Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In The Yangtze River Estuary And The Northern Jiangsu Coast

In this paper,the distribution characteristics of Hg,As,Cu,Pb,Cd,Cr and Zn in the sea water and sediment of the Yangtze River Estuary and the coastal area of Northern Jiangsu Province,as well as the distribution trend among the heavy metal regions,the seasonal variation trend of the heavy metal elements in the Yangtze River Estuary,the distribution characteristics of the grain size components of the sediment in the study area and the types of the sediment in the study area are studied,and the correlation analysis is used methods and principal component analysis were used to analyze and study the sources of heavy metal pollution,as well as to evaluate the current situation and potential ecological risk level of heavy metal pollution by various methods,in order to provide basic data for the objective evaluation of heavy metal pollution in the Yangtze River Estuary and the coastal areas of Northern Jiangsu,and for the environmental treatment and protection of the region.The main conclusions of this paper are as follows:(1)The annual average concentrations of Hg,As,Cu,Pb,Cd,Cr and Zn in the surface seawater of the Yangtze River Estuary are 3.85?g/L,1.95?g/L,6.36?g/L,4.54?g/L,0.29?g/L,6.20?g/L and 44.56?g/L,respectively.The concentrations of Hg,Cu,Pb and Zn are higher than the national standard limits of class I seawater.The concentrations of As,Pb,Cd,Cr and Zn in spring and summer are higher than those in autumn and winter,while the concentrations of Hg and Cu in autumn and winter are higher than those in spring and summer In season,it is mainly affected by runoff into the sea and human activities.The average concentrations of Hg,As,Cu,Pb,Cd,Cr and Zn in the surface seawater of the coastal area of Northern Jiangsu are 2.49?g/L,2.66?g/L,2.79?g/L,68.01?g/L,0.31?g/L,5.81?g/L and 107.53?g/L,respectively.The average concentrations of Hg,Pb and Zn are relatively high,which are basically lower than the three or four types of seawater quality standards,and the pollution is relatively serious.The concentration of heavy metals in the surface seawater of the Yangtze River Estuary is higher in the coastal area than in the offshore area,and it is decreasing gradiently from the mouth to the mouth,which is mainly related to the nearshore human activities and the sand rising of the marine power in the shallow water area;in the vertical distribution,the concentration of heavy metals in the North branch of the Yangtze River Estuary is higher than that in the South Branch.The concentration of heavy metals in the coastal waters of Northern Jiangsu is generally high near shore,and the concentration of heavy metals gradually decreases along the coast to the open sea;in the coastal areas from north to south,such as the eastern coastal waters,the concentration of heavy metals is relatively high,and the concentration of heavy metals in the coastal waters is relatively high,followed by that in the coastal waters,which may be related to the operation of largescale seaports and wharfs in the coastal waters of eastern Jiangsu and coastal Jiangsu Frequent marine transportation.(2)The annual average concentrations of Hg,As,Cu,Pb,Cd,Cr,Zn and other heavy metals in the surface sediments of the Yangtze River Estuary are 0.26 mg/kg,12.17 mg/kg,5.06 mg/kg,3.44 mg/kg,0.13 mg/kg,12.67 mg/kg and 77.03 mg/kg,respectively.Except Hg,the other elements are lower than the first class standard of marine sediment quality;the grain size of sediment in the Yangtze River Estuary is mainly silt content,followed by sand content,clay content is the lowest,and the sediment type is mainly clayey sand.The average concentrations of Hg,As,Cu,Pb,Cd,Cr and Zn in the surface sediments of the coastal waters of Northern Jiangsu are 1.22 mg/kg,19.65 mg/kg,5.02 mg/kg,5.56 mg/kg,0.13 mg/kg,22.98 mg/kg and 63.50 mg/kg,respectively.Only the average concentration of heavy metal Hg exceeds the national standard limit of sediment class I;the sediment composition in the coastal area of Northern Jiangsu is dominated by silt content,and the sediment type is mainly sandy sediment.The distribution of heavy metals in the sediments of the Yangtze River Estuary is higher in the near shore than in the far shore,decreasing gradually from near to far,and gradually changing from tongue like extension to strip-shaped extension;it is higher in the South and lower in the north,showing a low high low trend from South to north.In the north-south direction,the content of heavy metals in area of Beigangbeisha is higher,As,Cd,Cu and Pb are higher and tend to accumulate.This may be because the area is the confluence of the South Branch and the North Branch,which is easy to lead to the adsorption and deposition of heavy metals.The content of heavy metals in the sediments of the coastal areas of Northern Jiangsu is generally high in the coastal areas and low in the remote areas,decreasing step by step from near to far;vertically,the content of heavy metals in Dafeng and Rudong coastal areas is relatively low,only As and Zn are relatively high in this area,while the concentration of heavy metals in the coastal areas of Hai'an is relatively high,which has obvious aggregation phenomenon in this area.Heavy metals in the Yangtze River Estuary and the coastal areas of Northern Jiangsu all come from the transportation of land-based pollutants,and the runoff into the sea and the discharge of industrial sewage are the main sources;the use of agricultural pesticides and fertilizers,the dumping of domestic garbage and traffic pollution are also the important sources of pollution.(3)The single factor pollution index shows that the pollution order of heavy metal elements in the coastal waters of the Yangtze River Estuary is Hg > Pb > Zn > Cu > Cd > Cr> As,and the pollution indexes of Hg,Pb and Zn are relatively large,which are at the level of serious pollution,strong pollution and medium pollution respectively.The pollution degree of heavy metal elements in the sediment is Hg > As > Zn > Cd > Cr > Cu > Pb,and the pollution index of Hg is relatively high,In the middle pollution level,the other elements are low pollution level;the pollution level of land accumulation index is Hg > As > Cd > Zn > Cr > Cu > Pb,and Hg and As are in the middle pollution level and light pollution level respectively;the potential ecological risk is Hg > Cd > As > Cu > Zn > Pb > Cr,and the other elements are in the low ecological risk level except Hg.The pollution degree of heavy metals in the coastal seawater of Northern Jiangsu is Pb > Hg > Zn > Cu > Cd > As > Cr,Hg,Pb,Zn are all in the serious pollution level,and other elements are in the non pollution level;the pollution degree of heavy metals in the coastal sediment of Northern Jiangsu is Hg > As > Zn > Cr > Cd > Cu > Pb,in which,Hg is in high pollution level,As is in medium pollution level,and other elements are in low pollution level;the pollution degree of land accumulation index is Hg > As > Zn > Cr > Cu > Cd > Pb,except Hg is in medium pollution level,other elements are not polluted;the potential ecological risk is Hg > As > Cd> Cu > Pb > Zn >Cr,in which Hg is at a very strong level of ecological risk,and the other elements are at a low level of ecological risk.