In this study, we found that thermal decomposition of per- and polyfluoroalkyl substances (PFAS) in soil was rapid at moderate temperatures of 400 to 500 oC, regardless of whether the soil was contaminated by a single PFAS compound or a PFAS mixture. Substantial degradation (&gt;99%) of 15 PFAS compounds in soil, including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), cationic and zwitterionic PFAS, and PFAS alternatives, occurred in 30 min at 500 oC in both a sealed reactor in air and a horizontal reactor under a continuous flow of N2. The effect of initial PFAS level in soil (0.001 to 10 µmol/g) and soil texture was insignificant provided a sufficiently high temperature was applied. This study showed, for the first time, that kaolinite dramatically decreased the apparent yield of F from PFAS heated at &gt;300 oC, likely due to the chemisorption of F radicals on kaolinite. This phenomenon was not observed when kaolinite and an inorganic fluoride salt (NaF) were thermally treated. Various nonpolar thermal degradation products were reported for the first time. The profile of fluorinated volatiles, particularly perfluoroalkenes, was similar between PFOA, PFOS, and their cationic and zwitterionic precursor compounds. The results support a radical-mediated degradation pathway of the perfluorinated chain of PFAS.

Investigation of thermal air degradation and pyrolysis of PFAS and PFAS alternatives in soil

ACS Spring 2022

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