Urban surface water flows contribute more PFAS to marine environments than treated wastewater.

Despite the increased number of studies on PFAS globally, our understanding of mass transport pathways remains limited. To address this, we investigated major rivers and creeks feeding into Port Phillip Bay, Melbourne, Australia, for 52 PFAS. We collected 76 grab samples and deployed 28 Polar Organic Chemical Integrative Samplers (POCIS) from 7 locations over 2-months to identify differences PFAS profiles across catchments, the influence of land uses and rainfall. There were 25 PFAS detected in grab samples and 26 in POCIS. Mean ƩPFAS for grab samples was 76.4 ng/L, with ∼90% made up of ten PFAS. PFOS was the most common but pre-cursors were also present. Our surface water flow model showed a wide range of land uses influenced PFAS profiles across catchments, including those not traditionally associated as point sources, highlighting further investigation is needed. We estimated 57.4 kg/year ƩPFAS were exported to Port Phillip Bay, with surface water flows exporting over twice the ƩPFAS compared to wastewater discharges. Our findings show the importance of monitoring a wide range of PFAS in combination with land use and surface water flow models is crucial for mitigating diffuse pollution sources to effectively safeguard both marine ecosystems and community health, worldwide.