Electrochemical Transformations of Perfluoroalkyl Acid (PFAA) Precursors and PFAAs in Landfill Leachates

Landfill leachates possess a countless number of chemical classes of potential environmental and human concern, including per- and polyfluoroalkyl substances (PFAS). While detection and biodegradation studies of PFAS in leachates have been conducted previously, the degradation of precursors of perfluoroalkyl acids (PFAAs) in landfill leachates with oxidative technologies has not been addressed. Thus, information regarding the oxidative transformations of PFAA precursors typically present in leachates is lacking. Target and suspect PFAS were identified in a landfill leachate, and their concentrations during electrochemical treatment were quantified over time. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF) measurements of the leachate showed a total PFAS concentration of 157 ± 10 nmol/L that included 53 PFAS and 19 different classes. Multiple PFAS are reported for the first time in landfill leachates. The molar composition of the leachate was comprised of 33% PFAAs, 7% electrochemical fluorination (ECF) precursors, and 60% fluorotelomer (FT) precursors. Further analysis with total oxidizable precursor (TOP) assay revealed an additional concentration of precursors that was not identified with LC-QToF. The evaluation of the intermediate and final products generated during the electrochemical treatment showed evidence of known electrochemical degradation pathways. However, this is the first study to have more evidence for electrochemical pathways in landfill leachates. In brief, sulfonamide-based precursors and fluorotelomer-based precursors were electrochemically transformed into perfluoroalkyl carboxylic acids (PFCAs) during treatment of the leachate.