BIOACCUMULATION OF DIETARY 2,2',4,4',5,5'-HEXACHLOROBIPHENYL AND INDUCTION OF HEPATIC ARYLHYDROCARBON HYDROXYLASE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Juvenile rainbow trout (Oncorhynchus mykiss) were fed either 5 or 20 m u g 2,2',4,4',5,5'-hexachlorobiphenyl (245-HxCB)/g diet (wet wt.) for 4, 8, or 12 weeks. Hepatic xenobiotic-metabolizing enzyme activities a nd dietary 245-HxCB accumulation in liver, muscle, and remaining carca ss were determined. Liver-to-body weight ratios were not altered by ei ther of the two 245-HxCB concentrations. Relative growth rate increase d with time but was not altered by 245-HxCB concentration. Bioaccumula tion of 245-HxCB was dose and time dependent in all tissues without re aching apparent steady state. Hepatic arylhydrocarbon hydroxylase (AHH ) activities increased with 245-HxCB dose and with time. Ethoxyresoruf in-O-deethylase (EROD) activities also increased in fish fed 20 mu g 2 45-HxCB/g diet. No 245-HxCB-induced changes in uridine diphosphoglucur onosyl transferase (UDP-GT) or NADPH-cytochrome-c reductase (NCCR) act ivities were determined. High-resolution GC-MS analysis of the 245-HxC B standard revealed trace (0.4-0.5%) contamination by two mono-ortho p entachlorobiphenyls (PnCBs): 2,3,3',4,4'-PnCB and 2,3,4,4:5-PnCB. Tota l liver accumulation of these contaminants was inversely related with corresponding EROD and AHH activities and estimated to contribute mini mally to their induction. Results from this study suggested that long- term dietary 245-HxCB exposures induced cytochrome P4501A activities i n rainbow trout liver.