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Ryan F Lepak

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This dataset describes mercury (Hg) stable isotope values in fish dorsal muscle from different freshwater environments across the globe. Fish were collected at numerous field sites in North America, South and Central America, Africa, and Asia from 2006-2020. Sub-samples were provided by cooperators to the U.S. Geological Survey Mercury Research Laboratory and the University of Wisconsin for mercury stable isotope analysis. Samples were analyzed for mercury stable isotopes from 2017-2021. These specimens represent multiple trophic levels and body sizes from different food webs and when adequate mass was available, multiple species from the same food web were examined. Cooperators include, but are not limited to:...
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This dataset consists of concentration and isotopic data for a method designed to isolate and analyze methylmercury. Several matrices (lab-based, and natural) were tested to ensure that the method was capable of recovering methylmercury amendments. Additionally, natural matrices (plankton and sediment) with ambient methylmercury were also analyzed to ensure that the method could be successfully applied to natural matrices. Separation tests for sediment, water, and biotic matrices showed acceptable recoveries (98 ± 5%, n = 54) and reproducible δ202Hg isotope results (2SD < 0.15 ‰) down to 5 ng of MeHg. This dataset is part of a complimentary paper published in Analytical and Bioanalytical Chemistry (https://doi.org/10.1007/s00216-019-02277-0)...
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Under the Great Lakes Restoration Initiative, the U.S. Geological Survey Mercury Research Lab (USGS MRL) conducted a multiyear assessment of mercury across the Laurentian Great Lakes. Biannual sampling was conducted across all five lakes onboard the U.S. Environmental Protection Agency (US EPA) research vessel Lake Guardian (in years 2010–2014, 2018) at pelagic sampling locations established by the long-term US EPA Great Lakes monitoring program. In addition to the regularly scheduled biannual sampling, in September 2013 and 2014 Lake Michigan and Lake Erie (respectively) were sampled with increased focus on shallow nearshore locations. Throughout these sampling efforts, sediments, mussels, surface water, and plankton...
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Fish collected for taxonomic and systematic purposes are often preserved and then archived in museum collections. Preserved fish are commonly first fixed in a formalin solution and then transferred to ethanol for long-term storage. The wet preservation method can potentially introduce mercury (Hg) contamination or unintentionally extract Hg from tissue. An experiment was designed to test the utility of museum preserved fishes in reconstructing spatiotemporal trends in methylmercury (MeHg) concentration and Hg stable isotope ratios, which is used to trace Hg sources to fishes. Wet preserved fish specimens from the Congo River and river basins within Gabon were subsampled from archives at the the Royal Museum of Africa...
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Adult walleye were caught in Fox River (Wisconsin) during April 2014. Age-0 walleye were caught in Fox River during October 2014. Total length, weight, age, and proportion of weight represented by water were determined for each of the walleye. Whole-fish homogenates were prepared during 2014-2015 and during 2017. Total mercury (HgT) concentration, methylmercury (MeHg) concentration, and mercury (Hg) isotope ratios were determined in the homogenates during 2014-2015 and during 2017-2018. All mercury determinations were made at the USGS Mercury Research Laboratory in Middleton, Wisconsin.
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