Measurement of isotope fractionation of non-traditional elements has become a valuable tool to study the biogeochemical cycle of metals. Recent advances in multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS) now also allow the determination of mercury isotope fractionation in nature. Our recent work has shown significant deviations of mercury isotope ratios among a variety of natural samples.

Mercury is a unique isotope system having multiple even and uneven isotopes, and displays not only classical mass dependent, but also rare mass independent fractionation of isotopes. The latter is potentially caused by nuclear field shift and/or magnetic isotope effects. We now propose to systematically investigate these three modes of fractionation and link them to specific reaction pathways that mercury experiences in the environment. Specifically, we will be investigating the reduction of oxidized forms of mercury in aqueous ecosystems leading to volatilization of metallic mercury into the atmosphere, where it is distributed globally. As well, we propose to study the fractionation of mercury during bioaccumulation in food webs. This will be crucial to link local mercury sources to mercury found in fish. To improve the power of the relationship, we will develop methods for compound specific isotope ratio determinations. This will allow a direct determination of isotope ratios in methylmercury, which is the very toxic mercury compound that is bioaccumulated in biota.

All of the gathered information will be assembled to create a comprehensive theoretical framework describing fractionation of the mercury isotope system. Especially, the unusual and unique mass independent fractionation mechanisms hold great promise not only for tracing the biochemical cycling of the element, but also for following mercury from pollution sources to receptor sites such as the Great Lakes or the Canadian Arctic.