In this recent publication in Environmental Science and Technology, Professor Mengyan Li's team uncovered a bifurcated biotransformation framework in which redox conditions steer fluorotelomer carboxylic acids (FTCAs), an important group of PFAS, toward either terminal PFCA formation or cascading chain shortening and biodefluorination. By combining targeted LC-MS/MS and nontargeted Nano-ESI-HRMS, they identified previously unreported intermediates and revealed how oxygen availability shapes transformation pathways and rates. These findings advance our understanding of PFAS precursor fate in environmental systems and may help inform future strategies for PFAS mitigation.