Biomarker responses in rainbow trout (Oncorhynchus mykiss) exposed to sewage treatment plant effluent

In October 1997, juvenile rainbow trout Oncorhynchus mykiss were exposed to effluent water from two different sewage treatment plants (STPs) in the Göteborg area: Gråbo, a small STP north of Göteborg and GRYAAB, a large STP that processes the sewage from the city of Göteborg. In Gråbo, two groups of fish were caged, one upstream and one downstream. Fish were sampled after 2 and 4 weeks. In GRYAAB, fish were exposed to outlet water in aquaria. The exposure concentrations were 0, 2, 20, and 50% diluted with dechlorinated tap water. Fish were sampled after 5 days, 2, 4 and 10 weeks. The CYP1A (EROD activity) showed a time-dependent dose-response induction in the GRYAAB experiment. In Gråbo, EROD activity was lower in the exposed group compared with the control. The different EROD responses caused by the two effluents may be due to the high levels of estrogens in the Gråbo effluent (Parkkonen et al., (2000). Marine Environmental Research 50(1–5), this issue). The conjugating enzyme glutathione-S transferase and the antioxidant enzymes catalase, glutathione reductase and DT-diaphorase showed no significant responses.