Determination of heavy metal mobile forms by different extraction methods

Abstract

Heavy metals exist in the soil in immobile (sulphides, phosphates, silicates, etc.) and mobile forms. The mobile forms occur with the exchange processes in the soil and with the changing composition, pH, etc. of soil. Determination of the mobile forms of heavy metals is important for understanding their migration patterns in the soil and their uptake by plants. The aim of this work was to compare some determination methods of immobile and mobile forms of heavy metals. The total content of Cd, Cu, and Pb was determined in aqua regia (mixture of HCl, HNO 3 and H 2 O 2 ) and 2M HNO 3 extracts by boiling. The results obtained by both methods show a good correlation. The content of the mobile form of heavy metals depends on the nature of metal ion, the nature of extractant and pH. The mobile forms of Cd, Cu and Pb were determined by using ammonium nitrate, ammonium acetate (pH 7 and 4.8), 0.1M HCl and 0.05 M NH 4 –EDTA (pH 7). The smallest amounts were extracted with ammonium salt solutions. The content of heavy metals extracted with ammonium acetate (pH 4.8) was higher than that extracted with ammonium acetate (pH 7). Even greater contents of heavy metals were extracted with 0.1 HCl. 0.05 M NH 4 –EDTA (pH 7) is capable of extracting from the soil not only the heavy metals participating in the exchange processes, but also the heavy metals in carbonates and organic complexes (bound). A comparison of the mobile forms of heavy metals extracted from clean and highly polluted soils has revealed that in the polluted soils the greater portion of heavy metals exists in a mobile form.