Spatial Distribution and Ecological Risk Assessment of Heavy Metals in Surface Sediment of Songhua River, Northeast China

The Songhua River, one of the seven major rivers in China, locates in Northeast China with 1897 km long. This study aims to investigate the concentrations, distribution, source apportionment and ecological risk assessment of heavy metals including copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), nickel (Ni) and chromium (Cr) in main stream and tributaries of the Songhua River in Jilin Province, Northeast China. Surface sediment samples (0-15 cm) were collected from 39 sampling sites in the Songhua River in July 2012. Concentrations of Cu, Zn, Cd, Pb, Ni and Cr were analyzed. The mean concentrations of heavy metals were (24.0 +/- 9.2) mg/kg, (59.3 +/- 18.0) mg/kg, (4.0 +/- 2.1) mg/kg, (39.0 +/- 27.9) mg/kg, (18.5 +/- 8.6) mg/kg and (56.1 +/- 17.6) mg/kg for Cu, Zn, Cd, Pb, Cr and Ni, respectively. The average contents of Cu, Cd, Pb, Cr and Ni were higher than their background values. Higher concentrations of heavy metals were found in the lower reaches with industrial enterprises and cities along the Songhua River. Zn, Pb and Ni might come from industrial sewage and mineral processing, while Cu and Cd were derived from electroplating wastewater and agricultural non-point source sewage. Cr originated from lithogenic sources. The concentrations of Cu, Zn and Cr were below the effect range low (ERL) at all sites, while Cd, Pb and Ni concentrations were detected ranging from ERL to the effect range median (ERM) at more than 15% of samples. Concentrations of Ni exceeded ERM in more than 50% of samples. The mean toxic units of heavy metals in the Songhua River decreased following the order: Cd (6.7) > Pb (2.2) > Ni (1.6) > Cu (0.7) > Cr (0.5) = Zn (0.5). Potential ecological risk index was found to be higher in middle and lower reaches of the Songhua River, where Cd could impose an extremely high ecological risk.