Environmental assessment of risks associated with the Ordovician Dictyonema shale in the eastern part of the Baltic Klint

Sergej V Lebedev ,Petr V Fedorov ,V V Kurilenko ,Stanislav Dubrova ,Willington Siabato

doi:10.21638/11701/spbu07.2018.202

Abstract

The results of research considered in this article made it possible to expand the understanding of the environmental risks associated with the highly radioactive bituminous argillites of the Baltic Sea region. The natural patterns of the distribution of natural radionuclides 226Ra, 232Th and 40K are established along the strike and thickness of layers. The average value of the effective specific activity (ESA) for all samples in the Koporka River valley amounted 1270 Bq/kg. The minimum value of ESA was 650 Bq/kg (the closest to the seam roof level), and the maximum value was 3750 Bq/kg (the second from the seam floor level). Conversion to mass fractions of natural radionuclides (NRN) showed that the average content of uranium in the sample amounted up to 90.7 g/t, thorium up to 11.4 g/t and of potassium up to 4.1%. The high heterogeneity of the content distribution of NRN along the strike of the Dictyonema shale seam was confirmed by studies of separate outcrops of highly radioactive rocks along the banks of the Tosna River. In general, the level of the argillites radioactivity has abnormally high value and exceeds the natural background more than ten times. The average annual values of the effective dose amounted from 5,8 to 10,7 mSv/year, that should be classified as the territories of emergency ecological danger and zones of ecological disaster.

Highlights

A geological formation with a high content of natural radionuclides (NRN) belongs to the category of natural geological objects defining the environment in the study area
We have tried to significantly clarify the understanding of the environmental risks associated with the highly radioactive bituminous argillites of the Leningrad region based on the determination of NRN and the natural unevenness of their distribution along the strike and thickness of layers and to calculate the potential radiation exposure to the components of the environment
A change in the thickness strata of radioactive bituminous argillites or bituminous mudstones, traditionally called the Dictyonema shale, occurs near the base of the Ordovician sedimentary sequence of the Leningrad region and reveals numerous rivers and streams cutting through the ledge of the eastern part of the Baltic Klint (the Ingrian (Ingermanland) Klint)

Summary

Introduction

A geological formation with a high content of natural radionuclides (NRN) belongs to the category of natural geological objects defining the environment in the study area. One is the determination of NRN by considering the natural unevenness of their distribution along the strike, thickness of layers and calculating the radiation dose provided by the geological formation on the environment Another way to estimate the environmental risk is a direct determination of the radiation dose to biota and humans by exploring the components of the envi-. We have tried to significantly clarify the understanding of the environmental risks associated with the highly radioactive bituminous argillites of the Leningrad region based on the determination of NRN and the natural unevenness of their distribution along the strike and thickness of layers and to calculate the potential radiation exposure to the components of the environment. To the south of the Klint the bituminous mudstones immerse under the carbonate rock strata composing the Ordovician plateau (Alexandrova, 1971)

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