Biochemical and morphological changes in carp (Cyprinus carpio L.) liver following exposure to copper sulfate and tannic acid

As a consequence of human activity various toxicants reach the aquatic ecos ystems; humics may interact with them and may change their toxicity. Many f ish are exposed to a considerable concentration of humics and pollutants. B ecause of paucity of data on the biochemical action of tannins in the prese nce of the fungicide CuSO4 a comparative study was undertaken. The alterati ons of redox-parameters in carp liver were monitored and tissue necrosis wa s followed by measuring the plasma transaminase activities and by electron microscopy. Tannic acid, a representative phenolic/humic compound, exerted prooxidant effects in carp, which may be partially due to formation of proo xidant intermediates/end-products via its biotransformation. Alternatively, tannic acid may partially inhibit the antioxidant enzymes of fish. The res ponse to CuSO4 was more severe. Although tannic acid alone acted as a proox idant in fish, electron micrographs demonstrated that it reduced the necrot izing effect of copper, which may be due to the complexing activity of tann ic acid with the biomolecules of the hepatocytes and to the H2O2-degrading activity of tannin-CuSO4 combination. Our results indicate that the heavy m etal-detoxifying capacity of tannin may be significant; however, tannin-exp osure alone or combined with metals may be toxic for fish due to enzyme inh ibition and oxidative stress induction. (C) 2001 Elsevier Science Inc. All rights reserved.