Radioecological studies of urban soils in the Arkhangelsk region

Abstract

The aim of the study: to analyze the radioecological status of soils in the Mezen city and the Kamenka village (Mezensky district of the Arkhangelsk region) and to identify low-intensity anomalies in soil ¹³⁷Cs, ²²⁶Ra, ²³²Th and ⁴⁰K specific content on the studied territory.

Location and time of the study. Field work was carried out in the summer of 2021 on the territory of the Mezen city and Kamenka village and their environs (Mezensky district of the Arkhangelsk region).

Methodology. To accomplish the task, the soil from the upper 5 cm layer of Urbikvizems, Culturozems and Replantozems at 68 sites was sampled in the study area. Under laboratory conditions, the samples were air-dried and placed in Marinelli vessels to measure specific activity of isotopes by gamma spectrometry. The registration of gamma radiation from a soil sample, as well as the processing of the spectra, was carried out using the Progress-gamma software and hardware complex FVKM.412131.002-03. The energy calibration of the gamma spectrometer was carried out after each measurement using a combined control source OISN-137-1 in a 1-liter Marinelli vessel. The minimum exposure time for the counting sample was 3600 seconds.

Results. The specific activity of ¹³⁷Cs in the upper 5 cm layer varied from 1,6 to 24,2 Bq/kg in Mezen and from 2,4 to 26,1 Bq/kg in Kamenka, with an average value of 5,88 and 8,27 Bq/kg, respectively; higher specific activities of this radionuclide was observed in the Kamenka soils as compared with the Mezen soils. For ²²⁶Ra and ²³²Th higher activity was also observed in the Kamenka soils. The ⁴⁰K specific content in the urban soils of the studied area was almost uniform. The specific activity of technogenic ¹³⁷Cs and natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in the upper 5 cm of soil layer on pastures and grasslands was comparable to the urban soils in Mezen and Kamenka. In forest soils the ¹³⁷Cs specific activity was more than three times higher, reaching 65,4 Bq/kg. Analysis of the spatial distribution of the specific activity of technogenic ¹³⁷Cs and natural radionuclides ⁴⁰K, ²²⁶Ra and ²³²Th showed that small local anomalies (SLA) of ¹³⁷Cs (T_1/2=30.17 years) were confined to the park zone of the central and southern parts of Mezen, where 4 MLAs were recorded. The natural radionuclides ²²⁶Ra (T_1/2=1590 years), ²³²Th (T_1/2=1, 41*1010 years) and ⁴⁰K (T_1/2=1.3*109 years) were found mainly in meadow soddy soils on the western outskirts of the city, in areas of one-story buildings (private sector), along banks of the Tova River and also in the airport area. In the rest of the Mezen city, the measured concentrations of the studied radionuclides were minimal. The spatial distribution of the studied radionuclides, revealed in the upper soil layer in the Mezen city, was also typical for Kamenka, where SLA of ¹³⁷Cs were found in the soils of park areas in the southwestern part of the village without intensive anthropogenic impact. ²²⁶Ra and ²³²Th were characterized by increased concentrations on the outskirts of Kamenka in the north and south. The distribution of ⁴⁰K is almost uniform throughout the entire study area, including not only the outskirts, but also the central parts of the village.

Conclusions. The content of natural and technogenic radionuclides in the urban soils of the Mezen city and Kamenka village do not exceed the maximum allowable concentrations and are typical for urban settlements in the Arkhangelsk region. Higher activity of ¹³⁷cs the Kamenka soils as compared with the one in the Mezen soils can be explained by varying degrees of anthropogenic impact on soils in the studied area. SLA of ¹³⁷Cs in park soils are due to the minimal anthropogenic impact; moreover, the soddy soil layer firmly fixes the atmospheric input by humic acids. SLA of ²²⁶Ra and ²³²Th in the meadow soddy is soils closely associated with the underlying sandy quaternary deposits, concentrating the elements. The SLA of potassium in these areas can be explained by the dense herbaceous vegetation, which easily involves the element in the biological cycle, thus contributing to its accumulation in the upper soil horizon.