The Sediment Heavy Metal Pollution,source,and Ecological And Health Risk Assessment In East Dongting Lake

Heavy metals have significant toxicity,persistence and non-degradability,as well as bioaccumulation effects in the food chain.Heavy metal pollution seriously threatens the aquatic ecological environment.Sediments contain a large number of various colloids,which can bind heavy metals through adsorption,complexation,precipitation,etc.,and are the accumulation of heavy metals in lake water.However,with the change of environmental conditions（p H value of water body,organic matter content,water body disturbance,etc.）,sediment heavy metals are easily released and diffused into the lake water body,causing"secondary pollution".Therefore,the content of heavy metals in sediments is often used as an important factor to judge the environmental quality of lakes,and has long been the focus of environmental research.In order to explore the latest heavy metal pollution status,sources,ecological risks and health risks in the sediments of East Dongting Lake,the contents of 10 heavy metals such as As in 63 surface sediment samples which were collected in East Dongting Lake,including seven functional areas of wetland protection area,Chenglingji port area,waterway area,urban residential area,tourist area,farmland and reed field,were determined.The sources were identified and analyzed by absolute principal component analysis-multiple linear regression（APCS-MLR）model.And the degree of heavy metal pollution and human exposure risk were evaluated by the geo-accumulation index method(I_geo),the enrichment factor method（EF）,the Hakanson potential ecological risk index method（E_rⁱ,RI）and the US EPA health risk assessment method.The following main conclusions are drawn as follows:（1）The average contents of As、Cd、Cr、Co、Cu、Mn、Ni、Pb、Sr and Zn in the sediments of East Dongting Lake were 14.53,6.49,70.39,19.66,27.91,933.26,42.36,41.48,93.83 and 164.91 mg/kg.The average content of each heavy metal was1.13,19.67,1.60,1.91,1.37,2.07,2.00,1.78,1.17 and 1.98 times higher than the background value of Dongting Lake sediments,respectively.Among them,98%,97%,97%,94%,98%,and 94%of Cd,Cr,Co,Mn,Ni,and Zn samples exceeded the background value,respectively.From the regional spatial distribution,the average content of Cr in different regions was urban residential area>tourist area>Chenglingji port area>farmland>waterway area>reed field>wetland protection area.The contents of Cu and Ni were highest in the tourist area,higher in the northern part of the waterway,and lowest in the wetland protection area.The content of Sr was significantly higher in the farmland in the west of East Dongting Lake.The content of Cd in different areas was expressed as wetland protection area>reed field>waterway area>tourist area>farmland>Chenglingji port area>urban residential area.（2）I_geo values were calculated and the pollution level of Cd was severe(I_geo=3.39),other metals were all mild level(0<I_geo<1).The results of EF value showed that,except for the remarkable enrichment of Cd（EF=2.78）,the other 9 elements were all mild enrichment（EF<1）.The E_rⁱ of each heavy metal was calculated and the risk degree of Cd was found to be extremely high（E_rⁱ=662.13）,while the other 9metals belonged to the mild level（E_rⁱ<10）.Ecological risk assessment results showed that the descending order in different functional areas was as follows:wetland protection area>reed field>waterway area>tourist area>farmland>urban residential area>Chenglingji port area.Health risk assessment found that the non-carcinogenic index（HI<1）of heavy metals in surface sediments for adults was acceptable.The non-carcinogenic risk for children caused by As Cd Pb is beyond the acceptable range in the waterway area along East Dongting Lake.（3）The sources of 10 heavy metals in the surficial sediments of East Dongting Lake can be divided into three categories.Cr,Co,Cu and Ni mainly originate from the natural sources,such as soil-forming parent materials.As,Pb and Zn mainly originate from the mining source of large amount of metal mineral exploitation,beneficiation,smelting and tailings weathering and leaching.Cd,Sr and As mainly come from agricultural sources,including pesticide and fertilizer application,livestock breeding and domestic waste.On the whole,compared with other shallow lakes in China,the heavy metal pollution in the surface sediments of East Dongting Lake is at a higher pollution level.