• • The optimized Online SPE-LC/MS/MS method achieved detection limits of 0.2–0.3 ng·L−1 for 19 PFASs, with linear correlation coefficients ≥0.990 and spiked recoveries of 75.2%–130.0%, enabling reliable trace analysis in surface water.
• • PFBA, PFPeA, PFHxA, and PFOS were identified as dominant PFASs, with total concentrations (∑19PFASs) ranging from 126.1–2584.3 ng·L−1 in dry season, 3.5–3567.6 ng·L−1 in normal season, and 26.3–294.6 ng·L−1 in wet season, indicating strong seasonal variation.
• • Ecological risk quotients (RQ) were below 1 for all PFASs except PFDoDA during dry season, suggesting minimal ecological risk under most conditions, but PFDoDA warrants attention.
• • Health risk assessment showed that only PFOA and PFOS posed potential risks (hazard ratio >0.1) to adults and children at some sites during dry and normal seasons, despite the river not being a direct drinking water source, highlighting the need for monitoring these compounds.