Distribution of cadmium, copper, lead, and zinc in mudflat salt-soils amended with sewage sludge

Applying sewage sludge to mudflat salt-soils can rapidly improve soil physicochemical properties and enhance pollution potential. Nevertheless, the heavy metal distribution in leachate and mudflat salt-soils with sludge amendment remains unclear. The present work was aimed primarily at investigating the fates of Cd, Cu, Pb, and Zn in mudflat salt-soils amended by sludge. A leaching column experiment in a greenhouse was conducted to analyze the leaching losses of the metals in the sludge-amended soils and to evaluate the uptake of these metals by maize (Zea mays L.) seedlings, using a mudflat salt-soil amended with 0, 30, 75, 150, and 300g sludge per kg soil. The results indicated that metal concentrations were significantly correlated negatively with pH and positively with dissolved organic carbon concentration in leachate of sludge-amended soils. The sewage sludge application enhanced metal uptake without inhibiting the growth of maize. The sludge treatments enhanced metal concentrations in top layer (0-20cm) of soil in the leaching column but did not change metal concentrations in soil layer of 20-40cm (p>.05). Immobile fraction of Pb and mobile fraction of Cd, Cu, and Zn increased with increasing rates of sludge addition. Long-term field studies are required for further evaluation of the impacts of recycling sludge on heavy metal behaviors including leaching, accumulation, and dynamic change of metal fractions in mudflat salt-soils.