Pilot study on the mitigation of PFAS bioavailability to plants using biochar as a soil amendment

Authors: HU, JIAJUI - University Of California, Riverside; LI, ZHENG - University Of California, Riverside; Schmidt, Michael; Ibekwe, Abasiofiok; Ashworth, Daniel

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/4/2025
Publication Date: 4/15/2026
Citation: Hu, J., Li, Z., Schmidt, M.P., Ibekwe, A.M., Ashworth, D.J. 2026. Pilot study on the mitigation of PFAS bioavailability to plants using biochar as a soil amendment. Presented at the Northeast Waste Management Official's Association (NEWMOA), The Science of PFAS: Public Health and the Environment Conference, April 14-16, 2026, Worcester, MA

Interpretive Summary:

Technical Abstract: Per- and polyfluoroalkyl substances (PFAS) are persistent, non-degradable chemicals that threaten ecological health and food safety in agricultural systems. Widespread contamination arises from the use of PFAS-polluted wastewater for irrigation and land application of polluted-biosolids, resulting in PFAS accumulation in soil and subsequent uptake by crops. Biochar, a cheap and readily available material produced from biomass through pyrolysis, has been recognized as an efficient and sustainable soil amendment to mitigate PFAS bioavailability; however, practical implementation remains challenging due to a lack of pilot-scale studies, limited understanding of biosolid-biochar-soil-plant interactions, and reduced effectiveness for short-chain PFAS. This pilot study aimed to clarify the mechanisms by which biochar mitigates PFAS accumulation in plants and to explore strategies for enhancing its effectiveness. Large-pot experiments (50 kg sandy soil per pot) were conducted focusing on six PFAS: three perfluorocarboxylates (PFBA, PFOA, PFNA) and three perfluorosulfonates (PFBS, PFHxS, PFOS), representing short- to long-chain compounds. Two PFAS sources—irrigation wastewater (100 ng/mL) and biosolids (100 ng/g dry weight)—were compared. Two types of biochar—biosolid-derived biochar (BBC) and pine biochar (PBC)—were separately applied to the sandy soils. Spinach was chosen as the model crop and cultivated outdoors in California from May to June 2025, with daily irrigation. PFAS concentrations in dried leaves and roots were quantified using LC-MS/MS, and the mitigation efficiency of biochar was assessed by comparing the bioconcentration factor ratio (BCFcontrol/BCFbiochar). Mitigation was stronger for biosolid-derived PFAS compared to irrigation-derived PFAS. For example, biochar treatments decreased BCFs in leaves by 1–2-fold for irrigation sources but by 2–200-fold for biosolid sources, likely due to longer adsorption times and enhanced PFAS–biochar interactions in biosolid matrices. BBC and PBC effectively reduced accumulation of PFBA, PFOA, PFNA, PFHxS, and PFOS in leaves and roots, with minimal influence on PFBS. Moreover, PBC yielded higher mitigation efficiency than BBC for long chain PFAS due to higher specific surface area and point of zero charge, and lower O/C ratio. The interactions among biosolids-soil-biochar were investigated by varying the mixing sequence: PFAS-contaminated biosolids were either pre-mixed with BBC for 7 days prior to soil incorporation (premix) or mixed with soil and BBC simultaneously. Premixing enhanced mitigation of long-chain PFAS but diminished mitigation of short-chain PFAS, indicating competitive adsorption in which long-chain PFAS preferentially occupy biochar sorption sites. In addition, PBC was post-heat treated to enhance its capacity to retain short-chain PFAS such as PFBA and PFBS. Compared with untreated PBC, this modification significantly improved mitigation efficiency, increasing the capacity (BCF_control/BCF_biochar) for PFBS from 1.5× to 3.9× and for PFBA from 1.6× to 50×, indicating that post-heat treatment is an effective strategy for short-chain PFAS control. This work provides a pilot-scale demonstration of biochar-mediated PFAS mitigation under realistic soil conditions. The results highlight biochar as a practical and scalable solution for reducing PFAS bioavailability from both irrigation water and biosolid sources, supporting safer crop production and sustainable management of contaminated agricultural soils.