Returning to normal? Assessing transcriptome recovery over time in male rainbow darter (Etheostoma caeruleum) liver in response to wastewater‐treatment plant upgrades

Abstract

The present study measured hepatic transcriptome responses in male rainbow darter (Etheostoma caeruleum) exposed to 2 municipal wastewater-treatment plants (MWWTPs; Kitchener and Waterloo) over 4 fall seasons (2011-2014) in the Grand River (Ontario, Canada). The overall goal was to determine if upgrades at the Kitchener MWWTP (in 2012) resulted in transcriptome responses indicative of improved effluent quality. The number of differentially expressed probes in fish downstream of the Kitchener outfall (904-1223) remained comparable to that downstream of Waterloo (767-3867). Noteworthy was that year and the interaction of year and site explained variability in more than twice the number of transcripts than site alone, suggesting that year and the interaction of year and site had a greater effect on the transcriptome than site alone. Gene set enrichment analysis revealed a gradual reduction in the number of gene ontologies over time at exposure sites, which corresponded with lower contaminant load. Subnetwork enrichment analysis revealed that there were noticeable shifts in the cell pathways differently expressed in the liver preupgrade and postupgrade. The dominant pathways altered preupgrade were related to genetic modifications and cell division, whereas postupgrade they were associated with the immune system, reproduction, and biochemical responses. Molecular pathways were dynamic over time, and following the upgrades, there was little evidence that gene expression profiles in fish collected from high-impact sites postupgrade were more similar to those in fish collected from reference site. Environ Toxicol Chem 2017;36:2108-2122. © 2017 SETAC.

Assessing recovery of in vitro steroid production in male rainbow darter (Etheostoma caeruleum) in response to municipal wastewater treatment plant infrastructure changes

“…Total effluent estrogenicity followed a pattern similar to that of nitrogenous products over time. Recent studies showed that there were various pharmaceuticals detected in the Waterloo MWWTP effluent over time (2011–2015), further confirming that its quality remained extremely variable (Marjan et al ; Hicks et al ).…”

“…Consequently, this was associated with an approximately 10‐fold reduction of total effluent estrogenicity in 2015 compared with the pre‐upgrade period (2011). Moreover, pharmaceuticals such as naproxen and ibuprofen, which are considered to be reliable indicators of effluent quality and process changes (e.g., nitrification), also showed a significant reduction following the upgrades (Marjan et al ; Hicks et al ). For instance, Hicks et al () reported a 135‐fold reduction in ibuprofen and a 20‐fold reduction in naproxen in the post‐upgrade period compared with the pre‐upgrade period.…”

“…Infrastructure upgrades at the Kitchener MWWTP have resulted in reduction of intersex severity and prevalence in rainbow darter (Hicks ). Functional analyses of the rainbow darter liver transcriptome suggested that fewer stress‐related pathways were affected, and rainbow darter collected below the 2 MWWTP outfalls showed greater divergence in biological pathways after the upgrade implementation (Marjan et al ) at Kitchener. Gonadal histology and molecular responses showed that recovery in rainbow darter in response to MWWTP upgrades was likely occurring, especially after 2013.…”

Impacts on Metabolism and Gill Physiology of Darter Species (Etheostoma spp.) That Are Attributed to Wastewater Effluent in the Grand River

“…Concentration limits for effects of CECs are difficult to set due to the potential synergistic, antagonistic, or additive effects of contaminant combinations [46,47]. Although concentrations have significantly decreased compared to pre-upgrade concentrations, they may still have the potential to cause sub-lethal effects on fish populations [12,48]. In the summer, there is a decrease in the flow in the river and this may be exposing the fishes downstream to a higher concentration of contaminants than in other seasons due to less dilution [49].…”

“…Responses documented at US2 and DS2 may indicate that fish were responding to other stressors upstream, such as non-point sources of agricultural and urban inputs. These inputs should be considered for future studies, as effects can be hard to differentiate from the MWWTP inputs [1,48]. ).…”