Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals that are harmful to both the environment and human health. Using self-interaction-corrected Born-Oppenheimer molecular dynamics simulations, we provide the first real-time assessment of PFAS degradation in the presence of excess electrons. In particular, we show that the initial phase of the degradation involves the transformation of an alkane-type C-C bond into an alkene-type C&z.dbd;C bond in the PFAS molecule, which is initiated by the trans elimination of fluorine atoms bonded to these adjacent carbon atoms. Per- and polyfluoroalkyl substances (PFASs) are harmful man-made chemicals that have contaminated several drinking water resources worldwide. Our work provides the first real-time assessment of PFAS degradation in the presence of excess electrons.