AbstractPerfluoroalkyl and polyfluoroalkyl substances (PFAS) are a large class of ubiquitous and persistent environmental contaminants. Due to the extremely stable carbon-fluorine bonds, PFAS are difficult to destruct. Increasing research efforts are focusing on PFAS defluorination, and one of the key challenges is tracking down the breakdown products and achieving a reasonable mass balance. In this study, we demonstrate one vital but often overlooked aspect of PFAS destruction studies, using perfluorooctanesulfonic acid (PFOS) destruction with acoustic cavitation as a case. This study showed that PFOS–container interactions can significantly impact the destruction efficiency and provided an example whereby these interactions may be prevented using surface coating. A showcase of mass balance for PFAS defluorination using acoustic cavitation was also investigated by employing targeted analysis [liquid chromatography-mass spectrometry (LC-MS)] and complementary untargeted analysis (total organofluorine measurement). This study demonstrated the necessity for a thorough consideration of all aspects in PFAS destruction experiments and the necessity of early adoption of total organofluorine measurements.Practical ApplicationsThis case study provides a working example of mass balance challenges regarding the handling and destruction of PFAS compounds. In this study, we demonstrate that destruction efficiency decreased by over 50% due to interactions between the reactor and PFOS, as measured by recovering unreacted PFOS from the walls of the vessel with a solvent rinse. When the container interactions were addressed, destruction efficiency doubled. If these interactions are not considered, PFAS destruction efficiency may be overestimated and could lead to unexpected residual PFAS when applied in a treatment system. Not accounting for this residual PFAS could result in PFAS releases from destruction and treatment systems, presenting possible public health concerns. Furthermore, this study represents an early use of total organofluorine (TOF) measurements to validate destruction performance. This research can be used to inform the design of PFAS destruction reactors, improve destruction efficiency, and outlines an approach to reporting mass balances in PFAS destruction schemes.