Impact of dissolved organic carbon on per- and polyfluoroalkyl mobility in activated carbon-amended soils

The remediation of per- and polyfluoroalkyl substances (PFASs) remains a formidable challenge due to their recalcitrance and complex environmental behaviour. Dissolved organic carbon (DOC) plays a critical, yet insufficiently understood role, in modulating PFAS fate, transport, and the efficacy of remediation strategies. This study employs dynamic column experiments under environmentally relevant conditions to elucidate the influence of DOC on the sorption and mobility of fourteen PFASs in reference soils and soils treated with colloidal activated carbon (CAC). Results demonstrate that DOC significantly reduces PFAS sorption in CAC-treated soils, leading to increased aqueous phase concentrations of PFAS. The presence of DOC decreased soil-water partitioning coefficients (K_d values) for all PFASs by an order of magnitude, with long-chain PFASs and fluorotelomersulfonic acids (FTSAs) exhibiting the most pronounced decreases, by as much as 40-fold. Mass balance data showed that DOC increased PFAS elution by up to 10-fold in CAC-treated soils. The PFAS breakthrough curves revealed enhanced PFAS mobility in the presence of DOC, particularly in carbon-amended soils. These results underscore the critical role of DOC in facilitating PFAS transport, with significant implications for their persistence, risk assessment, and the optimization of sorbent-based remediation strategies in organic-rich environments.