ABSTRACT
Exposures of rainbow trout (Oncorhynchus mykiss) to effluents from kraft pulp mills resulted in measurable increases in hepatic mixed function oxygenase (MFO) activity (induction) in all cases, regardless of bleaching or effluent treatment technology. Effluent concentration thresholds for MFO induction ranged from 0.33 to 9.1%. Comparison of chemical analyses and effluent concentration thresholds showed poor correlations between MFO induction and effluent concentrations of adsorbable organic halogen (AOX), dissolved organic carbon (DOC), chlorophenolics or resin and fatty acid concentrations. Mill comparisons of MFO induction thresholds normalized for flow and pulp production suggested that the bleaching process is a major contributor to MFO induction at older mills, but that other process sources can contribute to MFO induction at modern mills or mills with no bleaching. Induction at a mill not employing bleaching and the lack of a correlation between MFO induction and concentration of organochlorines, including AOX, suggest that regulatory control of AOX is not a satisfactory strategy to eliminate the MFO-inducing potential of pulp mill effluents.
