Perfluoroalkyl substances (PFAS) are recognized for their significant environmental impact and complex environmental behaviors. Understanding the factors influencing PFAS concentrations and their sources is critical, especially in ecologically sensitive regions like the Beibu Gulf in the South China Sea. This study investigates the concentrations, compositions, and distributions of 29 PFAS compounds across 47 surface seawater samples (latitude: 21.37°N-17.34°N, longitude: 111.46°E-107.48°E) collected during both summer and winter, allowing for seasonal comparisons. The average PFAS concentrations were 1.440 ± 0.870 ng/L in summer and 1.435 ± 0.999 ng/L in winter. PFOA and PFBS dominated both seasons and were predominantly concentrated in coastal areas. A multiple linear regression model revealed a significant negative correlation between certain PFAS and seawater salinity, pointing to strong land-based sources, particularly for emerging PFAS. Results from the Extreme Gradient Boosting (XGBoost) model further supported this, identifying temperature as another key factor affecting PFAS concentrations, possibly through the degradation of precursor compounds. Positive matrix factorization (PMF) analysis highlighted precursors and their degradation products as major secondary sources, with atmospheric deposition also contributing to PFAS levels, in addition to land inputs. Seasonal variations were observed, suggesting that ocean currents might influence PFAS distribution. during winter, the Beibu Gulf receives inputs from the Western Guangdong Coastal Current (WGCC), which might carry pollutants from the Pearl River Estuary into the Beibu Gulf.

These findings contribute to our understanding of PFAS behavior in the Beibu Gulf and offer a scientific basis for environmental monitoring and regulatory guidance for industries in the region.