ABSTRACT
At the first conference on Environmental Impacts of Pulp Mill Effluents, reports of MFO induction in fish exposed to BKME in Scandinavia were confirmed in other countries and extended to mills not using chlorine bleaching. MFO activity was associated in field studies with effects on fish, particularly regulation of steroid hormones. Unknowns arising from the 1991 meeting included: (1) mechanisms linking MFO induction to other toxic effects, (2) sources of inducers within mills, (3) effects of effluent treatment, (4) role of chlorine bleaching, (5) the nature and identity of inducers, and (6) the environmental fate and distribution of inducers in the environment. While known inducers are quite toxic and may have various effects, the links between induction and effects in effluent-exposed fish are not clear. Induction can be caused by effluents or effluent extracts from pulp mills using either chlorine bleaching or no bleaching, and one of the strongest sources within mills is spent cooking liquor. Additional contributions from C- and E-stage effluents imply either further release of inducers from lignin or increased potency of inducers due to chlorination. However, optimized waste treatment processes reduce induction potency of effluents. Inducers isolated from effluents exhibit properties of PAHs rather than of dioxins or furans, but their precise identity remains unknown. Induction downstream of pulp mills can be found at distances of up to 230 km, implying environmental persistence of some inducers, but others appear to be readily metabolized and excreted by fish.
