Dioxin type and mixed type induction of the cytochrome P-450 system of common eider ducklings ( Somateria mollissima) by PCBs: with indications for biotransformation

Abstract

In order to investigate the effects of PCBs on biotransformation enzymes and metabolism, 4-week-old common eider ducklings were exposed to single ip doses of 3,3′,4,4′ tetrachlorobiphenyl (CB 77) (5 or 50 mg/kg) or the technical mixture Clophen A50 (Clo A50) (50 or 200 mg/kg). The control group was injected with corn oil only (5 ml/kg). Comparison of CB patterns in adipose tissue of the Clo A50 injected groups with the original Clo A50 mixture revealed specific reduction of congeners with vicinal H atoms in the meta and para positions, suggesting biotransformation by the monooxygenase system (MO) as the most probable cause. For the group injected with 200 mg Clo A50, a difference in congener pattern was shown between liver and adipose tissue. This indicates either a saturation of the hepatic biotransformation capacity, or slow redistribution of the congeners from the adipose tissue to the site of metabolism (liver). Using only one adipose tissue concentration point in time, indicative biological half-lives for metabolisable congeners were calculated from congener pattern changes, ranging from 3.6 days for CB 44 to 16.1 days for CB 101. CB 77 caused a dose-dependent induction of total cytochrome P450, whole liver cytochrome P450, EROD and PROD activity. On the contrary, Clo A50 had no inducing effects after this specific incubation period. PROD activity measurements suggest that the PROD assay may not be not a suitable indicator for CYP2B induction in common eider ducklings. Sex difference and parasitic infection had no influence on the biochemical responses measured. Internal dose-induction response curves were established; a very tentative maximum no effect level on toxic equivalents (TEQ) basis is suggested (7 ng TEQ/g lipid). Under these incubation conditions, exposure to CB 77 and Clophen A50 did not influence the infection rates of the intestinal parasite Polymorphus botulus (Acanthocephala).