Translocation and biotoxicity of metal (oxide) nanoparticles in the wetland-plant system

Engineered nanoparticles(ENPs)threaten the environment through wastewater discharging.Generally,constructed wetlands(CWs)are efficient methods for ENPs removal.However,the biotoxicity of ENPs on plants in CWs is unclear.Here,we investigated the distribution and bio-impacts of different ENPs(Ag NPs,TiO_(2) NPs,and CeO_(2) NPs)in plants under 5-and 60-day exposure to 1 and 50 mg/L concentrations.Results showed that ENPs appeared in the vascular bundle and mesophyll cell space,which induced the variation in antioxidase activities(e.g.,superoxide dismutase[SOD],peroxidase[POD],and catalase[CAT]activities)as well as overproduction of malondialdehyde(MDA).Additionally,Ag NPs inhibited photosynthesis rate and root activity during two exposure phases.CeO_(2) NPs had positive and negative impacts on plants in 5-and 60-day exposure,respectively.Inversely,TiO_(2) NPs enhanced photosynthesis and root activity under 60-day exposure.Finally,the contents of the C,N,and P elements in plants fluctuated in response to ENPs stress.All results have a positive correlation with the wetland performance under ENPs exposure except for TiO_(2) NPs treatment.Overall,our study systematically reveals aquatic plants'responses to ENPs and provides a reference for building ecological treatment systems to purify wastewater containing ENPs.