MOLECULAR DOSIMETRY OF DNA-ADDUCTS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) EXPOSED TO BENZO(A)PYRENE BY DIFFERENT ROUTES

Farm raised rainbow trout (Oncorhynchus mykiss) were exposed by variou s routes to benzo(a)pyrene (BP) as a representative carcinogenic polyc yclic aromatic hydrocarbon (PAH). Following exposure of fish to the ch emical by intraperitoneal (i.p.) injection, P-32-postlabelling studies indicated that non-feral trout were relatively resistant to the forma tion of BP-DNA adducts in liver. No adducts were detected in fish expo sed to single doses (20 mg/kg) of BP. Multiple exposures (e.g. 2 x 25 mg/kg) were necessary in order for adducts to be detected, indicating that induction of the metabolising enzymes required for the bioactivat ion of BP is necessary. These studies provided reference information o n DNA adducts for comparison with data from subsequent experiments at environmentally realistic low level exposures. Two types of low level aquatic exposure were carried out. The first procedure exposed fish fo r 30 days to a nominally constant low level (1.2 and 0.4 mu g/l) of a homogeneous dispersion of BP in water, to simulate low level aquatic e nvironmental exposures. Following P-32-postlabelling analysis of the l iver DNA of exposed fish, BP-DNA adducts were not detected. In the sec ond procedure, fish were exposed to a constant low level of BP (ca. 0. 5 mu/l) for 15 days then to a pulse (60 mu g/l) which was allowed to n aturally decline (to ca. 2 mu g/l) during a further 15 days. Following this exposure, significant levels of BP-DNA adducts were detected in livers of trout. The effect of dietary exposures was investigated by f eeding trout a diet containing either 58 mu g or 288 mu g BP per day f or 6 days, equivalent to total doses of 43 mg/kg and 216 mg/kg. In bot h cases BP-DNA adducts were detected in livers of exposed fish. The re sults provide useful information on the types of exposures to PAHs whi ch may pose a genotoxic risk to fish in the environment.