[Fraction Characteristic and Risk Assessment of Heavy Metals in Surface Sediments of the Yellow River Mainstream].

ABSTRACT

Heavy metals(HMs) are highly toxic and do not easily degrade in the environment. They can accumulate in the human body through the food chain, with serious impacts on the ecological environment and human health. In this study, 14 sampling sites along the mainstream of the Yellow River were investigated, and the total content and chemical fractions of six heavy metals(As, Cd, Cr, Cu, Pb, and Zn) in sediments were analyzed. The geo-accumulation index, potential ecological risk index, and risk assessment coding were used to assess the contamination level and bioavailability of HMs in sediment. Principal component analysis and redundancy analysis were used to identify the main sources of HMs. The results showed that the average content of heavy metals was in the order of Cr>Zn>Cu>Pb>As>Cd. Cd had the highest excess rate relative to the background value of each reach, reaching 85.7%. In the sediments, As, Zn, Pb, and Cu were predominantly in the oxidizable fraction(F3sulfide and organic matter-bound), Cd was mainly occupied by the acid-soluble(F1exchangeable and carbonate-bound) and a residual fraction(F4mineral matrix-bound), and Cr was predominantly in the residual fraction. As, Cr, Cu, Pb, and Zn showed the lowest bioavailability in the upstream, increased in the midstream, and finally decreased in the downstream. The risk assessment showed that Cd, the element with the highest pollution risk level in the Yellow River, was prone to pose a serious threat to the ecological environment and should be prevented and controlled first. The PCA and RDA analyses revealed that fine sediment and total organic matter controlled HMs contamination. Therefore, the prevention and control of soil erosion and sediment migration should be emphasized to control HMs pollution in the Yellow River Basin.