Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7a. Advances in the Analysis of Non-Target Per- and Polyfluorinated Alkyl Substances (PFAS)

Formatted Title:

Development of a New Surface Testing Method to Comprehensively Assess Supramolecular PFAS on Surfaces

Background/Objectives:

As a result of a detailed understanding of how per- and polyfluoroalkyl substances (PFAS) attach to surfaces in the form of supramolecular assemblies a surface swabbing method and chemical analytical method for detection PFAS on non-porous surfaces has been developed.

This multi-swab approach has been proven to comprehensively detect PFAS on the surface of pipework impacted by firefighting foams and has been applied to demonstrate effective decontamination of fire suppression systems.

Approach/Activities:

As all fluorinated firefighting foam contain fluorosurfactants, termed polyfluoroalkyl PFAS, for which there are no analytical standards, the use of targeted analysis (i.e., USEPA method 1633) is inappropriate for detection of the PFAS contained within aqueous film forming foams (AFFFs) and fluoroprotein foams. These proprietary polyfluoroalkyl PFAS can adsorb onto the surface of fire suppression systems, self assemble to form supramolecular assemblies which form a reservoir of PFAS, coating the surfaces. As the vast majority of PFAS in firefighting foams are not detected using chemical analytical methods which detect target analytes a more comprehensive approach is required to prove fire suppression system decontamination has been effective.

The triple swabbing method was developed to target both PFAS that are neutral, cationic, anionic and zwitterionic, as combinations of these PFAS are usually present within firefighting foams.

Swabbing is done repeatedly within a 100 cm² area and the swabs are then combined for sequential base-acid extraction. The swabs are extracted using a sequential base-acid approach that has been proven on soils, where it was demonstrated that this approach was required to extract >97% of the PFAS present. The analytical method used to assess the extracted PFAS from the swabs comprises the total oxidisable precursor (TOP) assay, to provide assurance that both per- and polyfluoroalklyl PFAS present in firefighting foams can be detected. As part of the development work, each swab was assessed using TOP assay data from sequential swabs are shown in Figure 1.

The triple swabbing method has been shown to be effective for assessment of PFAS impacted pipework by measuring the total elemental content of the pipe surfaces using time of flight elastic recoil detection (TOF-ERD). The difference in surface elemental composition of PFAS-impacted pipework on an area that had been swabbed, using this method, vs an unswabbed area. The TOF-ERD data has demonstrated that the swabs remove over 95% of the fluorine associated with the pipe surface. Further work with additional repeat swabs are being performed.

Results/Lessons Learned:

The swabbing procedure, extraction approach and analytical method were tested and shown to be effective for assessment of PFAS on surfaces, so the method is now commercially available, while further detailed studies of the methods efficacy are done in collaboration with university partners.

It is important that the PFAS within firefighting foam are measured during decontamination as they will be transformed in the environmental by micro-organisms to create the regulated perfluoroalkyl acids (PFAAs), such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), which are termed PFAA-precursors. Determining the presence of these precursors will be critical when proving decontamination to comply with European / UK regulations for PFAS in firefighting foams which includes the PFAS (i.e., PFOA-related compounds). With the US National Defence Authorisation Act (NDAA) stipulating a target of 1 ppb of total PFAS, the use of analytical methods that comprehensively assess PFAS will be critical to achieve compliance.

When considering future release of fluorine free firefighting (F3) foams, they can become heavily contaminated with PFAS as a result of ineffective fire suppression system decontamination and these precursors transform in the environment to generate PFAAs, such as PFOA and PFOS, so soil and groundwater will become impacted with PFAAs.

A method to quantify PFAS on the inner surface of fire suppression systems is required to validate that equipment decontamination has been successful.

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Geraint Williams