Influence of field and experimental exposure of mussels (Mytilus sp.) to nickel and vanadium on metallothionein concentration

In mussels impacted by the V- and Ni-rich oil dispersed in the environment after the « Erika » wreck, a significant and positive correlation was observed between metallothionein (MT) and V concentrations whereas no correlation was observed between MT and Ni concentrations. Mussels were exposed separately to V and Ni in the laboratory. The highest concentrations tested (≥ 2000 ng V per individual; ≥ 50 ng Ni per individual) were responsible for V and Ni bioaccumulation. In the case of V, the metal was preferentially stored in the insoluble fraction of the soft tissues but with increasing body burden, the part of soluble V increased from 19 to 41%. Metallothionein was induced in mussels exposed to V but not in those exposed to Ni. In addition, in mussels originating from a shellfish farming area which showed abnormally high levels of V, depuration showed concomitant decreases of V and MT. It is the first report in the literature of a functional link between MT and V. When interpreting surveys of metal pollution based upon the use of MT, one must be aware that V may be responsible for MT synthesis, explaining likely high levels of this biomarker in the absence of metals known as MT inducers.