Environmental Source Tracking of Per- and Polyfluoroalkyl Substances within a Forensic Context: Current and Future Techniques

Abstract

The source tracking of per- and polyfluoroalkyl substances (PFASs) is a new and increasingly necessary subfield within environmental forensics. We define PFAS source tracking as the accurate characterization and differentiation of multiple sources contributing to PFAS contamination in the environment. PFAS source tracking should employ analytical measurements, multivariate analyses, and an understanding of PFAS fate and transport within the framework of a conceptual site model. Converging lines of evidence used to differentiate PFAS sources include: identification of PFASs strongly associated with unique sources; the ratios of PFAS homologues, classes, and isomers at a contaminated site; and a site’s hydrogeochemical conditions. As the field of PFAS source tracking progresses, the development of new PFAS analytical standards and the wider availability of high-resolution mass spectral data will enhance currently available analytical capabilities. In addition, multivariate computational tools, including unsupervised (i.e., exploratory) and supervised (i.e., predictive) machine learning techniques, may lead to novel insights that define a targeted list of PFASs that will be useful for environmental PFAS source tracking. In this Perspective, we identify the current tools available and principal developments necessary to enable greater confidence in environmental source tracking to identify and apportion PFAS sources.

Environmental Sources, Chemistry, Fate, and Transport of Per‐ and Polyfluoroalkyl Substances: State of the Science, Key Knowledge Gaps, and Recommendations Presented at the August 2019 SETAC Focus Topic Meeting

“…Forensic analysis of such complex comingled sources requires multiple lines of evidence to better understand source identifications and differentiations. These include (1) PFAS isomer profiles and chain length ratios; (2) unique source‐specific markers (Charbonnet et al, 2021; Guelfo & Adamson, 2018; McGuire et al, 2014; Swedish Chemicals Agency [KEMI], 2015); and (3) advanced analytical tools, such as HRMS (e.g., NTA and suspect screening methods) to identify and characterize a broad suite of PFAS analytes (Charbonnet et al, 2021; Ruyle et al, 2021). Selection of a broad suite of analytes will be helpful for understanding the signatures of multiple PFAS sources.…”

“…By considering the broad suite of data collected from HRMS, although the influence of the many components included in the broad data set may be small, they still might be important for classification of sources. Hence, consideration of a broad suite of PFAS analytes to perform advanced statistical analysis might provide better information about the classification of sources (Charbonnet et al, 2021; Strozier et al, 2016).…”

“…(2) unique source-specific markers (Charbonnet et al, 2021;Guelfo & Adamson, 2018;McGuire et al, 2014; Swedish Chemicals Agency [KEMI], 2015); and (3) advanced analytical tools, such as HRMS (e.g., NTA and suspect screening methods) to identify and characterize a broad suite of PFAS analytes (Charbonnet et al, 2021;Ruyle et al, 2021). Selection of a broad suite of analytes will be helpful for understanding the signatures of multiple PFAS sources.…”

“…Furthermore, source attribution of these three clustered groups was performed based on the geospatial analysis data of watersheds (Zhang, Lu, et al, 2016). The application of generalized source clustering based on geospatial analysis for probable broader source categorization, might have limitations due to the lack of knowledge about the unique signatures of diverse sources based on the common persistent PFAAs (few known analytes) and the presence of comingled sources (Charbonnet et al, 2021).…”

Communicating Confidence of Per- and Polyfluoroalkyl Substance Identification via High-Resolution Mass Spectrometry

“…The observation of both branched and linear isomers should always be reported: the co-occurrence of linear and branched isomers usually indicates synthesis by electrochemical fluorination, 19 and the relative abundance of branched and linear isomers can inform PFAS forensics. 20 , 21 …”