A SURVEY OF PULP AND PAPER-MILL EFFLUENTS FOR THEIR POTENTIAL TO INDUCE MIXED-FUNCTION OXIDASE ENZYME-ACTIVITY IN FISH

The potential of 31 secondary-treated pulp and paper mill effluents fr om eight different mills to induce mixed function oxidase (MFO) activi ty, in the liver of rainbow trout (Oncorhynchus mykiss), was investiga ted by short-term (4-day) laboratory exposures to 10% effluent concent ration. Two of six thermomechanical pulp (TMP) mill effluents investig ated caused increased EROD activity while there was no increase caused by the two chemi-thermomechanical pulp (CTMP) mill effluents tested. In contrast, with one exception, EROD activity was significantly induc ed as a result of exposure to bleached as well as unbleached kraft mil l effluents. The replacement of chlorine in the bleaching of kraft pul p by chlorine dioxide or non-chlorine containing compounds (such as pe roxide) did not eliminate the final mill effluent's ability to induce EROD activity. Rather, the kraft cooking process used to convert wood into pulp may itself be a source of MFO-inducing substances.