Abstract:

River plays a critical role in biogeochemical cycling of toxic heavy metal, mercury (Hg), across Earth’s surface spheres, thus it is important to identify the sources, transformations and fates of Hg in river system. Over the past fifteen years, the unique “three-dimensional” Hg isotopes system has been widely used as a powerful tool for tracing the biogeochemical cycling of Hg, which has largely improved the understanding of Hg systematics in rivers. In this study, the recent development of pretreatment and analysis methods essential for Hg isotopes study is first summarized, including the anion-exchange resin and purge and trap for dissolved Hg, the pyrolysis and digestion for particulate Hg, and the distillation-gas chromatography and distillation-ion exchange resin for methylmercury (MeHg). Then we introduce systematically three application aspects of Hg isotopes in rivers, with the first to quantitatively determine the sources of different Hg species and their contributions, the second to reveal the geochemical behavior of Hg and its migration into the ocean, and the third to clarify the environmental and ecological effects of riverine Hg. Finally, Hg isotopes are integrated into the river-coastal Hg flux model, and the source-sink balance is examined. As the study on Hg isotopes in rivers is still at the beginning, future research should be systematically performed not only to develop the analysis method, but also to advance our knowledge of Hg isotope fractionation mechanisms during the interaction between riverine Hg with other ecosystems such as soil, atmosphere, and ocean, with a goal to better constrain the fate of riverine Hg and its environmental and ecological effect.

Key words: mercury isotopes, mass-dependent fractionation, mass-independent fractionation, river