Epsilon Open Archive

Abstract

Many of the natural, pharmaceutical and industrial chemicals that are present in the aquatic environment can interfere with the endocrine system of fish. There is a demand for sensitive and robust test systems for risk assessment of the endocrine disrupting chemicals (EDC). The aim of this thesis was to develop a partial life-cycle test to be used for evaluation of EDC. The test was based on exposure of juvenile zebrafish to EDC during the period of gonad transformation and differentiation. The main endpoints studied were the induction of the estrogenic biomarker protein vitellogenin (Vtg) and gonad development. Zebrafish were exposed to single model substances to investigate if exposure during the period of gonad transformation and differentiation affects Vtg production and gonad development. Exposures to the synthetic estrogen 17α-ethinylestradiol (EE2) resulted in a dose-dependent increase in Vtg production, as well as female-biased sex ratios, including all-female stocks. Exposures to the androgens 17α-methyltestosterone (MT) and 17β-trenbolone (Tb) resulted in decreased Vtg concentrations, as well as male-biased sex ratios, including all-male stocks. In a comparative study with Japanese medaka a higher sensitivity of both Vtg and sex ratio of the zebrafish was shown after exposure to EE2 and Tb. Exposures to binary mixtures of the differently acting substances EE2 and Tb demonstrated that effects on both Vtg and gonad development can be detected. Application of this zebrafish partial life-cycle test on a chemically complex pulp mill effluent revealed both estrogenic and androgenic effects. In conclusion, the zebrafish respond to EDC at environmentally realistic concentrations. The results support that zebrafish is a suitable model species for evaluation of EDC.