Measurement and modelling of sorbent-amendment impacts on seasonal and long-term PFAS transport through unsaturated...

This study investigated the effectiveness of waste-derived biochar amendments and commercial sorbents in stabilizing PFAS-spiked soils in field-scale in situ lysimeters over nearly one year under seasonal changes in Sweden. All tested sorbent amendments reduced average PFAS leachate concentrations by over 99 % for long-chain and 83-96 % for short-chain PFCAs and PFSAs, even under fluctuating water levels. Sewage sludge-derived biochar performed comparably to tested commercial sorbents. Long-chain PFAS remained evenly distributed in the soil, while short-chain PFAS accumulated in lower sections due to higher mobility. Higher PFAS leaching occurred in the spring due to snowmelt events and during summer months due to heavy rainfall. A 1D-transport model was developed to derive retardation factors and identify the fraction sorbed at the air-water interface before and after treatment, as well as PFAS leaching over 100 years. In no-sorbent lysimeters, 30-65 % of perfluorooctane sulfonate (PFOS) was retained at the air-water interface, with seasonal variations of up to 20 %. Inclusion of the sorbent reduced air-water interface effects, as solid-phase sorption became dominant. Over 100 years, nearly all PFOS are predicted to leach from no-sorbent lysimeters, while less than 1 % will leach from soil treated with sewage sludge- derived biochar. Such sorbent amendments can be integrated into ongoing remediation projects.