Abstract
The effluent from municipal wastewater treatment plants is a major point source of contamination in Canadian waterways. The improvement of effluent quality to reduce contaminants, such as pharmaceuticals and personal care products, before being released into the environment is necessary to reduce the impacts on organisms that live in the river downstream. Here, we aimed to characterize the metabolic and gill physiological responses of rainbow (Etheostoma caeruleum), fantail (Etheostoma flabellare), and greenside (Etheostoma blennioides) darters to the effluent in the Grand River from the recently upgraded Waterloo municipal wastewater treatment plant. The routine metabolism of darters was not affected by effluent exposure, but some species had increased maximum metabolic rates, leading to an increased aerobic scope. The rainbow darter aerobic scope increased by 2.2 times and the fantail darter aerobic scope increased by 2.7 times compared to the reference site. Gill samples from effluent-exposed rainbow darters and greenside darters showed evidence of more pathologies and variations in morphology. These results suggest that darters can metabolically adjust to effluent-contaminated water and may also be adapting to the urban and agricultural inputs. The modification and damage to the gills provide a useful water quality indicator but does not necessarily reflect how well acclimated the species is to the environment due to a lack of evidence of poor fish health.
Highlights
In the Grand River, located in Southwestern Ontario, contaminant inputs from effluent discharged by municipal wastewater treatment plants (MWWTPs) enter the water and have effects on the fish populations living downstream from the outfall
Effects on reproduction, growth, sex ratios, metabolism, and molecular signatures have all been identified as maladaptive phenotypes in downstream locations from MWWTPs in this area, which were attributed to effluent exposure [3,4,5]
Gill physiological endpoints are useful in monitoring water quality but are not necessarily an indicator of how fishes are acclimating to their environment due to there being no evidence seen here on the impact on oxygen uptake ability. The purpose of these experiments was to investigate the response of darters to Waterloo municipal wastewater treatment plant effluent in the Grand River after upgrading to secondary treatment with an increased solids retention time and nitrification
Summary
In the Grand River, located in Southwestern Ontario, contaminant inputs from effluent discharged by municipal wastewater treatment plants (MWWTPs) enter the water and have effects on the fish populations living downstream from the outfall. Effects on reproduction, growth, sex ratios, metabolism, and molecular signatures have all been identified as maladaptive phenotypes in downstream locations from MWWTPs in this area, which were attributed to effluent exposure [3,4,5]. Rainbow darters downstream from the MWWTPs in the Grand River have experienced changes in gene expression, skewed sex ratios, altered gonad size, and intersex or feminized fish populations are found, largely due to the presence of EDCs [6,7].
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