REPRODUCTIVE HEALTH ASSESSMENT OF FATHEAD MINNOW (PIMEPHALES PROMELAS) POPULATIONS INHABITING AN EFFLUENT DOMINATED STREAM, WASCANA CREEK, SK
Date
2019-10-18
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Journal Title
Journal ISSN
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ORCID
Type
Thesis
Degree Level
Masters
Abstract
Concerns have been raised regarding the release of municipal wastewater effluents (MWWEs) into aquatic systems in recent decades due to their potential adverse effects on resident aquatic organisms. MWWEs contain complex mixtures of contaminants, and many of which are considered to have endocrine disrupting properties that may alter growth, development and reproduction of exposed organisms. Waterbodies in the southern Canadian Prairies, a semi-arid region, may be at particular risk to the exposure with contaminants released within MWWEs, including endocrine disrupting chemicals (EDCs), due to the uniqueness of prairie surface water systems. For example, during low flow periods small prairie streams such as Wascana Creek, SK downstream of the City of Regina’s outdated lagoon-based treatment facility can contain up to 100% treated effluent. Therefore, the objective of this study was to evaluate the potential impacts of MWWEs on reproductive health and endocrine homeostasis of wild fathead minnow (Pimephales promelas; FHMs) populations downstream of the City of Regina’s WWTP in Wascana Creek, Saskatchewan, Canada. Specifically, field studies were conducted on spawning FHMs during the summers of 2014 and 2015 to assess responses in terms of overall health (condition factor, ovosomatic indices) and reproduction (secondary sexual characteristics, gonad histopathology), and to evaluate molecular biomarkers (plasma hormone analysis, gene expression analysis) to determine any potential underlying mechanisms. Additionally, chemical analysis was done on surface water samples from both up- and down-stream sites to identify potential causative agents for any observed biological effects. FHMs downstream of the effluent fallout had lower gonadosomatic indices and significantly greater hepatosomatic indices compared to upstream populations. In both male and female FHMs significantly greater occurrence and severity of gonadal degradation and delayed maturation were observed in downstream fish compared to upstream fish; however, no indications of exposure to estrogenic compounds such as occurrence of testicular oocytes were observed. Furthermore, exposed males displayed lower scores of secondary sexual characteristics. While no significant differences were found in plasma hormone concentrations between fish populations up- and down-stream of the City of Regina’s wastewater treatment plant, trends of increased estradiol and decreased 11-ketotestosterone in females and males, respectively, were detected between years and sampling sites. Key biomarkers of estrogenic exposure, such as induction of vitellogenin (VTG), were not observed in exposed male FHMs. Lowered expression of estrogen (ERα, ERβ, VTG) in populations downstream suggest that estrogenic compounds likely did not cause the effects observed in the parallel study. In exposed fish downstream there was evidence of down-regulation of key steroidogenic genes, CYP19β and StAR, coupled with lowered FSHR and LHR expression, suggesting that steroidogenic capacity in the gonads of fish exposed to the MWWEs had been reduced. Overall, delays in maturation and histological alterations evident in populations downstream were supported by the general suppressive molecular responses. The general inhibition of reproductive functions of fish at RDS are in accordance with two parallel studies with lab exposed fish showing reduced fecundity in addition to similar delays in maturation and predominant antagonistic potentials detected in vitro by ER and AR receptor assays. Taking into account the overall lack of estrogenic effects across the in vivo studies (ie. Lack of VTG induction and no occurrence of intersex) and low estrogenic potential of the effluents entering RDS reported by the in vitro study, it is likely that the effects observed were not due to estrogenicity in the effluents. This is also in accordance with chemical analysis that revealed greater concentrations of compounds with the ability to act as ER and AR antagonists, while there were low, or no presence of chemicals previously shown to agonistically interact with these receptors. With continuous exposure to a diverse number of stressors including high nutrient and ammonia levels and presence of a variety of PPCPs and other contaminants, Wascana Creek should be considered as an ecosystem at risk with regard to effects from MWWEs on resident fish populations. While this study was regional in nature, due to similarities, inferences can likely be made among different semi-arid regions around the world in regards to the ecological impacts of MWWEs.
Description
Keywords
fathead minnow, wastewater effluents, field-study, endocrine disruption
Citation
Degree
Master of Science (M.Sc.)
Department
Toxicology Centre
Program
Toxicology