Polystyrene nanoplastics act as environmental buffers to alleviate the ecotoxicity of PFOS and alternative F-53B toward the submerged macrophyte Elodea nuttallii.

The increasing co-occurrence of polystyrene nanoplastics (PS-NPs) and per- and polyfluoroalkyl substances (PFAS) in aquatic environments poses potential risks to submerged macrophytes and their associated microbial communities. This study investigated the individual and combined effects of PS-NPs (1 mg L⁻¹), perfluorooctane sulfonate (PFOS, 100 μg L⁻¹), and its chlorinated alternative F-53B (100 μg L⁻¹) on the submerged macrophyte Elodea nuttallii (E. nuttallii) during a 30-day exposure. PS-NPs alone showed no significant inhibition of plant growth but slightly enhanced chlorophyll content and antioxidant enzyme activities. In contrast, PFOS and F-53B significantly reduced plant biomass by 26.09% and 33.44%, respectively, decreased photosynthetic pigments, induced oxidative stress, and caused severe ultrastructural damage, with F-53B exhibiting greater phytotoxicity than PFOS. Notably, co-exposure with PS-NPs markedly alleviated PFAS-induced toxicity, primarily through adsorption-mediated reductions in PFAS bioavailability and bioaccumulation. Meanwhile, E. nuttallii maintained effective nutrient (TN, NH₄⁺-N, and TP) removal despite pollutant exposure, indicating strong ecological resilience. PS-NPs also reshaped the epiphytic microbial community by enriching stress-tolerant taxa, including Proteobacteria, Actinobacteriota, and Firmicutes, while mitigating the inhibitory effects of PFAS on sensitive microorganisms. Overall, these findings demonstrate the dual role of PS-NPs as both carriers and mitigators of PFAS toxicity, providing new mechanistic insights into the environmental behavior, ecological risks, and interactions of coexisting emerging contaminants in aquatic ecosystems.