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Size- and charge-dependent phytotoxicity of polystyrene nanoplastics to Vallisneria natans
Summary
Scientists found that tiny plastic particles (nanoplastics) harm underwater plants, and the smallest, positively-charged particles caused the most damage—stunting growth, disrupting photosynthesis, and even lodging inside plant roots. This matters because these plants are a key part of freshwater ecosystems, and their decline could ripple through waterways that eventually connect to our drinking water and food supply, adding to growing evidence that plastic pollution affects life at every level, from plants to potentially humans.
The pervasive contamination of nanoplastics (NPs) in aquatic ecosystems has raised significant ecological concerns, yet their size- and charge-dependent effects on submerged macrophytes remain poorly understood. This study systematically investigated the phytotoxicity of polystyrene nanoplastics (PS-NPs) with different sizes (30 nm and 300 nm) and surface functional groups (-NH and -COOH) on Vallisneria natans (V. natans) for a 30-day exposure period. Results showed that all PS-NPs treatments inhibited plant growth and reduced photosynthetic pigment content, with the 30 nm PS-NH group exhibiting the most pronounced toxicity. Specifically, 30 nm PS-NH exposure led to a 29.5% reduction in biomass compared to the control group and a significant decline in maximum photochemical efficiency (Fv/Fm), non-photochemical quenching (NPQ), and photochemical quenching (qP), indicating severe impairment of Photosystem II. Microscopic observations via SEM and TEM revealed that PS-NPs formed "particle-microbe complexes" on leaf surfaces and that 30 nm particles effectively translocated into root vascular bundles, inducing chloroplast deformation and starch granule accumulation. Furthermore, PS-NPs stress triggered an oxidative burst, evidenced by elevated HO and MDA levels despite the activation of antioxidant enzymes (SOD, CAT, POD, and APX). 16S rDNA sequencing further demonstrated that PS-NPs markedly restructured the epiphytic bacterial community, altering the ecological balance of leaf-associated microorganisms. Collectively, this study highlights that smaller and positively charged PS-NPs pose the greatest risk to submerged macrophytes, driving physiological impairment and microecological shifts. These findings provide critical insights into the biological impacts and environmental risks of PS-NPs in freshwater ecosystems.