Metal accumulation and metallothionein in two populations of brown trout, Salmo trutta, exposed to different natural water environments during a run-off episode

Cd, Cu and Zn concentrations were measured in ambient water as well as in g ills, liver and kidney tissues of two natural populations of brown trout (S almo trutta) during a run-off episode in two rivers with different metal co mpositions due to mining pollution. Metallothionein (MT) was also measured in these tissues. The two rivers, Rugla (Cu contaminated) and Naustebekken (Cd and Zn contaminated), are located in two neighboring drainage basins se parated by the topographic divide near the city of Roros in the County of S or-Trondelag, Norway. In Rugla, the Cu concentration increased from 15 mu g /l at the low water level to 41 mu g/l during the run-off episode. In Naust ebekken, corresponding values for Cd were 90-170 ng/l and those for Zn were 49-91 mu g/l. Gill concentrations of Cu and Cd/Zn MT in both populations o f native trout clearly reflect the presence of these metals in the rivers d uring the run-off, in accordance with the hypothesis of protection caused b y MT induction. When Rugla trout were transferred to Naustebekken and vice versa, both the amounts of MT itself and the Cu contents reflected the conc entration of this metal in the new environment, indicating that MT inductio n also protects against acutely increased metal levels. The measured levels of MT in both native and transferred trout can account for all the Cd pres ent in the tissues, but not for all of the Cu and Zn. The capacity of MT to regulate Cd and Cu in the trout populations in their natural habitat there fore seems clearly present. Our data also indicate that the MT I and II iso forms may bind metals selectively. (C) 2000 Elsevier Science B.V. All right s reserved.