MFO INDUCTION IN FISH BY SPENT COOKING LIQUORS FROM KRAFT PULP-MILLS

Within bleached kraft mills, the main sources of compounds inducing th e mixed function oxygenase (MFO) activities of fish are waste cooking liquor, black liquor, and effluents from the first stages of the bleac hing process. We measured the potency for MFO induction in rainbow tro ut (Oncorhynchus mykiss) Of black liquors from pulp mills using kraft pulping and either softwood or hardwood furnish. Concentrations causin g induction ranged from 0.0032 to 0.2%(v/v), and below critical thresh olds, concentration-response relationships were linear. Above threshol d concentrations, activity declined, and lethality occurred at concent rations greater than 0.1% (v/v) black liquor during 4-d exnosures. Har dwood pulping generated black liquor that was less potent than that fr om softwood, but much of the difference was due to a higher water cont ent; hardwood black liquor was more dilute as indicated by normalizing results to dissolved organic carbon. Compounds inducing MFO activity may be natural wood extractives associated with wood resins, or compou nds created by the digestion of lignin. A high potency of black liquor from alcohol pulping supports the hypothesis of a natural compound be cause alcohol extraction does not chemically alter lignin to the same extent as kraft pulping; inducing compounds can also be extracted from wood chips with dichloromethane. The high potency of black liquor com pared to bleaching or extraction-stage effluents suggests that control of black liquor losses may be very important in limiting exposure of fish to inducing compounds.