Radioactivity of soils enriched with pyrogenic artefacts in the land of Pernik city, Bulgaria

This article aims to study the radioactivity of soils enriched with pyrogenic artefacts and the possible enhancement of radioactive background and the dose load on the population as a result of coal mining and electricity generation in mine-energetic region Pernik, Bulgaria. Content of major radionuclides responsible for radiation loading – 238 U, 232 Th, 40 K, their progenies 226 Ra and 210 Pb, and technogenic 137 Cs was determined in fi ve soil types representative for the region. Data show that the activity (Bq kg -1 ) of 238 U, 226 Ra, 232 Th and 40 K in studied soils slightly fl uctuates around average values in Bulgarian soils, accepted as background levels in this study. The activity of 210 Pb and 137 Cs was also comparable to that established in other uncontaminated soils. The mixing of materials and artefacts containing pyrogenic carbon (coal-clayey substrate occurring in the unproductive coal strata and slag produced in the local thermal power plant) during the formation of reclaimed soils increases the content of studied radioactive elements, but the highest levels are found in soils (Cam-bisols) enriched with soot. Thus, a typical anthropogenic enhancement of radiation background was observed but it is also not hazardous to the population. Gamma radiation emanating from studied soils is below the recommended values and vary from 0.23 to 0.57 for external hazard index, and from 0.29 to 0.61 mSv y -1 for outdoor annual effective dose. The established interlink between 210 Pb activity and pyrogenic carbon content show that 210 Pb could be used as a marker of the recent deposition of pyrogenic carbon formed during the coal combustion and other activities emitting pyrogenic carbon-containing aerosols.