Dietary accumulation and sustained hepatic mixed function oxidase enzyme induction by 2,3,4,7,8-pentachlorodibenzofuran in rainbow trout

Accumulation of and hepatic monooxygenase induction by 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) were studied in juvenile rainbow trout (Onchorhynchus mykiss) by feeding treated food for 31 d followed by a 180 d depuration period. Efficiency of assimilation was 44 and 41% at exposure concentrations of 9.0 and 0.82 ng g−1 PnCDF, respectively. Depuration of PnCDF followed first-order kinetics with half-lives (based on toluene extraction of 14C-radiolabel corrected for growth dilution) of 61 and 69 d at the low and high exposure concentrations, respectively. Monooxygenase enzyme induction measured by ethoxyresorufin-O-deethylase (EROD) activity in individual trout livers was 84- and four-fold higher after 31 d of exposure to 9.0 and 0.82 ng g−1, respectively, than in livers of unexposed fish. Sustained EROD activity at the high treatment concentrations was observed during the 180 d depuration phase. Ethoxyresorufin-O-deethylase activity declined at approximately half the rate of elimination of PnCDF. No significant differences between growth rates of treated and control fish were found.