Basin-scale occurrence and seasonal behavior of per- and polyfluoroalkyl substances (PFAS) in a cold-region river system: The Songhua river basin, Northeast China

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants frequently detected in surface waters, yet their behavior in cold-region river basins remains insufficiently characterized. In this study, 26 PFAS were measured in river water and sediments at 27 sites across the Songhua River Basin, Northeast China, during warm and cold seasons. The objectives were to characterize PFAS occurrence, evaluate spatial and seasonal variability at the basin scale, examine sediment–water partitioning behavior, and conduct a screening-level risk prioritization. PFAS were widely detected in both environmental compartments, with total concentrations in river water ranging from 5.66 to 110 ng/L. Short-chain PFCA and fluorotelomer sulfonates, particularly PFBA and 6:2 FTS, dominated across sites and seasons. Sediment concentrations were generally low in warm season but increased approximately 5 times in the cold season, although total burdens showed limited differences among upstream, midstream, and downstream reaches. Spatial variability was more evident for individual compounds than for summed concentrations, indicating localized accumulation patterns. Partitioning analysis showed that short-chain PFCA exhibited unexpectedly high and variable log K_d values, while long-chain PFCA displayed a more regular increase in log K_d with carbon chain length. Positive matrix factorization (PMF) resolved five major source factors. Risk prioritization combining hazard potential and exposure highlighted 6:2 FTS and PFOS as compounds of concern in both seasons. Overall, this study improves understanding of PFAS behavior in cold-region river systems and supports the need for multi-season assessments.