Optimization And Application Of Stable Mercury Isotope Analysis Method

In this study,an analytical method for determination of stable mercury isotope with multi-collector inductively coupled plasma spectrometer(MC-ICP-MS)was optimized.By using the proposed method,the stable mercury isotope composition in fish samples collected from Tibet,Three Gorges Reservoir,Xiaolangdi Reservoir and Bohai Sea were studied.The fractionation characteristics of stable mercury isotope in fish from different aquatic ecosystem and possible factors affecting the mass dependent fractionation(MDF)and mass independent fractionation(MIF)of mercury were also discussed.(1)An analytical method for determination of stable mercury isotope with multi-collector inductively coupled plasma spectrometer(MC-ICP-MS)was optimized.Samples were introduced to MC-ICP-MS with a cold vapor generator(CVG).Mass bias correction was corrected by Tl internal standard correction and sample standard bracketing(SSB).The external accuracy of the method was ±0.06‰,which was obtained from determining a Hg standard solution(NIST SRM 3133)without pretreatment.The δ202H and Δ199Hg values in UM-Almadén was-0.56±0.07‰,0.00±0.03‰,respectively.Hg isotope compositions in standard reference materials(DORM-4,NIST SRM 1947)were in good agreement with literatures.(2)Negative δ202Hg(-0.26±0.30‰)and positive Δ199Hg(0.79±0.08‰)were observed in fish samples collected from Xiaolangdi reservoir,Henan province,which are similar to those in fish species from freshwater reservoirs reported in previous studies.The slope of Δ199Hg/Δ201Hg in fish was 1.22,indicating the MIF in fish from the Xiaolangdi reservoir might be induced by photodegradation of monomethylmercury.Positive δ202Hg(1.48±0.38‰)and near-zero Δ199Hg(0.01±0.02‰)in sediments indicated the influence of anthropogenic Hg emission.The relationships between mercury isotope compositions and δ15N in fish indicated that the MDF occurred during trophic transfer,while MIF was not observed.(3)The results showed that mercury fractionation characteristic was similar among Tibet,Three Gorges Reservoir and Bohai Sea.All samples displayed MDF,with δ202Hg values of-0.22±0.12‰,-0.54±0.19‰,-1.65±0.43‰ obtained for Tibet,Three Gorges Reservoir and Bohai Sea,respectively.Meanwhile,the samples displayed positive MIF,with the Δ199Hg values being 0.87±0.36‰,0.31±0.24‰,0.21±0.13,respectively.The Δ199Hg/Δ201Hg in fish samples of Tibet,Three Gorges Reservoir and Bohai Sea were 1.23,1.21 and 1.09,respectively,indicating that methylmercury in fish samples from the three regions underwent photodegradation of different degrees.