Relationships between Heavy Metal and Metalloid Contents and Major Soil Characteristics in Soils around the Former Kremikovtsi Metallurgical Plant Following Its Closure in 2009

Soils around the former metallurgical plant Kremikovtsi were subject of continued interest due to the environmental problems resulting from the plant's activities and especially heavy metal pollution. The aim of the present study was to investigate the contamination of the studied soils by metals and metalloids, several years after the closure of the plant (2009) and to relate their concentrations to basic soil parameters, pH, electrical conductivity, cation exchange capacity, clay content and total organic carbon, which will contribute to better assessment of their behaviour and remediation strategies. Total concentrations (aqua-regia) of the elements Al, B, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Zn and As were determined. Elevated levels of the heavy metals Pb, Cd, Zn, and the metalloid arsenic (As) were found at the studied sites. Lead (Pb) exceeded maximum permissible concentrations (MPC), regulated by Bulgarian legislation for arable lands between 2 and 15 times, cadmium (Cd) between 3 and 5 times, arsenic (As) between 3 and 6 times, and zinc (Zn) was higher than MPC in three of the sampled sites. Soil pH values were in significant correlation with EC (R** = 0.805), CEC R** = 0.781), B (R* = 0.638), Cu (R* = 0.669), Fe (R** = 0.766) and Mn (R*** = 0.916) contents. Aluminium, cadmium, lithium and lead concentrations were related to the content of the clay fraction in soil. Positive correlation was obtained in multiple regression models between Pb, Al, Cd, TOC and soil pH, and negative relationship was observed with electrical conductivity (EC). The obtained results showed complex relationships between soil characteristics and the metals and metalloids, which emphasize the need for their simultaneous assessment, remediation and careful use for agricultural purposes.