The behaviour of heavy metals in sewage sludge-amended soils

Soils amended with sewage sludges generally contain elevated concentrations of a wide range of heavy metals and are therefore of interest with regard to their potential impact on human health. This review considers the concentrations of heavy metals in sewage sludges and in the soils amended with them. The effects of sludge amendments on soil properties, the speciation of heavy metals and their bioavailability are reviewed. Variations in heavy metal accumulation between crop species are considered, together with the effects of sludge-borne heavy metals on soil microorganism activity. Perhaps the most important questions to be addressed are the changes in the bioavailability of the heavy metals and their distribution in the soil profile during the residual period. The consequences of the application of sewage sludges to agricultural soils, with regard to the long-term bioavailability and movement of metals in soil profiles, are incompletely understood.