Suspended Particulate Matter Mediates PFAS Source-to-Sink Transport and Multiphase Partitioning During Extreme Hydrological Events.

The mechanisms governing suspended particulate matter (SPM)-mediated partitioning of per- and polyfluoroalkyl substances (PFAS) at water-solid interfaces during extreme hydrological events remain poorly understood. This study elucidates the spatiotemporal source-sink dynamics and multiphase partitioning mechanisms of SPM-mediated PFAS before, during, and after flood events. The results identified SPM as a critical reservoir for C8-C11 PFAS. During floods, SPM functions as an exogenous carrier, transporting surface-derived PFAS into rivers via pump station overflows and exhibiting strong flocculation and deposition tendencies. In the post-flood period, resuspended sediments become the dominant source of SPM, acting as an endogenous reservoir that continuously releases PFAS into the dissolved phase. During non-flood periods, point-source-derived SPM promotes deposition of PFAS into sediments. Conversely, in the absence of point-source pollution, SPM generated through sediment resuspension facilitates the remobilization of sediment-bound PFAS into the dissolved phase. A flood-inclusive log Kd-SPM model combined with SHAP analysis demonstrated that environmental factors accounted for 48.1% of PFAS partitioning behavior, lower than that of intrinsic molecular properties (51.9%). Scenario simulations further revealed that PFAS distribution between the dissolved and SPM phases is governed by the synergistic interaction of molecular characteristics and external environmental drivers. Among these, water temperature and cumulative rainfall-runoff volumes over 6 days prior to sampling (T6) are key environmental factors influencing partitioning behavior. Collectively, these findings provide critical scientific insight into the environmental source-sink processes and multiphase partitioning behavior of SPM-mediated PFAS under extreme hydrological conditions.