Geochemical Characteristics Of Heavy Metal Contamination For Delta Sediments From The Xiangjiang River, Hunan Province, China

The Xiangjiang River is one of the rivers that are most seriously polluted by heavy metals in China. In present study, four sediments cores, named WH, XY, QN, and QS respectively, and loacated in delta area of the river, were selected for sampling and geochemical studying. Then, the 128 subsamples were collected, and 87 of them were analyzed for abundances of major and trace elements using XRF and ICP-MS techniques after PH value of each sediment was determined. The pollution exyensity of the heavy metal contamination of sediments was then evaluated using Index of geoaccumulation (Igeo) and Enrichment Index (EI).Major elements analyzing resluts show that the delat sediments are highly concentrated in elements Fe, Al, Mn, P and Ti were highly concentrated in the riverbed of the delta area, while Ti, Al, Fe, Mn, Mg, Ca, and P were significantly enriched in the lakebed, which indicated that the pollution sources of riverbed and lakebed were different. Sediments in both areas, especially the sediment core from the riverbed of the estuarine delta, were highly weathered. Similarity distribution of major elements in the XY and WH sediment cores showed they share the same sources and the similar sediment environment.Concentrations of heavy metals, especially Cd, Sc, Sn, Sb, Zn and Pb, were significantly enriched in the sediments of the estuarine delta, which decrease in the lake area. The contents of most heavy metals in the sediments increased downstream along the river. Vertical distribution of these contents in the WH and XY sediment cores indicated that the pollution was decreasing slowly in recent years. According to the EF value of the heavy metals, Cd was extremely enriched (EF>20) in the sediments in the riverbed of the delta, while enrichment of Cu and Zn were moderate (2≤EF<5). Their EF value decreased significantly in the sediment core of the lakebed. The enrichment of Ba, Sc, V, Cr, Co, Ni, Mo, Tl, Th and U were slight(EF<2). Similar results were obtained by using Igeo estimation. The EI of heavy metals in the sediments showed the pollution extents of the four sampling place were QN>WH>XY>QS.Relativity analysis of the heavy metals and major elements showed that Ba, Sc, V, Cr, Co, Cu, Zn, Mo, Pb, Tl and U were mainly hosted in the clay minerals of the sediments, while the Ba, Sc, V, Cr, Co, Ni, Cu, Zn, Mo, Cd and Pb were in Fe-Mn-oxides. Ba, Sc, V, Cr, Co, Ni and Cu were also hosted in undissolved assistant minerals.Through characteristic analysis of the major elements and the heavy metals, it could be concluded that the pollution of Sc, V, Cr, Co, Cu, Zn, Mo, Cd, Sn, Sb, Tl, U and Pb were mainly affected by human activity, while the Ba, Ni and Th came mostly from natural sources.