Recycling wastes in agriculture: heavy metal bioavailability

Abstract Recycling wastes in agriculture is an essential disposal method, and according to waste characteristics can produce supplementary organic-matter resources (sewage sludge, compost) for crop production, or valuable soil amendments (coal fly-ash). However, since heavy-metal content in waste materials is often higher than in the soil, application rates have to be carefully controlled, to obviate the possible accumulation of toxic metals in agricultural soils. The risk of the possible pollution of crops by heavy metals makes it necessary to use guidelines for waste utilization. Generally, guidelines and legislation refer to the total amounts of heavy metals in wastes and in soil. The total amount however, is of very low environmental importance and much international experimentation concerning these elements is actually engaged in determining the real availability of heavy metals to plants in relation to the chemical forms of heavy metals in the soil. This paper emphasizes the extractability of metals in relation to soil chemistry, and plant uptake bioassay as an important diagnostic tool for metal bioavailability.