The growth of Brassica chinensis in heavy-metal-contaminated sewage sludge compost from Hong Kong

A plant growth experiment was performed to evaluate the growth of Chinese cabbage (Brassica chinensis) in a sewage sludge compost derived from both industrial and domestic sewage containing high metal and salt contents. A loamy soil was amended with sewage sludge compost at application rates equivalent to 0, 5.9, 11.7, 29.2 and 58.5 tonne ha(-1) on dry weight basis. Addition of sludge compost caused a slight increase in soil pH, and a significant increase in electrical conductivity (EC) and soluble K, Ca, Mg, NH4+ and PO43- contents. DTPA-extractable Cu and Zn contents increased significantly according to the compost application rate, while a significant increase was noted only in soil with the highest compost application rate for Cd, Pb and Ni. The yield of Chinese cabbage was significantly increased with sludge compost amendment as compared to the control without fertilizer and with the highest yield at 5-10% application rate. An accumulation of Cu, Cd, Zn, Ni and Pb was observed with an increase in compost amendment. Among the metals studied only Cd had a tissue content higher than the maximum permitted concentration of Cd in vegetables at a compost amendment rate of 10%. Therefore, stringent guidelines should be set for the sludge compost produced in Hong Kong for edible crop production. Besides, the long-term effect of the sludge compost on the accumulation of trace metals in edible plants should also be investigated. Copyright (C) 1997 Elsevier Science Ltd.