RESPONSES OF CYTOCHROME P4501A IN FRESH-WATER FISH EXPOSED TO BLEACHED KRAFT MILL EFFLUENT IN EXPERIMENTAL STREAM CHANNELS

Cytochrome P4501A induction was used to evaluate exposure of fish to bleached kraft mill effluent in experimental stream channels. Immunodetectable P4501A and associated ethoxyresorufin-O-deethylase (EROD) activity were elevated in largemouth bass (Micropterus salmoides) and channel catfish (Ictalurus punctatus) throughout 263 days of exposure to 8% and 4% effluent from a mill that used 70% chlorine dioxide substitution for chlorine in the pulp bleaching process. In largemouth bass, P4501A was elevated as high as 55-fold over control fish. Large temporal and species variations were observed in enzyme levels and activity. Levels of chlorinated organic compounds present in effluent also varied throughout exposures. However, there was no apparent relationship between P4501A and any of those compounds measured. P4501A and EROD in channel catfish declined to control levels within seven days after transfer of fish to clean water or after terminating introduction of effluent into the channels. In another exposure, induction was observed in largemouth bass at 4 and 12% effluent after the mill began using oxygen in the delignification process and 100% substitution of chlorine dioxide for chlorine.