| Summary: | The effects of biologically treated effluents from bleached sulphite pulp production were studied using brown trout (Salmo trutta) as test organism. Continuous-flow exposures under laboratory conditions were conducted at two dilutions (1:40 and 1:400) for eight weeks, followed by a six-week recovery period. Physiological and biochemical biomarkers including liver histology, hematology and hepatic enzyme assays were used and the exposure was verified by analysing fish bile and fish tissue concentrations of resin acids and chlorophenols. The conjugated chlorophenols and resin acids levels in the exposed fish bile are considered as low. Only two significant responses were observed, both in liver function.The MFO associated EROD activity was induced parallel to lower liver glycogen levels. Otherwise, the changes in physiological parameters analysed were few as compared to reference fish. The small differences in physiological parameters between the reference group and the exposure group (1:40) after six-week recovery period show that the observed responses were reversible. The spectrum and pattern of results observed in this study are very much the same as seen in laboratory and field studies with bleached kraft mill effluents from modern mills.
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