The importance of contaminated food for the uptake of heavy metals by rainbow trout (Salmo gairdneri): a field study

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Abstract
The concentrations of Zn, Cu, Cd, Pb, Cr, Ni, and Mn have been measured in water, sediments, and organisms from two contaminated rivers situated in an industrial area and near a motorway on the southern city boundary of Bolzano, Italy. The low metal contents of water are in contrast to the elevated concentrations of sediments indicating a chronic rather than an acute contamination of the rivers. The metal concentrations of the dominant moss Fontinalis antipyretrica are higher than those of sediments, the lower branches of the plant being more concentrated than its upper parts. Among benthic invertebrates the dominant animals are the isopod Asellus aquaticus and the snail Lymnaea truncatula. Both species feed on contaminated moss or detritus and accumulate the heavy metals to an even greater extent than the water plants. The dominant predator is the rainbow trout (Salmo gairdneri) which feeds mainly on metal enriched isopods and snails. As a consequence, there is an absorption of heavy metals from lumen of fish into the gut tissue and a flux to other organs such as liver, kidney, and muscle. Since the metal concentrations of water are low it is suggested that the absorption through the gills of fish may be of secondary importance compared with the excessive supply through the food.