The Total Oxidizable Precursor (TOP) Assay as a Forensic Tool for Per- and Polyfluoroalkyl Substances (PFAS) Source Apportionment

TOP assay data were used to identify PFAS contaminationsources based on visualizing a two-component PCA and similaritiesin chemical composition. Per- and polyfluoroalkylsubstances (PFASs) are a class of synthetic,organic chemicals that contaminate drinking water and natural ecosystems.PFAS source apportionment is challenging because there are many sources,and standard analytical methods quantify fewer than 100 of the thousandsof PFASs in commerce. The total oxidizable precursor (TOP) assay augmentsthe number of PFASs that can be quantified and is increasingly incorporatedinto routine site investigation. Here we examine the ability of theTOP assay to identify PFAS sources, including aqueous film-formingfoam (AFFF) impacted sites, municipal wastewater treatment plants(WWTPs), and municipal solid waste landfills in 145 samples from 46locations and three countries. The bootstrapped mean composition ofPFASs from each source was dominated by precursors, particularly insamples from WWTPs where precursors that form short-chain perfluoroalkylcarboxylates during the TOP assay were most common. Compared to whenTOP assay data were excluded, inclusion of TOP assay data in dimension-reducingalgorithms, such as principal component analysis (PCA), improved separationamong sources. We converted the PCA tool into a web application thatallows users to initiate PFAS source apportionment efforts on datafrom sites where contaminant sources are unknown.