FORMS OF TRACE-METALS FROM INORGANIC SOURCES IN SOILS AND AMOUNTS FOUND IN SPRING BARLEY

Barley (Hordeum vulgare L.) was grown on a sandy soil given different doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite) in a pot experiment conducted in a greenhouse. The element compounds were added to the soil in amounts equivalent to the following levels of the metals: Cd 5, 10, 50 muq-1; Cu and Pb 50, 100, 500 mug g-1; Zn 150, 300, 1500 mug g-1. Sequential extraction was used for partition these metals into five operationally-defined fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The residue was the most abundant fraction in the untreated soil for all the metals studied (43 to 61% of the total contents). The concentration of exchangeable Cd (0.2 mug g-1), Cu (0.01 mug g-1), Pb (0.1 mug g-1), and Zn (1.4 mug g-1) were relatively low in the untreated soil but increased markedly in the treated soils for Cd (up to 31 mug g-1) and Zn (up to 83 mug g-1), whereas only small changes were observed for Cu and Pb. The pot experiment showed a significant increase in the Cd and Zn contents of barley grown on the treated soils, but only small changes in Cu and Pb concentrations.