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Abstract Title: Methylmercury ë13C Compound Specific Stable Isotopic Analysis of Natural Biological Samples by PT-GC-C-IRMS
Presenter Name: David Point
Company/Institution: G‚osciences Environnement Toulouse, CNRS/IRD/Universit‚ Paul Sabatier Toulouse III
Session: Analytical methods for Hg speciation to assess impacts of Climate Change
Co-Authors: David Point,Christelle Lagane,Luisa Malberti,Annee Lorrain,Regine Maury-Brachet

Abstract Information :

Mercury (Hg) is a global pollutant that impacts human health and ecosystems. Mercury integrates into the natural carbon cycle, where it is transformed into methylmercury (MeHg, CH3Hg), an organometallic neurotoxin with biomagnification properties in food webs. Despite significant improvements in environmental Hg science, we still lack answers to some of the most fundamental questions about Hg cycling: where and how MeHg is produced in aquatic ecosystems. Current Hg analytical tools offer only limited resolution to characterize and quantify complex in situ biogeochemical processes operating at ultratrace levels. The purpose of the compound specific carbon stable isotopic analysis (ë13C-CSIA) of the methyl group of MeHg, is to explore the interaction mechanisms between the carbon cycle and Hg sources and its contribution to MeHg formation in the context of global changes. The stable isotopic composition (ë13C) of the carbon atom embedded in MeHg toxin may hold key information about its source origin and fate. In this study, we detail an advanced and original technique based on purge and trap system (PT) coupled to a gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) with the objective of analysing MeHg in a low nanogram scale. For this purpose, we developed and optimized a precise and robust methodology using hydride generation, with the formation and analysis of MeHgH compound from previously digested natural biological samples. Using this methodology, we obtained a MeHg ë13C value of -22.2?0.5 ? on ERM CE-464 Tuna reference material. This value is not different from what we obtained before (-22.1?1.5? ) by the halogenation of MeHg (MeHgI), liquid extraction and injection GC-C-IRMS (Masbou et al. 2015), which required higher MeHg amounts for analysis. Results on different marine and freshwater fish samples will be presented to highlight the opportunities and challenges behind this new methodology to explore the MeHg cycle.

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