Mercury Isotope Fractionation by Internal Demethylation and Biomineralization Reactions in Seabirds: Implications for Environmental Mercury Science

• Published in: Environmental Science & Technology
• Main Authors: Manceau, Alain, Brossier, Romain, Janssen, Sarah, Rosera, Tylor, Krabbenhoft, David, Cherel, Yves, Bustamante, Paco, Poulin, Brett
• Other Authors: Université Grenoble Alpes (UGA), Upper Midwest Water Science Center, U.S Geological Survey, Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), LIttoral ENvironnement et Sociétés - UMRi 7266 (LIENSs), Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS), Department of Environmental Toxicology, University of California
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Mercury; Isotope fractionation; Toxicology; Bird; [SDE]Environmental Sciences; Kerguelen; Kerguelen Islands; Antarc*; Antarctica; Giant Petrels
• Online Access: https://hal.archives-ouvertes.fr/hal-03401749; https://doi.org/10.1021/acs.est.1c04388

International audience A prerequisite for environmental and toxicological applicationsof mercury (Hg) stable isotopes in wildlife and humans is quantifyingthe isotopic fractionation of biological reactions. Here, we measured stableHg isotope values of relevant tissues of giant petrels (Macronectes spp.).Isotopic data were interpreted with published HR-XANES spectroscopic datathat document a stepwise transformation of methylmercury (MeHg) to Hgtetraselenolate(Hg(Sec)4) and mercury selenide (HgSe) (Sec =selenocysteine). By mathematical inversion of isotopic and spectroscopicdata, identical δ202Hg values for MeHg (2.69 ± 0.04‰), Hg(Sec)4 (−1.37 ±0.06‰), and HgSe (0.18 ± 0.02‰) were determined in 23 tissues of eightbirds from the Kerguelen Islands and Adélie Land (Antarctica). Isotopicdifferences in δ202Hg between MeHg and Hg(Sec)4 (−4.1 ± 0.1‰) reflectmass-dependent fractionation from a kinetic isotope effect due to the MeHg→ Hg(Sec)4 demethylation reaction. Surprisingly, Hg(Sec)4 and HgSe differed isotopically in δ202Hg (+1.6 ± 0.1‰) and massindependentanomalies (i.e., changes in Δ199Hg of ≤0.3‰), consistent with equilibrium isotope effects of mass-dependent andnuclear volume fractionation from Hg(Sec)4 → HgSe biomineralization. The invariance of species-specific δ202Hg values acrosstissues and individual birds reflects the kinetic lability of Hg-ligand bonds and tissue-specific redistribution of MeHg and inorganicHg, likely as Hg(Sec)4. These observations provide fundamental information necessary to improve the interpretation of stable Hgisotope data and provoke a revisitation of processes governing isotopic fractionation in biota and toxicological risk assessment inwildlife.