The presence of contaminants with hormone-like activity and their potential harmful effects on the aquatic ecosystems has been a major concern for over three decades. Despite the presence of very low levels of environmental contaminants in Alberta rivers, the occurrence of feminization has been reported in these sites. Bisphenol A (BPA), Nonylphenol (NP) and Bis(2-ethylhexyl)phthalate (DEHP), which are known as weak environmental estrogens, were found to be among the most abundant contaminants in the Oldman River.
The primary goal of this thesis was to investigate the in vivo effects of BPA, NP, and DEHP at environmentally relevant concentrations, individually and in a mixture, on gene expression patterns in goldfish (Carassius auratu) and fathead minnows (Pimephales promelas) under controlled laboratory conditions. Results of my study indicate that these contaminants at very low concentrations have endocrine disrupting abilities in a gender-specific manner. In addition, the altered transcript levels suggest that growth, steroidogenesis, gonadal development, and sperm biosynthesis might be possibly disrupted as a result of exposure to low concentration of endocrine disrupting compounds (EDCs).
The findings in this thesis indicate that the mRNA expression levels in response to exposure to various doses of BPA do not always follow a monotonic curve. The low dose of BPA could dysregulate the genes involved in steroid synthesis and gamete production while higher concentrations could induce estrogenicity and activate the detoxification mechanism. Furthermore, this thesis provides novel information on the potential mechanisms, canonical pathways, and regulators that are associated with exposure to these contaminants. It was possible to identify the genes that were affected significantly by all treatment groups, which can be used as suitable biomarkers in ecotoxicology studies. I also demonstrate that the gene expression patterns were different when fish were exposed to a mixture of the contaminants. Overall, the results of this study provide novel information on mechanisms of actions and the health impacts of the tested contaminants, and identified a number of new biomarkers that can be used in environmental toxicity testing.