Column experiments to investigate the fate of per- and polyfluorinated alkyl substances (PFAS) in the subsurface during soil stabilisation with activated carbons.

Remediation of sites contaminated with per- and polyfluorinated alkyl substances (PFAS) is key to reduce the contamination of drinking water sources and human exposure. PFAS use is increasingly being restricted worldwide resulting in reduction of point sources; however, legacy plumes are still posing a threat due to the persistence of these chemicals against degradation. One of the most widely studied soil remediation techniques for PFAS is stabilisation (fixation) which results in the long-term entrapment of the contaminants with the addition of activated carbons in the subsurface, aiming to restrict their leaching from soil to groundwater. In relation to this, the aim of this study was to identify the leaching behaviour of various PFAS in a treatment scenario using activated carbons. Silt loam soil sampled from central Sweden was tested, as well as a mixture of the soil with powdered activated carbon (PAC) and colloidal activated carbon (CAC) at 4% w/w concentration. Spiked groundwater was prepared with 21 PFAS, at a concentration of 2.4 μg mL^-1 for each individual compound. The leaching of PFAS from the solid phase was simulated using column experiments in saturated conditions. Additionally, the partitioning behaviour of the substances with increasing concentration was studied through the definition of sorption isotherms for each matrix. For this purpose, batch-shaking tests were performed, and sorption isotherms were defined by fitting the data with the Freundlich and Langmuir models, using five concentration points in the range of 0.1-100 μg mL^-1 for the sum of PFAS. Analysis of the compounds was conducted using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Preliminary results from the batch tests show significantly increased sorption in soil amended with activated carbons compared to the untreated soil and a better overall performance of CAC compared to PAC. The study is expected to provide essential information on the efficiency and longevity of stabilisation with activated carbons as a remediation strategy for PFAS-contaminated soils.