Stabilizing per- and polyfluoroalkyl substances (PFAS) through amending an adsorbent to contaminated soil planted with alfalfa.

The persistence and toxicity of per- and polyfluoroalkyl substances (PFAS) in soils pose significant environmental and human health risks. Although various chemical, biological, and physical PFAS remediation technologies for soils have been developed, they often suffer from high costs, energy demands, and the generation of secondary contamination by mobilizing short-chain PFAS or causing desorption from soils. As an alternative, stabilization strategies that promote the formation of bound residues (BR) to retain PFAS in soils have gained momentum. However, binding short-chain PFAS and ensuring long-term stability remain major challenges. In this study, we evaluated six adsorbents, including four existing commercial products (powdered activated carbon (PAC), RemBind 100×, two types of biochar) and two newly synthesized materials (modified PAC (MPAC) and biosorbent aerogel), for their ability to stabilize eight PFAS in contaminated soils cultivated with alfalfa (Medicago sativa). The results showed that high-affinity adsorbents such as RemBind, MPAC, PAC, and the two biochars lowered total PFAS water leachability by 77.0-98.5 % and alfalfa uptake by 96.1-99.9 % compared to the unamended control. In contrast, the biosorbent exhibited limited stabilization capacity. Alfalfa cultivation generally reduced water-leachable PFAS but had mixed impacts on basic methanol-extractable fractions, highlighting the complicated interactions in the plant-soil-PFAS-amendment systems. Analysis of hydrolysable and non-hydrolysable BR revealed that adsorbent type strongly influenced the percentage and structure of BR of PFAS in soils. Overall, the findings point to a practical solution for managing soils contaminated by PFAS. The feasibility of this approach warrants to be evaluated in field scale over long period of time.