Heavy metal speciation in the surface sediments of Yang River System (Guanting Reservoir)

Guanting Reservoir (GR) is one of the most important drinking water sources in Beijing, while the sediment contamination of Yang River (an important input river of GR) may directly affect the water quality of GR. In this paper, the surface sediments of Yang River System were selected to evaluate the pollution and risk of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) based on their speciation, including ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC). The results showed that all the six metals in the surface sediments of study area were dominated by B4 (residual) fraction. In the secondary phase, Cd, Cu, Ni, Pb and Zn were all dominated by B2 (reducible) fraction, and Cr was dominated by B3 (oxidizable) fraction. Spatially, Cd was mainly distributed in B2 fraction both in the middle reach of mainstream and Qingshui River (QR, a tributary of Yang River), while Zn was mainly distributed in B2 and B1 (exchangeable/acid soluble) fractions in the middle reach, but B2 fraction in QR. The RSP showed that the studied sediments were slightly polluted by Cd and Zn in whole study area, but heavily in QR, which may be due to the industries of chemical raw materials and chemicals. The RAC shows that Cd and Zn in the studied sediments posed a medium risk to the water environment, Ni and Cu posed low risk, while Cr and Pb posed no risk.