| In recent years,the pollution of heavy metals in estuarine environment is becoming more and more serious in China,thus pose great risks to aquatic ecosystems and human health.Bivalves as the dominant fiter-feeders play important role in keeping ecological balance of estuarine ecosystem and in biomonitoring of trace metal pollution.Based on this,we studied oyster species in 15 stations in the coastal areas of Xiamen Bay.Firstly,we investigates the changes of heavy metal content in oyster,sediment and water in estuarine environment,and analyzes the relationship between the oyster and environmental media,and the feasibility of the oysters as a bioindicators of heavy metal pollution in estuaries were also discussed.Secondly,the effects of oyster on accumulation and elimination of metals and physicochemical parameters in two different estuarine environments were studied,the metal pollution in estuarine environment and the bioavailability of oysters to metals were also identified.Finally,because of the high toxicity of arsenic and its high concentration in estuarine environment,the transformation,metabolism,detoxification mechanism and possible influencing factors of oysters on two different pollution levels were further analyzed,and the biotransformation and self-protection mechanism of oysters to metal arsenic in the environment of relative pollution were clarified.The main results are as follows:1.The contents of heavy metals in oysters,sediment and water at 15 stations in February and August in Coast area of Xiamen Bay were determined.The oyster in Maluan Bay show higher concentration of Cu and Zn,the concentration of Cd in Zhangzhou port and As in Weitou port and Shenhu port were higher than other stations,indicating that these stations are polluted by different degrees of metals.The metal concentrations of Qiongtou,Aotou and Xiangshan are at a relatively low concentration level,so they can be considered as less disturbed areas.The accumulation of Cr,Co,Fe,Cd,Cu and Pb decreased with the increase of individuals,the growth dilution of organisms was the main reason for this phenomenon.Salinity,dissolved oxygen and pH are also important environmental factors affecting metal accumulation.There is a significant correlation between Cu,Zn,Cr,Ni in oysters and Cu,Zn,Cr,Ni,and Ag in the sediments,indicating that these metals have a common source of pollution or promote each other in bioaccumulation.There is no significant correlation between oyster and sediment,indicating that suspended particles and dissolved heavy metals are main source of heavy metals in oyster rather than sediment.This study indicates that accumulation of heavy metals in oyster can reflect the concentration of heavy metals in the estuarine environment.Therefore,oyster is a suitable indicator organism for monitoring heavy metal pollution in estuarine environment.2.The results of the transplanting experiment showed that the concentration of As in Shenhu port is higher than in Qiongtou.As in Shenhu port decreased with time,and the net discharge rate constant Ke is 0.0024 d-1.The concentration of Cu and Zn is higher than that of Qiongtou,and there is.a slight increase in exposure time,which indicates that Cu and Zn in clean water can still lead to net accumulation.The concentrations of Cu and Zn in oysters did not change significantly over time,indicating that they had reached equilibrium in the environment.Owing to Se and As have similar chemical properties,the excretion of Se is similar to As,and its net excretion rate constant Ke=0.010 d-1.Both transplanted oysters and native oysters accumulated Cd,and net accumulation rate was =0.034 hpg g-1 d-1.In Shenhu port,the accumulation of As in the oysters increased with time and the accumulation rate was?g g-1 d-1.The concentration of heavy metals,Cu,Zn,Se and Cd in the original oysters has no significant change,which indicates that the concentration of heavy metals in the environment can indicate accurately the concentration level of heavy metals in the environment.The accumulation of metals in oysters shows the bioavailability of metals,reflecting the concentration levels of metals in the environment.Temperature,salinity,pH and dissolved oxygen are important factors affecting the accumulation and elimination of metals by oysters.3.The accumulation and elimination of As in oyster depend on the As concentration in the environment.At the same time,Owing to the high toxicity of arsenic,we further analyze the arsenic speciation.The results showed that the concentration of inorganic arsenic in the oysters remained at a certain concentration level before and after the transplantation,and it was unaffected by the environment.Organic arsenic was the main form of arsenic,it shows that oyster has high selectivity for the enrichment and metabolism of arsenic.Although Shenhu port showed higher concentration of arsenic,no toxic organic arsenic is the main form,it will not pose any potential threat to organisms.Temperature,salinity,pH and dissolved oxygen are important environmental factors affecting MMA accumulation. |
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