MFO induction in fish by filtrates from chlorine dioxide bleaching of woodpulp

Spent bleaching liquors from pulp bleached with chlorine dioxide were asses sed for their potency to induce hepatic mixed function oxygenase enzymes (M FO) in rainbow trout, as indicated by activity of ethoxyresorufin-o-deethya se (EROD). Filtrates were collected from two kraft mills in Central Canada to assess the potency of filtrates from hardwood and softwood bleaching. Al l mill-scale bleaching filtrates induced MFO activity, and filtrates from s oftwood pulp bleaching appeared more potent than filtrates from hardwood bl eaching. Filtrates from the final bleaching stage were most potent, and fil trates from the first stage were the least potent. In laboratory bench-scal e bleaching experiments, pulp from softwood and hardwood kraft mills in Eas tern Canada was bleached via an industry-standard 5-stage chlorine dioxide bleaching sequence. The filtrates were collected and used in fish bioassays to assess EROD-inducing potency. Potency of bench-scale filtrates varied d epending on wood furnish (i.e. softwood vs. hardwood) and the bleaching sta ge, with all bench-scale filtrates being much weaker EROD inducers than mil l-scale filtrates. Recycled paper mill washwater is a possible source of co mpounds causing increased potency of the mill-scale filtrates. (C) 2001 Els evier Science Ltd. All rights reserved.