Quantitative assessment of poly- and perfluoroalkyl substances (PFASs) in aqueous film forming foam (AFFF)-impacted soils: a comparison of analytical protocols.

Quantitatively assessing all per- and poly fluoroalkyl substances (PFASs) in an environmental sample, particularly soils impacted by aqueous film forming foams (AFFFs), has proven to be a challenge. To make such an assessment, a comprehensive sample processing procedure and analytical tool must be used. However, doubts remain whether current analytical tools such as high-resolution mass spectrometry (HRMS) with targeted quantitation and semi-quantitative analysis of suspects (Semi-Q HRMS) or total organic fluorine (TOF) are capable of accurately quantifying all non-polymeric PFASs in a sample. Further, current comprehensive soil PFAS HRMS methods are incompatible with TOF, preventing direct comparisons of the approaches. To enable direct comparisons, a soil sample processing procedure that is comprehensive as well as compatible with multiple analytical tools is needed. In this study, we assessed the performance of a previously developed soil PFAS method, EPA Method 1633, and a hybrid solid phase extraction (SPE)-based method for characterizing AFFF-impacted soil composites while maintaining compatibility with multiple analytical tools (i.e., Semi-Q HRMS and TOF). Comparative results for AFFF-impacted soil composites indicate analysis via EPA Method 1633 (as compared to the novel hybrid method) results in maybe up to 75% of the PFAS mass being missed by only analyzing for compounds listed in EPA Method 1633. Simply expanding the EPA Method 1633 analyte list was insufficient to account for the missing mass: up to 69% of the PFAS mass was still missed because of EPA Method 1633's extraction and cleanup bias. Additionally, the novel method developed offers a more comprehensive analysis with minimal reductions to sensitivity when compared to those reported in EPA Method 1633, with limits of quantification ranging from 0.12 to 2.4 ng/g as compared to 0.16-4.0 ng/g, respectively. For these reasons, an alternative hybrid SPE-based method is proposed for comprehensive evaluation of PFASs in AFFF-impacted soils.