HEAVY-METAL CONTENTS OF VEGETABLE CROPS TREATED WITH REFUSE COMPOST AND SEWAGE-SLUDGE

Refuse compost and sewage sludge were mixed with a loamy sand at various rates in pots and sown with Brassica chinensis, Daucus carota and Lycopersicon esculentum in a glasshouse. A commercial fertilizer was also applied to the same soil for comparison. Dry matter production of the three crops and contents of Cd, Cu, Mn, Pb and Zn in the harvested tissues were determined at the end of the experiment. In general, crop yield in refuse compost treatment was improved over that in sandy soil alone, but was less than that in the sludge and fertilizer treatments. Despite the relatively high heavy metal contents of refuse compost, crops grown on compost-treated soils accumulated lower levels of metal than those grown on sludge-treated soils. This is probably due to the high pH and organic matter content of the composted refuse. Higher levels of heavy metals were found in the roots than in the aerial parts of B. chinensis and L. esculentum, but the reverse was found in D. carota. In the edible tissue of the three crops, L. esculentum accumulated metals to a lesser extent than the other two.