Mercury Hg) is widespread in the world. Due to the long residence time of gaseous elemental Hg (Hg 0 ), it can transport in a long rang and deposit in remote regions, like polar regions and alpine regions. Once deposited, Hg can undergo various reactions to particip ate into the local Hg circulation. During circulation, Hg can be transformed into various compound s , among which methylmercury (MeHg) is highly n eurotoxic and easily accumulated through the food chain. Consequently, it can cause severe health damage to ind igenous creatures.
Together with the Arctic, the Tibetan Plateau and the Antarctic are called polar regions. These regions are vulnerable due to harsh climatic conditions, low species diversity . More and more studies have found that these regions were "sin ks" of Hg and play important role in the global Hg cycling, so it is critical to study the Hg circulations in these regions. This study analyzed the sources, transf er , and transform of Hg through the Hg isotope compositions of natural media from the Tibeta n Plateau and Antarctic .
First, we studied the reliability of two different pretreatment methods (acid digestion and combustion trapping treatment for measuring Hg isotop e compositions.The results indicated that the recoveries of total Hg (THg) in certi fied reference materials (CRMs) were ranged from 98 to 106%, and their Hg isotopic compositions were agree with the published values. Therefore, both these two pretreatment methods were accurate and reliable for isotopic analysis. The acid digestion method had high efficiency, while the combusiton trapping method can be used to pretreat samples with relatively low contents of Hg This work provided reliable pretreatment methods for future Hg isotope analyses.
We analyzed the concentrations and isotopes of H g in feathers and muscles of eagles from the Tibetan Plateau to trace the biogeochemical circulation of Hg in the terrestrial ecosystem. Our results found the low concentrations of Hg, which may be caused by the short food chain. T he Δ 199 Hg value could up to 2.89 ± 0.06‰ (2SD),which can be explained by t he strong ultraviolet radiation induced the high photochemical reactions degree in the Tibetan Plateau. I n addition, the Δ 199 Hg values of eagles and fish from the same region were sign ificantly different although their MeHg% were > 95% 95%, indicating the different generation and transformation processes of MeHg between terrestrial and aquatic ecosystems. This study provided clues that the contribution of photochemical reactions of MeHg in terrestrial ecosystems was larger than those in aquatic ecosystem s In addition, w e measured the concentrations and isotope compositions of Hg in mosses, conifer needles, and surface soils from the Shergyla Mountain to understand the source and distributio n of Hg in the Tibetan Plateau . The ir concentration s and isotope compositions of Hg had clear correlations with altitude , indicating altitude is an important factor that can effect the distribution of Hg B ased on the isotopic analyses, atmospheric Hg 0 was the primary Hg source of mosses and conifer needles. The contribution of atmospheric Hg 0 accounted for approximately 87 % of atmospheric Hg in soils.
We analyzed the Hg isotope compositions of natural media around the Chinese Great Wall Station on the Kin g George Island . First, we analyzed the concentrations and isotopes of Hg in sediment A gas Arch a eogastropoda )), Ngas Neogastropoda )),and fish from the Antarctic. The different Δ 199 Hg/δ 202 Hg a nd Δ 199 Hg/Δ 201 Hg ratios in
Agas, Ngas, and fish indicated the d ifferent circula t i on history of Me Hg in them. Me Hg accumulated by Agas and Ngas was produced in the sediment and lacked of photochemical reactions. MeHg in fish was a mixture of MeHg produced in the sediment and the water. Subsequently, the Δ 199 Hg values o f bioavailable MeHg and inorganic Hg ( IHg in sediments were quantitatively calculated Δ 199 Hg MeHg : 1.56 ±0.05‰0.05‰; Δ 199 Hg I Hg : 0.39 ± 0.02‰ According to the different Δ 199 Hg/Δ 201 Hg ratios of various reactions, t he bioavailable Hg in the sediments contribut ed to approximately 44% of the total Hg in fish. Then, we analyzed the normal biomonitor moss and lichen to find the alternative passive sampling method. We found the distinct Δ 199 Hg values between Antarctic lichen and moss, indicating the different bioac cumulation of Hg in them. The similarity of Δ 199 Hg values between mosses and atmospheric Hg 0 indicated atmospheric Hg 0 was the dominate Hg source of moss. The relatively high MeHg/Hg (~ 40%) and Δ 199 Hg/Δ 201 Hg ratios ( 1.23 ) indicated lichen in Antarctic can accumulated MeHg from surrounding environment. Because the high bioaccumulaiton and neurotoxicity of MeHg, it was meaningful to further study the sources and biogeochemical of Hg in lichen.
In summary, this study studied two reliable pretreatment method for Hg isotope analyses, then chose the Tibetan Plateau and the King George Island of the Antarctic as study areas to analyze the concentrations, species and isot o pe compositions of Hg in natural media The distribution, sources, transfer, and transform of Hg were analyzed
in detailed. Becase the special geographic positions and environmental conditions of study area, our study is critical for understanding long range transport, tracing the global geochemical circulation history and estimating the ecologica l risk of Hg.