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La métallothionéine (MT) est un ligand protéinique intracellulaire important à causede son implication dans les processus de régulation des métaux traces essentiels etnon-essentiels. Bon nombre de travaux ont été conduits en laboratoire pour bien comprendreles mécanismes de synthèse de cette protéine, mais les études réalisées en milieu aquatiquesont beaucoup plus rares, particulièrement dans les rivières (milieu lotique). Dans cecontexte, la présente étude avait deux objectifs principaux : (1) identifier en milieulotique les métaux traces (argent "Ag", cadmium "Cd", cuivre "Cu", nickel "Ni", plomb "Pb"et zinc "Zn") susceptibles d'induire la synthèse de la MT chez trois espèces sentinelles,soit le mollusque bivalve Pyganodon grandis, lalarve d'éphémère Hexagenia limbata et le grandbrochet du nord Esox lucius ; (2) définir lesvariables physico-chimiques ou toxicologiques pouvant influencer la prise en charge desmétaux traces et conséquemment les concentrations en MT chez le mollusque P. grandis etl'éphémère H. limbata. Deux rivières de la régionde l'Abitibi ont été échantillonnées à l'été 2001 afin de récolter les espèces sentinelles à21 stations. Les concentrations en métaux traces, ainsi qu'en métallothionéine, ont étémesurées dans les branchies des mollusques, dans le rein des brochets et dans le corpsentier des éphémères. La métallothionéine a été mesurée à l'aide d'une technique desaturation au mercure. D'après nos résultats, le cadmium tissulaire semble être le meilleurprédicteur de la concentration de MT chez les trois espèces sentinelles. Cependant,l'implication d'autres métaux est également possible. Dans le cas de P. grandis, la concentration de manganèse (Mn) dans lessédiments pourrait influencer la prise en charge du Cd et la synthèse de MT.Metallothionein (MT), an intracellular metal binding protein, is recognized for itsrole in the regulation of essential and non-essential trace metals. The mechanisms ofsynthesis of this protein have been studied in the laboratory but much less work has beencarried out in the field, particularly in lotic environments. According to the literature,metallothionein protects tissues from metal damage, and may be used as a direct measure ofthe biochemical state of the affected tissue. Metallothionein shows high affinity for groupIB and IIB metals ions (e.g. Cd, Cu, Zn), and consequently can sequester and detoxifymetals. The use of MT as a biomarker for elevated levels of trace metals in aquaticenvironments has therefore been proposed as a tool in ecotoxicological studies. Changes atthe biochemical level offer distinct advantages as biomarkers, since molecular alterationsare normally the first detectable responses to environmental changes.The present study focused on two objectives, the first of which was to identify whichtrace metals (silver "Ag", cadmium "Cd", copper "Cu", nickel "Ni", lead "Pb" and zinc "Zn")may induce MT synthesis in three sentinel species collected in two northern Quebec rivers(Colombière River, close to Val d'Or, and Matagami River close to the town of Matagami) in amining region (Abitibi, Québec). The three sentinel species were the adult bivalve Pyganodongrandis, the larval mayfly Hexagenia limbata, and the adult great northern pike Esox lucius.The second objective was to define variables that could influence the uptake of these tracemetals and consequently the concentrations of MT in the sentinel species. The selection ofthese sentinel species was based on the following criteria: their relative abundance in theaquatic systems studied; their relative immobility; the ease of sampling; metal tolerance;metal bioaccumulation capacity; dynamics of metal accumulation; capacity to synthesizemetallothionein; and availability of physiological and behavioural data.In 2001, physico-chemical conditions (e.g.: temperature, oxygen, transparency,phosphorus, chlorophyll a, etc.) were monitored during two sampling campaigns at 21stations. Trace metals were measured in water and sediment in all stations, and in tissuesof the sentinel species that were collected when present at the station (P. grandis - gills;H. limbata - whole body; E. lucius - kidney). Dialysis cells were used to collect watersamples for the determination of concentrations of total dissolved metals, major anions andcations, humic and fulvic acids, and dissolved organic carbon. At each sampling site, diverscollected three replicate sub-samples from two sediment cores for metal analyses. The coreswere extruded in the boat and samples taken from the uppermost 0.5 cm, i.e. from theoxidized layer.The two rivers differ in their morphometry, their physico-chemistry, and theirbiology. The Allard River is larger (200 m vs. 7 m) and deeper (30 m vs. 3 m) than the Colombière River. The Colombière River isslightly more acid (pH: 6.2 - 6.7) and less productive (14 - 32 µg total PL-1) than the Allard River (pH: 6.7 - 7.4; 24 - 45 µg total PL-1). However, the rivers present some similarities such as slowcurrent conditions and limited water transparencies. The range of Ag, Cu and Niconcentrations in water and sediment was greater in the Colombière River, whereas Pbconcentrations were higher in the Allard River and Cd concentrations were similar in the tworivers. Zinc was the dominant metal in both rivers, but variations were more significant inwater in the Colombière River. Although trace metal and MT concentrations were highlyvariable among species, stations and rivers, no consistent spatial gradients were detectedin animals collected downstream from mining activities.As was the case for the ambient environment, Zn was also the dominant metal inorganisms of both rivers. Zinc concentrations were similar in mayflies from the two rivers,but higher in molluscs and lower in pike collected from the Colombière River than incomparable animals from the Allard River. Following Zn, Cu was the second metal inimportance in species from the two rivers, whereas the concentrations of Ag were low in allorganisms and were undetectable in pike. Cadmium was more concentrated in mayflies andmolluscs from the Colombière River than in those from Allard River, and also higher in thepike collected in the contaminated zone of the Colombière River. The concentrations of Ni inall species were comparable between rivers, but were more elevated in mayflies than in theother sentinel species.The range of Pb concentrations was comparable between rivers for all species, butconcentrations were lower in the pike (kidney). The concentration of MT was higher in thepike than in the two other species. Mayflies had higher MT levels in the Allard River, whileMT concentrations were higher in molluscs of the Colombière River. The relationships betweenmetals and MT were very variable between rivers and species. Nevertheless, MT concentrationswere most strongly related to those of accumulated Cd in the three sentinel species. Therelationships between MT and Cd for all three species were stronger in the Allard River thanin the Colombière River. In the case of P. grandis,because the number of stations where the bivalves could be collected from the ColombièreRiver was low (n=4), no statistically significant relationship was observed between MT andCd in the tissues, in spite of the high correlation coefficient (r=0.98). For the bivalves,manganese (Mn) concentrations in the sediment were negatively correlated with accumulated Cdconcentrations and with MT levels. In H. limbata,in addition to Cd, other metals such as Cu (-) and Zn (+) also exhibited weak relationshipswith MT. Finally, in bivariate analyses, Pb concentrations in pike liver were significantlycorrelated with those of MT in this species, but based on multiple regression models, novariable other than Cd affected the level of MT in E. lucius

Réponses de trois espèces sentinelles aquatiques à la contamination en métaux traces dans deux rivières de l'Abitibi, Québec