The Distribution,Source And Risk Assessment Of The Heavy Metals In The Coastal Waters And Estuaries Of Qinzhou

As a hug of the link between the rivers and the sea,nearshore and estuaries become an environmental system with complex dynamic changes,and most of pollutants by human activities are input to inshore areas mainly through estuary,and then transported to the open sea.Among these environmental pollutants,heavy metals have attracted widespread attention due to their easy accumulation and difficulty in biodegradation.In recent years,the coastal ports and coastalindustries in Qinzhou have developed rapidly,and the discharge of large quantities of industrial wastewater and domestic sewage has become more and more serious in the ecological environment of Qinzhou.This paper analyzed the content distribution and pollution condition of Zn,Cu,Pb,Cd,Cr in seawater,suspended particulate matter and sediments of nearshore and estuary in Qinzhou,and the solid-liquid distribution and enrichment of heavy metals were preliminarily discussed and possible sources of heavy metals were analyzed.The main conclusions of this study are as follows:(1)The average contents of Zn,Cu,Pb,Cd and Cr in coastal waters and estuaries of Qinzhou were 29.95,1.96,1.47,0.09 and 0.40?g/L,respectively,where the contents of Cu,Cd and Cr in all sampling points were lower than the First-Class Seawater Standard,while the average contents of Zn and Pb were higher than the First-Class Seawater Standard.The Cd element was first increased and then decreased from west to east,and the Pb element overall trended to rise from the northwest to the southeast,and the spatial distribution of Zn,Cu and Cr was relatively uniform.And 78.79%of the study area were basically pollution-free by the heavy metals,and some areas were mildly polluted,where Zn and Pb were the major contributors to the pollution.(2)The average contents of Zn,Cu,Pb,Cd and Cr in Qinzhou coastal waters and estuaries were 127.2,30.3,40.9,0.50 and 47.9?g/L,respectively.The spatial variation of Cd element in the study area was the largest,the contents of Cu,Pb and Cr generally showed low in the bay and high in the rivers,while the Zn content was higher near the east coast of Qinzhou bay and in the sea runoff.And according to the comprehensive potential ecological risk indexs of five heavy metals,48.5%of the study area were of medium potential ecological risk,and the main pollution areas were Maolingjiang river,Qinjiang river,Dafengjiang river and Qinzhou port,and Zn,Pb and Cd were the major contributors to pollution,of which Cd was the most important ecological risk factor.(3)The mean values of Zn,Cu,Pb,Cd and Cr in the coastal waters and estuaries of Qinzhou were 83.3,18.4,23.2,0.17 and 23.4?g/L,respectively,which were all lower than the First-Class Marine Sediment Quality Standard.The contents of Cd were high in west but low in east overall,the Cu and Pb content showed a trend of gradually reducing from the rivers to the sea,the Zn content was low near the coast area,and the high value area of the Cr content was mainly near the coast area and the Dafengjiang river near the upstream area.In the sediments,Pb,Cr,Zn and Cu were mainly dominated by residual states,and carbonate binding state was mostly dominant for Cd,which would bring about more impact on the environment.The sediments just showed no obvious enrichment effect on the Pb element.According to the comprehensive potential ecological risk indexs of five heavy metals,the 93.9%of the study area was attached to low potential ecological risk,except which the main areas of pollution were Maolingjiang river,Qinjiang river and Qinzhou port,and Zn,Cu and Cd were the major contributors to pollution in the study area,among which Cd was the most important ecological risk factor,but would not produce adverse biological effects for a while,while Zn and Cu would occasionally produce biotoxic effects.(4)The contents of Pb and Cr in the study area were mainly affected by the seawater outside Qinzhou bay,which were diluted reversely from the rivers to the sea.The increase of salinity would enhance the desorption of Cu,Pb and Cr,and the increase of pH would weaken the adsorption effect of Cr.Dissolved Zn were vulnerable to the adsorption of Fe-Mn oxides and organic matter and then were settled to sediments,dissolved Cr combined with suspended particulate matter would quickly fall into sediments,particles and sediments contained Cu would always keep the process of settlement and resuspension.(5)The heavy metals in the study area were mainly from industrial sewage,agricultural waste water,domestic sewage,ship transportation,rock weathering and natural erosion,which were influenced by human sources andnatural sources.