From glacier to delta: Spatial distribution of PFAS and tire-derived contaminants along the entire Rhône River continuum.

The widespread occurrence of PFAS and tire-derived contaminants is a major challenge due to their persistence, continuous emission, and resistance to removal by conventional environmental treatment processes. Large river systems integrate diffuse and point-source contamination across entire catchments and act as major pathways for contaminant transport toward coastal environments. Their simultaneous occurrence and spatial dynamics along large European rivers remain poorly characterized. This study aimed to provide the first integrated dry-weather baseline assessment of PFAS and tire-derived contaminants along the entire Rhône River continuum from alpine headwaters to downstream urbanized areas. Surface water samples were collected at 52 stations distributed along approximately 760 km of the Rhône River. Sampling was conducted under dry-weather baseflow conditions providing a dry-weather baseflow baseline. A total of 50 PFAS and 15 tire-derived contaminants were analysed using LC-MS/MS. Fourteen PFAS and two tire-derived contaminants were detected above their method LOQ. Trifluoroacetic acid (TFA) dominated the contamination profile, occurring in 96% of samples and reaching up to 3252 ng/L, exceeding all other PFAS. Perfluorooctanesulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) showed significant downstream enrichment toward urbanized regions. Among tire-derived contaminants, diphenylguanidine was widely detected, whereas N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine quinone (77PD-Q) was identified at low concentrations and sporadic occurrence, representing one of the first reported detections of this quinone in European surface waters. These results provide the first integrated source-to-sea dry-weather baseline for PFAS and tire-derived contaminants in the Rhône River and establish a reference framework for future environmental surveillance and regulatory assessment.