chornobyl Exclusion Zone. Concentrations of both radionuclides follow a lognormal distribution with a large scatter of values measured in the trees within the stands (GSD ranges from 1.6 to 2.0). No correlation was found between the concentrations of the two radionuclides measured in individual trees, or between their concentrations and tree diameter. The average 137Cs and 90Sr Tag were 8.4 × 10−4 m2 kg−1 and 8.8 × 10−3 m2 kg−1 for pine, respectively, and 9.3 × 10−4 m2 kg−1 and 1.1 × 10−2 m2 kg−1 for birch, indicating a much higher availability of 90Sr for uptake by the studied species. For 137Cs, the Tag values are within the range recommended by the IAEA Handbook (IAEA, 2010), while the values for 90Sr exceed the recommended range for birch and are close to its upper value for pine.
The highest concentrations of 137Cs in pine at the height of 1.3 m were measured in the youngest sapwood rings; they were lower in the rest of the sapwood and decreased further in the heartwood, but remained relatively high even in annual rings that were the heartwood at the time of deposition, suggesting sapwood-to-heartwood translocation of the radionuclide by diffusion and/or ray transport. In contrast, 90Sr concentrations increased through the sapwood from the trunk periphery in pine trees up to 80 years old and remained stable through the sapwood in older trees (except for higher concentrations in the young annual rings), but dropped to zero in physiologically inactive heartwood tissues. In most birch trees, regardless of age, 137Cs concentrations demonstrated an increasing trend from the trunk periphery towards the pith, while concentrations of 90Sr were relatively stable in the whole trunk except in the oldest annual rings, where they increased sharply, likely indicating active transport of the radionuclide to senescing tissues.
•137Cs and 90Sr concentrations in pine and birch wood vary widely at the stand level.•There is no correlation between 137Cs and 90Sr concentrations in wood.•In pine, 137Cs concentrations increase from the trunk center to the periphery.•In birch, 137Cs and 90Sr contents decrease from the trunk center to the periphery.•The effect of tree age on the radionuclide radial distributions was clarified.
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