Bioavailability of copper in compost-amended soils

The application of industrial-source composts from municipal solid wastes ( MSW) and sewage sludge can result in the accumulation of heavy metals in wa ter courses, soils and crops with potential biomagnification throughout the food chain. Because of the possible pollution of the ecosystem by heavy me tals, guidelines for waste utilization have been established in many countr ies. However, the total amount of a metal in a soil, a waste material or co mpost is of limited environmental importance; the real availability of the metal to plants and potential contamination of the food chain is the issue. Of the heavy metals present in composts, copper is one of the elements that causes the greatest concern because of its relatively high content and pot ential toxicity for plants. This literature review summarizes the progress and problems in estimating Cu bioavailability in compost-amended soils, som e extraction methods for determining the bioavailable forms of copper in so ils, and copper-tolerant and copper-hypoaccumulator plants. The main conclu sions From this review are: 1) The application of composted MSW to agricult ural soils does not in all cases increase Cu bioavailability to plants; 2) Compost maturity is a factor which can reduce Cu availability to plants; 3) There is no one (single or sequential) chemical extraction of soils amende d with composts or biosolids that can precisely estimate the bioavailabilit y of Cu to plants; 4) A number of plant species have been found to be Cu to lerant or Cu hypoaccumulators. Very few agronomic crops, however, are Cu to lerant. We suggest that there should be different guidelines for trace elements in composts based on the crop being grown, soil and compost properties. The va lues for maximum trace elements in type A and B composts should be based on the bioavailable trace element content in the soils and on the results of long-term field experiments.