Endocrine disrupting chemicals (EDCs) exert effects at very low concentrations and can cause serious problems for the hormonal balance of various organisms. Exposure of wildlife to EDCs is not necessarily continuous, but may often occur in pulses. Consequently for the evaluation of the long-term effects on populations, it is essential to know whether such EDC-related effects are reversible. Three different substances selected for different modes of action were tested for their long-term impact on sex ratio, gonadal development, vitellogenin (VTG) induction and aromatase activity in zebrafish: the androgen trenbolone binds directly and very effectively to the androgen receptor. Ethinylestradiol, a synthetic derivative of estradiol, causes feminization in wildlife and humans. The fungicide prochloraz acts as an aromatase inhibitor by direct interference with the aromatization of androgens to estrogens. All compounds have previously been shown to cause striking effects in zebrafish, but recovery has never been studied in detail. In order to test whether EDC-related effects are reversible, an exposure scenario limited to 60 d was followed by (a) a recovery period of 40 d or (b) continued exposure for another 40 d. Four effects levels were examined: (1) population level: sex ratio; (2) organism level: growth; (3) organ/tissue level: histology of gonads (light microscopy); and (4) molecular level: vitellogenin induction (ELISA) and aromatase expression (RTq-PCR). Results show clear correlation of effects at all levels, but clear-cut differences between the two different exposure groups. We conclude that endocrine disruption in zebrafish following discontinuous exposure is only partially reversible and may thus have serious implications for fish.
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6th SETAC World Congress and SETAC Europe 22nd Annual Meeting, 2012