Risk assessment of bioavailable heavy metals in the water and sediments in the Yongding New River, North China.

To explore the pollution status of heavy metals and potential risks in the Yongding New River of Tianjin, China, a comparative study of concentrations of heavy metals (Cd, Cr, Cu, Pb, Zn, As, and Hg) in surface sediments from submerged areas (SA), fluctuant flooded district (FFD), and non-flooded district (NFD) was conducted. In the present study, a modified three-stage European Community Bureau of Reference sequential extraction procedure and EDTA-Na2 single extraction were used to determine the heavy metal distribution in different sediment samples. Results showed that Cd was the metal with the highest contamination level compared to a background value of Tianjin soils, particularly in SA, followed by As. The concentrations of Cr, Pb, Cu, and Zn were relatively higher in upstream. Cu and Pb had higher bioavailability when compared with the other metals, indicating the two metals were easier to be mobilized. The Pearson correlation coefficient is applied to assess the degree of correlation between heavy metals. As, Cu, Zn, and Hg had the strong correlation, implying they may have common sources. Human activity in the riparian such as agricultural production, vehicle, and burning coal increased inputs of heavy metals in the surface sediments and influenced their distribution spatially. Besides, we also calculated geo-accumulation indexes (Igeo) and eco-risk index to assess the degree of risk of heavy metals in sediments. The Igeo were higher in SA than in FFD and NFD. Based on Igeo and potential eco-risk index, Cd has the highest risk, followed by As and Hg.