title: Higher mass-independent isotope fractionation of methylmercury in the pelagic food web of Lake Baikal (Russia).
abstract: Mercury undergoes several transformations that influence its stable isotope composition during a number of environmental and biological processes. Measurements of Hg isotopic mass-dependent (MDF) and mass-independent fractionation (MIF) in food webs may therefore help to identify major sources and processes leading to significant bioaccumulation of methylmercury (MeHg). In this work, δ(13)C, δ(15)N, concentration of Hg species (MeHg, inorganic Hg), and stable isotopic composition of Hg were determined at different trophic levels of the remote and pristine Lake Baikal ecosystem. Muscle of seals and different fish as well as amphipods, zooplankton, and phytoplankton were specifically investigated. MDF during trophic transfer of MeHg leading to enrichment of heavier isotopes in the predators was clearly established by δ(202)Hg measurements in the pelagic prey-predator system (carnivorous sculpins and top-predator seals). Despite the low concentrations of Hg in the ecosystem, the pelagic food web reveals very high MIF Δ(199)Hg (3.15-6.65‰) in comparison to coastal fish (0.26-1.65‰) and most previous studies in aquatic organisms. Trophic transfer does not influence MIF signature since similar Δ(199)Hg was observed in sculpins (4.59 ± 0.55‰) and seal muscles (4.62 ± 0.60‰). The MIF is suggested to be mainly controlled by specific physical and biogeochemical characteristics of the water column. The higher level of MIF in pelagic fish of Lake Baikal is mainly due to the bioaccumulation of residual MeHg that is efficiently turned over and photodemethylated in deep oligotrophic and stationary (i.e., long residence time) freshwater columns.
authors.affiliation: Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut Pluridisciplinaire de Recherche sur l'Environnement et les Matériaux, CNRS-UPPA-UMR-5254, Hélioparc, 2 Avenue du Président Pierre Angot, Pau, 64053, France. v.perrot@etud.univ-pau.fr
authors.forename: Vincent
authors.initials: V
authors.lastname: Perrot
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Pastukhov
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Epov
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
authors.forename: Olivier F X
authors.initials: OF
authors.lastname: Donard
authors.forename: David
authors.initials: D
authors.lastname: Amouroux
mesh_terms: D000818:Animals; D010872:Caniformia / Q000378:metabolism; D002247:Carbon Isotopes; D005591:Chemical Fractionation / Q000379:methods*; D004784:Environmental Monitoring; D005399:Fishes / Q000378:metabolism; D020387:Food Chain; D005843:Geography; D060106:Lakes / Q000737:chemistry*; D008027:Light; D008628:Mercury / Q000378:metabolism; D008629:Mercury Isotopes; D008745:Methylation / Q000528:radiation effects; D008767:Methylmercury Compounds / Q000378:metabolism*; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism; D009587:Nitrogen Isotopes; D012426:Russia; D012623:Seawater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical; D008628:Mercury