Assessment of PFAS in Soil and Groundwater: Direct Comparison of New Analytical Technologies for Comprehensive Analysis of PFAS Including Precursors

In addition to PFOS and PFOA there are numerous other “precursor” compounds in firefighting foams which present an ongoing source of PFOS and PFOA and other perfluorinated sulphonates and carboxylates. PFAS contaminated source zones are often associated with large plumes as in some firefighting foam formulations the majority of PFAS are anionic and are not retarded significantly in aquifers, however in some foams cationic or zwitterionic precursors are at significant concentrations or dominate the formulations. These cationic / zwitterionic will bind to soils via ion exchange mechanisms, producing a lesser mobile source mass, which can evolve more mobile anionic perfluoroalkyl acids (PFAAs) as “dead end” daughter products via biotransformation reactions.

Precursors are not accounted for by US. EPA method 537 (LC-MS/MS) but have been identified as a source of PFAA’s, so to characterize soil, sediment and waters impacted with PFAS, it is important to assess the precursor concentrations. This presentation will describe new analytical methods to quantify the total concentration of precursors and PFAA’s in water and soil samples.

Soil and groundwater from PFAS contaminated sites as well as soil spiked with characterized AFFF were analyzed by conventional, and new and detailed analytical methods. Results demonstrate that PFOA and PFOS only account for only a small portion of the PFAS present in some impacted soil and groundwater.

This next generation of new PFAS analytical techniques will generate more comprehensive analytical data supporting more robust conceptual site models and improve understanding of PFAS fate and transport. Accounting for precursors will be key for successful design of remedial systems.