Combined Effects of Polystyrene Nanoparticles and Cadmium on Freshwater Submerged Macrophyte Vallisneria natans: Bioaccumulation, Chlorophyll Content, and Oxidative Stress

The coexistence of nanoplastics (NPs) and heavy metals in aquatic ecosystems poses a potential threat to aquatic organisms and has garnered considerable attention. However, the combined effects of NPs and heavy metals on submerged macrophytes remain poorly understood. Here, we investigated the bioaccumulation and toxicity of polystyrene nanoparticles (PSNPs) and cadmium (Cd) in the freshwater-submerged macrophyte Vallisneria natans following 14 days of individual and combined exposures. Results indicated that V. natans exhibits a high capacity for absorbing both PSNPs and Cd. Under 5 µg/L Cd exposure, the presence of PSNPs increased Cd accumulation from 2.50 µg/g to 3.27 µg/g. Moreover, the co-presence of Cd significantly enhanced PSNPs accumulation, rising from 4.36 µg/g (PSNPs alone) to 84.49 µg/g. Total chlorophyll content decreased to 34.72% of control values at 5 μg/L Cd. However, the addition of PSNPs did not significantly alter the total chlorophyll content. Compared to Cd exposure alone, the addition of PSNPs led to a significant decrease in superoxide dismutase (SOD) and peroxidase (POD) activities. At the same time, malondialdehyde (MDA) content increased significantly, indicating a pronounced oxidative damage. Additionally, owing to its relatively high bioaccumulation capacity for both PSNPs and Cd, V. natans could be considered a promising candidate for phytoremediation efforts targeting combined pollution from PSNPs and Cd. The findings of this study contribute to a deeper understanding of the adverse effects arising from the co-exposure of NPs and heavy metals on aquatic ecosystems while offering valuable insight for developing future phytoremediation strategies addressing co-pollution by NPs and heavy metals in freshwater environments.