Assessing a polluted river environment by oxidative stress biomarker responses in caddisfly larvae

The effluents of wastewater treatment plants (WWTPs) contain various anthropogenic pollutants that produce negative effects in river ecosystems. Although the oxidative stress responses in aquatic organisms are useful tools for assessing such effects, the responses of aquatic insects to WWTP effluents are poorly understood. This work investigated the responses of antioxidants (superoxide dismutase, catalase, and oxy-radical absorbance capacity), oxidative damage (lipid peroxidation), and energy reserves in caddisfly (Stenopsyche marmorata) larvae caused by the WWTP effluent in two parts of the Chikumagawa River during different seasons. It was found that effluent strongly influenced the antioxidants and oxidative damage and depleted the energy reserves. Hence, both the oxidative stress biomarkers and energy reserves in aquatic insects can be used for assessing the impacts of wastewater effluents. Lipid peroxidation proceeded more intensely at some reference sites than at the effluent-impacted sites, indicating that the use of a single biomarker could lead to a misunderstanding of the effect of pollutant mixtures in field studies. To mitigate this issue, a new reference-impacted approach based on the integrated biomarker response (IBR_RI) method has been developed to assess anthropogenic impacts while considering spatiotemporal fluctuations due to the natural variations in a river system. This approach produced larger IBR_RI values at higher concentrations of anthropogenic pollutants, which correlated with higher ammonium and nitrate concentrations. Therefore, IBR_RI is a potentially useful tool for assessing the impact of WWTP effluents under variable spatiotemporal conditions.