Previous studies exposing fish to xenoestrogens have demonstrated vitellogenin (VTG) induction, delayed gametogenesis, altered sex distribution, and decreased reproductive performance, with a majority of those studies focusing on exposure to single chemicals. The objective of this study was to determine the effects of binary mixtures of a weak estrogen receptor agonist, nonylphenol (NP) and a potent estrogen receptor agonist, 17α-ethinylestradiol (EE) on sex distribution, gametogenesis, VTG induction, heat shock protein 70 (HSP70) expression and reproductive capacity in zebrafish (Danio rerio). Fish were exposed from 2 to 60 days post-hatch (dph) to nominal concentrations of 10 or 100 µg/l NP (NP10 or NP100, respectively), 1 or 10 ng/l EE (EE1 or EE10, respectively), 1 ng/l EE + 10 or 100 µg/l NP (EE1+NP10 or EE1+NP100, respectively), 10 ng/l EE + 10 or 100 µg/l NP (EE10+NP10 or EE10+NP100, respectively) or solvent control (0.01% acetone v/v) in a static-renewal system with replacement every 48h. At 60 dph, fish from each treatment were euthanized for histological examination of gonads, and whole body VTG and HSP70 levels. Remaining fish were reared in clean water until adulthood (240 dph) for breeding studies. In all EE10 exposure groups (EE10, EE10+NP10 and EE10+NP100), increasing NP concentration acted less than additively to the action of EE in terms of VTG induction at 60 dph. Similarly, a less than additivity of effect was observed with egg production, where EE1+NP100 exposure resulted in significantly more eggs produced per breeding trial than EE1 alone. Histological staging of oogenesis revealed suppressed gametogenesis in females at 60 dph. There were no differences among treatment groups in whole body HSP70 expression in 60 dph fish or in gonadal HSP70 expression in adult fish. Although there was no statistical evidence of non-additivity, breeding trials in adults revealed significant reductions in egg viability, egg hatchability and/or F1 swim-up success, suggesting that developmental exposures to xenoestrogens may cause irreversible effects on egg quality and progeny even after depuration. In conclusion, these results suggest that environmentally relevant mixtures of NP and EE can produce additive or non-additive effects depending on the particular response being determined and the respective exposure concentrations of each chemical. Thus, it is recommended that caution be exercised in ecological risk assessments when assuming additivity in piscine responses to xenoestrogen mixtures.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-09172007-204748 |
| Date | 18 September 2007 |
| Creators | Lin, Leo |
| Contributors | Krone, Patrick H., Janz, David M., Blakley, Barry R. |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-09172007-204748/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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