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, SB 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 SB 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 SB 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.