Spatio-seasonal distribution, precursor transformation, and ecological risks of per- and polyfluoroalkyl substances in port sediments: Insights from a subtropical urban harbor

This study conducted a comprehensive investigation of 39 per- and polyfluoroalkyl substances (PFAS) in surface sediments of Kaohsiung Harbor, Taiwan, during both dry and wet seasons. A total of 26 PFAS were detected, with concentrations ranging from 0.155 to 125.4 ng/g dry weight (dw). Higher concentrations were observed in estuaries compared to port entrances, suggesting that riverine discharge is the primary source. Among the PFAS, emerging compounds—particularly 2-(N-methyl perfluoro octane sulfonamido) ethanol (EtFOSE) and its analogs—accounted for 45–99 % of the total PFAS load. Median concentrations of traditional PFAS (PFCAs and PFSAs) were lower than those of emerging PFAS. Seasonal differences and strong correlations between precursors and degradation products (e.g., EtFOSE–NEtFOSAA, 6:2 FTSA–PFHxA) indicated potential in-situ transformation and mobilization during storm events. PFAS concentrations positively correlated with total organic carbon, suggesting organic matter-driven partitioning. Principal component analysis distinguished industrial, consumer product-related, and historical sources. Ecological risk assessment indicated moderate risks in estuarine areas, largely driven by PFOS and precursor compounds. These findings highlight the complex interplay between source input, hydrological events, and geochemical behavior of PFAS urban and harbor systems, offering valuable insights for pollution control, sediment management, and future environmental risk assessments in urbanized harbor systems. • A total of 26 PFAS were detected in sediments with clear spatial and seasonal patterns. • River discharge and heavy rain events drive PFAS input to the port. • Emerging PFAS, notably EtFOSE and EtFOSAA, dominate in sediments. • Precursor-product links reveal active transformation and diverse sources in sediments. • Risk assessment revealed moderate risk at estuaries and low risk at port entrances.