Developing a simple robust method for the quantification of PFAS in soil

Soil is a major environmental reservoir of per- and polyfluoroalkyl substances (PFAS), which are ubiquitous and persistent contaminants that threaten ecosystems and human health via migration into water, plants, and animals. However, analyzing PFAS in soils remains challenging primarily due to extraction efficiencies of this diverse chemical group and matrix interferences in mass spectrometry. This study aimed to develop and validate an optimized extraction and clean-up method for quantifying PFAS in soils using LC-MS/MS. A spiked soil (5 ng/g PFAS) was extracted with methanol (MeOH), acetonitrile (ACN) and isopropyl alcohol (IPA), either alone or with pH modifiers, and subjected to various dispersive solid-phase extraction (dSPE) and cartridge-based clean-up methods. Agilent Carbon S cartridge demonstrated the best matrix removal efficiency, while basic MeOH (10 mM NH₄OH) outperformed basic ACN (10 mM NH₄OH), except for the perfluoroalkane sulfonamides (FASAs) class, where basic ACN showed better recovery. An optimized sequential extraction approach using 5 mL basic MeOH and a 3 mL basic ACN wash followed by Agilent Carbon S clean-up, provided high matrix removal and recovery rates (70-130 %) for 50 of the 68 PFAS included in this study. When applied to 15 soil samples from diverse land use types, the method detected eight PFAS in 12 samples, with Σ₈PFAS concentrations ranging from 0.14 to 4.6 ng/g, lower than levels reported in other studies. PFOS was the dominant PFAS, detected in 73 % of the samples, though concentrations remained below the National Environmental Management Plan guideline. The small sample size limits drawing broad conclusions, highlighting the need for a broader, state-wide survey to better understand PFAS distribution in Victorian soils.