title: Mercury tissue residue approach in Chironomus riparius: Involvement of toxicokinetics and comparison of subcellular fractionation methods.
abstract: Along with the growing body of evidence that total internal concentration is not a good indicator of toxicity, the Critical Body Residue (CBR) approach recently evolved into the Tissue Residue Approach (TRA) which considers the biologically active portion of metal that is available to contribute to the toxicity at sites of toxic action. For that purpose, we examined total mercury (Hg) bioaccumulation and subcellular fractionation kinetics in fourth stage larvae of the midge Chironomus riparius during a four-day laboratory exposure to Hg-spiked sediments and water. The debris (including exoskeleton, gut contents and cellular debris), granule and organelle fractions accounted only for about 10% of the Hg taken up, whereas Hg concentrations in the entire cytosolic fraction rapidly increased to approach steady-state. Within this fraction, Hg compartmentalization to metallothionein-like proteins (MTLP) and heat-sensitive proteins (HSP), consisting mostly of enzymes, was assessed in a comparative manner by two methodologies based on heat-treatment and centrifugation (HT&C method) or size exclusion chromatography separation (SECS method). The low Hg recoveries obtained with the HT&C method prevented accurate analysis of the cytosolic Hg fractionation by this approach. According to the SECS methodology, the Hg-bound MTLP fraction increased linearly over the exposure duration and sequestered a third of the Hg flux entering the cytosol. In contrast, the HSP fraction progressively saturated leading to Hg excretion and physiological impairments. This work highlights several methodological and biological aspects to improve our understanding of Hg toxicological bioavailability in aquatic invertebrates.
authors.affiliation: Department Chrono-Environment, UMR UFC/CNRS 6249 UsC INRA, University of Bourgogne Franche-Comté, 16 route de Gray, F-25030 Besançon Cedex, France. Electronic address: frederic.gimbert@univ-fcomte.fr.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gimbert
authors.affiliation: Université Reims Champagne Ardenne, Unité Mixte de Recherche-Ineris (UMR-I02) Stress Environnementaux et Biosurveillance des milieux aquatiques, Unité de Formation et de Recherche Sciences Exactes et Naturelles, Moulin de la Housse, BP 1039, F-51687 Reims Cedex 2, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Geffard
authors.affiliation: ISTerre, Université Grenoble-Alpes, IRD-UMR 5275 (IRD/UJF/CNRS)-BP 53, F-38041 Grenoble, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Guédron
authors.affiliation: Institute F.-A. Forel, University of Geneva, 10 route de Suisse, CP 416, CH-290 Versoix, Switzerland.
authors.forename: Janusz
authors.initials: J
authors.lastname: Dominik
authors.affiliation: Centre Ecotox, Eawag/EPFL, EPFL-ENAC-IIE-GE, Station 2, CH-1015 Lausanne, Switzerland.
authors.forename: Benoit J D
authors.initials: BJ
authors.lastname: Ferrari
mesh_terms: D000818:Animals; D005591:Chemical Fractionation; D002683:Chironomidae / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D054750:Ecotoxicology / Q000379:methods*; D007814:Larva / Q000737:chemistry / Q000187:drug effects; D008628:Mercury / Q000032:analysis* / Q000378:metabolism*; D008668:Metallothionein / Q000378:metabolism; D066007:Toxicokinetics; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism* / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical; D008668:Metallothionein; D008628:Mercury
keywords: Bioaccumulation; Excretion; Metal partitioning; Toxicity; Uptake