COMPARISON OF SELECTED METHODS FOR DETERMINATION OF AVAILABLE ZN IN CONTAMINATED SOILS

In this study, a comparison was made of the applicability of various extraction solvents for determination of available zinc in contaminated soils. A grey-brown Podzolic Soil (loamy sand) was used, with acid reaction (pH 5.3) and medium level of Zn. The soil was contaminated with ZnSO4 center dot 7 H2O (150, 300, 450, 900 and 1350 mg Zn center dot kg(-1) d.m. of soil). In the soil material, the level of Zn accepted as available for plants was determined in 1 mol HCl center dot dm(-3) and 0.01 mol CaCl2 center dot dm(-3). The total content of the metal was determined in a mixture of concentrated HCl and HNO3 at the ratio of 3:1. To determine the content of the forms of the component in the soil, also sequential chemical extraction of the metal was performed with the BCR (Community Bureau of Reference) method. As a result of acid extraction in 1 mol HCl center dot dm(-3), the amounts of Zn released from soil contaminated with the doses of 150 and 300 mg Zn center dot kg(-1) constituted 67-76% of the determined total content of the component. As the level of contamination increased to 1350 mg Zn kg(-1), the solution extracted increasing amounts of the metal, up to 98% of the total form. The weaker extraction solution (0.01 mol CaCl2 center dot dm(-3)) released from the soil lower amounts of Zn available for plants. The share of the available form of Zn in the total content of the component was 38-74%, and increased also with increasing level of soil contamination. At the highest levels of zinc concentration in soil (450-1350 mg Zn kg(-1)), 1 mol HCl center dot dm(-3) extracted amounts of the metal equivalent to those extracted by concentrated acids. Correctness of the analyses is evidenced in the comparable amounts of zinc determined in HCl, or 0.11 mol CH3COOH center dot dm(-3) according to the BCR method. Also, similar results concerning the total zinc content were obtained using aqua regia and 6 mol HCl center dot dm(-3) + 14 mol HNO3 center dot dm(-3), and summing up the zinc amounts obtained through sequential extraction.