Nickel, cobalt, zinc and copper levels in brown trout (Salmo trutta) from the river Otra, southern Norway

The Flåt Nickel mine at Evje in southern Norway was mined extensively from 1914 to 1945 with little regard for any potential environmental effect. Much of the ore extracted was smelted at a site adjacent to the river Otra south of Evje. Recent studies have revealed heavy metal pollution in the land surrounding the smelter and in water draining from the mine leading to concern for the aquatic ecosystem in the river Otra. Brown trout were sampled from an uncontaminated lake 9 km upstream from the smelter, from the base of the Oddebekken (a tributary draining the mine water into the Otra), from sites immediately upstream and down stream of the smelter and from a site 4 km down stream from the smelter. Fish from sites adjacent to the smelter and the base of the Oddebekken were smaller than those from the lake and down stream site. Concentrations of the metals were highest in fish sampled where the mine water entered the Otra and gradually decreased in fish further down the river. Fish from the uncontaminated lake had the lowest level of metals.