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Flounder (Platichthys flesus) and plaice (Pleuronectes platessa) were exposed to three different levels of pollution involving contaminants from harbour dredged spoil in a large-scale mesocosm study lasting 30 months. Exposure of fish to PCBs and PAHs was estimated from liver concentrations of CB-153 and biliary levels of 1-OH pyrens in flounder. Both marker compounds were significantly elevated in fish from the polluted mesocosms in comparison to the reference mesocosm. Of the three parameters used to characterise CYPIA induction in flounder, only CYPIA-mRNA in female fish was significantly induced by pollution. However, significant induction of EROD activity and immunochemically measured CYPlA protein content was observed in plaice. To investigate in more detail the apparent lack of CYP1A induction, a parallel experiment was run in which flounder were injected with a single i.p. injection of benzo[a]pyrene (BaP) and sacrificed after 48 hours. Since this approach did result in significant induction of all the parameters used to characterise CYP1A induction (EROD, CYPIA, CYPIA mRNA), it appears that external factors may have prevented induction in the mesocosm experiments. Down-regulating effects of the possible presence of a compound with oestrogenic activity, or altered membrane-CYPIA or membrane-receptor interaction, could have contributed to this apparent lack of response, despite the intrinsic ability of flounder to increase CYPIA levels after exposure to a model inducer (BaP). |
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