Induction of hepatic EROD in fish exposed to leachates from wood pulp

Aqueous leachates from softwood and hardwood pulp collected from two different pulping stages in a kraft mill (i.e. pre- and post-oxygen delignification) were assessed for their ability to induce hepatic ethoxyresorufin-O-deethylase (EROD) in rainbow trout (Oncorhynchus mykiss). Immature rainbow trout were exposed to aqueous leachates from wood pulp for 21 days in a flow-through system. The leachates from softwood pulp collected at both pulping stages and leachates from pre-oxidation hardwood pulp elevated EROD activities 2.5 to 6-fold above reference fish, beginning at 7 days from the start of exposure. The EROD activity remained elevated in these treatments throughout exposure, but declined rapidly during a 14 day post-exposure period. Leachate from the softwood pulp appeared to be a more potent EROD inducer than leachate from hardwood pulp. The results of this study indicate that relatively hydrophilic chemicals capable of inducing MFOs in fish are present in wood pulp even before extensive mill processing.