These disparities suggest that the reaction mechanisms go beyond the previously known "zippingoff" mechanism, where the removal of terminal functional groups (i.e., -COO -, -SO3 -, and -CH2CH2-SO3 -) exposes the RF-CF2• for stepwise defluorination of the two C-F bonds and oxidation of the carbon into CO2 (Fig. ). The odd/even number of -CF2-in PFCAs appears to have interesting effects on the gap from 100% defluorination (<10% for n=2,4,6 versus >20% for n=3,5,7 CnF2n+1-COO -). It is also very interesting to observe the much lower defluorination from all three n=8 structures than their n=2 and 4 analogs. Elucidating the underlying mechanisms go beyond the scope of this work but definitely warrants further study. PFSA and FTS by EO treatment and the previously known "zipping-off" pathway. Reaction conditions: individual PFAS (25 µM, except 1000 µM for TFA for the ease of F -measurement) spiked in 20 mL water with 100 mM Na2SO4 as electrolyte; current density of 15 mA/cm 2 applied to a 16 cm 2 BDD anode. Data are presented as mean values of triplicates ± standard deviation.