Environment International 146 (2021) 106282

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Environment International

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Current radiological situation in areas of contaminated by the Chornobyl accident: Part 2. Strontium-90 transfer to culinary grains and forest woods from soils of district

I. Labunskaa’*, S. Levchukb, V. Kashparov b,c, D. Holiakab, L. Yoschenkob, D. Santilloa, P. Johnston a a Greenpeace Research Laboratories, Innovation Centre Phase 2, Rennes Drive, University of Exeter, Exeter, UK b Ukrainian Institute of Agricultural Radiology (UIAR) of National University of Life and Environmental Sciences of Ukraine, Mashinobudivnykiv str.7, , Region 08162, Ukraine c CERAD CoE Environmental Radioactivity/Department of Environmental Sciences, Norwegian University of Life Sciences, 1432 Aas, Norway

ARTICLE INFO ABSTRACT

Handling Editor: Olga Kalantzi 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 Keywords: remains important for agricultural production. Although characterized by soils with low exchangeable calcium 90Sr values, which can enhance the bioavailability of certain radionuclides, information on the transfer of 90Sr to food Grain contamination crops and trees in the region has remained limited to date. Analysis of 116 grain samples (wheat, rye, oat, barley Wood contamination or Triticale) collected from fields in 13 settlements in the region between 2011 and 2019 revealed 90Sr and 137Cs The accident Effective dose activity concentrations above Ukrainian limits in almost half of those samples, with annual averages exceeding Transfer factor 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.

1. Introduction the territory of Ukraine (9% of the land area) were contaminated with 90Sr at a deposition density above 4 kBq/m21 , with 3,092 km2 of agri­ Vast areas of Ukraine were contaminated with a range of radionu­ cultural land receiving a deposition density above 5.5 kBq/m2 (IAEA, clides including Strontium-90 (90Sr) as a result of the explosion of the 2006; Kholosha, 2008; Nadtochiy, 2003). 4th reactor at the Chornobyl Nuclear Power Plant (ChNPP) in 1986 The majority of the 90Sr (over 85% of its activity) was released from (former name is the Chernobyl Nuclear Power Plant). This radionuclide the reactor as part of the fuel particles (FP) matrix - a specific physico­ is one of the major radioactive products of nuclear fission, and was chemical form of Chornobyl radioactive fallout (Kashparov, 2003; released in significant quantities in the explosion. Over 55,400 km2 of Kashparov et al., 2003, 2019, 2020; Salbu et al., 2018). FP, which

DOI of original article: https://doi.org/10.1016Zj.envint.2018.04.053. * Corresponding author. E-mail address: [email protected] (I. Labunska). https://doi.org/10.1016/j.envint.2020.106282 Received 24 May 2020; Received in revised form 20 October 2020; Accepted 20 October 2020 0160-4120/© 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). I. Labunska et al. Environment International 146 (2021) 106282

consisted of uranium oxides (UO2-U3O8) together with various addi­ contrast, around half of the samples of wheat, rye, and oats collected tives, had a density of 8-10 g/cm3 and were sized from several microns from Ivankiv district during 1997-2011 (Kashparov et al., 2013) to several hundred microns. As a consequence, FP were deposited pri­ exceeded the Ukrainian PL-2006 (Ministry of Health of Ukraine, 2006). marily within the 30 km zone surrounding ChNPP, also called the As we have previously shown (Kashparov et al., 2013), the aggre­ Chornobyl Exclusion Zone (ChEZ). Some territories adjacent to ChEZ gated transfer factor of 90Sr (TFag - the ratio of the activity concentration were also affected, though to a lesser extent. We have previously shown (Bq/kg) in a grain to the activity density (kBq/m2) of soil contamina­ (Kashparov et al., 2001, 2003, 2018) that the contamination density of tion) is inversely proportional to the concentration of exchangeable 90Sr steadily decreases with increasing distance from the ChNPP. For calcium in the soil. Hence, two major factors that contributed to example, the contamination density with 90Sr may reach tens of thou­ elevated levels of 90Sr in grains of Ivankiv district were: a) density of soil sands of kBq/m2 within the ChEZ while outside it does not exceed 100 contamination by 90Sr, which was the highest among all affected areas kBq/m2. located outside of the ChEZ (see Fig. 1), and b) the properties of the Unfortunately, detailed mapping of the contamination density of sandy soils in the area (Podzoluvisol) that facilitated increased uptake of 90Sr, conducted by the Ukrainian Institute of Agricultural Radiology 90Sr by vegetation due to a low content of exchangeable calcium in these (UIAR) of the National University of Life and Environmental Sciences of soils (IAEA, 2010; Gupta et al., 2018). Ukraine (NUBiP of Ukraine) (Kashparov et al., 2001, 2018, 2020), was In addition, trees growing on 90Sr contaminated areas may play an only carried out within the ChEZ in 1987 and 1997, and within the important role in redistribution of radionuclides by ‘pumping’ radio­ Ivankiv district only in 2014. These limitations arise from a variety of nuclides back to the surface soil through root uptake and subsequent leaf reasons, including the complexity and cost of the analysis for 90Sr. litter fall (Kashparov et al., 2012; Thiry et al., 2009). Moreover, our Nonetheless, from these surveys it was found that the highest contami­ recent research (Holiaka et al., 2020a, 2020b) had shown that currently nation density with 90Sr that was detected outside of the ChEZ had about 30% of the total 90Sr load in the pine trees ecosystem (e.g., pine occurred in the north-east part of the Ivankiv district, Kyiv region, trees forests) may be accumulated in wood pulp, bark, branches and Ukraine, reaching up to 96 kBq/m2 in 2014 (see Fig. 1) (Kashparov et al., brushwood of the Scots pine (Pinus sylvestris L.) that potentially may be 2018). used as a fire wood. The territory of Ivankiv district is populated and is a location of At the same time, the usage of forest trees (especially small brush­ traditional agricultural production. Production includes the growing all wood) as a fuel in rural private households is commonplace in Ukraine. main types of culinary grains (e.g., wheat, rye, oats, and corn), vegeta­ Further, there is an existing thermal power plant (TPP) within the areas bles, fruits, and oilseeds. In general, all food-grade commodities pro­ of Ukraine contaminated by 90Sr, utilizing locally grown wood, and duced in Ukraine are assessed for the conformity to hygienic standards there are plans to build more. The operating plant, located in Ivankiv of Ukraine (known as PL-2006) and this assessment includes the content town and with a capacity of 18 MW, may utilise up to 600 tonnes of of both 90Sr and 137Cs (Ministry of Health of Ukraine, 2006) and takes wood per day sourced from local forests. In addition, a community boiler into account an appropriate estimate of measurement uncertainties (see plant located on the territory of ChEZ burns timber harvested within the Section 2.5.2 for details). From the only two governmental monitoring ChEZ to produce heated water for Chornobyl town inhabitants; and programmes of Chornobyl-affected settlements for 90Sr in Ukraine (in there are plans to build a TPP in the ChEZ that would also use locally 2011 and 2012), including some in Ivankiv district, it was reported that sourced wood. This situation is of considerable concern due to the po­ 90Sr activity concentration in cow’s milk and vegetables did not exceed tential for these TPPs to enhance the spread of radiation in the sur­ Ukrainian permissible levels (PL) (Lihtarov et al., 2012, 2013). In rounding territories. An issue of particular concern is the formation of

Fig. 1. Map of Ivankiv district showing 90Sr terrestrial density contamination as well as location of sampling points of grain (G1-G13, brown ovals) and wood (W1- W12, green rectangles). None of the area shown falls within a zone of compulsory (unconditional) resettlement (with 90Sr above 111 kBq/m2), within which res­ idential use and commercial production would be prohibited; however much of the east of the District falls within the zone of guaranteed (voluntary) resettlement (with 90Sr in range of 5.5 - 111 kBq/m2), within which residence and production of agricultural goods is allowed with some conditions (Supreme Council of Ukraine, 1991a,b). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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90Sr-enriched ashes. Burning of strontium-contaminated wood results in 2.2.1. Grain samples formation of ashes that have a higher 90Sr activity concentration as Grain samples, including wheat (Triticum aestivum), rye (Secale compared to that in uncombusted wood by a factor of hundreds and may cereaie), oat (Avena sativa), barley (Hordeum vulgare) and Triticale even exceed the level of 10 kBq/kg (Ladygiene et al., 2010), which (Triticosecale hybrid) were collected during harvesting time in August- would in theory impose the requirement to classify these ashes as September, and in most cases directly from agricultural fields. A total radioactive wastes with corresponding regulations for handling and of 116 grain samples were collected and analysed over the 9-year period, disposal (OSPU, 2005; IAEA, 2011). Despite this, such ashes are with the number of grain samples analysed each year ranging from 7 (in commonly used as a fertilizer on private allotments, which may thereby 2018) to 18 (in 2017) depending on sample availability, as explained in contribute to the production of contaminated food products. Section 3.1.2. A further three samples of wheat of known provenance (a Overall, however, there is a lack of current information about 90Sr field near Fedorivka village) were donated by the farmer in September behaviour and prevalence of contamination by this radionuclide in parts 2015 from his grain storage. of Ukraine affected by the Chornobyl accident where local residents Grain sampling was conducted in accordance with the standard continue to grow crops and may use radioactively contaminated wood as procedure established by the Ministry of Agricultural Policy and Food of fuel. This contamination could potentially increase population exposure Ukraine (SOU 01.1-37-426:2006) described previously (Kashparov to 90Sr together with other radioactive elements. Ultimately, this could et al., 2013). In brief, about 1 kg of ears of grains was manually collected pose a risk to health, particularly among children (Fucic et al., 2008). at a location within a field that was distanced at least 100 m away from Accordingly, the aims of the current study were: a) to fill gaps in the the field edge. data concerning the current situation in relation to grain and wood contamination by 90Sr in areas of Ukraine located outside of the ChEZ 2.2.2. Soil samples that were radioactively contaminated as a result of the Chornobyl ac­ Soil samples were collected from each field at the same time as grain cident and b) to investigate temporal trends of 90Sr activity concentra­ sampling. Field measurements and sample collection were performed as tions in grain and wood in these areas of Ukraine. reported previously in a wider survey of soils in the region that was conducted in 2014 (Kashparov et al., 2018). Sampling points were 2. Materials and methods chosen at the distances of not less than 100 m away from roads and at places where accumulation or wash-off of radioactive contamination 2.1. Description of the study area was considered to be most probable. Composite soil samples were ob­ tained using a 5 single-point sampling technique (“envelope sampling” • • The study was conducted in Ivankiv district, Kyiv region, Ukraine • ) to achieve statistically significant relative error for the median (area: 3616 km2, population: 29 574) that lies immediately to the south • • of the ChEZ (see Fig. 1). Ground contamination by 90Sr in this district density of soil contamination 8Y=0.9s = 20% (SOU 74.14-37-425:2006) was reported as not exceeding 96 kBq/m2 in 2014 (Kashparov et al., and relative error of measuring 90Sr and 137Cs activity 8meas = 10-20% 2018). The most typical soil type in the Ivankiv district is Podzoluvisol (Khomutinin et al., 2001). At each sampling location, a composite (soddy-podzolic sand and sandy soils according to CIS countries classi­ sample of >2 kg was prepared. 5 single-point samples were collected by fication), or sand soil according to IAEA, 2010 classification). This soil is using the envelope procedure with a pitch of 2-5 m and at a depth of 20 characterised by a low content of clay minerals (<18%), exchangeable cm, utilizing a 37 mm diameter soil sampler. calcium, and organic matter (0.5-3.0%), as well as by relatively high acidity of the soil solution (pH = 3.5-6.5) (Panagos et al., 2011; IAEA, 2.2.3. Wood samples 2010; Kashparov et al., 2013). Such soil properties tend to facilitate the Sixty wood samples were collected from twelve sampling locations maximum 90Sr uptake by vegetation (IAEA, 2006, 2010). from the forests of Ivankiv district in both 2015 and 2019 (see Fig. 1 & Table S2 in SI). At each location, five mature standing trees were 2.2. Sample collection sampled and their diameters recorded. Average trunk diameter (N = 5) varied from 22 to 38 cm. Distance between sampled trees at an indi­ Paired grain and soil samples were collected over a number of years vidual sampling point varied from 2 m to 10 m. Each sample was taken between 2011 and 2018 from fields in the vicinity of 13 settlements by drilling through a tree trunk at 1.3 m height with a specially designed within Ivankiv district (with further grain samples collected from the Presler growth drill (Haglof, Sweden): length — 400 mm, diameter — same areas in 2019). Those settlements were , Karpylivka, 5.15 mm. Samples from five trees were then combined to form a pooled Pisky, Domanivka, Gornostaypil’, Zorin, Orane, Prybirsk, Rusaky, sample from each sampling location. It should be noted that, although Fedorivka, Pyrogovychi, Frunzylivka and Gubyn (see Fig. 1 & Table S1 an earlier study focused on activity concentrations of 90Sr in small in Supporting Information (SI)). Wood samples were collected from brushwood, reflecting that commonly used for domestic purposes forests in Ivankiv district in both 2015 and 2019 (see Fig. 1 & Table S2 in (Otreshko et al., 2015), in this study we focused on standing trees as SI). At each sampling point, the ambient equivalent dose rate (EDR) of these are now being harvested for use in both industrial and domestic photon ionizing irradiation was measured at 1 m and 0.1 m height using settings in the region. dosimeter RKS-01 “STORA-TU” (ECOTEST, Ukraine). This measurement Environmentally friendly sealant was applied to each sampled tree to allowed the exclusion of points that had a disturbed surface layer protect it after sampling. In 2019, the second round of sampling was characterised by the differences in dose rate between measurements conducted at the same twelve locations as described above, resulting in a made at a height of 1 m and at a height of 10 cm (Khomutinin et al., further sixty samples that also were analysed as twelve composites. 2020). Hence, soil samples were collected only from places that didn’t exceed a 30% difference in dose rate measurement at these distances. 2.3. 90Sr and 137Cs activity concentration measurement Sampling coordinates were determined utilizing GPSmap (Garmin, USA) in World Geodetic System 1984. Both Ukrainian standards SSTU (SOU The measurement of 137Cs activity concentration in soil, grain and 74.14-37-424:2006, SOU 74.14-37-425:2006 and SOU 01.1-37­ wood samples was performed as previously reported (Labunska et al., 426:2006), as well as International standards (IS0 18589-2, IS0 2018), utilising a low-level gamma-spectrometer with a high-purity 18589-3, IS0 18589-5) were taken into account for field program germanium detector (GEM-30185, EG&G Ortec, USA) equipped with a planning and execution. multichannel analyzer (ASPEC-927) and a passive protection device. This instrument was operated using the GammaVision software (ORTEC, 2015). All QC/QA procedures and validation of the overall method were

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also conducted as described in Labunska et al. (2018). Cgrain(or wood) The analysis of 90Sr in soil samples was based on the standard pro­ CR = —----—------cedure ISO18589-5:2009 (International Organization for Standardiza­ Csoil

tion, 2009), according to which 90Sr activity concentration was where Cgrain(or wood) and Csoil are activity concentrations of 90Sr in a grain estimated through the measurement of its daughter product, 90Y. The (or in a wood) and in a soil, respectively (in Bq/kg, dry weight). To radiochemical preparation involved digestion of the ashed sample in 8 compare calculated CR values with the aggregated transfer factor values M HNO3 followed by oxalate precipitation. Strontium was purified using (TFag, in m2/kg) specified by IAEA (IAEA, 2010), we converted the latter ammonia and saturated sodium carbonate solution. The resultant to CR (dimensionless) taking into account: strontium carbonate was dissolved in 2.5 M HNO3; Y carrier was added and stored for 2 weeks such that 90Y reached equilibrium. Yttrium was - the average density of dry sod-podzolic soil of 1250 ± 250 kg/m3 then precipitated as oxalate and 90Y was measured using a beta spec­ that was determined for samples analysed throughout our study; trometer (SEB-70, AKP, Ukraine). The radiochemical separation yield - a standardized depth of soil (i.e., 0.20 m) for 90Sr specific activity was calculated using carriers such as stable Sr and Y measured using determination as recommended by IAEA (IAEA, 2009). atomic absorption spectrophotometry (Varian). Quality assurance and quality control of radioanalytical procedures were based on ISO/IEC Thus, the relationship between CR and TFag for sod-podzolic soil can 17025 standards (ISO, 2005). be expressed as: For 90Sr analysis in grains, samples of ears of grains were dried and de-seeded manually in the UIAR laboratory. Both wheat and rye lost CR = TFag x 1250 x 0.2 their husks during the de-seeding process, but additional manual sepa­ ration was required in the case of the oats. 2.5.2. Criteria for radiation safety standards (PL-2006) Both dried wood and dried grain samples were subjected to calci­ According to governmental hygienic guidelines (PL-2006) promul­ nation at 450 °C followed by a radiochemical analysis according to a gated by the Ministry of Health Protection of Ukraine (MHPU, 2006), the standard procedure (Pavlotskaya, 1997) utilizing a beta-spectrometer content of 137Cs and 90Sr in foodstuffs should meet the following radi­ SEB-70 (AKP, Ukraine). ation safety standards:

PL = C?j C%, + Cfr/ + 0.66 • ^AC^/С^ У + (ас*/ У < 1

Regular calibrations of both the gamma- and beta-spectrometers were performed using a certified mixed radionuclide source contain­ where CiCCs (^Л c<"'--,^ ), CiCSr (tA^ cfSr^^ ) are datadniri ioifni" 137cs^c andnnd 90si^r specificnz-riTzih/ activity ing 137Cs and 40K (density 1 g cm 3) (Odessa Research and Production measurements in product i with the corresponding error of measurement Centre for Ecological Safety, Ukraine) and Standard Radionuclide So­ (in brackets), in Bq/kg; are permissible levels of 137Cs and lution of 90Sr (D.I. Mendeleyev Institute for Metrology, ), respectively. Verification of the analysis was performed using Reference 90Sr for product i, in Bg/kq, that account for 50 Bq/kg and 20 Bq/kg, Material IAEA-375 “Radionuclides and Trace elements in soil” (IAEA, respectively. 2000) and IAEA-473 “Milk powder” (Austria). The laboratory has Values of PL > 1 signify the exceedance of the Ukrainian radiation regularly participated in international and national proficiency tests (e. safety standards for foodstuffs. g. International Atomic Energy Agency tests) with satisfactory outcomes In cases in which a specific activity of a radionuclide falls below the in all cases. limit of detection (LOD), it is assumed that its specific activity is equal to 1.2 LOD.

2.4. Determination of agrochemical properties of soil 3. Results and discussion

2.4.1. Determination of soil exchangeable calcium 3.1. Root uptake of 90Sr by grain plants Exchangeable calcium in soil was determined complexometrically in a 1.0 N NaCl solution with application of murexide (for calcium deter­ To investigate the transfer of 90Sr from the soil to grains, several mination) and chromogene black (for the sum Ca + Mg determination), parameters were taken into account in our research between 2011 and in each case followed by a titration with Trilon B. On the basis of the 2019, including determination of 90Sr activity concentration in grains difference between the two titrations with Trilon B, the magnesium and in soil from the same fields (e.g., paired soil-grain samples), mea­ content in solution was determined. Contents of both ions are expressed surement of pH of the soil from fields where grains were growing, and in cmol/kg of soil (Gorodniy et al., 2004). the content of exchangeable calcium in field’s soil. Additionally, 137Cs activity concentration in paired soil-grain samples has also been deter­ 2.4.2. Determination of soil solution pHH2O mined as a reference to allow comparison of measurements with the The pH of soil was detected potentiometrically in soil:water solution Ukrainian PL-2006 that includes the content of both 90Sr and 137Cs (ratio 1:2.5) using a WTW Vario 2 V00 pH meter (Xylem, USA) (Gor- (Ministry of Health of Ukraine, 2006). Of the 116 samples reported in odniy et al., 2004). the current study, 2 have not been measured for 90Sr activity concen­ tration due to samples loss (in 2016). Detailed results of these analyses obtained for each year are presented as Supporting Information (SI) in 2.5. Calculations Tables S3-S11.

2.5.1. 90Sr concentration ratio (CR) 3.1.1. Soil pH and the content of exchangeable calcium The 90Sr soil-grain and soil-wood CR were calculated as below: An important variable that influences the effectiveness of 90Sr

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leaching and mobilization from FP is the pH of soil solution (Kashparov Balonov et al., 2018). The variation in annual average 90Sr activity et al., 2004). This factor also determines the behavioural dynamics of concentrations in grains apparent in Fig. 2 was, most likely, due to the this radionuclide in soil (Kashparov et al., 2003, 2013) including its four-course crop rotation system that is in place in Ivankiv district, bioavailability. The average pH of soil solution determined in our study under which specific crops were grown on less contaminated fields in (i.e., in samples of soil paired with grain samples) was 5.6 ± 0.8 and some years while other agricultural crops (e.g., sunflower or others) ranged from 3.9 to 8.1, which was slightly greater than the range occupied the more contaminated areas. For example, it was not possible specified for sandy soil groups in the IAEA classification (pH = 3.5-6.5) to collect grain during 2016-2018 from the field near Dytiatky village (IAEA, 2010). To the authors’ knowledge, there are no other peer- that has one of the most elevated soil 90Sr activity concentrations in the reviewed published data on the acidity of the farmland soils in Ivankiv area because grain crops were simply not grown in this field in these district, Kyiv region, Ukraine. The apparently elevated pH values years. In 2019, however, both samples of grains collected from the determined in our study as compared to IAEA (2010) indicative values highly contaminated field near Dytiatky contained levels of 90Sr that did may be due to increased liming of acidic soils in Ivankiv district either not comply with the Ukrainian hygienic norms for food products (see during the agricultural processes of cultivation of crops or possibly as a Table S11 in SI). For the same reasons, the percentage of samples remedial measure previously recommended for contaminated territories exceeding the Ukrainian PL-2006 for the most common grains grown in (IAEA, 2006; Fesenko et al., 2007). Ukraine (i.e., oat, rye, and wheat) was the lowest during 2014-2017 (see The second important factor influencing the effectiveness of 90Sr Table S12 in SI) when these crops were grown on the less contaminated uptake by plants from soil is the soil content of exchangeable calcium fields. Similarly, two samples of Triticale (triticosecale) that were har­ (Anenkov and Yudintseva, 2014; Kashparov et al., 2013). The average vested in 2016 & 2017, did not exceed the PL of 20 Bq/kg for 90Sr (9 and content of exchangeable calcium in farmland soil in our study (i.e., 100 17 Bq/kg, respectively) while a single sample of Barley (HOrdeum vul- samples of soil paired with grain samples) was 1.4 ± 0.7 cmol/kg (range: gare) collected in 2018 (24 Bq/kg) was only slightly above the permis­ 0.3-3.3 cmol/kg). This falls well below the range of 2.1-3.5 cmol/kg sible level. When the crop rotation system is taken into account, (Putyatin and Seraya, 2008) (at pH within 6.1-7.2) that has been re­ therefore, it provides a possible explanation for the wide variation in ported to facilitate the lowest biological availability of 90Sr for major activities documented between years in similar crop types. agricultural crops including winter rye, spring wheat, and barley, among Overall, the activity concentrations of 90Sr in grains alone exceeded others. the Ukrainian PL in 45% of 114 grain samples, while combined 90Sr and 137Cs activity concentrations exceedance was detected in almost half 3.1.2. 90Sr content in grains and its relationship with soil pH and (48%) of all of the 116 grain samples collected and analysed over the 9­ exchangeable calcium year period (two of 116 samples of grains were analysed for 137Cs only Our data for 2011-2019 show that the situation regarding grain but not for 90Sr due to samples loss). contamination by 90Sr in Ivankiv district does not appear to be markedly There could be a number of factors that influence soil-grain 90Sr improving (see Fig. 2). The average combined 90Sr and 137Cs activity transfer, including increased bioavailability of this radionuclide (Salbu concentrations in grain samples harvested in 2018 and 2019 were still et al., 2018). above the Ukrainian PL-2006 (67% and 43%, respectively), taking into The decrease in the activity concentration of 90Sr and 137Cs in grain account the measurements of uncertainty for both radionuclides (see in the Ivankiv region has been extremely slow. Half of the samples Section 2.5.2). 90Sr activity concentration was consistently higher than exceeded the permissible levels of PL-2006 in recent years, with a half­ that of 137Cs in all grain samples. Numbers for radionuclide activity life comparable to the period of radioactive decay of radionuclides. concentrations in bold in Tables S3-S11 indicate those that were above Consequently, the problem of radioactive contamination of food grains Ukrainian PL-2006. By comparison, somewhat stricter regulations for in the area under consideration will likely persist at least for another 90Sr are in place in : 11 Bq/kg and 3.7 Bq/kg for food-grade decade from the point of view of compliance with hygienic standards of grains and grains used in children’s diet, respectively (RDU, 2006; food safety.

Fig. 2. Average activity concentration of 90Sr in grains of Ivankiv region 2011-2019. Red horizontal line - Ukrainian PL for 90Sr in grains; error bar - standard deviation. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Indeed, as it was reported previously (Bobovnikova et al., 1991), at averaged across all three staple grains (oat, wheat, and rye; number of the initial time after the accident (April - May 1986), deposited 90Sr was samples N = 111) in our study (0.50.2.6і1) is over 3 times higher than characterized by low mobility in the environment, with only 3% of the that specified by IAEA (CR = 0.14.3.0і1; number of samples N = 123). radioactive strontium from Chornobyl fallout being in a mobile This could be due to the low content of exchangeable calcium in the exchangeable form. Podzoluvisol soil that is predominant in Ivankiv district, as discussed in Over time, radionuclides incorporated into FP have leached into soil Section 3.1.1. This would be consistent with our earlier research solution, introducing 90Sr to the processes of biogeochemical migration showing that CR for soil-grain 90Sr transfer via the root uptake has an and resulting in an increase of its activity concentration in vegetation inverse relationship with the content of exchangeable calcium in a soil (IAEA, 2006; Salbu et al., 2018; Kashparov et al., 1999, 2013, 2019). (Kashparov et al., 2013): CR = 0.53 . [Ca] 1.3, although in our 9-year Our recent studies (Kashparov et al., 2013, 2019) have shown that FP study overall, we observed only a relatively weak inverse correlation deposited in Ivankiv district have almost completely dissolved. between these factors (R2 = 0.34, see Fig S1a in SI). This has resulted in an up to 85% increase of exchangeable 90Sr in Of interest is the fact that the opposite tendency was observed for sod-podzolic and sandy-loam soils of this district. We hypothesize that another radionuclide, caesium (137Cs), in one of our studies (UIAR, improper agricultural practices (such as application of excessive 2019): CR GM of 137Cs soil-grain transfer (CR = 0.030.2.8і1, N = 68) amounts of acidic nitrogen-containing fertilizers without liming, and was of the same order as specified by IAEA (2010) (CR = 0.039.3.3і1, N uncontrolled use of plant growth regulators) have also been among the = 156). major reasons for the increase of 90Sr bioavailability in the farmland We can speculate that this may be due to both large variations or soils of Ivankiv district during the last few years. Such increases could be uncertainties of the CR values given above and differences in properties attributed to the methods of use of mineral fertilizers or even simply due of the sandy soils (e.g., the content of calcium and other clay minerals to the absence of any land-reclamation measures. Moreover, the positive and soil acidity, among others) that were the subject of our research impacts of liming lasts approximately only for 4 years assuming that the compared to those provided in the IAEA handbook (2010). appropriate dosage to soil has been applied. Thus, the agricultural In addition, although it has previously been reported for radioac- countermeasures that were undertaken in Ivankiv district in late 90s tively contaminated farmland in Belarus that CR of 90Sr soil-grain may be expected by now to have completely lost their effectiveness, transfer decreases linearly with rising soil solution pH (in the range of contributing to a gradual acidification of farmland soils and, hence, pH increase from 4 to 7) (Putyatin and Seraya, 2008), we found no such increased 90Sr bioavailability. Low crop yield is one of the parameters correlation in our study (see Fig. S1b in SI). This apparent discrepancy indicative of improper agricultural practices. This has been observed for may be explained by differences in the agricultural activities undertaken example, in 2013 in fields near Dytiatky village when the rye crop yield on specific fields, such as the intensity of liming applications that may was only 130 t/km2, while the average for this crop yield accounted for result in changes and variations in both the content of exchangeable 210 t/km2 and 228 t/km2 in Kyiv region and in the whole of Ukraine calcium and the pH of the soil solution. Thus, we would like to stress that (SSSU, 2019), respectively. the current study has some limitations arising from: To evaluate 90Sr soil-grain transfer parameters, we calculated the concentration ratios (CR) of the activity concentration of radionuclide in 1. The unpredictable rotation of crops growing on the same fields. Such the plant (Bq/kg) to that in the soil (Bq/kg) (see Section 2.5). These are rotation was irregular until about 2010, since when it has been presented in Table 1, together with the parameters published previously mainly a 4-year rotation (e.g., various grain crops, sunflower plants, (IAEA, 2009, 2010), to place the data in context. The conversion of TFag and maize) performed mostly by large agricultural companies. values specified by IAEA to CR values was calculated as presented in 2. Liming of the agricultural soil. Liming of the soils in the study area Section 2.5. In general, CR of 90Sr soil-grain transfer behaves lognor- was very sporadic and it was not possible to find, in many cases, the mally according to the random values distribution law (Khomutinin pattern of lime applications on any particular field. As a rule, liming et al., 2001). should be applied every 4 years to decrease the root transfer of 90Sr The relatively higher values of CR geometric mean (GM) of soil-grain to plants. It was, however, not possible to get reliable information on transfer observed for oats (CR = 0.69.2.7і1, N = 34) as compared with whether this had been carried out in the study area. rye (CR = 0.47.2.5і1, N = 48) and wheat (CR = 0.37.2.4і1, N = 29) are considered to be due to the fact that oat grains are covered by a hard 3.1.3. Estimation of prospective 90Sr content in grains produced in Ivankiv separable husk, which accumulates a significant portion of the radio­ district nuclides taken up (IAEA, 2010). The removal of the oat husk decreased As noted earlier, monitoring of 90Sr content in grains is a time 90Sr activity concentration in oat cereal grains by up to half, which was consuming, expensive and laborious process that requires special confirmed in our laboratory experiments. equipment and trained personnel. More importantly, such monitoring is Overall, the geometric mean for CR for 90Sr soil-grain transfer possible only after consumer products (e.g., cereal grains) are produced. To overcome these difficulties, we estimated current levels of grain

Table 1 contamination by 90Sr in the whole Ivankiv district based on our long­ Concentration ratio (CR) of 90Sr soil-grain transfer for sandy soils. N - samples term research, with an aim of helping to support appropriate planning number, GM - CR geometric mean, GSD - CR geometric standard deviation, AM - of agricultural activities in this area. We compiled a hand-contoured CR arithmetic mean, SD - CR standard deviation. isoline map (Fig. 3), based on GM of CR = 0.5.2.6і1 for 90Sr soil-grain transfer obtained in this study and the data on levels of soil radioac­ Grain type Source N GM GSD AM SD CR Range tive contamination with 90Sr in Ivankiv district (Kashparov et al., 2018), assuming that new input of 90Sr from FP to soil is currently insignificant. Oat (Avena) Current 34 0.69 2.7 1.2 1.3 0.08-6.0 Rye (Secale study 48 0.47 2.5 0.72 0.79 0.04-3.7 Estimated 90Sr activity concentration of grains was calculated (to 95% cereale) probability) according to the formula below: Wheat 29 0.37 2.4 0.53 0.48 0.08-1.9 (Trfticum) Cg„i„ = Csoil x CR Combined 111 0.50 2.6 0.80 0.95 0.04-6.0 Cereals where Cgrain is estimated current 90Sr grain activity concentration (Bq/ Grain kg); Csoil is estimated current 90Sr soil activity concentration (Bq/kg) Cereals Grain (IAEA 123 0.14 3.0 0.23 0.23 0.004-1 calculated based on our measurements data from 2014 and taking into 2009, 2010) account the half-life of 90Sr; CR is GM of 90Sr soil-grain transfer factor

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Fig. 3. Map of estimated current levels of 90Sr activity concentration (95% confidence interval) in cereal grains growing in Ivankiv district, Ukraine. Ukrainian PL for 90Sr in grains is 20 Bq/kg.

obtained in this study (i.e., 0.5-2.6±1). activity concentration of 90Sr in grains is not expected to exceed 40 Bq/ According to our estimation, contamination of grains by 90Sr in kg for most of the areas in the Ivankiv district. For comparative pur­ Ivankiv district may be expected to decrease by only approximately poses, although there are no regulations currently in place in Ukraine 2-3% per year. concerning the limits of 90Sr in animal feed, permissible levels for animal The isolines for areas where contamination of grains by 90Sr is pre­ feed grains in Belarus and Russia are set at 100 Bq/kg and 140 Bq/kg, dicted to 95% confidence to be below Ukrainian PL are presented. Our respectively (RDU, 2006; MARF, 2001). Overall, without countermea­ modelled data show that the greater part of the Ivankiv district could sures to reduce 90Sr soil-grain transfer in the north-eastern part of produce grains containing 90Sr below Ukrainian PL-2006. However, the Ivankiv district, there is still a high probability that the cereal grain production of grains in the north-eastern part of the district may still produced in this area of Ukraine could exceed the Ukrainian PL of 20 result in contaminated grain products containing 90Sr at up to twice the Bq/kg. Targeted remedial actions such as liming and application of Ukrainian PL-2006, though in fairly limited areas only. The estimated mineral and organic fertilisers may reduce the activity concentration of

Fig. 4. 90 Sr activity concentration in composite wood samples (n = 5 for each composite) collected from forests of Ivankiv district in 2015 and 2019. W01 - W12 - sample codes as presented in Table S2 and Fig. 1; error bar - STD; red horizontal line - Ukrainian 90Sr PL for firewood. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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90Sr in grains by about half (Fesenko et al., 2007, 2013). In practical Ukraine that were contaminated as a result of the accident at the ChNPP. terms these measures may help bring the quality of the grain produced For example, a study by Lazarev and co-authors (2018) reported that across the whole Ivankiv district in conformity with the Ukrainian contamination of firewood by 137Cs still persists in Zhytomyr region, regulation (PL-2006). There is an urgent need for a purpose-orientated which was one of the areas in Ukraine most impacted by the Chornobyl government program to implement and reinforce such countermea­ accident but where people still reside. The specific activity concentra­ sures. Such a program would have a beneficial effect on agricultural tion of 137Cs in samples of firewood-originated ash obtained from pri­ production within the territories of this district. Moreover, the findings vate households in that area varied significantly - from 230 to 32900 of this study could be applicable to other areas in the world with Bq/kg - as was detected in the rural town of Narodychi. Furthermore, in documented 90Sr contamination. These include Braginsky and Hoyni- about 30% of ash samples from this town, the specific activity concen­ kovsky districts of the Republic of Belarus that were also contaminated tration of 137Cs exceeded 10000 Bq/kg, which could be classified as low as a result of the accident at the ChNPP. The regulatory limits for 90Sr in activity radioactive wastes that are subject to a regulatory control ac­ grains (RDU, 2006) are much stricter in these districts than in Ukraine. cording to Ukrainian regulations (OSPU, 2005). In this regard, several In addition, the finding could be applicable to land radiologically measures may be introduced in order to prevent or reduce the exposure contaminated as a result of the accident in Kyshtym, Russia, in 1957 of population to radioactive materials, such as contaminated ash, (Pozolotina et al., 2010). including:

3.2. 90Sr in forest wood samples - to decrease or, if possible, to eliminate the usage of radioactively contaminated woods as firewood; 3.2.1. 90Sr activity concentration - to establish a monitoring program to determine the levels of radio­ The results of 90Sr activity concentration analyses in composite active contamination of ash formed in both households and at the samples of wood collected in 2015 and 2019 are presented in Fig. 4. In local TPP; both studies, 75% of samples (i.e., nine of each twelve composite sam­ - to provide the population with the information on safe handling of ples) collected from tree trunks contained 90Sr concentrations exceeding radioactively contaminated ash; and Ukrainian PL for firewood of 60 Bq/kg (Ministry of Health of Ukraine, - to establish a centralized disposal service for such ash. 2005), at between 1.1 and 4.6 times the limit value. This is consistent with an earlier study conducted by UIAR in Ivankiv district in 3.2.2. Estimation of 90Sr content in forest wood in Ivankiv district 2012-2013 (Otreshko et al., 2015), which showed that activity con­ The estimation of 90Sr content in wood was based on the same as­ centrations of 90Sr in small brushwood (26 samples, length ~20 cm, sumptions as we presented in Section 3.1.3 (for estimation of 90Sr con­ diameter ~5 cm) exceeded Ukrainian PL in samples collected from lo­ tent in grain) and using CR GM values of 90Sr soil-wood transfer factor cations in about half of the district territory. calculated in this study. Table 2 presents the parameters of CR 90Sr soil­ The composite sample from one location (W07) reached the 90Sr PL wood lognormal distribution together with the corresponding parame­ in 2019 while its equivalent from 2015 fell below the value. In general, ters reported previously (IAEA, 2009, 2010) - for comparison. the situation with respect to contamination by 90Sr in the study area of CR GM of 90Sr soil-wood transfer for both pine (CR = 11.5.3.6і1) and Ivankiv district has not changed much over the 4 year period to 2019. birch (CR = 11.2.2.2і1) calculated in this study were more than an order This is in broad agreement with another study conducted in 2018 of magnitude greater than CR values of 0.4 and 0.6, respectively, (Lazarev et al., 2018) that reported high frequency of 90Sr PL exceedance calculated using TFag specified by IAEA (2010) and the average density in samples of pine (100%, n = 16) and birch (67%, n = 9) from Ivankiv of dry sod-podzolic soil (1250 ± 250 kg/m3, dry weight) that was district. measured in 0.2 m deep soil samples analysed throughout our study in The results of the current study suggest that there is a persistent Ivankiv district (see Sections 2.2 and 2.5 for details). This difference is, exceedance of 90Sr PL in wood of Ivankiv district that could potentially most probably, due to differences in properties of the soil that we be used as fuel wood in both private households and in the local TPP. investigated in Ivankiv district and those soil properties used in calcu­ Therefore, alternative energy sources (e.g., solar and wind) should be lations carried out by IAEA. Our study was conducted on trees grown on used instead of local wood resources in this region. Podzoluvisol soils of Ivankiv district of Ukraine that were characterised, Largely for financial reasons, local residents have become increas­ at the time of our investigation, by low content of exchangeable calcium, ingly reliant on firewood that they can collect in the forest for heating which is typical of growing conditions for either pine or birch trees in and cooking rather than purchasing commercial supplies. Moreover, Ukraine. usage of locally grown wood at the Ivankiv TPP, which is located inside CR values specified by IAEA were obtained based on a) the more of the 3rd Zone of Chornobyl radioactive contamination area, is a cause of great concern due to formation of radioactively enriched ashes at the Table 2 power plant, the fate of which is not currently known. Concentration ratio (CR) of 90Sr soil-wood transfer. N - number of composite In a low ash content wood, radionuclides may concentrate greatly in samples, GM - CR geometric mean, GSD - CR geometric standard deviation, AM - the mineral residue after burning, resulting in a 50-100 fold increase in CR arithmetic mean, SD - CR standard deviation, n/a - not available. ash activity (IAEA, 2003; Ladygiene et al., 2010) as compared to initial Plant Source N GM GSD Min Max AM SD uncombusted raw materials; such ashes may even reach levels charac­ teristic of radioactive wastes. As an example, in 2015 we collected one Pine (Pinus Ivankiv 33 11.5 3.6 0.7 81 19.5 18.3 sample of ash from a local private house that continuously used brush­ sylvestris district L.) studiesa wood as a fuel for a cooking oven. The ashes from this oven have been Birch 15 11.2 2.2 2.3 38 15.0 11.5 traditionally spread over the domestic vegetable plot every year. Anal­ (Betula ysis of this sample for both 90Sr and 137Cs revealed the presence of these pendula) radionuclides at the activity concentrations of 6950 Bq/kg and 650 Bq/ Pine (Pinus (IAEA, 5 0.40 n/a 0.15 2.5 n/a n/a sylvestris 2009, kg, respectively, which for 90Sr was 25 times higher than the most 90Sr L.) 2010) contaminated composite wood sample in our study (i.e., 278 Bq/kg, Birch 5 0.60 n/a 0.15 1.5 n/a n/a from location W09), and around 100 times the Ukrainian PL for this (Betula radionuclide in wood. pendula) Unfortunately, it is not only 90Sr that still contributes significantly to a - calculation based on data from: current studies for the years 2015 & 2019 and the radioactive contamination of forest-derived wood in some areas of Otreshko et al. (2015) in the case of 2013.

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fertile soils in the southern Urals, Russia, investigated during relatively (over 87 years). early stages (in 1966-1972) of the Kyshym disaster - the accident at the Mayak nuclear waste reprocessing plant near Kyshym town (IAEA, 4. Conclusions 2009), and b) soils in Ukraine affected by Chornobyl, but again, inves­ tigated in the early period after the accident (1991-1992) when 90Sr had The analysis of grain and wood samples collected in Ivankiv district, only partially leached from fuel particles into soil. Hence, its content in Ukraine, located to the south and south-west of the Chornobyl nuclear the root habitable layer of soil (20 cm) had not decreased significantly power plant (ChNPP), during the period from 2011 to 2019, has through the processes of biogeochemical migration (Kashparov et al., reconfirmed that high and radiologically significant levels of 90Sr 2003, 2018; Thiry et al., 2009; Otreshko et al., 2015). The recent study contamination still persist 34 years after the accident: (Bilous et al., 2020) investigating 90Sr content in the stem-wood of Silver birch, Black alder and Common aspen in forests within Ukrainian • 45% of grain samples collected over the 9-year period from fields in Polissya has also reported CR values for 90Sr exceeding corresponding Ivankiv district, approximately 50 km from ChNPP, contained 90Sr at values provided by the IAEA. A more recent study on vertical distribu­ concentrations above permissible level for human consumption, and tion of 90Sr in soil profiles and its uptake by Scots pine growing within in two cases were more than double this limit. the ChNPP territory (Holiaka et al., 2020a, 2020b) has also reported • Combined 90Sr and 137Cs activity concentrations exceedances of the much higher soil-pine transfer factors (GM of TFag for sapwood and PL-2006 were detected in almost half (48%) of all 116 grain samples. wood core were 0.02 m2/kg and 0.028 m2/kg, respectively) than that • 82% of composite wood samples collected in Ivankiv district in 2013, reported by IAEA (2010) of 1.6 • 10 3 m2/kg. Holiaka et al. (2020a, 75% in 2015, 88% in 2018, and 75% in 2019, exceeded the Ukrai­ 2020b) suggested that 90Sr soil-pine transfer factor may change due to a nian permissible level for 90Sr in firewood. decrease of the 90Sr content in the 20-cm root-bearing layer due to a • Ash from household ovens in areas affected by the Chornobyl acci­ vertical migration of radionuclides to both deeper layers of soil and to dent in Ukraine that use local brushwood as fuel, may reach or even the forest stand. exceed levels of 90Sr (and 137Cs) activity concentration specified for Based on the obtained CR GM for 90Sr transfer from soil to pine and low activity radioactive wastes. birch trees (see Table 2) and levels of radioactive contamination of soils in Ivankiv district that we reported earlier (Kashparov et al., 2018), we Our studies indicate that 90Sr transfer coefficient (CR) from soil to estimated current levels of forest wood contamination by 90Sr for the plants has changed over time following the initial contamination. This is whole Ivankiv district and compiled a hand-contoured isoline map (see likely due to a number of biogeochemical processes and, in the case of Fig. 5). grains, may be mainly attributable to insufficient application of coun­ Our estimates of forest wood contamination by 90Sr presented in termeasures. We report values of CR of 90Sr for culinary grains and forest Fig. 5 suggest that there is a high probability that firewood obtained in woods calculated for the late-stage of the initial radiological contami­ the majority of forests in Ivankiv district could exceed 90Sr PL of 60 Bq/ nation that can be used to estimate food or wood activity concentrations kg. Only a small portion of the forests located in the eastern part of for 90Sr in areas of similar soil type. Ivankiv district are likely to comply with the Ukrainian hygienic norms Taking into account that the governmental monitoring of goods for stipulated for firewood. The activity concentration of 90Sr in wood of the 90Sr in Ukraine has not been carried out since 2013, the situation with forests located in vast areas of the north-east part of Ivankiv district the 90Sr contamination of the grains grown in the Ivankiv district re­ could exceed 90Sr PL for firewood by up to 8 times. It is to be expected mains of major concern and deserves further urgent investigation. that the woods growing on these territories may still be radioactively Similarly, further research is urgently indicated in order to assess the contaminated above the PL for a period exceeding three half-lives of 90Sr effects of the Ivankiv TPP activity on the environment and upon local

Fig. 5. Map of estimated levels of 90Sr activity concentration (95% confidence interval) in forest wood growing in Ivankiv district, Ukraine. Ukrainian 90Sr PL for firewood is 60 Bq/kg.

9 I. Labunska et al. Environment International 146 (2021) 106282 residents, which still remains mostly unknown and the risks incom­ strategies in the long term after the Chernobyl accident. J. Environ. Radioact. 119, pletely characterised. 39-47. https://doi.org/10.1016/j.jenvrad.2010.08.012. Fucic, A., Brunborg, G., Lasan, R., Jezek, D., Knudsen, L.E., Merlo, D.F., 2008. Genomic The current lack of routine and comprehensive environmental and damage in children accidentally exposed to ionizing radiation: a review of the food monitoring programs is a major omission in current regulatory literature. Mutation Res./Rev. Mutation Res. 658 (1-2), 111-123. https://doi.org/ efforts. It continues to place severe limits on the assessment of radio­ 10.1016/j.mrrev.2007.11.003. Gorodniy, M.M., Lisoval, A.P., Bykin, A.V., et al., 2004. Agrochemical Analysis. Tutorial. logical risk and on the design and implementation of measures that (Ed) Gorodniy M.M., Pub. Aristey, Kyiv, 522p. could otherwise help limit exposures to radioactive elements in local Gupta, D.K., Schulz, W., Steinhauser, G., Walther, C.l., 2018. Radiostrontium transport in communities. If areas of high contamination are to be identified and plants and phytoremediation. Environmental Science and Pollution Research. Springer. https://doi.org/10.1007/s11356-018-3088-6. properly managed to avoid further spread of radionuclides, and if the Holiaka D.M., Levchuk S.E., Yoschenko, V.I., Kashparov, V.A., Yoschenko, L.V., Holiaka, burden of radiation-related disease in these impacted communities M.A., Pavliuchenko, V.V., Diachuk, P.P., Zadorozhniuk, R.M., Morozova, V.S., 2020. (including psychological aspects) is to be reduced, it is vital that such 90Sr and 137Cs inventories in the deports and biogenic fluxes of the typical forest stands in the . Nuclear Physics and Atomic Energy (in scientific surveillance programs are reinstated and properly financed press). (In Ukrainian). into the future. Holiaka, D.M., Levchuk, S.E., Kashparov, V.A., Holiaka, M.A., Yoschenko, L.V., Otreshko, L.N., Kosarchuk, O.V., Lazarev, N.M., 2020b. Vertical distribution of 90Sr in soil profiles and its uptake by scots pine (Pinus Sylvestris L.) wood growing within CRediT authorship contribution statement the Chernobyl exclusion zone. Nucl. Phys. At. Energy 21, 157-165. http://jnpae. kinr.kiev.ua/21.2/html/21.2.0157.html. I. Labunska: Conceptualization, Formal analysis, Investigation, IAEA, 2011. Radiation protection and safety of radiation sources : international basic safety standards : general safety requirements. - Interim edition. Part 3 No. GSR Part Writing - original draft, Visualization. S. Levchuk: Conceptualization, 3 (Interim) [WWW Document]. Int. At. Energy Agency, Vienna. URL http://www-p Methodology, Formal analysis, Investigation, Writing - review & editing, ub.iaea.org/MTCD/publications/PDF/p1531interim_web.pdf. Visualization. V. 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Assessing radiation doses to the public from radionuclides in timber and Declaration of Competing Interest wood products. TECDOC-1376. IAEA, Vienna. IAEA, 2000. Reference material IAEA-375. Radionuclides and trace elements in soil [WWW Document]. URL https://nucleus.iaea.org/rpst/Documents/rs_iaea-375.pdf The authors declare that they have no known competing financial (accessed 3.13.18). interests or personal relationships that could have appeared to influence ISO/IEC,2005. General requirements for the competence of testing and calibration the work reported in this paper. laboratories. https://www.sis.se/api/document/preview/906087. Kashparov, V.A., Oughton, D.H., Zvarich, S.I., Protsak, V.P., Levchuk, S.E., 1999. Kinetics of fuel particle weathering and 90Sr mobility in the Chernobyl 30-km exclusion zone. Acknowledgments Health Phys. 76 (3), 251-259. 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Territory contamination Kriston who contributed to the graphical abstract for this article. We also with the radionuclides representing the fuel component of Chernobyl fallout. Sci. would like to thank three anonymous reviewers whose constructive Total Environ. 317 (1-3), 105-119. https://doi.org/10.1016/S0048-9697(03) 00336-X. comments helped greatly in improving this paper. Kashparov, V.A., Ahamdach, N., Zvarich, S.I., Yoschenko, V.I., Maloshtan, I.N., Dewiere, L., 2004. Kinetics of dissolution of Chernobyl fuel particles in soil in natural conditions. J. Environ. Radioactivity 72 (3), 335-353. https://doi.org/10.1016/j. Appendix A. Supplementary material jenvrad.2003.08.002. Kashparov, V.A., Levchuk, S.E., Otreshko, L.N., Maloshtan, I.M., 2013. Contamination of Supplementary data to this article can be found online at https://doi. agricultural production with 90Sr in Ukraine at the late phase of the chernobyl org/10.1016/j.envint.2020.106282. accident. Radiation Biol. 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