The role of free iron oxides in the association of lead and cadmium in gleyic phaeozems [black earths]

Twelve samples, collected from four pedons of cultivated soils (black earths) were analyzed by sequential extraction to characterize the role of free iron oxides in the association of lead and cadmium. Amounts of lead and cadmium retained varied from 11 to 89.3% of the total Pb and from 4.8 to 48.7% of the total Cd. Metals associated with amorphous Fe oxides are at least ten times higher than with crystalline Fe forms. Under the existing soil conditions (high pH and CaCO3 content) free iron oxides are components of great importance in the Pb and Cd binding process. However, the results may indicate a stronger association of Pb than Cd with iron oxides in the studied black earths.