Urban soils encounter more severe per- and polyfluoroalkyl substance contaminations and associated exposure risks

Per- and polyfluoroalkyl substances (PFASs), as persistent hazardous contaminants, have been increasingly identified in diverse environmental media. To date, however, information regarding the distribution and risks of PFASs in soils, particularly across urban-rural gradients, remains scarce. Therefore, this study performed high-resolution monitoring of PFASs at 119 sampling sites in the Qinhuai River Basin. The findings revealed that 18 targeted PFASs were identified in all soil samples, except for 6:2 Cl-PFESA, which exhibited a detection frequency of 78.2 %; concurrently, legacy PFASs remained the predominant pollutants. Elevated concentration levels were observed in urban soils, with C5, C8-C13 PFCAs, C6-C8 PFSAs, 6:2 Cl-PFESA, and HFPO-TA identified as the main contributors. Variogram analysis found a robust spatial structure of PFASs with respect to geographic distance, indicating that the sampling design can accurately capture basin-scale patterns and identify localized hotspots (e.g., sites #64, #45, and #31). The geographic heterogeneity of soil PFASs was significantly regulated by f_oc, CEC, dust particles above 10 μm, and per capita GDP. In addition, seven sources were identified as explanatory variables for PFASs, exhibiting notable variation in their contributions between urban and rural soils. Legacy and emerging fluoropolymer-related activities dominated urban soil contamination, while firefighting and metal plating were the primary contributors to rural soil pollution. The dietary ingestion constituted the primary exposure pathway for soil PFASs, with children and urban residents possibly encountering a greater exposure risk; their estimated daily intake for individual PFASs varied from 0.01 to 30.1 ng/kg bw/day. This work provides critical insights into the occurrence and risks of PFASs in urban-rural gradient soils and highlights the importance of trade-offs in sampling strategies.