Physiological Responses and Absorption Removal Effects of Three Floating Macrophytes to Polystyrene Nanoplastics Pollution

Microplastics exert toxic effects on aquatic plants, thereby impacting ecosystem functions and services. Currently, research on the effects of nanoplastics on aquatic plants has mainly focused on algae, while floating macrophytes have received less attention. To investigate the physiological responses and uptake and accumulation effects of floating macrophytes to polystyrene nanoplastics (PS-NPs), we exposed Limnobium laevigatum, Pistia stratiotes and Eichhornia crassipes to 0.1, 1 and 10 mg·L−1 of PS-NPs (20/100 nm) for 45 days. The results showed that, in general, with increasing concentration and exposure time, the three plant species exhibited a decrease in chlorophyll content, a decline in root activity, an increase in cell membrane permeability and an up-regulation of antioxidant enzyme activities. Meanwhile, the contents of proline, soluble sugars and soluble proteins showed dynamic changes. These findings indicate that under PS-NPs stress, the plants suffered structural damage and they alleviated oxidative injury and maintained osmotic balance by actively accumulating osmoregulatory substances and up-regulating antioxidant enzyme activities. Furthermore, the effects of uptake and accumulation PS-NPs differed among species. At low concentration levels, Limnobium laevigatum exhibits higher uptake and accumulation potential, while at high concentrations, Pistia stratiotes demonstrates greater uptake and accumulation potential.