Iron plaque-mediated control of GenX accumulation by size-dependent α-Fe₂O₃ nanoparticles in hydroponic lettuce

This study elucidates the regulatory role of distinct particle sizes (20 nm and 200 nm) of α-Fe₂O₃ nanoparticles (NPs) on the migration of the emerging perfluorinated substitute hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) in lettuce (Lactuca sativa). Our key findings demonstrate that both sizes of α-Fe₂O₃ NPs significantly enhance iron plaque (IP) formation on root surfaces, leading to markedly reduced GenX accumulation in roots. Specifically, compared to the GenX-only control, treatments with 20 nm and 200 nm α-Fe₂O₃ NPs substantially decreased root GenX content by 82.4% and 79.0%, respectively. A key feature of this study is the discovery of a distinct size-dependent concentration effect that higher concentrations of 20 nm NPs were more effective in promoting IP formation, consequently strengthening the barrier effect against GenX transport into roots. Furthermore, the inhibitory effect of 20 nm NPs on GenX root uptake exhibited a concentration-dependent response, while there was no significant difference in the inhibitory effect on GenX uptake among the different concentrations of 200 nm NPs. Both sizes NPs effectively alleviated GenX-induced plasma membrane damage in roots. Notably, different oxidative stress response patterns were observed between the two NP sizes, 20 nm NPs were associated with a concentration-dependent change in antioxidant enzyme activities, whereas 200 nm NPs showed little effect. Transcriptomic analysis revealed that α-Fe₂O₃ NPs treatment was associated with significant changes in the expression of transport-related genes, including the upregulation of ATP-binding cassette (ABC) transporter and aquaporin-related genes, and the downregulation of organic anion transporter-related genes. These transcriptional responses were associated with the reduced GenX uptake and alleviated damage observed in α-Fe₂O₃ NPs-treated plants.