Gamma-Spectrometric Characterisation of Reclaimed Soils from Three Mining-affected Areas in Bulgaria

Abstract

Reclaimed soils formed on mine spoils may modify the local natural radiation background because of differences in parent material, texture, and sorption properties. The present study evaluates the activity concentrations and distribution patterns of natural and anthropogenic radionuclides in reclaimed soils from three mining-affected areas in Bulgaria: Maritsa Iztok, Chukurovo, and Asarel-Medet. Gamma-ray spectrometry (HPGe detector; BDS EN ISO 18589-3) and selected physico-chemical analyses (pH, cation exchange capacity, organic carbon, and particle-size composition) were conducted on horizon-wise samples from the main soil profiles (Profiles 1–5). Natural radionuclides (U-238 series, Th-232 series, and K-40) exhibited object-specific patterns consistent with geogenic and textural controls. Spearman correlation and principal component analysis identified a geogenic/texture component dominated by U-238, Ra-226, and Th-232, which were positively associated with fine fractions and cation exchange capacity, and an opposing K-40 trend linked to coarser material. Pb-210 was more closely associated with sorption-related soil properties, suggesting combined control by texture, pH, and the sorption complex. Cs-137 was predominantly below the detection limit, with measurable values mainly in Maritsa Iztok and Chukurovo (West), and no consistent depth-related pattern indicative of substantial downward migration. The external hazard index (Hex) remained below 1 in all studied sites, indicating no radiological concern regarding external exposure.