Environmental geochemistry of heavy metals in surface soils within sewage irrigation areas of Shijiazhuang City

Abstract：In this paper, the contents and chemical speciation of Pb, Hg, Cr, Cd, As, Cu and Zn in farmland surface soils along three sections in sewage irrigation areas of Shijiazhuang City were investigated, and the heavy metal pollution was evaluated. The results show that heavy metals (with the exception of As) of surface soils along three sections in sewage irrigation areas of Shijiazhuang City have been concentrated in varying degrees： the contents of Hg and Cd are high, and the average contents of heavy metals in the downriver surface soils exceed their contents in the upriver and middle reach areas. Geoaccumulation indexes indicate that As in the surface soils has not caused pollution, and Hg and Cd in the surface soils have caused mild-moderate degrees of pollution in the surface soils, as evidenced by the arithmetic means of natural soils of Hebei Province. Chemical speciation of Pb, Hg, Cr, As, Cu and Zn in surface soils is mainly in the residual form, and Cd is mainly existent in exchangeable fractions and carbonate state. Cd has a certain degree of bioavailability and potential ecological harmfulness.