CD AND ZN RELEASE THROUGH THE SELECTED EX TRACTANTS

A set of 27 soil samples was extracted by six different extractants (0 .01 mol.l-1 CaCl2, 0.005 mol.l-1 DPTA, 0.43 mol.l-1 acetic acid, 0.05 mol.l-1 EDTA, 2 mol.1-1 HNO3, aqua regia) and Cd and Zn contents were ascertained by the atomic absorption spectrometry method. The total co ntent of elements was determined by the same method after earlier deco mposition of the sample into the mixture of nitric and hydrofluoric ac ids. It followed from the experiments that extractable concentrations of Cd and Zn in soil samples depend on the solvent applied. The highes t contents of elements were determined after the earlier total decompo sition of an analyzed material using the hydrofluoric acid in the reac tion mixture. The extraction by the aqua regia, in case of Cd, can be considered as equivalent to the total decomposition, in case of Zn, 73 .4% on an average of its total content succeeded to release. Extractab le concentrations of Cd and Zn were further decreased in the sequence: nitric acid, EDTA, acetic acid, DTPA and CaCl2 through which only 2.5 % of total Cd and 0.3% of total Zn released. There are some significan t differences in efficiency of individual extractants, that is why eac h study assessing the contents of elements in soil or relation soil-pl ant based on the extractable amounts of these elements should be added by detailed description of extraction or total decomposition of a sam ple. In case of Cd mutual close to very close dependence was found out among used extractants and total content of this element in the sampl es, except for CaCl2 where the values of regression coefficient ranged within r = 0.32 and 0.63 what confirms easy extractability of this el ement. Extractable contents of Zn were not in correlation with the tot al content of this element in soil samples, because a significant port ion of Zn is bound to silicate matrix of a sample and can be released exclusively through the hydrofluoric acid. The concentration of Cd rel eased through different agents neither depended on the content of orga nic matter and except extraction of CaCl2, nor on the exchangeable pH of soil. The competence for the use of investigated extractants for ev aluation of the uptake of Cd and Zn by plants should be assessed only on the basis of relations of concentrations of these elements in plant s and given extractants.