Biological responses to contaminants in darters (Etheostoma spp.) collected from rural and urban regions of the Grand River, ON, Canada

Urban and agricultural activities may introduce chemical stressors, including contaminants of emerging concern (CECs) and current use pesticides (CUPs) into riverine systems. The objective of this study was to determine if fish collected from various sites in the Grand River, ON, Canada show biomarkers of exposure to these classes of contaminants, and if the biomarker patterns vary in fish collected from urbanized and agricultural sites. Female rainbow darters (Etheostoma caeruleum) and female fantail darters (Etheostoma flabellare) were collected from the Grand River in June, 2014 for biomarker analysis from two urbanized sites and three agricultural sites. Over the same period of time, Polar Organic Chemical Integrative Samplers (POCIS) were deployed for 2 weeks at each site to monitor for the presence of CUPs and CECs. Data on the liver somatic index for darters indicate site-specific differences in this condition factor (p < 0.05). Significant differences in the levels of thiobarbituric acid reactive substances (TBARS) in gill tissue (p < 0.05) of darters collected from the various sites indicate site-specific differences in oxidative stress. The activities of ethoxyresorufin-O-deethylase (EROD) in the liver tissue of rainbow darters were significantly different between sites (p < 0.05), indicating differences in exposure to chemicals that induce or inhibit CYP450 1A metabolic activity. Finally, acetylcholinesterase (AChE) activity in brain tissue was significantly different between rainbow darters collected from rural and urban sites (p < 0.05). These data showing different impacts from chemical inputs related to land uses in the watershed may be useful in developing mitigation strategies to reduce impacts on fish and other aquatic organisms in receiving environments.