INTERACTION OF BENZO[A]PYRENE, 2,3,3',4,4',5-HEXACHLOROBIPHENYL (PCB-156) AND CADMIUM ON BIOMARKER RESPONSES IN FLOUNDER (PLATICHTHYS-FLESUS L)

Interactive effects of a mixed pollutant exposure on biomarker respons es were studied in European flounder (Platichthys flesus L.). The mode l chemicals, benzo[a]pyrene (BaP, 2.5 mg kg(-1)), 2,3,3',4,4'5-hexachl orobiphenyl (PCB-156, 2.5 mg kg(-1)), and cadmium (cadmium, 1 mg kg(-1 )), were administered to fish by subcutaneous injections. Biomarker re sponses were quantified both following administration of single chemic als and sequential combinations of the chemicals in pairs. Significant induction of CYP1A protein levels and corresponding ethoxyresorufin-O -deethylase (EROD) activities was observed in BaP and PCB-treated flou nder after 2 and 8 days, respectively. The strongest induction (44-fol d) was caused by BaP No further induction was observed after additiona l treatment with PCB-156. CYP1A induction caused by BaP was inhibited (40% compared with BaP treatment alone) in flounder pre-treated with c admium, whereas induction by PCB-156 appeared to be unaffected by pre- treatment with cadmium. Flounder treated with cadmium only had signifi cantly elevated hepatic levels of metallothionein (MT) after 15 days. Pre-treatment with BaP and PCB prior to cadmium inhibited the MT induc tion (30-50%) compared with cadmium alone. Furthermore, significantly higher glutathione S-transferase activities were observed in flounder administered cadmium alone, and in flounder treated with BaP or PCB-15 6 prior to cadmium. GST selenium-independent peroxidase activities app eared to be unaffected by any of the treatments in the present study. The results indicate that chemical mixtures may affect biomarker respo nses differently from compounds administered alone, and that the sensi tivity of both CYP1A and MT are influenced by pollutants other than th eir primary inducers.