Characteristics of heavy metal accumulation on fly ash- and sewage sludge-amended calcific soil

Land disposal of fly ash (FA) and sewage sludge (SS) is a major problem due largely to their potentially harmful constituents. In this paper, a potting experiment was performed to evaluate the effects on the plant growth and to discuss in particular the potential hazard to soils and plants according to the characteristics of heavy metal accumulation and migration when FA and SS are used as the amendments of calcific soil in a limestone mining area. The results showed that the application of FA-SS mixture is capable of accelerating the growth of plants and improving the biomass production at either 1:1 or 1:2 FA-SS mixture: soil (w/w). The highest yields were obtained at 1:1 (w/w) mixing ratio. When compared with the Element Background Values of Soils in China, the analysis on heavy metals indicated that the contents of Pb, Cr, Hg, Cd, As, Ni, Cu and Zn in the amended soils came up to the second-class environmental quality standards, only Hg and Cd showed significant accumulation. At the same time, though the metal concentrations in roots were higher than those for the control, the concentrations except Cu, Zn in shoots were lower. And all the heavy metal contents in the plants were substantially lower than the toxicity limits. The results indicated that the combined use of FA and SS at a rational rate of application should pose no danger to both soil and food chain based on the characteristics of the FS and SS, heavy metals and calcific soil.