Effects of Emerging Contaminants on Native Canadian Fish Species

Abstract

The presence of emerging contaminants (ECs) detected in municipal wastewater effluents (MWWE) is increasing in much of the developed and developing world. For this reason, effects of these compounds to aquatic wildlife in receiving water bodies is becoming a growing concern globally. However, toxicity of many ECs, including 17α-ethynylestradiol (EE2), fluoxetine (FLX), and hexabromocyclododecane (HBCD), have limited or no data regarding their toxicity to aquatic organisms, particularly with native North American species of interest. Additionally, while testing of the effects of ECs to native species is warranted, challenges exist when conducting whole animal studies with wild fish species. Therefore, alternative assays such as in vitro assays or short-term molecular mechanistic studies are increasingly being implemented, including the tissue explant assay and the whole transcriptome experiment described in this thesis. Specifically, the primary objectives of this study were to 1) characterize and further expand our knowledge on the toxicity of selected ECs for which little toxicological knowledge regarding fish exist; and 2) to establish an in vitro approach that enables assessing the responsiveness of four selected fishes of relevance to North American fresh waters to three priority ECs. To address the information gap regarding toxicity of selected ECs, high-throughput, next generation sequencing technologies were utilized to identify key molecular pathways that were altered in liver of rainbow trout (Oncorhynchus mykiss) after a 96-hr waterborne exposure to the EC, fluoxetine (FLX). Pathway analysis yielded changes in a total of 144 different pathways, many of which were shared with previous studies. Altered pathways were predominantly involved in oxidative stress (downregulated) as well as metabolic function and other biological processes (upregulated). In vitro tissue explant assays with gonads and livers from lake trout (Salvelinus namaycush) and northern pike (Esox lucius), as well as livers from rainbow trout and white sturgeon (Acipenser transmontanus), exposed to serial concentrations of EE2, FLX or HBCD were then conducted and transcript abundances of reproductive and antioxidant genes were measured to characterize species-specific changes in gene expression to these compounds. Antioxidant genes to be measured with exposure to FLX were chosen based on pathway analysis in Chapter 2. Results from the in vitro tissue explant experiments with rainbow trout exposed to fluoxetine confirmed and validated the findings from the first study; however, gene expression was highly variable, and other in vitro endpoints should be explored. Rainbow trout were consistently one of the more sensitive species in our study, and they appear to represent an appropriate model organism for many scenarios; however, in a few cases other species were more sensitive (with exposure to HBCD, for example), caution should be taken when extrapolating across species. Results of the tissue explant assays successfully characterized gene expression in native fish species to these ECs of concern and, if validated, could represent a useful tool for toxicity screening of chemicals in the future.