Acute and chronic responses of macrophyte and microorganisms in constructed wetlands to cerium dioxide nanoparticles: Implications for wastewater treatment

The extensive release of cerium dioxide nanoparticles (CeO2 NPs) causes increasing potential health and environmental risks. In this study, acute and chronic responses of macrophyte and microorganisms were evaluated following exposure to CeO2 NPs in constructed wetlands (CWs). It was found that most of the CeO2 NPs were retained in the CW substrate, with minor amounts accumulated in plant tissues. Photosynthetic activity experiment indicated that environmentally relevant concentration (1 mg/L) of CeO2 NPs enhanced the net photosynthesis rate of plants, while chronic exposure to a high concentration (50 mg/L) of CeO2 NPs inhibited photosynthesis. The variations of the malondialdehyde (MDA) content and antioxidant enzyme activities in plant tissues revealed that acute exposure to CeO2 NPs induced oxidative stress to plants, while there was no obvious chronic effect. Moreover, the biomass increased marginally under exposure to 1 mg/L CeO2 NPs, whereas exposure to 50 mg/L CeO2 NPs reduced the total biomass of plants by 29%. The release of lactate dehydrogenase (LDH) suggested that chronic exposure to CeO2 NPs inhibited microbial viability. Metagenome and enzymatic activities analyses further revealed that CeO2 NPs significantly changed the microbial community structure and inhibited the activities of dehydrogenase, urease, ammonia monooxygenase, and phosphatase. This resulted in the decline of contaminant removal efficiency. Overall, acute and chronic exposure to CeO2 NPs had multiple effects on macrophyte and microorganisms in CWs, which significantly impacted the treatment performance of the ecological system.