ACCUMULATION, DEPURATION AND HEPATIC MIXED-FUNCTION OXIDASE ENZYME-INDUCTION IN JUVENILE RAINBOW-TROUT AND LAKE WHITEFISH EXPOSED TO DIETARY 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN

Juvenile rainbow trout (Oncorhynchus mykiss) and lake whitefish (Coreg onus clupeaformis) were exposed to three concentrations (40, 190, 400 pg g(-1)) of dietary 2,3,7,8-[H-3]tetrachlorodibenzo-p-dioxin (TCDD) t o compare bioaccumulation and hepatic monooxygenase enzyme (MO) induct ion. Fish were exposed for 30 days followed by a 180 day depuration ph ase. Differences in the accumulation and depuration of TCDD were found between rainbow trout and lake whitefish, despite similar body size a nd lipid content. Assimilation efficiencies of TCDD were greater in la ke whitefish (66-76%) than rainbow trout (43-58%), but TCDD half lives were shorter in lake whitefish (32-39 days) than in rainbow trout (73 -83 days). Biomagnification factors (BMF) ranged from 1.6 to 1.8 in ra inbow trout and from 0.8 to 0.9 in lake whitefish, confirming the know n potential for biomagnification of TCDD in aquatic food webs, Reverse phase HPLC showed that a majority of the radioactivity in the rainbow trout bile was TCDD, with minor amounts present as a hydroxylated TCD D and as a glucuronide conjugate. MO enzyme induction, measured by eth oxyresorufin-O-deethylase (EROD), was observed in the rainbow trout af ter 10 days of exposure to 400 pg g(-1) TCDD, and in the lake whitefis h after 5 days of exposure to 380 pg g(-1) TCDD. The whole fish thresh old concentration for EROD induction by TCDD ranged between 15 and 45 pg g(-1) (wet weight) for both species. EROD activity returned to cont rol levels 120 and 80 days after the cessation of the treatments in th e rainbow trout and lake whitefish, respectively. Growth rates were si gnificantly reduced in trout and whitefish at whole fish concentration s (wet weight) of 150 +/- 4.6 and 85 +/- 8.3 pg g(-1), respectively. H istological effects of the TCDD were found in the spleen and liver of the rainbow trout which had whole fish concentrations (wet weight) of 150 +/- 4.6 pg g(-1) and 72 +/- 8.0 pg g(-1) TCDD, respectively.