Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) as a tool to discriminate between differently contaminated small river systems.

Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) were exposed to native waters and acetone sediment extracts of Krähenbach and Körsch, two small rivers in south-west Germany with different levels of chemical contamination, and were investigated by means of electron microscopic and enzyme biochemical techniques to evaluate sublethal cytotoxic effects. Between both rivers as well as between free water phase and sediment, significant differences in the toxic burden could be detected. Results document that dilutions of Krähenbach and Körsch surface water and sediment extracts induce time- and dose-dependent morphological and biochemical changes. Especially in water and sediments of the river Körsch, strong contamination could be observed. After exposure to samples from the Körsch, both morphological and biochemical responses of isolated hepatocytes were more prominent than following exposure to samples of Krähenbach, thus reflecting the different chemical burden of the two river systems. Cytopathological effects also included deformation of nuclear envelopes and increase of heterochromatin, heterogeneity of mitochondria, vesiculation of cisternae of the rough endoplasmic reticulum, as well as proliferation of the smooth endoplasmic reticulum. Moreover, peroxisomal and lysosomal proliferation could be correlated to a stimulation of the corresponding marker enzymes, catalase and acid phosphatase. In both rivers, activities of lactate dehydrogenase and alanine aminotransferase as markers of cytosolic glycolysis and protein metabolism were increased indicating a general stimulation of cellular metabolism. Cytological changes in isolated hepatocytes thus not only serve to discriminate between different levels of contamination of water, but may also help to differentiate between pollution levels of sediments.