Biochemical and physiological effects in fish exposed to bleached kraft mill effluents

The studies were performed on perch (Perca fluviatilis) caught outside Husum and Iggesund kraft pulp mills in 1985 and 1987, respectively, and the results were compared to previous observations from 1984 to 1985 in the receiving waters of the Norrsundet kraft pulp mill. The studies revealed that the biochemical and physiological variables, i.e., EROD activity, gonad size, number of lymphocytes, carbohydrate metabolites, and plasma ion composition, can be used as sensitive and reliable indicators of toxic effects on natural populations of fish exposed to conventional chlorine-bleached kraft mill effluents. However; the effects were generally less pronounced and indicated less geographic extension than those seen in perch previously investigated in the receiving waters of the Norrsundet kraft pulp mill. Based on these studies on perch at Husum and Iggesund and the previous studies at Norrsundet it can be concluded that the chlorine-bleached kraft mill effluents cause serious disturbances to vital biochemical and physiological functions, which can affect the health status and presumably also the survival of the fish. Finally, the responses do not reflect the present situation in the receiving waters since all three mills have taken extensive measures for process alterations and discharge reductions after the time of the investigations.