Occurrence of per- and polyfluorinated alkyl substances (PFAS), including ultra-short-chain compounds. Seasonal variation in rainwater from the Swedish west coast

Per- and polyfluoroalkyl substances (PFAS) are a group of highly fluorinated compounds which comprises of more than 4700 substances. A smaller number of those substances is rou-tinely measured, usually the short (C4-C7) and long chain PFAS (>C7). Detection of PFAS in different water matrices including wet precipitation have been done previously in a limited number of studies, including ultra-short chain compounds (C1-C3). Ultra-short chain com-pounds have however not been investigated to a larger extent. In this study, twelve rainwater samples from Råö have been analysed, each representing a composite sample of one month. Long (C8-C18), short as well as ultra-short chain PFAS have been included in the analysis. Long and short chain compounds were analysed with ultra-performance liquid chromatography tan-dem mass spectrometer (UPLC-MS/MS) and ultra-short chain compounds with ultra-perfor-mance convergence chromatography tandem spectrometer (UPCC-MS/MS). Long and short-chain PFAS had a total detectable concentration of 5.1-110 ng/L. A seasonal trend was also studied, which showed a significant difference when performing a Kruskal Wallis test in meas-ured total mean long and short chain PFAS concentration. Dunnet´s test indicated a significant difference between all the seasons. Highest concentrations were measured during summer and lowest during winter. Ultra-short chain compounds analysed by UPCC MS/MS had a total concentration between 16-410 ng/L. No significant difference in total ultra-short PFAS mean concentration could be seen between different seasons using a Kruskal Wallis test. The total PFAS concentration in the rain samples ranged from 28 to 540 ng/L, where ultra-short chain PFAS contributed to 58-92 % of the total concentration. Which makes them an important group to include in future measurements of PFAS in water samples and especially in rainwater sam-ples