Tracking the Spread of PFAS and EOF in Shanghai Soils over a Decade: Insights from 2007, 2012, and 2017

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous contaminants in the soil environment, yet their spatiotemporal distribution and long-term trends remain poorly understood. This study investigated the temporal variations and spatial patterns of legacy and emerging PFAS in soil of Shanghai, China, by analyzing 162 soil samples collected in 2007, 2012, and 2017. The results revealed that sum PFAS concentrations ranged from 110 to 18000 pg/g, with an upward trend over the decade (median levels: 1090, 1190, and 2390 pg/g in 2007, 2012, and 2017, respectively). Long-chain PFAS dominated the contaminant profile with perfluoroalkyl carboxylic acids (PFCAs) (1370-2090 pg/g) consistently exceeding perfluoroalkyl sulfonic acids (PFSAs) (145-466 pg/g). For soil samples collected in 2017, a significant amount of F-53B was noted (median: 148 pg/g) as compared to PFOS (median: 95.7 pg/g) and PFOA (median: 1250 pg/g), highlighting the importance of measuring this compound in the Chinese environment. Spatially, PFAS contamination expanded over time, with the pollution center shifting from urban Shanghai to the southwest, forming a new hotspot in that sector. However, no significant correlation was observed between the PFAS distribution and land use. A mass balance analysis indicated that unidentified organofluorine constituted a substantial proportion of extractable organofluorine (90.1, 92.7, and 88.2% in 2007 (target PFAS 11), 2012 (target PFAS 11), and 2017 (target PFAS 20), respectively), highlighting significant gaps in current contaminant identification. These findings provide critical insights into the long-term dynamics of PFAS in a soil environment and underscore the need for future research to prioritize the characterization of unknown fluorine compounds in environmental monitoring.