HEPATIC METALLOTHIONEIN LEVEL AND MIXED-FUNCTION OXIDASE ACTIVITY IN FINGERLING RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AFTER ACUTE EXPOSURE TOPULP AND PAPER-MILL EFFLUENTS

Hepatic metallothionein (MT) levels and mixed function oxidase (MFO) a ctivity (7-ethoxyresorufin-o-deethylase or EROD) were measured in fing erling rainbow trout (Oncorhynchus mykiss) exposed to sublethal concen trations of 12 pulp and paper effluents, after completion of 96 h stat ic acute lethality assays. Barring one primary-treated effluent where MFO levels were significantly depressed and two secondary-treated effl uents where no significant MFO induction were observed, all other effl uents triggered significant induction of MT and EROD, regardless of mi ll process/treatment or of effluent lethality and chemical characteris tics. MT and EROD inductions were significant, however, at higher conc entrations for secondary-treated effluents than for primary-treated on es. Lethal (96 h LC50s) to sublethal (MT and EROD lowest observable ef fect concentrations) ratios were variable and indicated that significa nt biochemical effects were present at effluent concentrations that we re roughly 4-33 (MT) and 3-59 (EROD) times lower than the LC50. Enzyme induction ranged from 1.3 to 2.5-fold for MT and from 1.3 to 9.4-fold for EROD compared to controls. Limited chemical data available sugges t that there were indeed classes of compounds present capable of induc ing MT or EROD. Observed patterns of MT/MFO responses also suggest tha t contaminant interactions may have interfered with induction for some of the effluents studied. Refinements of this combined (sub)lethal bi oassay procedure are envisaged to determine whether it can provide an efficient means of detecting hazardous chemicals in industrial wastewa ters.