COMPARING THE EFFECTS OF TWO MUNICIPAL WASTEWATER EFFLUENTS ON REPRODUCTIVE OUTPUT AND ENDOCRINE STATUS IN THE FATHEAD MINNOW (PIMEPHALES PROMELAS)

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 Treatment plants often feature outdated technologies that inefficiently remove contaminants and when coupled with the increasing water demands, present a risk to receiving environments.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.