CYTOCHROME P4501A INDEXES AS BIOMARKERS OF CONTAMINANT EXPOSURE - RESULTS OF A FIELD-STUDY WITH PLAICE (PLEURONECTES-PLATESSA) AND FLOUNDER(PLATICHTHYS-FLESUS) FROM THE SOUTHERN NORTH-SEA

Within the framework of the Integrated North Sea Programme (INP), samp les of two flatfish species, flounder, Platichythys flesus, and plaice , Pleuronectes platessa, were collected during August/September 1991 a nd May/June 1992 in the southern North Sea. The aim of the study was t o examine the induction of hepatic cytochrome P4501A (CYP1A) in both s pecies when exposed to environmental PCBs and PAHs. Plaice and flounde r occupy different but partly overlapping habitats. Flounder live main ly in estuaries and coastal areas whereas plaice can be found througho ut the North Sea. CYP1A was measured by a semiquantitative immunochemi cal ELISA technique and also by the activity of its catalyst, 7-ethoxy resorufin O-deethylase (EROD). In plaice, both hepatic CYP1A protein l evel and EROD activity were significantly higher at offshore sampling locations than at coastal locations, by a factor of 1.5 to 2. In floun der, which were only collected at coastal locations, the range of valu es of EROD activity was much greater than in plaice, but the response in the ELISA test using polyclonal trout CYP1A1 antibodies was compara ble in both species. Multiple regression analysis of data from plaice and flounder did not show any significant correlation between CYP1A in dices, water temperature and contaminant concentrations in fish tissue s. CYP1A indices also appeared to be unrelated to food type, as determ ined by visual screening of fish intestines. One possible explanation for the lack of correlation between CYP1A indices and indices of expos ure to pollution could be the influence of additional modifying factor s (biological, physical or chemical), which might mask CYP1A induction by PCBs and PAHs in this area. However, the low statistical power of the tests used, related to difficulties in collecting sufficiently lar ge sample sizes, should also be borne in mind. It can be concluded tha t the induction of CYP1A in plaice and flounder from the southern Nort h Sea is not related in a simple manner to exposure to PCBs and PAHs, two groups of chemicals that cause induction in the laboratory. Appare ntly other unknown modifying factors also have a considerable influenc e. From the point of view of use as a biomarker, the measurement of CY P1A protein level and EROD activity in plaice and flounder from the op en North Sea cannot be applied straightforwardly for monitoring exposu re to PCBs and/or PAHs in the absence of more knowledge about the ment ioned modifying factors.