Key Points of the Article

The research background focuses on the environmental risk of perfluorooctanoic acid (PFOA) in soil–plant systems. As a typical perfluoroalkyl substance (PFAS), PFOA is highly water-soluble and bioaccumulative, making it prone to vertical migration into groundwater through rainfall leaching and uptake by plants into the food chain, thereby threatening ecological safety and human health. PFOA concentrations in global soils can reach up to 50,000 μg/kg, and traditional wastewater treatment achieves limited removal efficiency (20–60%), highlighting the urgent need for efficient control strategies. Biochar, with its porous structure and strong adsorption capacity, is considered a promising remediation material; however, its long-term fixation mechanisms for PFOA and plant metabolic responses in dynamic systems remain unclear.

The research highlights include, for the first time, a 360-day greenhouse simulation experiment combined with chemical fractionation and metabolomics to reveal the long-term fixation mechanisms of PFOA by biochar: (1) rice husk biochar (pyrolyzed at 500°C) significantly increased PFOA adsorption capacity (162–260 μg/g), fixing 62.1–94.9% of PFOA in the topsoil (0–10 cm), and reducing leaching rates to <0.09%; (2) for the first time clarified the aging pathway of PFOA under biochar influence — rapidly forming hardly desorbable components (accounting for >25.9% within 90 days) and continuously transforming into non-extractable residues (NERs); (3) metabolomics confirmed that 2% biochar maintained normal lettuce metabolism, while 4% addition further activated flavonoid antioxidant pathways (e.g., quercetin upregulation), enhancing plant stress resistance.

The full text covers a comprehensive assessment of a dynamic soil–lettuce system: (1) experiments involving two soil types (Soil A from Jiangsu and Soil B from Inner Mongolia) and two growing seasons showed that biochar (2%/4% dosage) retained the majority of PFOA in modified topsoil (93.4–94.9%), with only 3.46–6.02% remaining in deeper soil layers; (2) chemical fractionation revealed the fixation mechanism: biochar micropores (141 m²/g) and aromatic structures adsorbed PFOA via hydrophobic and π-π interactions, promoting the conversion from readily desorbable states to hardly desorbable states (proportion increasing to 38.1% within 90 days) and ester-linked NERs (increasing to 12.6% at 360 days); (3) lettuce metabolic responses showed that 2% biochar reduced PFOA bioavailability (root/leaf concentrations <15.5 μg/kg) while maintaining photosynthetic pigment and D-amino acid metabolism homeostasis, whereas 4% biochar additionally upregulated flavonoid synthesis pathways (e.g., isorhamnetin), alleviating oxidative damage (MDA content reduced to 0.015 μmol/g).

The study concludes that biochar has strong long-term remediation potential in soil–plant systems: (1) biochar inhibits PFOA migration through dual mechanisms of physical retention (micropore confinement) and chemical aging (NER formation), reducing leaching by >99% (compared to 57.3% in controls); (2) metabolic regulation shows that a low dosage (2%) of biochar can eliminate PFOA phytotoxicity, while a high dosage (4%) further induces antioxidant defenses; (3) practical applications should consider soil differences (PFOA recovery: 64.9% in Soil B vs. 96.9% in Soil A) and long-term aging effects, providing technical support for remediating PFAS-contaminated farmland.

Illustrated Guide

Fig. 1. PFOA leached from (A) soil A and (B) soil B systems with or without biochar amendment.

Fig. 2. Temporal dynamics of PFOA concentration and relative fraction distribution in topsoil (0–3 cm) of soil A and soil B with or without biochar amendment.

Fig. 3. Vertical concentration and absolute fraction distribution profiles of PFOA in soil cores of soil A and soil B with and without biochar amendment.

Fig. 4. PFOA concentrations in leaves and roots of lettuce grown in soils with or without biochar amendment, harvested on two growing seasons (d 55 and 90 for the first season, d 270 for the second season).

Fig. 5. Photosynthetic pigment (A), MDA contents (B), and Photosynthesis parameters (C∼F) in lettuce leaves for different treatments. The transpiration rate was abbreviated as E; the stomatal conductance was abbreviated as gsw; the net photosynthetic rate was abbreviated as A and the intercellular CO2 concentration was abbreviated as Ci.

Fig. 6. (A) Metabolite intensity changes across treatments compared to the control. Dark blue, red, and gray shades indicate downregulation, upregulation, and no significant change, respectively. Bright blue circles highlight PFOA-related metabolites. (B) Heatmap of 45 differential metabolites across four treatment groups. Asterisks (* or **) denote significant differences from the control (FDR < 0.1 or 0.05). (C) Metabolite set enrichment analysis comparing treatment groups to the control. Red font indicates significant upregulation (FDR < 0.15).