Reducing PFAS Mobility and Plant Uptake in Agricultural Soils via Biochar Amendment

Biochar amendment represents a promising in situ strategy for per- and polyfluoroalkyl substances (PFAS) mitigation, yet its performance under realistic field conditions remains poorly understood. Here, we evaluated PFAS fate in soil–plant–leachate systems under irrigation-water- and biosolids-derived contamination settings. Pinewood biochar (PBC) significantly (P = 0.05) reduced PFAS leaching and plant uptake more so than biosolids-derived biochar (BBC), driven by its higher point of zero charge (PZC), C/H and C/O ratios, and specific surface area, with the strongest mitigation observed for PFHxS and PFOA. Air oxidation and iron oxide modification of PBC further suppressed short-chain PFAS accumulation in plants. Among the tested materials, air-oxidized PBC exhibited the highest mitigation efficiency (ME), reducing leaf bioconcentration factors (BCFs) of PFHxS and PFOA by 1328.5-fold and 285.3-fold, respectively, and suppressing perfluorobutanoic acid (PFBA) accumulation by 150.8-fold, attributable to enhanced surface area, electrostatic attraction, and hydrogen-bonding interactions. Dissolved organic matter (DOM) released from biosolids increased the mobility of PFBA, PFBS, PFOA, and PFHxS while reducing the bioavailability and translocation of PFNA and PFOS. Collectively, this work demonstrates that PFAS mitigation by biochar is governed by molecular structures, input pathways, and DOM interactions, providing mechanistic insight for targeted biochar deployment in PFAS-impacted agroecosystems.