Study on the regulatory effect of biochar-based materials on the migration and accumulation of perfluoroalkyl substances in paddy soil-water-plant systems

Perfluoroalkyl substances (PFAS), as persistent emerging contaminants, can migrate into rice systems through the soil-water interface (SWI) during irrigation, threatening food security and human health. However, the diffusion characteristics of PFAS at the SWI under carbon-based material regulation and their solute exchange kinetics remain unclear, particularly the quantitative differences between short-chain (PFBA) and long-chain (PFOA) PFAS behaviors. To address this, this study innovatively integrated molecularly imprinted polymer-diffusive gradients in thin films (MIP-DGT) and high-resolution pore water sampling (HR-Peeper) techniques to systematically investigate the regulatory mechanisms of control (WBC), rice husk biochar (RBC), and montmorillonite-modified biochar (MBC) on the migration and accumulation of PFBA and PFOA in the paddy sediment-water-plant system. The results showed that in WBC-treated soil, the surface CDGT-PFBA and CDGT-PFOA concentrations were 6.76 ± 1.44 ng L−1 and 7.21 ± 2.14 ng L−1, respectively, while biochar treatments significantly inhibited PFAS migration to deeper layers. Compared to WBC, RBC reduced CDGT-PFBA and CDGT-PFOA in deeper soil layers by 32.80 % and 87.50 %, respectively, with modified biochar exhibiting even stronger retention effects. The constructed 2D-DIFS (DGT-induced fluxes in soils/sediments) model indicated that PFAS re-supply capacity (R-value) from soil to pore water declined with irrigation cycles. PFBA had shorter response times (Tc) and higher mobility, while PFOA was more immobilized due to higher adsorption rate (k−1) and partition coefficient (Kd). Notably, compared to WBC, RBC reduced PFBA and PFOA accumulation in rice organs by 24.21 ~ 26.26 %, confirming the dual role of carbon-based materials in altering PFAS interfacial behavior and thereby inhibiting plant uptake. This study clarifies PFAS migration and biotransport responses to carbon-based materials under irrigation, supporting strategies to mitigate PFAS contamination in farmland.