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

Overview

This study challenges the established paradigm of PFAS environmental assessment by demonstrating that PFAS species form nanoscale clusters at dissolved organic matter interfaces rather than existing in molecularly dispersed states. Through in situ atomic force microscopy, the research characterizes the formation dynamics and mechanistic drivers of PFAS nanoclustering across diverse molecular structures, and establishes that this aggregation phenomenon significantly reduces plant phytotoxicity through diminished bioaccessibility.

Methods and approach

In situ AFM techniques were developed and deployed to directly visualize PFAS nanocluster formation at DOM interfaces. Intermolecular interaction analysis quantified binding forces between PFAS molecules and DOM functional groups across multiple PFAS classes including nonionic, anionic, cationic, and zwitterionic species. Plant exposure experiments utilized rice seedlings to assess phytotoxic responses to nanoclustered versus molecularly dispersed PFAS formulations. Uptake quantification and root surface localization were examined to elucidate mechanisms of toxicity mitigation.

Results

A strong inverse correlation (R = -0.983, P = 0.017) was established between nanocluster size and abundance across diverse PFAS structures, demonstrating that stronger DOM-PFAS binding interactions yield numerous small nanoclusters while weaker interactions produce larger, sparser aggregates. In situ AFM visualizations confirmed dynamic nanocluster formation at the DOM interface. Plant exposure experiments demonstrated universal mitigation of PFAS phytotoxicity in rice seedlings when PFAS existed in nanoclustered form compared to molecularly dispersed states. Nanoclustered PFAS exhibited significantly reduced root uptake, with sequestration occurring at root surfaces functioning as a physical barrier to translocation.

Implications

The identification of widespread DOM-driven PFAS nanoclustering fundamentally alters the conceptual framework for PFAS environmental fate and toxicological assessment. Current risk evaluations premised on molecular dispersal assumptions may substantially overestimate bioavailability and phytotoxic hazards in DOM-rich environmental compartments. The mechanism by which DOM functional groups regulate nanocluster morphology suggests that DOM composition and concentration constitute critical variables governing PFAS bioaccessibility in natural systems. These findings necessitate revision of existing PFAS exposure models and environmental quality standards to account for nanoscale aggregation phenomena. The nanocluster-driven phytotoxicity mitigation mechanism identifies a natural attenuation process that may inform remediation strategies. Further investigation into PFAS nanocluster dynamics across soil, sediment, and aquatic systems is warranted to establish the ecological generality and persistence of this interface phenomenon under varying environmental conditions.