Fractional Distribution of Lead and Cadmium in Sludge and Soil Amended with Sludge Compost

The modified three-step sequential extraction procedure proposed by the BCR was used to predict Pb and Cd fractional distribution in sewage sludge and tomato soil amended with sludge compost. There was no significant increasing of Pb and Cd contents in the soil with sludge application as compared with that in the reference soil. The Pb contents were much lower for the soil samples than for the National Soil Standards of Environmental Quality, but Cd contents in soil were much more than background mean Cd contents. Pb content in soil fractions was followed with residual Pb > reducible Pb > exchangeable and weak acid soluble Pb > oxidizable Pb. In all soil samples, the partitioning of Cd had the same extractability in the first two steps of the procedure and the residual fraction. Only a small fraction or almost zero extractability was observed at the oxidation step for Pb and Cd.