The Enrichment Characteristics And Source Analysis Of Heavy Metals Of Different Environmental Media In The Pearl River Delta,China

The accumulation mechanism and sources of heavy metals in the natural surface soil,stream sediment and suspended matter in the study area of the Pearl River Delta can be identified to understand the overall situation of heavy metal pollution in the study area.In this paper,the geochemical characteristics of As,Cd,Cr,Cu,Hg,Ni,Pb and Zn elements in three environmental media in the study area were analyzed.The enrichment factor,risk assessment,sediment quality reference coefficient and potential ecological risk index were used to evaluate the pollution degree and risk of heavy metals in the Pearl River Basin.Correlation analysis and factor analysis were used to identify the sources of heavy metals in different sedimentary environments.The results show that:The natural surface soil in the Pearl River network area is relatively mature,with high content of Al₂O₃,TFe₂O₃ and various heavy metal elements.The risk of Cd in heavy metals was high,89.36%of the samples exceeded the risk screening value.Almost all heavy metal elements and Al₂O₃,TFe₂O₃,SiO₂,organic matter belong to the same factor,so it is speculated that naturally the surface soil heavy metal elements are more inclined to combine with iron（hydrogen）oxides and clay minerals.The sediments of Beijiang River system are rich in Al₂O₃,TFe₂O₃ and SiO₂,while the sediments of Xijiang River are rich in CaO and MgO.The content of heavy metals in stream sediments was significantly higher than the background value.The identification results of sediment environmental reference values show that most heavy metals occasionally have toxic effects,and the risk is higher in Beijiang area.As,Cd,Hg,Pb and Zn tend to be enriched in Fe,Mn oxides and clay minerals,while Cu,Cr and Ni tend to be enriched in Ca and Mg carbonate minerals,which are affected by the weathering and erosion of the upstream carbonate rocks.The contents of Al₂O₃,K₂O,TFe₂O₃ and MgO in suspended solids in Beijiang River system are higher,while the contents of CaO in Xijiang River are higher,and all heavy metals are significantly enriched.According to the potential ecological risk assessment,the ecological risk pollution degree of As,Cd,Cu,Pb and Zn in Beijiang River is very high,and the ecological risk pollution degree of Cd and Ni in Xijiang River and Dongjiang River is very high.Pb,Zn,As,Ni,Cd,Hg are significantly correlated with Al₂O₃,MgO,TFe₂O₃,and Cr,Cu are correlated with CaO.The upper reaches of the Xijiang and Beijiang rivers exposed a lot of carbonate rocks in the process of weathered soil,could release large amounts of Ca ions and Cd element into the water,at the same time in the water,suspended matter and sediment formation of carbonate minerals can be adsorbed water medium Cr,Ni,such as metal,and migration with the river on the downstream alluvial plains,Caused the enrichment of Cd,Cr and Ni in the three sedimentary media.The large（super）sulfide deposits in the upper reaches of Xijiang River and Beijiang River will produce a large amount of wastewater rich in heavy metal elements during natural weathering and mining and smelting.,and the residual formation of clay minerals and iron manganese oxides（hydrogen）,after they enter the water through erosion,the adsorption of heavy metal elements,and migration with the river on the downstream alluvial plains,As,Cd,Cu,Hg,Pb,Zn and other heavy metals were enriched in the three sedimentary media.The developed industrial activities in the Dongjiang River also lead to the enrichment of heavy metals in some areas.