Geochemical patterns of soils in the Bobov dol valley, Bulgaria. Assessment of Cu, Pb and Zn contents

The content of Si, Al, Fe, Ti, Mn, Mg, Ca, Na, K, S, P, C, Cu, Pb and Zn were determined in order to reveal geochemical patterns of soils in the Bobov dol valley, Bulgaria. Since the Bobov dol Thermal-electric Power Plant (TPP) is situated in the valley this paper pays attention to the geospatial distribution of Cu, Pb, and Zn due to their diverse vital significance. Elements assemblages and geospatial distribution pathways are also discussed in the light of the past 40 years of operation of the Thermal Power Plant. According to the results obtained the average content of Cu (27.04 mg kg-1 ), Pb (21.96 mg kg-1 ) and Zn (57.95 mg kg-1 ) is higher than the average content of elements in local soil parent rocks: Cu (20.03 mg kg-1 ), Pb (6.07 mg kg-1 ) and Zn (46.60 mg kg-1 ). Compared to the precautionary threshold concentrations adopted for assessing the soil contamination in Bulgaria the elements contents are lower including their maximum values. However, the geoaccumulation indexes reveal an initial stage of contamination of soils with Pb. Lead tends to follow a separate mode of geospatial distribution which is controlled by both the geogenic factors and the aerosol emissions of TPP. Copper accumulation is more strongly affected by technogenic depositions and dominated in urban and technogenic zones under the form of oval spots. Konyavska Mountain is the domain of Zn revealing an altitudinal gradient of distribution. Its accumulation proceeds slowly in topsoil, but still, Zn is the most abundant element in studied soils from the Bobov dol valley. The petrogenetic pattern of geochemical suits still predominated in studied soils wherein the iron has the greatest affinity for studied elements. Soil medium reaction (pH) and organic carbon do not control the processes of distribution and accumulation of Cu, Pb and Zn. The lack of statistical correlation with organic carbon resulted from the siliciclastic nature of soil parent rocks and also reveals the prevailing geogenic origin of studied elements