Elevation of hepatic monooxygenase activity in the dab (<i>Limanda limanda</i> L.) in relation to environmental contamination with petroleum hydrocarbons in the northern North Sea

Dab (Limanda limanda L.) were caught at various distances from a group of oil platforms in the northern North Sea. Hepatic ethoxyresorufin-O-deethylase (EROD) and cyanoethoxycoumarin-O-deethylase (cECOD) activity were elevated in both male and female fish caught close to the platforms. This effect was more marked in females which showed a 10–20-fold increase in activity compared to a 4-fold increase in males for both EROD and cECOD. Both aliphatic and aromatic hydrocarbon analyses were carried out to determine the extent of sediment contamination at each trawling site and to measure the contamination of the livers of fish caught at each site. The results show significant contamination of sediments with base oil, unresolved mixtures of aliphatics and n-alkanes close to the platform. However, there was not a significant relationship between sediment contamination and levels of the monooxygenase enzymes measured in the livers of dab. In contrast, the concentrations of both aliphatic and aromatic hydrocarbons in the liver showed a significant negative regression to distance from the platform. Examination of the relationship between liver contamination and the levels of both EROD and cECOD showed a significant positive correlation for all groups of hydrocarbons measured and that this was most significant for the 5–6-ring aromatics.