Aqueous fire-fighting foams (AFFF) contain a high variety of per- and polyfluoroalkyl substances (PFAS). The soil at firefighting training sites is therefore highly contaminated with PFAS and acts as a source of contamination for groundwater and the soil biota.Previous studies investigating the leaching of PFAS from contaminated soils have considered model experimental situations, ranging from batch experiments to repacked soil columns. In essence, these experiments disregard processes that are known to contribute to the transport of contaminants in real soil: preferential, gravity-driven flow in soil macropores of biological or physical origin, and colloid-facilitated transport, a mechanism relevant for contaminants having a strong affinity for soil constituents. Actually, the possible transport of PFAS adsorbed onto mobile colloidal soil particles has been overlooked until recently, when 17% of PFOA leached from a previously spiked repacked soil column was found to be adsorbed onto colloidal soil particles.In our study, we further explored the contribution of colloidal particles to the mobility of PFAS in soils during a series of rainfalls simulated on four undisturbed soil columns excavated from an abandoned firefighter training site. As both rainfall intensity and the duration of the dry period before a rain have been found to affect the mobilization of colloidal soil particles, we studied the impact of these factors on PFAS leaching.The four cores had contrasting hydrodynamic behavior, ranging from matrix flow to preferential macropore flow. Although their mobility in soil is expected to be low, long chain PFAS were present in the leachates, both in the liquid phase and adsorbed to soil particles. Surprisingly, colloid-mediated leaching of PFAS was more important in cores where water transfer was dominated by matrix-flow. Regardless of the hydrodynamic behavior, the experimental results suggest that the leaching of PFAS molecules with C-chain length ≤ 8 was controlled by diffusion.Overall, these results show that quantifying PFAS concentration in both the liquid and the colloidal-phase —in the leachates of transport experiments or in groundwater— will help understand the contribution of soil particles to the transport of PFAS in the vadose zone.< Réduire