Abstract Atmospheric deposition is a key pathway for diffuse per‐ and polyfluoroalkyl substances (PFAS) pollution, making agricultural soils long‐term PFAS reservoirs. To assess PFAS adsorption and vertical transport in the vadose zone of agricultural soils, the agro‐hydrological model Daisy, including a new implementation of a model accounting for air‐water interface (AWI) sorption, was used. The fate of four PFAS: perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanoic acid, and perfluorobutanoic acid, was simulated in a sandy loam and sandy soil under humid temperate Northern European climate conditions with wet deposition of 1 ng L −1 . Two approaches to solid‐phase sorption were tested: one normalizing Kd to organic carbon ( K OC ) and another incorporating both organic carbon and clay content ( K OC + K clay ). Batch experiments were conducted to determine Kd values for representative soils. A linear isotherm was used due to the low concentrations expected from diffuse pollution. The dataset for modeling was expanded with literature data to cover a broader range of soil types, and the derived K OC and K clay values were used in Daisy. Simulations showed that although the sandy loam had potential for a higher AWI area ( A AWI ), its higher water content often reduced A AWI , especially from autumn to spring, limiting its retention effect. In contrast, in the sandy soil, AWI retention dominated for long‐chain PFAS (PFOS and PFOA). Adsorption to clay resulted in enhanced PFAS retention for all four PFAS in sandy loam. These results highlight the importance of soil‐specific sorption mechanisms for accurately modeling PFAS transport in diffusely polluted agricultural soils.
Jakobsen et al. (Fri,) studied this question.