Understanding Sources and Cycling of Mercury using Mercury Stable Isotopes.

Mercury Stable Isotopes;Geology and Earth Sciences;Science;Earth & Environmental Sciences

Sherman, Laura S.Lohmann, Kyger C. ;

University of Michigan

关键词: Mercury Stable Isotopes;    Geology and Earth Sciences;    Science;    Earth & Environmental Sciences;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/95961/lsaylors_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Mercury (Hg) is a neurotoxin that humans are exposed to primarily throughconsumption of fish. Significant gaps remain in our knowledge of Hg biogeochemistryand measurement of natural abundance Hg stable isotopes is beginning to answer some ofthe outstanding questions. Mass-dependent fractionation (MDF, reported as δ202Hg) andmass-independent fractionation (MIF, reported as Δ199Hg) of Hg isotopes occur duringmany biogeochemical processes. To better understand Hg cycling in volcanic systems we first investigated theisotopic composition of Hg emissions from Yellowstone volcanic field. We found thatthe light isotopes of Hg were preferentially emitted as Hg0(g) from hydrothermal waters,suggesting that natural Hg0(g) emissions may display negative δ202Hg values.Next, we used Hg isotopes to explore the role of photochemical reactions in Arctic atmospheric mercury depletion events. We found that a significant percentage of the Hg deposited during these events is subsequently photochemically reduced and lost,producing negative MIF of Hg remaining in the snow. We also found that a portion ofthe reemitted Hg accumulates on nearby ice crystals. These results suggest that althougha large percentage of the Hg deposited during these events is lost from the snow, aportion of the Hg is retained locally and may enter local aquatic ecosystems. Finally, weinvestigated whether Hg isotopes could be used to trace anthropogenic Hg emissions todeposition sites and ultimately into fish populations. We found that Hg in precipitationcollected downwind of a coal-fired power plant in Florida displayed anomalously negative δ202Hg values. We then explored whether this isotopic signature could be used to trace Hg emitted by the power plant into local sport fish. Instead, we found that Hg in largemouth bass was largely derived from accumulated Hg in lake sediments. This dissertation demonstrates that measurement of natural Hg isotopes in environmental samples is a powerful tool that can be used to gain greater understanding of complex Hg biogeochemistry. This relatively new technique may allow us to answer difficult questions about Hg atmospheric chemistry and biogeochemistry, to trace natural and anthropogenic Hg emissions, and to better understand pathways of human exposureto this hazardous trace metal.