Despite recent studies have investigated the strong influences of smelting activities on heavy metal contamination in the soil environment, little studies have been conducted on the current information about the potential environmental risks posed by toxic heavy metals in smelting contaminated sites. In the present study, a combination of the bioavailability, speciation, and release kinetics of toxic heavy metals in the indigenous zinc smelting contaminated soil were reliably used as an effective tool to support site risk assessment. The bioavailability results revealed that the bioavailable metal concentrations were intrinsically dependent on the types of chemical extractants. Interestingly, 0.02 mol/L EDTA + 0.5 mol/L CH₃COONH₄ was found to be the best extractant, which extracted 30.21% of Cu, 31.54% of Mn, 2.39% of Ni and 28.89% of Zn, respectively. The sequential extraction results suggested that Cd, Pb, and Zn were the most mobile elements, which would pose the potential risks to the environment. The correlation of metal bioavailability with their fractionation implied that the exchangeable metal fractions were easily extracted by CaCl₂ and Mehlich 1, while the carbonate and organic bound metal fractions could be extracted by EDTA and DTPA with stronger chelating ability. Moreover, the kinetic modeling results suggested that the chemical desorption mechanism might be the major factor controlling heavy metal release. These results could provide some valuable references for the risk assessment and management of heavy metals in the smelting contaminated sites.

Many countries around the world are suffering from serious problems associated with soil heavy metal pollution, especially developing countries. Heavy metal contaminants in soils mainly result from soil natural weathering and anthropogenic activities such as industrial and agricultural activities, coal-burning as well as transportation. It is widely acknowledged that heavy metal pollution may lead to the deterioration of soil environmental quality and the loss of soil ecological functions. Therefore, the control and remediation for soil heavy metal pollution need to be urgently carried out to guarantee human health and food security. To date, soil amendments are increasingly employed to remediate heavy metal contaminated soils. In recent years, the research progress at an international scale is reviewed with regard to soil amendments used for the remediation of heavy metal polluted soils by laboratory and field-scale studies. A summary is provided with soil amendment types, metal stabilization mechanisms, as well as the influences of soil amendment application on soil properties. At last, future research prospects are put forward to broaden the development of this field. It is expected to provide valuable references for the research and practice of heavy metal stabilization in polluted soils.