HR: 0800h
AN: V51E-0827    [Abstracts]
TI: Mass Independent Fractionation of Mercury Isotopes in the Environment
AU: * Ghosh, S
EM: ghosh@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Dept. of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Xu, Y
EM: yingfeng@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Dept. of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Humayun, M
EM: humayun@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Dept. of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Odom, A L
EM: odom@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Dept. of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AB: The toxicity of mercury's methylated species, biomagnification in aquatic food chains and global dispersion by the atmosphere makes it a worldwide health problem. Recent reports have observed natural mass dependent fractionation in mercury isotopes, and recent theoretical work has emphasized that isotopic separation in mercury is due primarily to nuclear field shifts (nuclear volume effect) or a magnetic isotope effect. Both effects produce mass-independent fractionation (MIF). Separation factors are closely proportional to mass number for even neutron number isotopes. Odd mass number mercury isotopes depart from this relationship, giving rise to a component of mass-independent fractionation. During equilibrium exchange reactions, the nuclear volume effect is a function of the oxidation state of the Hg chemical species: Hg⁰, and methylmercury, exhibit positive deviations, and oxidized species (e.g., Hg⁺²) exhibit negative deviations. We present analytical evidence of mass independent isotopic variations in mercury produced by both nuclear volume and magnetic isotope effects in a wide variety of natural environmental samples – peat, sediment, soil and moss. Even mass number isotopes exhibit a pattern indistinguishable from that produced by mass-dependent fractionation, with both positive and negative ¹⁹⁹Hg and ²⁰¹Hg anomalies. For majority of the samples analyzed, magnetic isotope effect seems to be more significant than nuclear volume effect. MIF is more accurately determined in Hg isotopes than mass dependent fractionation alone, and thus it provides a potentially important key in constraining models of mercury sources and pathways in the environment.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0461 Metals
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting