The role of metallothionein in cadmium accumulation of Arctic char (Salvelinus alpinus) from high alpine lakes

Cadmium, copper and zinc concentrations were measured in water and organs (gill, liver and kidney) of Arctic char (Salvelinus alpinus) from four alpine lakes in Tyrol, Austria. In comparison with control fish, concentrations of metals, especially of cadmium, were elevated in tissues of fish from low-alkalinity lakes. In contrast, low metal levels were detected in water of the alpine lakes, suggesting that the high net accumulation of metals in fish tissues might have been caused by increased availability of these metals under conditions of low alkalinity. After chromatographic purification and Reversed-Phase HPLC of tissue supernatants from lake fish, several metallothionein (MT) peaks were identified in liver and kidney. In both organs MT accounted for the sequestration of virtually all the cadmium present in the tissues, and of considerable proportions of copper and zinc. However, there were conspicuous organ-specific differences in the metal patterns of the isolated MTs. Whereas liver MT of lake fish was dominated by copper and zinc despite high amounts of cadmium in the tissue, kidney MT showed a reversed pattern with cadmium predominating at the expense of copper and zinc. At slightly elevated cadmium concentrations in the liver, sequestration of this metal was achieved by displacement of zinc from MT binding sites, whereas at higher concentrations more MT was synthesized to bind excess amounts of the metal. The concentration of (Cd,Zn)-MT in the liver was inversely correlated with lake alkalinity. Finally, significant positive correlations were observed between the age of Arctic char and hepatic concentrations of cadmium and (Cd,Zn)-MT.