Skin and liver diseases induced in flounder (Platichthys flesus) after long-term exposure to contaminated sediments in large-scale mesocosms.

Disease development in flounder (Platichthys flesus) was studied over a period of 3 years in three large mesocosms (40 m x 40 m x 3 m). Two of the mesocosms contained clean sand and the third, sharing a common water circulation with one of the clean-sand mesocosms, was stocked with contaminated dredged spoil. In this way, one of the clean-sand mesocosms was indirectly polluted via the water phase, and analysis of contaminant concentrations in sediments and flounder tissues showed that it had a status intermediate between the other two. Random samples of the flounder populations from the indirectly polluted and reference mesocosms were examined every 2 months for epidermal diseases (lymphocystis, skin ulcers, fin rot) and then released. In addition, every 6 months, random samples of fish from all three mesocosms were sacrificed for histological and chemical investigation. With regard to the development of epidermal disease, the results showed little difference between the reference mesocosm and the indirectly polluted mesocosm, with the exception that lymphocystis was significantly elevated in the indirectly polluted mesocosm. Although pollution may be a risk factor in the etiology of this disease, such a relationship would probably be obscured under field conditions due to variation arising from other factors. Histopathological analysis of the livers revealed in total four cases of hepatocellular adenoma (1.5% of sampled population) in fish from the polluted mesocosms, the first occurring after 2.5 years of exposure in fish from the indirectly polluted mesocosm. Furthermore, several other liver lesions, including foci of cellular alteration and hydropic vacuolated lesions, developed during the course of the experiment before tumor formation was apparent. Prevalences of these conditions were very much lower in the reference mesocosm than in the two polluted mesocosms. Densities of melanomacrophage centers in the liver showed a similar trend. The findings clearly indicate that long-term exposure to chemically contaminated dredged spoil can induce liver neoplasia and other liver lesions in flounder at contaminant levels comparable to those found in the natural environment.

Influence of diet on the bioaccumulation of PCBs.

The levels of several chlorinated biphenyls (PCBs) congeners were analysed in muscle of flounder (Platichthys flesus), which were kept in semi-field condition for 1 month. The influence of resuspended sediments and two diets (worms and shrimps) on PCB accumulation in these fish was tested. Highest concentrations were among PCB 138 and 153 in both abiotic (sediment and suspended particulate matter (SPM)) and biotic compartments (shrimps, worms and flounder). Whereas all PCB congeners vary in concentration between polluted and non-polluted sediment, SPM and mussels, only high chlorinated congeners (101, 105, 153, 180 and 187) are significantly different between the worms and shrimps. Differences in bioaccumulation of PCBs by fish induced by differences in food composition were not found. For the low chlorinated compounds, however, pollution exposure might account for the higher concentration found in exposed fish.

Changes in levels of hepatic biotransformation enzymes and haemoglobin levels in female plaice (Pleuronectes platessa) after oral administration of a technical polychlorinated biphenyl mixture (Clophen A40).

Female plaice (Pleuronectes platessa) were orally dosed with a gelatin capsule containing a solution of the technical PCB mixture Clophen A40 in sunflower oil. They were compared to plaice injected with a gelatin capsule containing only the sunflower oil at 10 and 16 days after injection. Even at 16 days after injection, the increase in concentrations of individual CB congeners in muscle was proportional to their contribution in Clophen A40. Biochemical effects are related to increases in concentrations of well-separable CB congeners in muscle, which increased by factors between 1.6 and 64 compared to the reference group of fish. Of both sampling points, total cytochrome P-450 levels were higher than the control groups, but surprisingly ethoxyresorufin-O-deethylase (EROD) activities did not differ between the groups. Enzyme-linked immunosorbent assay (ELISA) showed increased concentrations of the inducible cytochrome P-450IA1 in PCB-treated fish. The apparent lack of EROD induction may be due to competitive substrate inhibition by certain CB congeners present in the sample. The activity of glutathione-S-transferase (GST) (with CDNB as model substrate) was significantly elevated by PCB-treatment at day 16, but not at day 10. A longer time interval between injection with PCBs and induction of GST compared to P-450 monooxygenase activities has been reported earlier and may indicate that in fish both groups of enzymes are regulated individually and not as an [Arylhydrocarbon] gene battery as appears to be the case in mammals. Haemoglobin concentrations and MCHC were decreased in fish treated with Clophen A40. Haematocrit values did not differ between groups of fish.