HEPATIC METALLOTHIONEIN AND HEAVY-METALS IN DAB LIMANDA-LIMANDA FROM THE GERMAN BIGHT

During the Bremerhaven Workshop, the effect of heavy metals on dab Limanda limanda L. in the German Bight was assessed using the hepatic level of metallothionein (MT) and selected metals. Male and female adult dab were collected at 7 stations on a transect from the Elbe and Weser estuaries towards the Dogger Bank. Metallothionein, Cu, Zn and Cd concentrations in dab livers were determined using radioimmunoassay (RIA) and atomic absorption spectrophotometry (AAS). Hepatic MT levels were highest in both male and female dab at some of the offshore stations, decreasing towards the coast and towards the Dogger Bank. The levels of MT in dab livers reflected the hepatic concentration of metal in all dab, but the relative importance of specific metals differed between the sexes. In female dab, the best correlation was found between hepatic MT and Zn, whereas MT in male dab livers correlated most closely to a combination of Cu and Cd. The observed changes in hepatic MT appeared to have both an endogenous and an environmental component. The endogenous influence was only evident in female dab, whereas both sexes appeared to be moderately affected by environmental metal exposure. Hepatic MT and metal levels did not reflect metal concentrations in the sediment, but were consistent with the elevated metal content of 2 invertebrate species at offshore compared to coastal stations. In conclusion, dab hepatic MT was found useful as a biomarker for the effects of heavy metals on fish in an area with a complex contaminant input. Recommendations are given for future use of fish hepatic MT in monitoring programmes.