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VERTICAL DISTRIBUTION OF COPPER AND LEAD IN URBAN CONTAMINATED SOIL FROM AREAS WITH INDUSTRIAL ACTIVITIES

Adriana Ion

Abstract

The aim of the study was to determine the Cu and Pb content in soil profiles in relation to main responsible factors in vertical distribution: type of soil, pH and mineralogical composition. Were exanimate 34 soil profiles from the industrial area of Craiova City. For each profile was collected bulk samples at different depths (40, 100, 150, 200 and 300 cm). The analytical techniques employed for the investigation of soil and rock samples were Atomic Absorption Spectrometry (AAS) for determination of heavy metals and X-ray Powder Diffraction (XRD) for determination of mineralogical composition of soil. The content data was compared with standards and levels registered by Romanian Legislation. Representative soils of this area, according to the Romanian Soil Taxonomic Classification are luvisols (preluvosol) and aluvisols (protisoil), they are formed on deposits consolidated of loess (Upper Pleistocene) and sand deposits, (Lower Holocene). The mineralogical data show that the main constituents of the solid mineral phase in the upper horizon of the soil area: quartz, albite, microcline, illite and montmorillonite, while in the lower horizon, besides the minerals mentioned above, the anorthite and the kaolinite are also identified. The statistical analysis of the pH values distributed by depth classes highlights the neutral to alkaline character of the analyzed soil solution. Concentrations of copper vary widely within and between each depth class. Is remarkable the copper concentration for a depth of 40 cm where the alert threshold is exceeded for 38% of samples. For 3.4 % of the analyzed samples is exceeding intervention threshold. The same trend is observed in the lead vertical distribution concentration. Copper and lead distribution was characterized by a significant surface buildup, followed by a decrease in concentrations with increasing depth, coming close to the background values. The layer of clay minerals present in the soil profile has an essential role in decreasing of Cu and Pb concentration with depth. Clay minerals adsorb Cu and Pb by binding the cations to interlayer positions of the clay particles.

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