Beyond Molecules: In Situ Imaging Unveils DOM-Driven PFAS Nanoclusters with Mitigated Phytotoxicity

The environmental fate and plant toxicity of per- and polyfluoroalkyl substances (PFAS) have been assessed based on their presumed molecularly dispersed state. Here, we overturn this paradigm by reporting a widespread yet overlooked nanoscale phenomenon. Using a newly established suite of in situ atomic force microscope (AFM) techniques, we first visualized the dynamic formation of PFAS nanoclusters at the interface of naturally extracted dissolved organic matter (DOM). We further deciphered the underlying mechanism by probing intermolecular interactions, demonstrating that strong binding forces between PFAS molecules and specific DOM functional groups yield numerous small nanoclusters, whereas weaker interactions result in larger, sparser nanoclusters. This mechanism is quantified by a strong negative correlation (R = -0.983, P = 0.017) between nanocluster size and abundance across diverse PFAS structures (nonionic, anionic, cationic, zwitterionic). Crucially, plant exposure experiments demonstrate that this nanocluster formation universally mitigates PFAS phytotoxicity in rice seedlings. Compared to its molecularly dispersed state, the nanoclustered PFAS exhibit significantly reduced uptake, sequestered on root surfaces as a physical barrier. This work identifies the DOM-induced nanoclustering as a critical interface process that governs the bioaccessibility and risks of PFAS, thereby offering a transformative perspective for their environmental assessment and remediation.