SPATIAL DISTRIBUTION CHARACTERISTICS AND ECOLOGICAL RISK ASSESSMENT OF HEAVY METALS IN SURFACE SOILS OF THE YELLOW RIVER DELTA

The objective of this study was to determine the contamination status, source and potential risk of heavy metals in surface soils of the Yellow River estuary in the Yellow River Delta. A total of 106 soil samples (0-20 cm) were collected from the core, buffer and experimental areas of the Yellow River estuary in the Yellow River Delta and analysed for six heavy metals (Cd, Cu, Pb, Cr, Zn, and Mn). Multiple analyses (including index of geo-accumulation (Igeo) analysis, Ei/risk index (RI) analysis, principal component analysis (PCA), and correlation analysis (CA)) were applied to evaluate the pollution level and potential ecological risk of surface soil heavy metals and to identify their sources. The heavy metal contents varied greatly, and the concentration of Cd exceeded the background value, showing a minimum value 9 times greater than the background value. CA and PCA revealed that the main sources of surface soil heavy metals were anthropogenic activities and natural processes. Based on the Igeo value and pollution index of heavy metals in this study area, the exceedance rate and pollution level were higher for Cd than for the other heavy metals. Cd had an extremely high ecological risk status compared with that of the other heavy metals. The results provide a theoretical basis for the control of heavy metal pollution of surface soils and comprehensive ecological restoration in the Yellow River Delta.