Pollution Status And Risk Assessment Of Heavy Metals In The Sediments Of The West Bohai Estuary

With the increase of human activities,pollutants entering the sea have increased greatly,and heavy metals have become an important pollutant threatening the marine environment.In this paper,the contents of Cd,Cr,Ni,Cu,Zn,Pb and other heavy metals in the sediments of the intertidal zone of the Western Bohai Sea estuary were investigated and studied.Four ecological risk assessment methods were used to assess the potential ecological risks.The research results will provide scientific basis for the ecological environment protection,heavy metal pollution prevention and ecological risk management of the Western Bohai estuary.The main conclusions are as follows(1)The contents of Cd,Cr,Ni,Cu,Zn and Pb in the sediments of the Western Bohai estuary are 0.42-0,92,8.32-23.9,1.87-17.6,1.67-14.6,6.29-25.0,3.16-24.8mg/kg.Among them,Cd content exceeded the first class standard of marine sediment quality standard of China,and the contents of Cr,Cu,Zn and Pb belonged to the first class standard of marine sediment quality standard;the heavy metal content of the Western Bohai estuary increased from north to south.The highest values of Cd,Cr,Zn and Pb were 0.92 mg/kg,23.9 mg/kg,25.0mg/kg and 24.8mg kg,respectively;the highest values of Ni and Cu were 17.6mg/kg and 14.6mg/kg in the eastern Qinhuangdao estuary and the eastern Tianjin estuary,respectively.The high value areas of six heavy metals are mainly concentrated in the middle and low tide zones.(2)The Nemerow composite index method was used to assess the ecological risk of heavy metals in the sediments of the Western Bohai Sea.It was found that the PI values of Cd in the estuaries of the Western Bohai Sea ranged from 0.83 to 1.81,and most stations were at medium pollution level.The Pi values of other heavy metals(Cr,Cu,Zn and Pb)were less than 1,which belonged to low pollution level.The high value areas of single pollution index of all heavy metals are concentrated in the middle and low tide zone.The ecological risk of each metal was Cd>Pb>Cr>Cu>Zn.The comprehensive pollution index of heavy metals in the Western Bohai estuary is between 0.61 and 1.35,which is a light pollution level.The geoaccumulation index method was used to assess the ecological risk of heavy metals in the sediments of Western Bohai Sea.It was found that the pollution level of Cd in most stations in the Western estuary of Bohai Sea was grade 1,which was a mild pollution level;the pollution level of Cr in the southeast of Tianjin and the Eastern estuary of Cangzhou was 1,which was a mild pollution level,and the pollution level of other stations was 0,which was a clean level;Pb was in the southeast river of Tianjin The pollution level of the two stations is grade 1,which is light pollution level,while the pollution level of other stations is 0,which is clean level,Cu,Zn and Ni are clean in different tidal zones of 19 stations.The potential ecological risk index method was used to assess the ecological risk of heavy metals in the sediments of the Western Bohai Sea.It was found that the potential risk level of Cd in the sediments of the Western Bohai estuary was strong to very strong.Cr,Zn,Ni,Cu and Pb have slight potential ecological risks of heavy metals.The potential ecological risk of heavy metals in the Western Bohai estuary is Cd>Pb>Cu>Ni>Cr>Zn.The potential ecological risks of the six heavy metals were higher in the middle and low tide zone than in the high tide zone.Due to the high potential ecological risk of Cd,the potential ecological risk of heavy metals in the estuary of Western Bohai Sea is moderate to strong.The ecological risk assessment of heavy metals in estuaries of the Western Bohai Sea was carried out by using the sediment quality standard method.It was found that the concentration of Cd in the middle and low tide zones of the Bohai Bay and various stations was between the critical effect concentration and the inevitable effect concentration,indicating that long-term exposure is easy to produce toxic effects.The content of Ni in most sites was lower than the critical effect concentration of the element,indicating that long-term exposure of these sites would hardly produce toxic effects of Ni.The contents of Cr,Zn,Cu and Pb in the 19 stations were all lower than the critical effect concentration of each element,which indicated that the toxicity effects of Cr,Zn,Cu and Pb in the 19 stations were almost not produced by long-term exposure.To sum up,the ecological risk of the eastern Tianjin estuary and the eastern Cangzhou estuary is higher than that of the northwest Bohai Sea region,and the ecological risk of the middle and low tide zone is higher than that of the high tide zone.Cd is the primary pollutant of heavy metals in the sediments of the Western Bohai Sea estuary.