Mercury is a naturally occurring, pervasive element in the environment, with many chemical forms. Toxicology, environmental cycling and retention, and production of mercury by industrial processes and natural and manufactured emissions of mercury chemical species are the foremost concerns pertaining to this element and its congeners. Organomercury forms, particularly methylmercury, are some the most potent neurotoxins to animals, including humans. Therefore, the understanding of cycling, biochemistry and biogeochemistry of mercury compounds is important. Mercury isotopes are a useful tool for understanding the reactions, movements and transformations of mercury chemical species throughout the mercury biogeochemical cycle. Mercury isotopic composition is useful because it has two dimensions of the isotopic fingerprint: variations of mass dependent fractionation and mass independent fractionation. The objectives of our studies were several, with emphasis on constraining mercury concentration and isotopic compositions of invertebrates and fish in the northern Gulf of Mexico (NGOM) and interpreting possible mechanisms for these constraints. In Chapter 2, work was performed on four restricted areas in the NGOM and included organisms which were related by food web and habitats, with particular interest in the economically and recreationally important species gag grouper (Mycteroperca microlepis). The goal of this study was to better understand the interactions of mercury and mercury isotopes with regard to trophic level, age, size and bioaccumulation of methylmercury in the biological species. In Chapter 3, muscle and liver tissues from individual adult gag grouper were analyzed. The aim of this work was to investigate findings in the previous study of a large, consistent mass dependent fractionation variation in gag grouper muscle tissue and propose possible causes and mechanisms responsible for the variation. Chapter 4 studied specimens surrounding the 2010 BP Deepwater Horizon oil spill in the northern Gulf of Mexico. We analyzed a time series of pre-spill specimens and impacted post-spill specimens from the same area north-northeast of the blowout site for differences in mercury concentration and isotopic composition. Studies from Chapter 2 concluded that mercury isotopic composition is dependent on the two-dimensional constraints of geographic and spatial variability. Geographic variability in mass dependent fractionation is related to the percentage of dominant mercury input, especially terrestrially-derived dissolved organic and particulate matter. Two recent models of mercury sources and receptors in the Gulf of Mexico foster this finding. Spatial variability in mass independent fractionation is directly related to habitat, specifically the depth of an organism's habitat in the photic zone. This effect is prominent in the open ocean. Findings from the coastal seagrass area were somewhat anomalous to the oceanic trend, but explained by the correlation of dissolved organic matter to MIF variations in experiments by other groups. Of all four constrained study areas from Chapter 2, the coastal area has the most fluvial and estuarine dissolved organic matter content. In Chapter 3, we investigated causes of the large 2.0 / δ202Hg mass dependent fractionation in muscle tissues of 43 gag grouper from the Chapter 2 study. Muscle and liver tissues were analyzed from individual, adult gag grouper specimens from one of the same restricted offshore study areas as in Chapter 2. There were significant, systematic mass dependent fractionation variations between individual muscle and liver tissue pairs, but no significant variations in mass independent fractionation. However, both MDF and MIF variations were correlated with total length of specimens. δ202Hg is related to bioaccumulation of methylmercury and it was shown that specimens bioaccumulated mercury with age. As mass independent fractionation is related to source of mercury, the lack of MIF variation in individual tissue pairs demonstrates that mercury source in muscle and liver is the same. The proposed cause of mass dependent fraction between the two tissues is enzymatic demethylation in the liver, and therefore detoxification of methylmercury, which explains the large δ202Hg variation in gag muscle in the previous study. Another possible mechanism of fractionation is demethylation by oxidative protein metabolism in fish muscle, where remaining inorganic mercury is transported to and stored in the liver. Work in Chapter 4 demonstrated slight but not statistically significant metabolic effects of the BP oil spill reflected in mercury isotopic composition of red snapper (Lutjanus campechanus). However, comparison of red snapper from two other studies, as well as atmospheric and sediment isotope data, allowed for a synthesis of mercury isotope biogeochemical cycling in the northern Gulf of Mexico. This isotopic composition picture reinforced geographical and spatial constraints from Chapter 2, especially in red snapper, where terrestrial input increased from westernmost to easternmost study sites. Additionally, a relationship was proposed between dominant methylation in sediments and MDF signatures in fish. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2015. / April 13, 2015. / Gag Grouper, Gulf of Mexico, Mercury, Mercury Isotopes, Red Snapper / Includes bibliographical references. / Vincent J. M. Salters, Professor Directing Dissertation; Albert E. Stiegman, University Representative; Munir Humayun, Committee Member; William M. Landing, Committee Member; A. Leroy Odom, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_273637 |
| Contributors | Eller, Virginia Alice (authoraut), Salters, Vincent J. M. (professor directing dissertation), Stiegman, Albert E. (university representative), Humayun, Munir (committee member), Landing, William M. (committee member), Odom, A. L. (A. Leroy) (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (140 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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