Investigation of heavy metal mobility and availability by the BCR sequential extraction procedure: relationship between soil properties and heavy metals availability

In this study, surface soil and corn cob samples were collected from 15 different agricultural fields of Çanakkale, Turkey. These samples were analysed to determine the concentration of Cd, Cu, Mn, Ni, Pb and Zn. BCR sequential extraction was used to extract the binding forms of the metals in the soil samples. At the same time, a wet digestion method was used to determine the total concentration of heavy metals in soil and corn grain samples. The metal concentrations in the extracted phase were measured with flame atomic absorption spectrometer. The accuracy of the methods was confirmed by using BCR-701 and SRM-1570a certified reference materials. The results revealed that the quantity of the mobile fractions (i.e., acid soluble, reducible, and oxidisable) of the Mn, Cd and Pb were higher than that of the immobile fractions (residual). This might be caused by the anthropogenic sources. Pearson’s correlation was applied to determine the correlations between the selected physicochemical properties of soil samples and the amounts of heavy metals in each fraction. The pH, CaCO₃ and organic matter contents of soil samples played a dominant role in correlations of heavy metals in various forms and shapes. Hierarchical cluster analysis was applied to examine the relationships between the amount of heavy metal in each fraction of soil samples and the amount of heavy metal in corn grain. As a result, a firm correlation was detected between heavy metals in corn grain and more available (acid soluble and reducible) fractions. Current findings indicate that plants could uptake basically the heavy metals in acid soluble and reducible fractions. BCR sequential extraction not only provides information about potential heavy metal sources in detail and the potential mobility of heavy metals, but also provides information about the interactions between soil characteristics and metal fractions. This provides information on the bonding states of environmentally toxic metals (Cd, Cu, Mn, Ni, Pb and Zn) in the soil matrix, the amounts taken by the plants, and the intrusion means and rates of those metals into the food chain.