FRACTIONATION OF SELECTED HEAVY METALS IN AGRICULTURAL SOILS

The content of trace elements in soils varies widely and their mobility and availability depends not only on the total content but also on the form of in which these elements occur. The aim of this study was to determine the total content of nickel, lead, zinc and copper in soils used for agriculture, and assess the mobility and phytoavailability of these metals against a background of physical and chemical properties of these soils. In samples taken from three soil profiles (Phaeozem and 2 Fluvisols) the contents of Ni, Pb, Zn and Cu were determined using atomic absorption spectroscopy in the solutions obtained according to the protocol of modified BCR sequential extraction procedure supplemented with aqua regia digestion. The total content of the analyzed metals in most cases corresponded to the natural values, often not exceeding the geochemical background level. It was only in the one profile of the Fluvisols (Endogleyic Fluvisol) that a higher concentration of zinc and lead was noticed (especially in the surface horizon), slightly exceeding the legal limit. Among the studied metals the lowest phytoavailability was characterized by copper (exchangeable forms on average 4.73% of the total), and the highest by zinc (11.49%). Nickel was the most permanently bound with soil solid phase, and its content in the residual fraction reached 84.46% of the total. Approximately a half of the total lead content was determined as a fraction bound with iron and manganese oxides, while in the case of this metal a significant role in binding of this metal was playing organic matter (fraction bound with organic matter and sulphides - an average of 27.5%). Significant role in the binding of all investigated metals was credited to iron and manganese compounds.