Biomarker responses in female rainbow trout exposed to untreated and secondary treated whole mill effluent from production of TCF-bleached sulphate pulp

Juvenile, female rainbow trout (Oncorhynchus mykiss) were exposed for 8 weeks to 1:400 dilutions of treated and untreated totally chlorine free bleached kraft mill effluents (BKME). Individual growth, feed consumption, bile conjugates, liver enzyme 7-ethoxyresorufin-O-deethylase (EROD), liver histology, liver glycogen, muscle lipid, hematology parameters and plasma 17[beta]-estradiol levels were measured. Compared with the controls, no significant effects on growth, feed consumption, plasma 17[beta]-estradiol and EROD were observed. A significant positive relationship between growth and plasma 17[beta]-estradiol and muscle lipid content was found in fish exposed to treated effluent. The fish bile sterol levels did not correlate with the sterol levels analyzed directly from effluent samples. The treated effluent exposed fish excreted more cholesterol through bile than control fish. Livers of fish exposed to treated effluent had lower glycogen content and muscle lipid content than control fish. Only minor changes in liver structure and hematology of the BKME exposed fish were observed. Other studies has shown phytosterols to inhibite intestinal cholesterol absorbtion and this might explain why a higher liver energy metabolism was observed in fish exposed to treated effluent.