Mercury species in dab (Limanda limanda) from the North Sea, Baltic Sea and Icelandic waters in relation to host-specific variables

- Hg concentrations in common dab from the North Sea, Icelandic waters and the western Baltic Sea differed significantly.
- Highest Hg concentrations occurred in dab from the central North Sea close to oil and gas offshore industry.
- A significant relationship between Hg concentrations and the health status of dab was shown.

In the framework of the ICON project (Integrated Assessment of Contaminant Impacts on the North Sea), muscle tissue from a total of 135 common dab (Limanda limanda) (20-28 cm total length) was collected in seven offshore sampling areas in the North Sea, at Iceland and in the Baltic Sea during Aug/Sept and December 2008 for a chemical mercury speciation analysis by means of gas chromatography and detection by cold vapour atomic fluorescence spectroscopy (GC-CVAFS). There was a highly significant correlation between concentrations of methylmercury (MeHg+) and inorganic mercury (Hg2+) in individual fish, and the mean ratio of MeHg+ compared to Σ Hg (MeHg+ + Hg2+) was 94.0%. The results revealed statistically significant differences in concentrations of MeHg+ and Hg2+, respectively, between sampling areas. Mean concentrations in the German Bight (North Sea), in Icelandic waters and in Mecklenburg Bight (Baltic Sea) were low (MeHg+: 0.023-0.036; Hg2+: 0.001-0.002 mg/kg wet weight), while concentrations in dab from the Dogger Bank, Firth of Forth and the vicinity of the Ekofisk oil field (all North Sea) were significantly higher (MeHg+: 0.059-0.101; Hg2+: 0.003-0.004 mg/kg wet weight). Statistical correlation analysis on effects of host-specific factors revealed that neither length, weight, age, sex nor condition factor showed a significant relationship with Hg concentrations. However, Hg concentrations were significantly correlated with the Fish Disease Index (FDI), indicating a relationship between Hg concentrations and the health status of dab. Multiple linear regression analysis aiming to find factors affecting Hg concentrations revealed that only the sampling area had a highly significant main effect on Hg concentrations, and in some cases, additionally the condition factor contributed significantly to the final model. From the results, it cannot be excluded that elevated Hg concentration recorded in dab were linked to discharges from offshore oil and gas installations and that Hg affected the health status of dab.