Arch. Environ. Contam. Toxicol. 28,423-430 (1995) ARCHIVES OF: Environmental Contamination a n d Toxicology ® 1995 Springer-Verlag New York Inc. Sensitivity of Cytochrome P450 1A Induction in Dab (Limanda limanda) of Different Age and Sex as a Biomarker for Environmental Contaminants in the Southern North Sea H. M. Sleiderink l, I. Oostingh 1, A. GoksCyr2, J. P. Boon 1 Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands, z Laboratory of Marine Molecular Biology, University of Bergen, HIB, N-5020 Bergen, Norway Received: 27 July 1994/Revised: 19 November 1994 Abstract. The sensitivity of cytochrome P450 1A (CYP1A) induction as a biomarker for environmental contaminants in the flatfish dab (Limanda limanda) was evaluated by studying fish of different age and sex from the southern North Sea. Mature and juvenile dab from both sexes were collected in autumn and winter during two surveys from four different stations with varying levels of polychlorinated biphenyls (PCBs) contamina- tion in the southern North Sea. All groups of fish exhibited highest muscle PCB concentra- tions near the Dutch coast. CB153 was always the dominant congener. Since the concentrations of the other congeners mea- sured covaried to a large degree with CB153, this congener appears to be a good marker for general differences in PCB concentrations. In summer, bottom water temperature differences of up to 10°C can occur between stratified and vertically mixed areas. This was previously shown to have a strong effect on CYP1A expression. In autumn and winter, stratification has disap- peared, resulting in almost equal water temperatures between stations of the same survey. CYP1A levels were measured as 7-ethoxyresorufin O-deethylase (EROD) activity and immuno- quantitated CYP1A protein concentrations. Highest levels were also found close to the Dutch coast for mature fish from both sexes in October and for juvenile female and mature male fish in February during the spawning season. During this season, gravid female fish had significantly lowered contents of CYP1A protein and EROD activity compared to mature males and juveniles of both sexes. The sensitivity of CYP 1A induction in dab as a biomarker for halogenated aromatic hydrocarbons is highest in mature males when stratification during autumn is lacking. Halogenated aromatic hydrocarbons such as polychlorinated Correspondence to: H.M. Sleiderink biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and diben- zofurans (PCDFs) have been released into the environment from human activities, and their residues have been found in almost every component of the world's ecosystem (Safe 1990). Due to their lipophilic character, these compounds accumulate in fish and other aquatic organisms (Tanabe et al. 1989). In laboratory studies with fish, the planar compounds cause induction of the isoenzyme cytochrome P450 1A, which will be denoted as CYP1A (Andersson and F6rlin 1992; Gokscyr and F6rlin 1992). Elevated levels of CYP1A have been found in several field studies (Elskus et al. 1989; GoksCyr et al. 1991). Such environmental induction has been associated with in- creased concentrations of xenobiotic compounds. Therefore, this biochemical parameter may serve as a biomarker of expo- sure to especially planar aromatic contaminants, although the biological significance of CYP1A induction at higher levels of biological integration is yet uncertain. Since the flatfish dab (Limanda limanda) is a demersal fish with a large geographic distribution and abundance throughout the North Sea, it is presently being incorporated in pollution monitoring programs in the North Sea (North Sea Task Force, Joint Monitoring Programme). Induction of hepatic CYP1A protein and EROD activity in dab was found after exposure to the technical PCB mixture Clophen ® A40 (Sleiderink et al. 1995a). The Dutch coastal zone is influenced by the effluents of the rivers Rhine, Meuse, and Scheldt and belongs to one of the heaviest PCB-contaminated areas in the world (Klamer et al. 1991; De Boer et al. 1993). In fish caught in the Dutch aquatic environment, the toxic effect of PCBs, based on toxic equiva- lency values, is four times more important than that of PCDDs and PCDFs (De Boer et al. 1993). In the spring and summer, differences in sea water tempera- ture have a strong influence on the induction of CYP1A in dab (Sleiderink et al. 1995b); stratification of the water column can cause differences of bottom water temperatures up to 10°C between different sampling areas in the southern North Sea, making the contaminant response difficult to discern. In late autumn and winter, such large temperature differences are not present and these seasons appear more suitable to evaluate the