Seasonal reduction of trace organic pollutants and biotoxicity in hybrid constructed wetlands

Little research has been performed on reducing trace organic pollutants (TOPs) and their biotoxic effects from contaminated river water in hybrid constructed wetlands (HCWs) at pilot-scale. This study used a combination of chemical and biotoxicity analyses to evaluate the effectiveness of HCWs on the removal of TOPs and the ecological risks in spring and summer. A total of 28 TOPs, including 16 pesticides, 8 pharmaceuticals, and 4 UV filters were detected in influent (contaminated urban river water) of HCWs. The total concentration of TOPs in influent was seasonal and was characterized by higher in spring and lower in summer. Nevertheless, the concentrations of some pesticides were higher in summer than in spring due to agricultural activities in the surrounding area. The HCWs significantly decreased the concentrations of most TOPs and were more effective during spring than summer. The HCWs were also effective for reducing the acute toxicity and genotoxicity, but the effluent still showed non-negligible acute toxicity to luminescent bacteria. Moreover, the ecological risk assessment based on the detected TOPs showed that the HCWs could effectively reduce the risk quotient (RQTotal) of river water to an acceptable level in spring, but not in summer, which was mainly due to the poor removal of chlorpyrifos in the HCWs during summer. Chlorpyrifos had the greatest contribution to RQTotal and was extremely toxic to Daphnia magna. This study helps to explain the important role of HCWs in the removal of TOPs and reducing the ecological impacts of river water on the aquatic environment.