[Speciation and Risk Assessment of Heavy Metals in Surface Sediments from the Heavily Polluted Area of Xiaoqing River].

Th concentrations of Cu, As, Pb, Zn, Cr, Cd, Ni in interstitial water were analyzed by ICP-MS from the heavily polluted area of Xiaoqing River. A modified BCR's sequential extraction procedure was used to investigate the fraction of the heavy metals in the surface sediments. The aquatic toxicity of heavy metals in interstitial water was assessed by US Water Quality Criteria (CCC, CMC). Based on the speciation of the metals in the surface sediments, the ecological risk of heavy metals was assessed with methods of risk assessment code (RAC) and potential ecological risk index. The results showed that: The tested heavy metals would not pose chronic toxicity for aquatic ecosystem. The contents of heavy metals (Cu, Pb, Zn, Cr, Cd, Ni) in the surface sediments were higher than the background values of the local soils, indicating enrichment of heavy metals. Cu, As and Ni were mainly composed with residual fractions, Pb and Cr were mainly constituted of residual and oxidizable fractions, and mass fractions of Zn and Cd existed mainly in acid soluble and reducible factions. The contents of bio-available fractions of Cd, Zn, Cr and Pb in the sediments were higher those of residual fractions, indicating high potential for secondary release. Based on calculation of RAC method, Cu, Pb, Cr and As posed extremely low to low risk to the environment. Accordingly, Ni was of low to medium risk, Cd was of medium to high risk, and Zn was of medium to extremely high risk to the environment. The potential ecological risk of heavy metals in the sediments was in the descending order of Cd > Zn > Ni > As > Cu > Cr > Pb. Cd had high to very high potential ecological risk comparing with the other heavy metals. The potential ecological risk indexes (RI) of the heavy metals in the sediments were in the range of 136.83-264.83, and posed medium to high potential ecological risks for Xiaoqing River.