Speciation Distribution Characteristics of Heavy Metals and its Relationships with Soil Acid Chemical Properties in the Chengdu Plain

Based on the field investigation, 197 soil samples were collected to analyse the concentration and speciation distribution characteristics of Cd, Cu, Pb, Cr and Zn. The relationships between the soil acid chemical properties and the speciation of heavy metals were studied in this paper. The results showed that the content of Cd, Cu, Pb, Cr and Zn in the soil significantly increased compared with the Second National Soil Survey. Comparing with the standard of National Soil Environmental Quality, the heavy metals of soil in the Chengdu plain has polluted the soil to certain degree. For the form distribution of soil heavy metal, Cd was mainly presented in the Fe-Mn oxidation bound and Cu, Pb, Cr, Zn mainly consisted in the residual form. There was certain correlation between each active state (exchangeable form, carbonate state, Fe-Mn oxidation state and organic combination state), which could be converted mutually and had strong potential hazards to environment. The acid chemical properties of soil had notable or highly notable impact on the pattern distribution of heavy metals. Soil pH had obvious effect on the liable morphological changes of Cd, Pb and Zn. The soil acid buffer property (soil acid damage capacity) had highly significant positive correlation with exchangeable form, carbonate state, Fe-Mn oxidation state and liable speciation of Cd in the soil, while had highly significant negative correlation with exchangeable form, organic bound and liable speciation of Cr in the soil, and remarkable negative or positive correlation with exchangeable form, organic bound, carbonate state and Fe- Mn oxidation of Zn in the Chengdu Plain.