Comprehensive insights into the thermal decomposition behavior, mechanism, and mineralization of PFOS, PFOSA, F53B, PFOA, and 8:2 FTOH and toxicity prediction of their gaseous products

Due to the limited documentation on thermal treatment of per - and polyfluoroalkyl substances (PFAS), this study investigated the thermal degradation behavior, mechanisms, mineralization, and gaseous product toxicity of five environmentally ubiquitous PFAS, including perfluorooctanesulfonic acid (PFOS), perfluorooctane sulfonamide (PFOSA), 6:2 chlorinated polyfluoroalkyl ether sulfonate (F 53B), perfluorooctanoic acid (PFOA), and 1H,1H,2H,2H-perfluoro-1-decanol (8:2 FTOH). Results showed that thermal stability of PFAS is dictated by their functional groups, presenting a stability hierarchy of sulfonic acid (PFOS, F 53B) > sulfonamide (PFOSA) > carboxylic acid (PFOA) > hydroxyl (8:2 FTOH). Thermal decomposition of these PFAS was initiated with cleavage of bonds connecting the functional group to the perfluorinated chain followed by stepwise chain-shortening reactions, yielding various perfluoroalkanes, perfluoroalkenes, and hydrofluoroalkanes. Calcium hydroxide remarkably enhanced fluorine mineralization into calcium fluoride and suppressed the formation of organofluorinated compounds during PFAS thermal treatment. Toxicity predictions indicated reduced acute toxicity for thermal degradation products compared to parent PFAS, but they still pose potential risks to human health. This implies that optimizing thermal treatment conditions is essential, focusing not only on mineralization efficiency but also on suppressing the formation of harmful by-products. These findings provide a systematic understanding of PFAS thermal decomposition and identify potentially hazardous gaseous by-products.