The Influence Of Aquaculture On Mercury Speciation Change In Aquatic Environment

This study revealed the roles of aquaculture on mercury speciation,distribution and transportation in freshwater and marine water fish aquaculture sites.Water,sediment and fish samples were collected from Wujiangdu Reservoir,Guizhou Province,and Xiangshan Bay,Zhejiang Province.The results showed that:（1）Total mercury（THg）concentration in Wujiangdu reserviour ranged from 0.785-401 pmol·L^-1.For the vertical distribution,THg concentrations in surface and bottom layer of overlying water were higher than that in middle layers,which indicated that air deposition and sediment flux are the major sources of Hg in overlying water.Total methylmercury（TMeHg）concentration in intersurface betwenn sediment and overlying water was significantly higher than the other layers,which was due to the strong anaerobic condition are benefit for Hg methylaiotn.Dissolved MeHg（DMeHg）concentrations as well as the percent of DMeHg to dissolved Hg（DHg）in sediment porewater of aquaculture sites were significantly higher than reference sites.Moreover,the percent of DMeHg to DHg was positively correlated with organic matter concentration in sediment,which further demonstrated that fish aquaculture activities lead to the methylation of Hg in aquatic system.THg concentration in liver was significantly higher than the other tissues.In comparison,MeHg concentration in muscle of cultured fish was significantly higher than the other tissues.（2）THg concentrations in sediment of references sites of Xianshan Bay were higher than aquaculture sites.This is because reference sites were more close to the power plants than aquaculture sites in Xiangshan Bay.Emission gases from coal power plants contain high concentrations of Hg,which would result Hg contamination in local environment.Moreover,THg concentration in sediment that collected from summer was higher than that from winter,which was attributed to the monsoon climate system.MeHg concentration in surface sediment and MeHg concentration in sediment porewater of aquaculture sites were significantly higher than reference sites,which further demonstrated that fish aquaculture activities would promote MeHg formation in aquaculture sites.Higher concentrations of MeHg in summer than winter was attributed to the higher temperature are benefited for the activities of bacteria.The mean values of MeHg concentration in the muscle of marine cultured fish reached to 81.0 ng·g^-1（3）TMeHg、DMeHg and PMeHg concentrations in Wujiangdu reservoir were higher than those in Xiangshan Bay since the relavive higher Hg background value and lower pH vaule of water in bottom layer of Wujiangdu were lower than Xiangshan Bay.Hg concentration in the solid phase of Wujiangdu was higher than Xiangshan Bay,however,Hg concentration in the liquid phase in Xiangshan Bay was higher than Wujiangdu reservoir and the solid-liquid partitioning coefficient of Xiangshan Bay was lower than that in Wujiangdu since the high concentration of Cl-could complex with Hg2+,and further lead to the dissolve of Hg in liquid phase.Based on the Estimated daily intake formula mul of Hg,people who have 45.6 gram of black seabream would exceed the reference dose of MeHg that established by USEPA.The consumption of grass carp is safer than the other fish.631 grams of grass carp can be eaten per day.Compared with marine cultured fish,freshwater cultures fish are safer to consume since Hg concentration in freshwater cultured fish was lower than marine cultured fish.