Temperature and photoperiod affect the endocrine disruption effects of ethinylestradiol, nonylphenol and their binary mixture in zebrafish (Danio rerio)

We found that temperature and photoperiod significantly influence the transcription of the estrogen-responsive genes, vitellogenin1 (Vtg1), vitellogenin2 (Vtg2), estrogen receptor-α (ERα) and estrogen receptor-β (ERβ), after a 21-day exposure to environmentally relevant concentrations of 17α-ethynylestradiol (EE2), nonylphenol (NP) and EE2 plus NP (EE2 + NP). In general, gene transcription levels were higher as temperature and photoperiod length increased. The mRNA levels of Vtg1 in EE2 (10 ng/L) and EE2 + NP (10 ng/L and 25 μg/L, respectively) groups were induced more than 104 times both in 21 °C–12 L and 30 °C–14 L groups, but only 369 ± 23 and 178 ± 59-fold induced in 12 °C–10 L group compared to the control, respectively. Specifically, when exposed to a high concentration of NP (25 μg/L) for 21 days, the levels of all mRNAs examined were significantly increased (p < 0.05) in the 21 °C–12 L and the 30 °C–14 L groups compared to the controls. However, no obvious induction in transcription was observed in the 12 °C–10 L group. The results obtained in the present study clearly elucidate that temperature and photoperiod greatly influence the effect of EDCs, and thus suggest that to fully define the endocrine disruption effects seasonal and/or climate change effects must also be investigated.