Distribution,Sources And Risk Assessment Of Heavy Metals In The Environment And Organisms Of Marine Pastures In Haizhou Bay And Its Adjacent Waters

With the rapid development of China’s economy,heavy metal pollutants produced by human activities and industrialization are continuously discharged into the ocean through atmospheric deposition and surface runoff,which seriously damages the marine ecological environment.Heavy metals are highly fat-soluble,and once they enter aquatic organisms,they are difficult to be decomposed and transformed,and they will be transmitted to higher trophic organisms through biological enrichment and food chain amplification.In order to explore the current situation of heavy metals in Haizhou Bay Marine Ranch and its adjacent waters,water,sediment and biological samples were collected and investigated in October 2020 in Haizhou Bay Marine Ranch and its adjacent waters.Based on eight kinds of heavy metal data(Zn,Cu,As,Cr,Cd,Pb,Ni,Hg),the changing laws of heavy metal contents in water,sediment and organisms were analyzed,and the effects of external factors such as hydrodynamic and water environment conditions were combined.By using various analytical methods,such as correlation analysis,principal component analysis and positive definite matrix factor model,the sources of heavy metals in water and sediments are deeply studied,and the potential ecological risk of heavy metals is accurately evaluated by combining single factor index,geo-accumulation index and potential ecological risk index.The biological concentration factor is used to analyze heavy metals in organisms,thus providing reference for formulating ecological environment restoration measures in this sea area.The results are as follows:(1)Cr,As,Hg and Ni in Haizhou Bay Marine Ranch and its adjacent waters meet the first-class water quality standards,while Pb,Cu,Zn and Cd exceed the first-class water quality standards,and there is heavy metal pollution in the water body of the study area to some extent.On the time scale,Hg content showed a decreasing trend,while Pb,Cu,Zn and Cr content showed an increasing trend.From the inshore aquaculture area to the offshore natural sea area,the contents of Zn and Hg in the water body gradually increased,and the maximum value appeared in the offshore natural sea area.The contents of Cu,Pb,As and Ni decreased first and then increased,and the maximum value appeared in the inshore aquaculture area.The contents of Cd and Cr showed a decreasing trend,and the maximum value appeared in the inshore aquaculture area.Cd and Cr in water mainly come from pollutants discharged into the sea by Linhong River,that is,human activities such As industrial,agricultural and domestic sewage discharge.As,Ni,Cu and Pb mainly come from marine transportation,Hg mainly comes from natural sources,and Zn mainly comes from human activities and sedimentary parent materials.(2)The single factor index was used to evaluate the heavy metals in the marine pasture area of Haizhou Bay.The results showed that the risk rank of eight heavy metals was Cd > Pb > Zn > Cu > Hg > Ni > As > Cr.Cd,Pb and Zn in the water in the study area are polluted to some extent,while Hg,Ni,As and Cr are clean and pollution-free.The potential ecological risk index was used to evaluate the heavy metals in the marine pasture area of Haizhou Bay.The results showed that the risk rank of eight heavy metals was Cd > Pb > Hg > Cu > As > Ni > Zn > Cr.Overall,the study area is at a moderate level of potential ecological risk,and Cd is the main contribution factor to the potential ecological risk of water bodies in this sea area,and Cd should be the focus of ecological environment management in this sea area.(3)The contents of Cu,Pb,Zn,Cr,As,Hg and Ni in the sediments of Haizhou Bay Marine Ranch and its adjacent waters are all within the first-cl Ass standard range,and the average content of Cd is beyond the first-class standard range.The quality of sediments in the study area is generally good,but the average content of five heavy metals,such as Cu,Pb,Zn,Cd,As and Ni,exceeds the initial background value of the study area,and these five heavy metals are enriched in the sediments to some extent.The contents of Cu,Zn,Cd,Cr,As and Ni in sediments gradually decreased from the inshore aquaculture area to the natural sea area far from the shore,and reached the maximum in the inshore aquaculture area.Pb content decreased first and then increased,and reached the maximum in the inshore culture area.The content of Hg is gradually increasing,and the maximum value appears in the offshore natural sea area.Heavy metals As,Cu,Zn,Cd,Cr and Ni in the sediments of marine pasture in Haizhou Bay mainly come from pollutants discharged into the sea by Linhong River,Pb mainly comes from pollution caused by marine shipping,and Hg mainly comes from natural sources.(4)The application of geo-accumulation index to the evaluation of heavy metals in sediments of Haizhou Bay marine pasture showed that the order of ecological risks of eight heavy metals was Cd > Pb > As > Zn > Cu > Ni > Cr > Hg.The risk level of Cd in the sediments in the study area is mild pollution to moderate pollution,the risk level of Pb,As,Zn and Cu is no pollution to mild pollution,and the risk level of Ni,Cr and Hg is no pollution.The potential ecological risk index was used to evaluate the heavy metals in sediments of marine pasture area in Haizhou Bay.The results showed that the potential risk rank of eight heavy metals was Cd > As > Pb > Hg > Cu > Ni >Zn > Cr.The study area is generally at a low potential ecological risk level,and the sediments are in good condition,but the input of Cd-containing pollutants should be strictly controlled to prevent the pollution from intensifying.(5)The average contents of Cu,Pb,Zn,Cd,Cr,As,Hg,Ni and other eight heavy metals in the marine pasture of Haizhou Bay and its adjacent waters are 31.28,3.38,139.27,3.09,1.46,27.68,0.93 and 1.73 μg/g.The maximum contents of Cu,Zn,Cd,Cr and Ni appeared in bivalves Ostreidae,the maximum contents of As appeared in Cephalopods Loligo beka,the maximum contents of Hg and Pb appeared in crustaceans Oratosquilla oratoria,and the minimum contents of 8 heavy metals all appeared in fishes,such as Clupanodon punchtatus and Setipinna tenuifilis.(6)The enrichment degree of heavy metals in different organisms is quite different.In this study,eight kinds of heavy metals showed As: Cephalopoda >Gastropoda > Crustacea > Bivalves > Fish;Cr: bivalve > crustacean > gastropod >cephalopod > fish;Cu: crustaceans > bivalves > cephalopods > gastropods > fish;Hg:crustaceans > cephalopods > fish > bivalves > gastropods;Pb: crustaceans >bivalves > cephalopods > gastropods > fish;Zn: bivalve > crustacean > gastropod >cephalopod > fish;Ni: bivalve > crustacean > cephalopod > gastropod > fish;Cd:bivalve > gastropod > crustacean > cephalopod > fish.The values of BWAF and BSAF of bivalve Zn are obviously higher than those of other groups,while those of cephalopod As are obviously higher than those of fish,while those of fish As,Cu and Zn are obviously lower than those of other groups.