Brown trout (Salmo trutta) metallothioneins as biomarkers for metal exposure in two Norwegian rivers

The potential use of the metal binding protein metallothionein (MT) as a bi omarker for trace metal exposure has been evaluated in brown trout (Salmo t rutta) from the Cu-contaminated Rugla and the Cd/Zn-contaminated Naustebekk en Norwegian rivers, as well as in hatchery control trout. Metal concentrat ions were measured in gills, liver and kidney as well as in ambient water, and compared with Cd/Zn MT and Cu MT levels, measured by two Cd-saturation techniques. In addition haematocrit, plasma chloride and condition factors (weight x 100/length(3)) were measured, and genetic diversity determined. A negative correlation was found between the Cd/Zn MT content and the condit ion factor in the different trout populations, and Naustebekken trout, havi ng the lowest condition factor, were less heterozygous than Rugla trout, in dicating that Naustebekken trout have adapted to the metal in their environ ment. Significant positive correlations were found between accumulated leve ls of Cd and Cd/Zn MT in liver and kidney, suggesting that liver and kidney , but not gill, Cd/Zn MT can be used as a biomarker for chronic Cd exposure . Cu MT seems less suitable as a biomarker for Cu exposure. These data toge ther further emphasize that MTs must be applied with caution, when assessin g these proteins in biomonitoring of the natural environment.