Leachability and bioaccessibility of potentially toxic elements in urban soils of two Chinese cities

Heavy metals in soils may pose risks to both ecosystem and human health, especially in an urban environment. The objective of this study is to evaluate the chemical forms and environmental risk of heavy metals in the urban... [ view full abstract ]

Heavy metals in soils may pose risks to both ecosystem and human health, especially in an urban environment. The objective of this study is to evaluate the chemical forms and environmental risk of heavy metals in the urban soils using sequential extraction and short-term extraction procedures. A total of 40 contaminated urban topsoils were collected from industrial areas and roadsides of two Chinese cities (Luoyang and Hangzhou). The sequential chemical extraction, toxicity characteristic leaching procedure (TCLP) and 0.05 M EDTA (pH 7) extraction were performed. In order to obtain a measure of metal leachability and bioaccessibility, the ratios between the individual metal fraction and total concentration are calculated. Results show that there are great differences in leachability and bioaccessibility of metals in soils. In the Hangzhou urban soils, the order of TCLP-extractability is Cd>Zn>Pb>Cu>Cr, and EDTA-extractability is Cd>Cu>Pb>Zn>Cr. In the Luoyang urban soils, the order of TCLP-extractability is Pb>Cd>Zn>Cu>Cr, and EDTA-extractability is Pb>Cd>Zn>Cu>Cr. The Cr exhibits the lowest leachability and bioaccessibility among the investigated metals. The Cd has the highest TCLP leachability value in Hangzhou urban soils while Pb has the highest leachability in Luoyang urban soils. The high leachability and bioaccessibility of heavy metals indicates higher potential hazard for the human health and environment. Based chemical forms analysis, the metals Cd, Cu, Pb, and Zn are classified as potentially mobile elements and Cr is classified as immobile.