COMPARING THE EFFECTS OF TWO MUNICIPAL WASTEWATER EFFLUENTS ON REPRODUCTIVE OUTPUT AND ENDOCRINE STATUS IN THE FATHEAD MINNOW (PIMEPHALES PROMELAS)
Date
2019-01-25
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-9903-5884
Type
Thesis
Degree Level
Masters
Abstract
Municipal wastewater effluents (MWWEs) contain anthropogenic substances that can
exhibit endocrine disrupting activity. These substances, which disrupt endogenous endocrine
signalling, can impact normal fish reproduction and development and lead to effects that manifest
at the individual and population level. In the Prairie provinces of Canada, increasing urban
populations and industrial activities have resulted in greater water demand, and therefore, greater
amounts of MWWEs released into the aquatic environment. Treatment plants often feature
outdated technologies that inefficiently remove contaminants and when coupled with the
increasing water demands, present a risk to receiving environments. The objective of this study
was to utilize the 21-day fathead minnow reproductive assay to identify potential reproductive
effects of MWWEs from Regina and Saskatoon. Fish were exposed for 21 days to 0 %, 10 % and
50 % of the effluents. Impacts on reproductive success (fecundity, fertility) as well as
morphological, histopathological, and molecular/biochemical endpoints were assessed in male
and female fish. Exposure to 10 % and 50 % Regina MWWE resulted in a significant decrease in
fecundity compared to non-exposed minnows. There were significant differences in fecundity of
minnows exposed to Saskatoon effluent, although the effect was not dose-dependent.
Fertilization rate remained consistent regardless of treatment. Histological examination revealed a
significant increase in proportion of spermatogonia and testicular degeneration in male fathead
minnow testes in 50 % effluent concentrations compared to control minnows in both Regina and
Saskatoon exposures. Increased oocyte atresia was observed in female minnows exposed to both
Regina and Saskatoon 50 % treatment. No change in circulating sex steroid hormones (estradiol,
11-ketotestosterone) in male or female minnows was observed. Analysis of gene transcription
revealed that exposure to Regina effluent induced ERα mRNA in female fathead minnows while
exposure to Saskatoon effluent induced ERα in females and androgen receptor in males. No
change in the expression of the vitellogenin was observed in any effluent-exposed group. The
results from this study demonstrated that exposure to MWWE can impact the reproductive output
and gonadal development of fathead minnows; however, due to the lack of change in key
endocrine-related endpoints, it appears these effects are not due to estrogenic or androgenic
compounds in the effluent. Additional work conducted by two parallel AIME studies supported
this conclusion. Due to the complex nature of MWWE further work incorporating additional
endpoints (i.e. behaviour), exposure lengths, and multi-seasonal studies would provide valuable
insight regarding the biological impacts of MWWE.
Description
Keywords
Wastewater, Endocrine Disruption, Fathead minnow
Citation
Degree
Master of Science (M.Sc.)
Department
Toxicology Centre
Program
Toxicology