| 04 Dec 2025
Controlled chamber formation of per- and polyfluoroalkyl substances (PFAS) aerosols with Pseudomonas fluorescens: size distributions, effects, and inhalation deposition potential
Abstract. Per- and polyfluoroalkyl substances (PFAS) are recognised as atmospheric contaminants, yet processes governing their aerosol formation, size distribution, and interactions with atmospheric particle surfaces remain unknown. We investigated aerosolisation and size-resolved behaviour of 25 PFAS covering short-, medium-, and long-chain perfluoroalkyl carboxylic acids (PFCA), perfluoroalkane sulfonates, fluorotelomer sulfonates and emerging alternatives. Experiments were conducted under controlled chamber conditions using a water–organic solvent system, in the absence/presence of the model bacterium Pseudomonas fluorescens seed, representative of wastewater-impacted environments. Most PFAS exhibited unimodal mass–size distributions peaking at 0.3 µm, indicating dominant association with the fine mode. Sulfonated PFAS showed broadly similar aerosol-phase concentrations regardless of carbon-chain length, whereas PFCA displayed increasing aerosolisation with chain length. Perfluorooctane sulfonic acid (PFOS) showed additional ultrafine enrichment, 6:2 fluorotelomer sulfonate (6:2 FTS) and sodium 4,8-dioxa-3H-perfluorononanoate (NaDONA) exhibited broader size profiles, suggesting compound-specific effects linked to volatility and interfacial behaviour. Pseudomonas fluorescens seed did not enhance PFAS aerosol concentrations through condensation or heterogeneous uptake onto bacterial particles or shift in modal diameters, and no enrichment was observed at bacterial size mode, indicating limited PFAS-bioaerosol association under the tested conditions. Multiple-Path Particle Dosimetry (MPPD) modelling based on the measured size distributions predicted substantial deposition of the aerosol-bound PFAS in the pulmonary region, particularly for compounds enriched in ultrafine particles. Our findings indicate that PFAS aerosol behaviour in mixed-solvent systems is controlled primarily by physical droplet generation and evaporation, with implications for airborne transport and inhalation exposure from contaminated aqueous sources.
Competing interests: The corresponding author is one of the associate editors of the ACP
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General comments
This study represents a highly novel and scientifically valuable attempt to experimentally investigate interactions between atmospheric PFAS and bioaerosols (Pseudomonas fluorescens) under controlled chamber conditions. However, there are substantial limitations in how the wastewater treatment plant (WWTP) environment is represented by the experimental design, particularly the use of a 40:60 water–methanol mixed solvent and aerosol generation via a Collison nebulizer.
The reduced surface tension resulting from the presence of methanol creates a physical environment that differs markedly from natural bubble-bursting processes in wastewater aeration basins. As a consequence, the aerosol size distributions observed in this study appear to be strongly governed by the imposed experimental conditions rather than by intrinsic physicochemical properties of the PFAS compounds themselves. The authors are clearly aware of these limitations and have discussed them to some extent, which is appropriate.
The interpretation of the MPPD modeling results raises concerns. The authors conclude that the largely similar size distributions observed across most PFAS, regardless of molecular structure, are a consequence of physical constraints imposed by the nebulization process. If this is indeed the case, then the resulting modeled respiratory deposition should likewise be viewed primarily as an artifact of the experimental setup, rather than as compound-specific behavior. In this context, the subsequent discussion of differential inhalation risks among individual PFAS appears insufficiently justified.
I therefore encourage the authors to more critically acknowledge the dominant role of the experimental configuration in shaping the results and to revise the scope and framing of their interpretation accordingly. On this basis, I recommend Major Revision.
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