Water Sample Analysis. PFAS parent compounds and transformation products (TPs) were measured by high-performance liquid chromatography equipped with a high-resolution quadrupole Orbitrap mass spectrometer (HPLC-HRMS/MS, Q Exactive, Thermo Fisher Scientific). The instrument settings and quality assurance/control details are provided in the SI. The released fluoride ion (F -) was measured by an ion-selective electrode (ISE, Fisherbrand Accumet) with a Thermo Scientific Orion Versa Star Pro meter. Each sample was added with an equal volume of total ionic strength adjustment buffer (TISAB for fluoride electrode, Thermo Scientific). The measurement accuracy in the persulfate oxidation matrix has been validated in our previous report. The F -released from -COF and -SO2F in the hydrolysis pretreatment was not counted for the oxidative defluorination percentage (deF%).