Trade-off of abiotic stress response in floating macrophytes as affected by nanoplastic enrichment

Nanoparticles have been found in large-scale environmental media in recent years, causing toxic effects in various organisms and even humans through food chain transmission. The ecotoxicological impact of microplastics on specific organisms is currently receiving much attention. However, relatively little research to date has examined the mechanisms through which nanoplastic residue may exert an interference effect on floating macrophytes in constructed wetlands. In our study, the aquatic plant Eichhornia crassipes was subjected to 100 nm polystyrene nanoplastics at concentrations of 0.1, 1 and 10 mg L^-1 after 28 days of exposure. E. crassipes can decrease the concentration of nanoplastics in water by 61.42∼90.81% through phytostabilization. The abiotic stress of nanoplastics on the phenotypic plasticity (morphological and photosynthetic properties and antioxidant systems as well as molecular metabolism) of E. crassipes was assessed. The presence of nanoplastics reduced the biomass (10.66%∼22.05%), and the functional organ (petiole) diameters of E. crassipes decreased by 7.38%. The photosynthetic efficiency was determined, showing that the photosynthetic systems of E. crassipes are very sensitive to stress by nanoplastics at a concentration of 10 mg L^-1. Oxidative stress and imbalance of antioxidant systems in functional organs are associated with multiple pressure modes from nanoplastic concentrations. The catalase contents of roots increased by 151.19% in the 10 mg L^-1 treatment groups compared with the control group. Moreover, 10 mg L^-1 concentrations of the nanoplastic pollutant interfere with purine and lysine metabolism in the root system. The hypoxanthine content was reduced by 6.58∼8.32% under exposure to different concentrations of nanoplastics. In the pentose phosphate pathway, the phosphoric acid content was decreased by 32.70% at 10 mg L^-1 PS-NPs. In the pentose phosphate pathway, the phosphoric acid content was decreased by 32.70% at 10 mg L^-1 PS-NPs. Nanoplastics disturb the efficiency of water purification by floating macrophytes, which reduces the chemical oxygen demand (COD) removal efficiency (from 73% to 31.33%) due to various abiotic stresses. This study provided important information for further clarifying the impact of nanoplastics on the stress response of floating macrophytes.