Forms of Cd, Cu, Pb, and Zn in soil and their uptake by cereal crops when applied jointly as carbonates

The cereal crops (barley - Hordeum vulgare L., maize - Zea mays L., wheat - Triticum vulgare L.) were grown in a greenhouse using a sandy soil type treated with various doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite), added jointly. The following levels of these metals were used: Cd - 5, 10, 50 mu g g(-1) soil; Cu and Pb - 50, 100, 500 mu g g(-1) soil; Zn - 150, 300, 1500 mu g g(-1) soil. Sequential extraction was adopted to partition the metals into five operationally-define fractions: exchangeable, carbonate, Fe-Mn oxides, organic, and residual. The residual was the most abundant fraction in the untreated (control) soil for all the metals studied (50 to 60% of the total metal content). The concentrations of exchangeable Cd, Cu, Pb, and Zn were relatively low in untreated soil but increased (over the three year period) in treated soils for Cd, Zn, and Cu, whereas only small changes were observed for Pb. This experiment showed a significant increase in Cd, Zn, and Cu in tissue of plants grown on the treated soil, but a non-significant change in plant tissue with respect to Pb concentration.