Unraveling the biogeochemical cycling of mercury using stable mercury isotopes as source tracers

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Mercury contamination poses a significant threat for human health and natural ecosystems at local, regional and global scales. Although man-made mercury emissions have increased dramatically since pre-industrial times, natural emissions represent a substantial contribution the overall global inventory and fluxes. This poses a considerable challenge for regulators tasked with managing mercury in the environment, as it is often impossible to distinguish natural from anthropogenic mercury sources. Thus, a detailed understanding of the biogeochemical cycle of mercury is crucial, but not always sufficient. The measurement of stable mercury isotope ratios and determination mercury isotope fractionation is a new promising tool to trace sources of mercury and to gain new insights into their relative importance to the total mercury transport.The proposed research will combine field studies, including collection and measurement of samples from natural environments, with dedicated controlled laboratory experiments to investigate specific processes. Special focus will be on the newly and still unexplained observation of anomalous fractionation of even mercury isotopes (i.e. 200-Hg), which so far has been predominantly detected in aqueous samples (precipitation, snow, surface water). Field studies will investigate fractionation of mercury isotopes during bioaccumulation in aqueous food webs and will be supported by controlled laboratory experiments using the newly installed atmospheric chamber in Trent University's Micro-Environmental Laboratory. We will specifically investigate the (photo)chemical oxidation of elemental mercury by atmospheric reactants such as bromine atoms and BrOx radicals and determine their potential to create mass dependent and mass independent fractionation.The fundamental research proposed here is critical to eventually be able to employ measured mercury isotope fingerprints as a tool to track mercury from its source to various receptor sites in the environment and to finally be able to distinguish natural from anthropogenic sources of mercury.