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Abstract Title: Carbon and Mercury Stable Isotope Fractionation During Aqueous Monomethyl Mercury Photoreduction
Presenter Name: Luisa Malberti
Company/Institution: G‚osciences Environnement Toulouse, CNRS/IRD/Universit‚ Paul Sabatier Toulouse III
Session: Mercury in Marine Ecosystems
Co-Authors: Luisa Malberti,Christelle Lagane,JEROEN SONKE,David Point

Abstract Information :

The photo-demethylation of monomethyl mercury (MMHg) is one of the most important natural processes of MMHg decomposition and therefore is key in the understanding of its natural cycle. Different authors studied photo-demethylation to get insights into its kinetics and how it?s affected by salinity [1] or Dissolved Organic Matter (DOM) [2]. Others have examined Hg isotope fractionation during photo-demethylation. The isotopic composition of a compound carries information on the sources and transformation pathways of the said compound since the natural processes of breakdown and formation often leave specific and characteristic isotope fingerprints. In 2007 Bergquist and Blum [3] studied the photo-degradation of Hg2+ and MMHg in freshwater observing and characterizing Mass Independent Fractionation (MIF) for the odd isotopes of Hg. Later, in 2010, Zhang and Hsu-Kim[4] investigated more specifically the role of dissolved organic ligands on Hg stable isotopic fractionation during the photodegradation of MMHg. However, no studies from the perspective of carbon (C) isotopes of the methyl (-CH3) group of MMHg have been investigated so far. If we want to use the ë13C-MeHg to understand the origin of the C source in MMHg, then we need to account for C isotope fractionation during MMHg breakdown. In the present work we repeated the cited photodegradation studies to analyze and characterize C isotope fractionation of the methyl group of MMHg by using a new compound-specific isotope analysis technique (CSIA): purge and trap ? gas chromatography ? combustion ? isotope ratio mass spectrometry (PT-GC-C-IRMS) [5][6]. Our results show relatively minor enrichment of the heavy C isotopes in the residual MMHg during photo-demethylation. [1] Kim, et.al., 2016, DOI: 10.1080/19443994.2014.986829 [2] Qian, et.al., 2014, dx.doi.org/10.1021/ez500254z [3] Bergquist and J. D. Blum, 2007, Doi: [4] Zhang and H. Hsu-Kim, 2010, doi: doi:10.1038/ngeo892. [5] Masbou, et. al., 2015, doi: 10.1021/acs.analchem.5b02918. [6] Queipo-Abad, et.al., 2020, doi: 10.1016/j.chroma.2019.460821.

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