The use of compost: its effects on heavy metal levels in soil and plants

Three organic soil conditioners were tested in 14 different Malus domestica orchards: cattle manure, SE compost (from sewage sludge and poplar barks) and MSW compost (from municipal solid waste not source separated). These materials differed notably in their heavy metal content: the SE compost contained greater amounts of Zn, Cu and Pb than did the cattle manure, while the MSW compost had higher concentrations of all the metals studied. For 6 years the Zn, Cu, Ni, Pb, Cd and Cr content were monitored in the soil-both in 'total' and EDTA extractable form-and in leaves and fruits. The resulting data demonstrate that the SE compost did not cause any significant increase in heavy metal levels in soil and plants; this compost can thus be used to fertilise the soil with no danger in the short/medium term either to the environment or to crops. In contrast, the experiment clearly demonstrates that the MSW compost, used over a 6 year period, increased concentrations of Zn, Cu, Ni, Pb, Cd and Cr in the soil-both in 'total' and EDTA extractable form-and in the case of Pb and Cd also in the vegetation and the fruits. (C) 1997 Elsevier Science B.V.