Anaerobic defluorination of chlorine-substituted per- and polyfluorinated carboxylic acids triggered by microbial dechlorination

Chlorinated per- and polyfluoroalkyl substances (Cl-PFAS) have been manufactured and widely used in industrial and commercial products. Here, we report on significant anaerobic biodefluorinaiton structures and novel defluorination pathways of specific Cl-PFAS triggered by anaerobic microbial dechlorination. Compared to the H-substituted counterparts, the Cl-substituted per- and polyfluoroalkyl carboxylic acids PFCAs exhibited faster and deeper defluorination, which was attributed to the highly bioreactive Cl-substitutions. The Cl-PFCAs underwent reductive, hydrolytic, and eliminative dehalogenation reactions. It was the hydrolytic dechlorination that led to the following significant spontaneous defluorination forming di-carboxylic acids. The more Cl-substitutions, the more likely the hydrolytic dechlorination would occur at the multiple Cl-substitutions, leading to much higher defluorination and chain-shortening products. About 80% total defluorination was achieved for the chlorotrifluoroethylene tetramer carboxylic acid with four Cl-substitutions. The reductive dechlorination was a non-defluorinating pathway, and the H-substituted products were more recalcitrant to biodefluorination. This study advances the knowledge of the structure-biodegradability and the biodefluorination pathways of Cl-PFCAs in anaerobic conditions. It provides important guidance to assess the environmental fate and transport of Cl-PFAS, including fluoropolymers, and the potential environmental risks. It also sheds light on PFAS source-tracking by suggesting Cl-PFAS as an important source of some emergent PFAS structures detected in impacted fields.