Pollution Status And Source Identification Of Heavy Metals In The Seabed Sediments Of The Bohai Sea

The Bohai Sea in China is a semi-enclosed inland sea,including three bays(i.e.,Liaodong Bay in the north,Bohai Bay in the west,and Laizhou Bay in the south)and a central basin.It is connected with the Yellow Sea via the Bohai strait in the east.With the rapid social and economic development around the coastal areas of the Bohai Sea,discharge of heavy metal pollutants into the Bohai Sea is increasing,which has rapidly worsened the Bohai Sea environmental quality.Sediments act as a sink for various pollutants.Most heavy metals that enter into the marine environment will finally precipitate and become incorporated into sediments with other organic matter.Some metals in the sediments may be subsequently released to the overlying water as a result of either physical disturbance,or diagenesis,and can affect the health status of the marine ecosystem.Therefore,the metal content in surface sediments can reflect the pollution level of the water.In August 2017,66 seabed surface sediment samples were collected from Bohai Sea,and the contents of seven heavy metal elements such as Cr,Cu,Zn,As,Cd,Pb,Fe and TOC in sediments were analyzed to study the distribution characteristics,influencing factors and pollution status of heavy metals in surface sediments of the Bohai Sea.The average contents of six heavy metals in the surface sediments of Bohai Sea(unit: mg/Kg)ranked from high to low as follows: Zn(39.84)>Cr(30.22)>Pb(20.56)>As(12.15)>Cu(11.60)>Cd(0.09).The contents of heavy metals are also different in different sub-areas.The contents of all heavy metals in Laizhou Bay are relatively small.The contents of Cr,Cu and Zn are relatively high in Bohai Bay.The contents of As and Pb are relatively high in the central sea area of Bohai Sea,and the contents of Cd are relatively high in Liaodong Bay.The correlation between As and each of other 7 heavy metals is not obvious,indicating that the source of As is different from other 7 heavy metals.There is a positive correlation between TOC and each of Cr,Cu,Zn,Pb and Fe contents,indicating that TOC content is an important factor affecting the distribution of these heavy metals.The contamination factors,geo-accumulation index and enrichment factor were used to evaluate the seabed heavy metals in the surface sediments of the Bohai Sea.The evaluation results of these three methods were similar.The pollution levels of Cr,Cu and Zn in the surface sediments of the Bohai Sea were relatively low,while that of As,Cd and Pb was relatively high.The values of potential load index of all sampling sites in Bohai Sea are less than 150,which is at a slight ecological hazard level.Among the six heavy metal elements,the potential load index of Cd is the largest,and the potential hazard index of Zn is the smallest.The heavy metal pollution load index of the Bohai Sea is less than 1,indicating that the surface sediments in the Bohai Sea are not polluted.