Effect of organic waste amendments on cadmium and lead in soil fractions of two soils

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Abstract
Certain organic soil amendments have been found to ameliorate metal toxicity to plants. A study was undertaken to determine the effects of organic amendments on cadmium (Cd) and lead (Pb) distribution among soil fractions. Two soils (fine‐textured and coarse‐textured) were amended with five organic waste materials or commercial humic acid (HA) with and without 5 mg Cd kg‐1 or 300 mg Pb kg‐1, incubated, and fractionated using a sequential extraction technique. The added Cd and Pb were found mainly in the organic matter (OM) fraction, although significant amounts were in the exchangeable (EXC) fraction for the sandy Norfolk soil. Spent mushroom compost (SMC) and HA lowered Cd in the EXC fraction for both soils and raised Cd in the OM fraction for the sandy Norfolk soil. The SMC and HA lowered Pb in the EXC and OM fractions and raised Pb in the manganese oxide (MnO), amorphous Fe oxide (AFeO) and the crystalline Fe oxide (CFeO) fractions. Poultry‐litter amendment caused higher Cd and Pb in the EXC fraction for the sandy soil. It was concluded from these studies that certain organic amendments like the SMC will lower Cd and Pb availability by redistribution the metals from the EXC and/or the OM fraction to less available fractions. Other amendments have little affect on Cd and Pb distribution, or for sandy soils, poultry litter can cause higher Cd and Pb in the more available fraction presumably due to the formation of soluble organic complexes.