Wastewater treatment plants (WWTPs) have been identified as a significant pathway for the introduction of perfluoroalkyl and polyfluoroalkyl substances (PFASs) to natural waters. It was observed in several studies that the concentration of certain PFASs were higher in the WWTP effluent compared to the corresponding influent. The objective of the present study was the identification of potential precursor substances of persistent perfluoroalkyl acids (PFAAs) in WWTPs and indoor rooms in order to support the preparation of regulatory measures.