Plant and Soil 103, 191-197 (1987) Martinus Nijhoff Publishers, Dordrecht--Printed in the Netherlands PLSO 6898 Heavy metal contents of vegetable crops treated with refuse compost and sewage sludge* L.M. CHU and M.H. WONG 1 Department of Biology, The Chinese University of Hong Kong, Shatin, Hong Kong Received 29 May 1986. Revised June 1987 Key words: Brassica chinensis, crop yield, Daucus carota, heavy-metal accumulation, Lycopersicon esculentum, refuse compost, sewage sludge Abstract 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. Introduction The disposal of ever-increasing amounts of domestic refuse and sewage sludge is becoming a serious problem in many countries. Land applica- tion of such wastes is desirable on both environ- mental and economic grounds because they provide organic material, improve soil structure and offer the potential for recycling plant nutrients. Nevertheless, the agronomic efficiency and poten- tial hazards of waste re-utilization have to be assessed, preferably by direct experimentation. Some research has shown that the manurial * This study was partially supported by the EPCOM Special Project Grant from the Advisory Committee of Environmental Protection of Hong Kong. Part of the paper was presented in the 'International Conference on Ecological Aspects of Solid Waste Disposal, Dec 19-22, 1983, Hong Kong'. Present addresses: Department of Botany, University of Liverpool, Liverpool, England and Department of Biology, Hong Kong Baptist College, Kowloon, Hong Kong. 191 value of garbage compost is similar to inorganic fertilizer, and that compost applied at high rates can produce better crop yields than sludge, manure and NPK fertilizer (Hortenstine and Rothwell, 1968 and 1973). Other work, however, suggests that the nutrient content of compost from refuse can be quite low and that its addition to soil should be complemented by chemical fertilizers (Terman et al., 1973; Tietjen, 1964). The fertilizer and soil con- ditioning values of sewage sludge are well doc- umented. However, the use of both sludge and compost for crop production may be limited by the potential hazards of associated heavy metals. Ap- plication of municipal wastes can lead to heavy metal contamination in both soil and crops. In a previous study with leafy vegetables, the contents of Zn and Cu have been found to be greatly el- evated in the tissues of sludge- and refuse compost- treated crops of Brassicajuncea and B. parachinen- sis (Wong et al., 1983). The present experiment therefore aimed to deter-