Factors controlling the bioavailability of potentially harmful metals in wastewater treated soils

Sewage sludge contains significant proportions of nitrogen, phosphorus and organic matter. It therefore has a similar fertiliser value to animal manures and slurries. Typical applications can provide a significant contribution to the nitrogen and phosphate requirements of arable and grassland crops. In addition, sludge can contain potentially harmful substances, including pathogens, persistent organic pollutants and toxic metals. It is therefore necessary to control the use of sewage sludge in order to protect human and animal health and to maintain soil fertility and crop yields. The bioavailability of heavy metals can be affected by several factors. Some of these factors are related to soil and some others may be related to plant characteristics. Soil pH, organic mater content, redox status, carbonate content, chloride content, moisture, source and form of metals and plant genotype may be the most important. However, investigation of any factors which may reduce or enhance the availability of heavy metals in soil and uptake by plants would be crucial. Such knowledge and information on these factors could be used and would help the authorities to manage and control the environmental problems which are concerned with sludge application to agricultural land and could threaten the human health. This paper is going to review and describe the factors and circumstances of which the bioavailability of potentially harmful metals would reduce or enhance in soil