Microsomal monooxygenase activity in Tilapia (Oreochromis mossambicus) exposed to a bleached kraft mill effluent using different exposure systems

Bleached kraft pulp and paper mill effluents (BKMEs) are known to have adve rse effects on aquatic organisms. One of the effects of BKMEs is its abilit y to induce cytochrome P4501A activity in exposed fish. 7-ethoxyresorufin O -deethylase (EROD) activity is the most common biomarker used to measure th e mixed-function monooxygenase activity. In this study, Tilapia were expose d to BKMEs using different exposure systems and their hepatic EROD activity , as well as liver/somatic index (LSI), were determined. In the Phase I stu dy, Tilapia treated with beta NF and a whole (100%) BKME using a static, no n-renewal system exhibited statistically significant EROD induction, but LS I values were not altered. In the Phase II study, fish were either caged in the mill's fishpond with the whole effluent passing through or cultured in tanks receiving 100% of the BKME continuously using a flow-through system in the laboratory. Their EROD activities were then compared with the non-ex posed fish (control). The EROD activities in both groups of fish were eleva ted significantly with the greatest induction being observed in the field-e xposed group. The LSI values in all of the field-exposed fish were signific antly greater than the control Tilapia. The EROD assay was sensitive in det ecting biological changes in fish exposed to the BKME. Further studies are warranted to better understand the impacts of BKMEs on aquatic organisms in Taiwan. (C) 2001 Elsevier Science Ltd. All rights reserved.