1. A method of destroying PFAS in a PFAS-containing aqueous mixture, comprising: reacting the PFAS with an aqueous oxidant under supercritical conditions to produce an effluent, and further comprising treating the effluent from the step of reacting with an aqueous oxidant with an alkali or alkaline earth element, to convert the PFAS to a product mixture comprising carbon dioxide and an alkali or alkaline earth fluoride.