Key Takeaways & Executive Findings
- •• • Acetic acid enrichment suppressed PFASs release into overlying water more effectively than oxalic, citric, or lactic acids, with sulfur metabolism contributing 26.06% to PFASs immobilization as determined by ABT modeling. • • Acetic acid reshaped the soil microbial community, enriching sulfate-reducing bacteria and upregulating sulfur reduction gene SULT1A and nitrogen transformation genes nifN, nirI, nthB, promoting sulfate reduction to sulfite and sulfide. • • Sulfite (SO3^2−) oxidation indirectly altered dissolved organic matter (DOM) composition, weakening PFASs–DOM binding and significantly reducing PFASs concentrations in overlying water, as verified under varying sulfur redox conditions. • • The study integrated soil enzyme activity assays, XPS, 3D-EEM, microbial amplicon sequencing, and metagenomics to elucidate the molecular mechanisms, providing a multi-omics framework for assessing PFASs fate in paddy soils.
Abstract
The migration of perfluoroalkyl and polyfluoroalkyl substances (PFASs) at the water–soil interface in paddy fields is a critical determinant of their environmental fate and crop safety. This study investigated the influence of low-molecular-weight organic acids (LMWOAs) on PFASs mobility under waterlogged conditions. Four LMWOAs—oxalic, citric, lactic, and acetic acids—were individually enriched in paddy soils, and the migration of 15 PFASs was monitored. Acetic acid enrichment most strongly suppressed PFASs release into overlying water. Mechanistic analyses using X-ray photoelectron spectroscopy, three-dimensional excitation–emission matrix spectroscopy, microbial amplicon sequencing, and metagenomics revealed that acetic acid reshaped the microbial community, enriching sulfate-reducing bacteria and upregulating sulfur reduction genes (SULT1A) and nitrogen transformation genes (nifN, nirI, nthB). This drove sulfate reduction to sulfite and sulfide. ABT modeling identified sulfur metabolism as the dominant factor controlling PFASs immobilization (26.06% contribution). Experiments under varying sulfur redox conditions confirmed that sulfite (SO3^2−) oxidation indirectly altered dissolved organic matter (DOM) composition, weakening PFASs–DOM binding and reducing PFASs in overlying water. These findings demonstrate that LMWOAs accumulation, particularly acetic acid, can effectively impede PFASs migration at the paddy water–soil interface via microbial sulfur cycling and associated DOM structural changes, offering a potential strategy for PFASs remediation in agricultural systems.
1. Introduction
Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent organic pollutants that accumulate in agricultural soils, particularly in paddy fields, posing risks to crop safety and human health through food chain transfer. The mobility of PFASs at the water–soil interface is governed by complex interactions with soil organic matter, microbial activity, and redox conditions. Low-molecular-weight organic acids (LMWOAs), exuded by plant roots and produced during organic matter decomposition, are ubiquitous in paddy soils and can influence nutrient cycling and contaminant behavior. However, the specific role of LMWOAs in modulating PFASs migration via microbial sulfur metabolism remains poorly understood, limiting the development of targeted remediation strategies.
This study addresses this gap by systematically evaluating the effects of four common LMWOAs—oxalic, citric, lactic, and acetic acids—on the fate of 15 PFASs in waterlogged paddy soils. Using a combination of advanced analytical techniques, including XPS, 3D-EEM, and metagenomics, the research uncovers a novel mechanism whereby acetic acid enrichment stimulates sulfate-reducing bacteria and sulfur cycling, leading to enhanced PFASs immobilization. The findings provide mechanistic insights into the coupled roles of LMWOAs, sulfur metabolism, and DOM composition in controlling PFASs mobility, offering a potential in-situ bioremediation approach for PFASs-contaminated paddy fields.
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LI Lingxuan, HUANG Xinlin, TU Wenqing, WU Jianyi (2026). Molecular Regulation of Sulfur Metabolisms Induced by Low-Molecular-Weight Organic Acids on the Diffusion of Perfluoroalkyl and Polyfluoroalkyl Substances at the Water–Soil Interface in Paddy Fields. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2026011902
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Frequently Asked Questions
What is the relative effectiveness of different LMWOAs in suppressing PFASs migration, and which one is most potent?
Among the four LMWOAs tested (oxalic, citric, lactic, and acetic acids), acetic acid enrichment most strongly suppressed PFASs release into overlying water. This was attributed to its specific stimulation of sulfate-reducing bacteria and upregulation of sulfur reduction genes, leading to enhanced PFASs immobilization.
How does sulfur metabolism mechanistically contribute to PFASs immobilization in paddy soils?
Sulfur metabolism, particularly sulfate reduction to sulfite and sulfide, was identified as the dominant factor (26.06% contribution via ABT modeling). Sulfite oxidation indirectly altered dissolved organic matter (DOM) composition, weakening PFASs–DOM binding and reducing PFASs mobility. This was verified by experiments under varying sulfur redox conditions.
What analytical techniques were employed to elucidate the molecular mechanisms, and how do they complement each other?
The study integrated soil enzyme activity assays, X-ray photoelectron spectroscopy (XPS) for elemental speciation, three-dimensional excitation–emission matrix (3D-EEM) spectroscopy for DOM characterization, and microbial amplicon sequencing plus metagenomics for community and functional gene analysis. This multi-omics approach allowed correlation of microbial sulfur cycling genes with PFASs fate.
What are the practical implications of these findings for PFASs remediation in agricultural soils?
The results suggest that promoting acetic acid accumulation or stimulating sulfate-reducing bacteria could be a viable bioremediation strategy to immobilize PFASs in paddy soils, reducing their bioavailability and crop uptake. However, field-scale validation and cost-effectiveness assessments are needed before implementation.
Are there any potential trade-offs or unintended effects of enhancing sulfur metabolism on soil health or nutrient cycling?
While the study focused on PFASs, enhancing sulfate reduction may affect other biogeochemical cycles, such as nitrogen and carbon. The upregulation of nitrogen transformation genes (nifN, nirI, nthB) suggests potential interactions. Further research is required to evaluate long-term impacts on soil fertility and greenhouse gas emissions.
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