Integrating direct Total Oxidizable Precursor (dTOP) assay with suspect and non-target screening methods for analysis of PFAS in highly contaminated soils

Fluorochemical production (FCP) sites are key hotspots for per- and polyfluoroalkyl substances (PFAS), persistently contaminating nearby soils. Most studies on FCP-impacted environments have relied on targeted analyses, which may overlook emerging and unknown PFAS, such as precursors that can transform into stable products. To address this gap, an integrated analytical workflow combining the direct total oxidizable precursor (dTOP) assay with high-resolution mass spectrometry (HRMS)-based suspect and non-target screening (SS/NTS) was performed on PFAS-contaminated soils collected at and near an FCP site in Flanders, Belgium. The dTOP assay conditions was optimized through Design of Experiment, which identified relative quantities of sodium hydroxide and potassium persulfate as significant factors (p < 0.01), along with temperature and reaction time, applicable in both moderately and highly contaminated soils (oxidation efficiency > 99.3%). SS/NTS of post-dTOP samples also showed efficient oxidation of emerging PFAS classes (e.g., 95% oxidation of pentafluorosulfide perfluoroalkyl sulfonic acid), but also revealed increases in emerging non-target PFAS (NT-PFAS), which are oxidation products of other precursors. This study enabled the examination of the behavior of several NT-PFAS and the estimation of PFAS precursors.