Yerevan soil radioactivity: Radiological and geochemical assessment

Spatial pattern of naturally occurring radionuclides (NOR): ²²⁶Ra, ²³²Th, ⁴⁰K, and artificial ¹³⁷Cs was studied using soil samples of the multipurpose geochemical survey of the city of Yerevan, capital of Armenia. High purity Ge detector-based gamma spectrometry system was used for the determination of radionuclides activity concentrations in urban soils. A combination of compositional data analysis, geochemical mapping and radiological assessment were applied to reveal potential factors of technologically enhanced natural radioactivity and excess lifetime cancer risk for Yerevan's population due to NOR and artificial ¹³⁷Cs in the urban environment. Statistical methods with the geochemical mapping revealed the great contribution of soil-forming rocks to NOR distribution in urban soils. The spatial distribution of calculated radiological indices and dose rates levels follows the distribution patterns of NOR. The activity concentration of fallout radionuclide ¹³⁷Cs was within the range typical for the studied altitudes. Above baseline activity of ¹³⁷Cs was observed in the north-western and western part of the city that is in typical ranges of ¹³⁷Cs content in soil derived from global radioactive fallout. Urban soils of Yerevan were found radiologically safe, however, igneous rock derived soils are a sink of NOR and the main environmental source of continuous exposure to the residents. Values of excess lifetime cancer risk were higher than mean global value.