Land use and seasonal controls on Per- and Polyfluoroalkyl Substances (PFAS) distribution and partitioning from diffuse sources in subtropical urban waterways.

Per- and Polyfluoroalkyl Substances (PFAS) are persistent contaminants in urban aquatic environments, yet knowledge of their behaviour in waterways receiving diffuse urban inputs remains limited. This study investigated the occurrence, sediment-water partitioning, and seasonal variation of 15 PFAS compounds (6 short-chain, 9 long-chain) in subtropical urban creeks across contrasting land uses. Total PFAS concentrations in water ranged from 18.312 to 31.323 ng/L, and in sediment from 0.034 to 0.403 ng/g dw. Concentrations varied between seasons, with summer (November) rainfall mobilising contaminants from urban surfaces, resulting in the highest mean total concentration (31.323 ng/L), compared to 18.312 ng/L in dry winter (July), reflecting the wet-dry seasonality of subtropical catchments and the role of episodic rainfall in pollutant transport. Short-chain PFAS accounted for 70.384% of total PFAS in water, while sediments contained 75.911% of long-chain PFAS. Sorption was influenced not only by chain length and hydrophobicity, but also by functional group interactions between carboxylic and sulfonic acid PFAS. Legacy PFOA (21.759%) and PFOS (13.624%), alongside short-chain PFAS, suggest combined historical and contemporary sources. Residential and downstream sites exhibited elevated contamination, linked to land use. These findings highlight the importance of seasonal, compound-specific, and land use factors in assessing PFAS contamination.