Distribution Characteristics Of Mercury And Methylmercury In Fishes In The Three Gorges Reservoir

Mercury is liable to translate into hypertoxic alkyl mercury in aquatic environment. Many studies illustrate that reservoirs have mercury reactivity, new built reservoirs manifest the the phenomenon of abnormal higher methylmercury in water and fishes, and also the researches prove that inundated sediments and plants are the important source of the increased methylmercury in fishes in reservoirs. The Three Gorges Reservoir is the largest and world spotlight reservoir. The Three Gorges Reservoir which is the stream channel reservoir and has the special topography inundates large areas after it being reservoir, whether it can increase the methylmercury bioaccumulation rate of reservoir’s water and aquatic organism and emerge the mercury reactivity of reservoir is an important subject that is worth probing into. Therefore, this study choose the wild fishes in Three Gorges Reservoir as respondents, analysising the samples of water and fishes every month systematically at the sample sites of the Hanfeng Lake in Kai County, Shibao Stockaded Village and Tujing in Zhong County and Jane creek town in Fuling during June in2012and June in2013, exploring the seasonal changes of mercury and methylmercury in water, the distribution of mercury and methylmercury in different tissues or organs (such as gill, heart, muscle and swim bladder) in fishes and the bioaccumulation rate of fishes to discuss the subject of mercury reactivity in Three Gorges Reservoir after impounding. The research results as follows:(1) During the inquiry period, the changing range of the THg concentration in Three Gorges Reservoir’s water is1.24-45.63ng L-1, the DHg is0.51-9.84ng L-1, the RHg is0.03-2.53ng L-1the PHg is0.02-43.71ng L-1; the changing range of the TMeHg concentration in Three Gorges Reservoir’s water is0.13-2.60ng L-1, The DMeHg is0.01-1.76ng L-1, The PMeHg is0.01-2.28ng L-1, the suspended particulate matters of water control the distribution of mercury and methylmercury. The seasonal change of THg and PHg in different sample sites is that the concentrations of THg and PHg are higher in summer and lower in winter, but the concentrations of RHg and DHg don’t have marked changing regulation. To the different forms of methylmercury, the concentration of TMeHg and PMeHg in every site (excepting the Kai County) show up the higher level in winter and lower levels in other seasons, while the concentration of DMeHg does’t have the significant variation.(2) The changing range of the THg concentration in muscle of fihes in Three Gorges Reservoir’s is0.51-254.83ng·g -1, the mean value is51.26.±43.04ng·g-1, The changing range of the THg concentration in heart is0.46～254.29ng·g-1, the mean value is28.39±39.40ng·g-1, The changing range of the THg concentration in swim bladder is0.36±123.85ng·g-1, the mean value is14.08±16.71ng·g-1, The changing range of the THg concentration in gill is0.27～79.18ng·g-1, the mean value is11.49±12.98ng·g-1; The changing range of the MeHg concentration in muscle of fihes is0.05～188.89ng·g-1, the mean value is20.56±27.84ng·g-1, The changing range of the MeHg concentration in heart is0.03～180.93ng·g-1, the mean value is17.31±27.88ng·g-1. The changing range of the MeHg concentration in swim bladder is0.05～86.22ng·g-1, the mean value is6.32±11.20ng·g-1, The changing range of the MeHg concentration in gill is0.04～51.22ng·g-1, the mean value is4.89±8.18ng·g-1, the concentrations of THg and MeHg are lower than the food mercury restricted standard(the THg is300ng·g-1and the MeHg is200ng·g-1) in our country. Comparing with the rivers, lakes and reservoirs in China and overseas, the concentration of THg, MeHg and the ratio of MeHg/THg are in the low levels.(3) Different species of fishes have different concentration of THg and MeHg, different tissues and organs demonstrate that the concentration of THg is higher in muscles and hearts and lower in swim bladders and gills. The distribution of THg and MeHg in different trophic levels are: carnivorous> omnivorous> planktivorous> herbivorous, and the concentration of THg and MeHg in pelagic fishes are lower than the benthic fishes. The pearson correlation between mercury and weight and length in the different tissues of fish indicates that Topmouth Culter, Coreius heterokon, Squaliobarbus curriculus, Crucian, Bighead carp have a positive correlation with its weight and lenghth, while Cyprinus carpio, Pelteobagrus fulvidraco, Silver carp, Grass carp have no remarkable correlation with its its weight and lenghth.(4) The mean ratio of MeHg/THg in muscles of fishes in Three Gorges Reservoir is34.89±22.72%, the range is2.65～96.84%, The mean ratio of MeHg/THg in heart is43.21±20.60%, the range is0.61～89.10%, The mean ratio of MeHg/THg in swim bladder is32.69±21.16%, the range is4.17～91.29%, The mean ratio of MeHg/THg in gill is35.12±20.71%, the range is1.87-89.10%, the ratio of MeHg/THg increases with the trophic levels, and the ratio of MeHg/THg in different tissues or organs performance as:heart> gill> musle> swim bladder.(5) The bioaccumulation factors of THg in fishes’muscles in Three Gorges Reservoir is1.28×104(1.30×102～6.40xl04), heart is7.13×103(1.20×102-6.39×104), swim bladder is3.54xl03(0.90×102～3.11×104), gill is2.89×103(0.70×102～1.99×104), the bioaccumulation factors of MeHg in fishes’muscles is1.47×105(3.60×102～1.35×106), heart is1.24×105(1.90×102～1.29×106), swim bladder is4.51×104(3.30×102～6.16×105), gill is3.50×104(2.80×102～3.65×105), the bioaccumulation factors of MeHg in different tissues or organs is1-2order of magnitudes higher than the bioaccumulation factors of THg. The bioaccumulation factors of THg and MeHg of different trophic levels is:carnivorous> omnivorous> planktivorous> herbivorous, the bioaccumulation power of different tissues or organs is:muscle>heart>swim bladder>gill.(6) Comparing the survey results before impounding, the concentration of THg and organic mercury are lower than the pre-impounding and don’t have the obvious phenomenon of mercury reactivity of reservoir.(7) This study use PTWI as the measurable indicators of THg and MeHg, evaluating the risk of THg and MeHg to humans preliminarily and indicating that humans’intake of THg and MeHg of fihes is within the safety range...