Biotransformation and other physiological responses in whitefish caged in a lake receiving pulp and paper mill effluents.

Hepatic monooxygenase (MO) and conjugation enzyme activities, metabolites of chlorinated phenolics in the bile, and blood ionoregulatory parameters were studied in juvenile whitefish (Coregonus muksun Pallas and C. muksun X Coregonus peled Gmelin hybrid) held in cages downstream from a mill producing chlorine-bleached kraft pulp and printing paper. MO activities, measured as benzo[a]pyrene hydroxylase, 7-ethoxycoumarin O-deethylase, and 7-ethoxyresorufin O-deethylase, were significantly induced in whitefish caged about 5 km from the effluent outlet. The highest mean increase detected was 17 times the control value. In the nearest caging station (3 km) the induction was lower, indicating inhibition or toxicity caused by the effluent. The levels of bile metabolites of chlorinated phenolics showed highest concentrations at the nearest station and decreased levels at more distant locations over the whole water area studied (15 km). Bile metabolites in whitefish exposed in control areas confirmed low-level background pollution of the lake system due to chlorinated phenolics. Observations on blood ionic concentrations suggest that whitefish were able to regulate their hydromineral balance despite the environmental pollution affecting physiology of biotransformation.