Distribution and sources of emerging and legacy per- and polyfluoroalkyl substances (PFAS) in the East China Marginal Seas: Influence of terrestrial input and hydrography

The replacement of legacy PFAS by emerging alternatives is increasingly prevalent. Due to the unique geographical and complex hydrological conditions of marginal seas, investigating the environmental behaviors of both legacy and emerging PFAS in these regions is necessary. In this study, seawater sampling was conducted in the East China Marginal Seas during 2020 and 2021. Among the 32 PFAS analyzed, 8 (2020) and 9 (2021) were detected in over 30% of samples, with mean concentrations of 4.93±4.17 ng/L and 13.0±13.2 ng/L, respectively. Notably, hexafluoropropylene oxide trimer acid (HFPO-TA, 5.02±4.95 ng/L) and perfluorooctanoic acid (PFOA, 6.04±7.73 ng/L) had comparable concentrations and accounted for 39% and 46% of ΣPFAS, respectively, indicating an increasing substitution of legacy PFAS by emerging alternatives. The Yangtze River estuary showed a pronounced replacement of legacy PFAS by emerging alternatives. Coastal fluorochemical manufacturing and high-performance fluoropolymer use were identified as major drivers of compositional differences. Legacy PFAS showed nearshore retention, with their migration constrained by salinity fronts and water masses, whereas emerging PFAS displayed more complex behaviors, with some capable of crossing salinity fronts and undergoing long-range transport. Ecological risk assessment based on risk quotient (RQ) and hazard index (HI) further revealed spatially elevated risks in nearshore and estuarine zones, driven primarily by PFOA and HFPO-TA. Overall, spatial heterogeneity among marine regions reflects variations in industrial sources and usage patterns, underscoring the necessity of integrating regional industrial structures and pollution characteristics to strengthen ecological risk assessments.