Assessment of the current levels of 241Am and 137Сs in soils and foodstuff, as well as of public internal exposure to ionizing radiation in populated areas adjacent to the Chernobyl NPP exclusion zone (case study: the Bragin district of the Gomel region, Belarus)

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The results covered in this paper relate to the “Khoiniki” research sub-unit of a larger-scale sequence of studies focused on the local assessments of the present-day 241Am and 137Cs concentrations in the soils and locally produced foods, with the estimation of the public internal radiation doses in the residential areas of the Gomel region of the Republic of Belarus most closely adjacent to the ChNPP resettlement zone. The objective was to make a conservative estimate of a committed annual dose of internal exposure from 241Am and 137Сs received by the villagers of 96 farmsteads in 30 settlements of the private sector of Khoiniki countryside through both, inhalation and consumption of local foodstuffs. The results obtained in this study include an update of the existing contamination levels of 241Am and 137Сs present in the local soils and foods grown or produced in private backyards and households. 241Am in food samples was determined by alpha-spectroscopy radiochemical analysis with the use of selective extraction-chromatographic resins. Gamma-spectrometry techniques were used to measure 241Am in soil samples and 137Сs in soil and food samples. Based on our findings, the present-day deposition density of 241Am in the soils does not exceed 4 kBq/m2 , while the values of 137Cs contamination are by one to two orders of magnitude higher than that of 241Am and vary between 30 and 500 kBq/m2 . Generally, the values of activity concentration of 241Am detected in local soils are well within 10 Bq/kg in the majority of inspected villages, with the exception of three sites where higher levels of 241Am contamination is soils were detected ranging from 14 to 16 Bq/kg. The ambient dose rates in the countryside range from 0.05 to 0.38 μSv/hour, with the average of 0.15 μSv/hour. No cases of 137Сs contamination above the established reference levels of 80, 100 and 90 Bq/ kg have been found in the local food samples of, respectively, potatoes, vegetables (incl. roots and tubers) and grains. The content of 241Am in the staple foods produced in the area varies from single digits to tenths of mBq/ kg, which is less by three orders of magnitude than 137Сs activities concentrationd found in the same staples. Of the two pathways contributing to the local committed internal exposure from 241Am, the dominant one is through inhalation (0.006–0.038 mSv/year) prevailing over the consumption pathway of this same radioisotope by at least one order of magnitude. At the time of gardening and other household field works, the existing levels of 241Am contamination in soils are estimated to produce from 85 to 98% of the internal radiation dose received by individuals from inhaling the total of 241Am and 137Сs. The maximum committed annual doses of internal exposure from 137Сs are estimated to be above 1 mSv/year in 6 out of 30 villages engaged in our study. At the same time, the estimated internal radiation dose due to 241Am does not surpass 0.04 mSv/year. The 137Сs major contribution to the internal exposure of villages in the Khoiniki countryside is through food consumption.

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Section: Research Articlesunclassified

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241Am and 137Сs in the Khoiniki district of Belarus: updated radiological assessment of the local existing exposure situation

Нилова

Bortnovsky

Тагай

et al. 2021

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Validation of a method for in situ determination of 137Cs soil contamination density in kitchen gardens using the portable spectrometer-dosimeter MKS AT6101D

Рамзаев

Барковский

Братилова

2021

The collection of representative soil samples in the territory of settlements and subsequent measurements of the content of radionuclides in these samples under laboratory conditions (the so-called “ex situ method”) is a generally accepted technology for determining the density of soil contamination with 137Cs in the populated areas contaminated due to the Chernobyl accident. Recently, as a supplement or alternative to the ex situ method, researchers are developing field (in situ) gamma-spectrometry methods. These methods allow determining the density of soil contamination with 137Cs directly on site, without soil sampling and laboratory analysis. At the same time, the in situ methodology has several limitations, the most important of which is a lack of generally recognized metrological basis for measurements and interpretation of results. Hence, before using a particular technique and measuring device for carrying out large-scale in situ measurements, it is necessary to validate (to assess the suitability) of the selected in situ method using an established ex situ method. The aim of this study was to validate the method for determining the density of 137Cs soil contamination in kitchen gardens using the MKS AT6101D spectrometer-dosimeter in situ. The method was recently presented by a Russian-Swedish-Belarusian group of researchers in an article published in the Journal of Environmental Radioactivity (https://doi.org/10.1016/j.jenvrad.2021.106562). To validate this method, we selected 10 representative kitchen garden plots. The plots were located in six settlements of the Bryansk region in Russia. The territory of the settlements had been heavily contaminated with 137Cs as a result of the Chernobyl accident: the officially established levels of the density of soil contamination by 137Cs ranged from 111 to 511 kBq/m2 in 2017. Field gamma-ray spectra were recorded at a height of 1 m above the ground in the center of kitchen garden plots using the MKS AT6101D device. The measurement duration was in the range of 1207–1801 s (the mean value = 1383 s). Samples of soil in the kitchen gardens were taken layer by layer (with a step of 5 cm) to a depth of 20 cm using a demountable cylindrical sampler. The 137Cs content in each soil layer was determined in the laboratory using a stationary semiconductor gamma spectrometer. The values of the 137Cs contamination density of the sampled soils ranged from 77 to 548 kBq/m2. It was found that the results of the ex situ analyzes of soil samples were in a good agreement with the contamination density values obtained with the in situ method. On average, the difference between two methodologies was 7% (a maximum of 20%). The results of the study confirm that the method proposed by the international group is suitable for determining the density of soil contamination by 137Cs in kitchen gardens in remote period after the Chernobyl accident.

Ambient dose equivalent rate and soil contamination density with 137Cs in kitchen gardens in settlements of the Bryansk region, Russia in 2020–2021

Рамзаев

Barkovsky

Братилова

2021

The article provides results of application of the field (in situ) gamma spectrometry method for carrying out mass monitoring measurements of ambient dose equivalent rate and soil contamination density with 137Cs in kitchen garden plots located in the zone of radioactive contamination after the Chernobyl accident. In 2020 and 2021, 115 private farmsteads in 46 settlements of the Bryansk region were surveyed. At the time of the survey, the officially established average density of soil contamination with 137Cs in the settlements ranged from 27 to 533 kBq/m2 . The field spectra were measured using a portable scintillation gamma-spectrometer-dosimeter. Results of the field measurements and subsequent calculations of soil contamination density with 137Cs in the kitchen gardens were in good agreement with official data on the average soil contamination density with 137Cs in the surveyed settlements. The mean value of the ratio of the experimental data to the official data was 1.04. Individual values of experimental data deviated from corresponding official values by no more than two times. The use of the gamma spectrometry method in situ made it possible: 1) to determine separately values of the ambient dose equivalent rate from 137Cs and from natural radionuclides in the soil, and 2) to estimate the effective external doses to a person who worked in the kitchen gardens. The measured values of ambient dose equivalent rate varied from 17 to 53 nSv/h (mean ± standard deviation = 35 ± 9 nSv/h) for natural radionuclides and from 8 to 432 nSv/h (mean ± standard deviation = 125 ± 91 nSv/h) for 137Cs. The ambient dose equivalent rate from 137Cs normalized to the soil contamination density with 137Cs in the same kitchen garden was in the range of 0.41–0.84 (nSv/h)/(kBq/m2 ) with a mean value of 0.55 (nSv/h)/(kBq/m2 ). If a person stayed in kitchen garden for 840 hours per year, the estimated effective external doses from natural radionuclides and 137Cs were respectively in the range of 0.008–0.025 mSv/year and 0.004–0.20 mSv/year.