Abstract
To test the response of the freshwater bivalve Pyganodon grandis to increased metal exposure in the field, specimens were collected from 10 lakes located along a known metal gradient in a mining area in northwestern Québec. Total gill concentrations of metallothionein (MT) were determined by the 203Hg saturation method for molluscs from each lake, and the distribution of Cd among various cytosolic ligands, including MT, was determined by size-exclusion chromatography. Gill MT concentrations responded to environmental exposure to Cd but not to Cu or Zn exposure; these spatial variations along the Cd gradient were more important than the seasonal summer variations in gill MT concentrations. Bivalves exposed to concentrations of dissolved free Cd2+ higher than ~1 nM in the external medium exhibited a marked increase of Cd in the low relative molecular mass ligand pool. Symptoms of toxic effects at different levels of biological organization were associated with this biochemical anomaly.
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