Pollution characteristics and risk assessment of heavy metals in the sediments of Nansha River in Beijing

Nansha River is an important river for drainage and landscape in the north of Haidian District,Beijing. In order to have an overall understanding on the pollution characteristics of heavy metals in the sediment of Nansha River,the surface sediment samples were collected,and the concentrations and speciations of the heavy metals were analyzed. Based on the single factor index method,Hakanson comprehensive pollution index method,and potential ecological risk index method,the ecological risk of the heavy metals in the sediment was evaluated. The results showed that the heavy metals in the surface sediment of Nansha River had homogeneity,and the pollution degree of the heavy metals followed the order of CrCdZnCuPbNi. Based on the ecological risk index evaluation,the ecological risk of the heavy metals was in the order CdPb Cu≈CrNi≈Zn,and only Cd showed higher potential ecological risk. The comprehensive potential ecological risk index showed that Nansha River was predominantly at a low ecological risk level,except the section near the Jingzang Highway Bridge,which showed a high risk level. The analysis on the speciation of the heavy metals showed that weak acid soluble Cd had a high concentration and high transference ability,and was most likely to harm the biological environment directly. Pb and Zn and Cu and Ni had a moderate potential risk for the environment,and Cr had a little environmental hazard. These results could be used as a valuable database for the pol- lution management of Nansha River.