18 Jan 2023

Advances in Methodologies and Applications of Non-Targeted Analysis for PFAS

Natalia Quinete, Florida International University

Per- and polyfluoroalkyl substances (PFAS), regarded as forever chemicals, have been a topic of increasing concern due to their widespread use, persistence, bioaccumulation and biomagnification capabilities, and toxicity. PFAS are often present as complex mixtures, and there are thousands of PFAS structures known to exist with many having no available analytical standards or scientific knowledge on the fate and transformation of these contaminants. Non-targeted and suspect screening analysis (NTA) has been used as powerful and holistic tools to characterize and prioritize chemical composition in various environmental, commercial product and biological matrices without needing chemical standards. Additionally, NTA has recently contributed to more accurate, specific and reproducible assessments of PFAS in environmental and biological samples, helping to identify known PFAS that are not routinely monitored by targeted methods and also uncover novel PFAS and their transformation products.

This session, held at the SETAC North America 43rd Annual Meeting and supported by the Chemistry Interest Group (Chem IG), focused on the advances in methods and application of NTA to PFAS identification and prioritization in environmental (e.g., surface water, drinking water, groundwater, soil cores, etc.), biotic (e.g., animals, humans) and product (e.g.,textiles, consumer products) matrices.

The session began with a talk from Christopher Higgins, Colorado School of Mines, proposing a confidence scale to aid the tentative identification of PFAS by NTA using high-resolution mass spectrometry (HRMS). In this scale, the general concept of communicating confidence is maintained, while specific conventions and tools (e.g., the detection of homologous series, diagnostic fragmentation, and specific ranges of mass defects) used in PFAS classification and analysis were incorporated; therefore, aiming to increase confidence, accuracy and harmonization in the identification of PFAS structures.

With the shift in the production to emerging PFAS after PFOA/PFOS ban, the use of NTA to identify and quantify legacy and emerging PFAS in industrial effluents and contaminated environmental media (e.g., groundwater) is crucial. The study presented by James McCord, U.S. Environmental Protection Agency (USEPA), has identified multiple PFAS classes, including novel PFAS fluoroether species, chlorinated perfluoropolyethers (ClPFPECAs) and polyfluorinated side products of polyfluorovinylidine (PVDF) in the effluent of a polymer production site and legacy PFAS in electronical materials manufacturing. In the case study of a PFAS waste treatment, significant reduction across all measured PFAS was observed. There has been a great effort to ensure consistent and transparent reporting of NTA results to be used as actionable information in decision-making approaches.

Caitlin Glover, McGill University, has highlighted the need to complement the targeted qualitative identification of PFAS in aqueous film-foaming foams (AFFF) by performing NTA and suspect screening using Orbitrap HRMS coupled to surrogate techniques such as oxidizable precursor (TOP) assay and total organofluorine analysis (TOF) to be able to close the fluorine mass balance needed for risk assessments and mitigation efforts. This comprehensive PFAS characterization was performed in 25 foams, including two fluorine-free foams (F3) and two non-AFFFs. It revealed little PFAS or no PFAS on F3 and non-AFFFs and a wide concentration range (high ppm levels) in PFAS containing AFFFs, including 18 novel classes of electrochemical fluorination (ECF)-based PFAS and seven novel classes of fluorotelomer (FT)-based PFAS. Good agreement in fluorine mass balance was achieved for the FT-AFFFs by comparing total fluorine with the molar sums of fluorine from the PFAS obtained by quantitative and semi-quantitative HRMS.

The application of novel imaging technologies for surface characterization consisted of infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) coupled with high-resolution, accurate mass spectrometry (HRAM-MS) to image PFAS in soil cores from an AFFF-impacted sources in the study presented by Theresa Guillette, Arcadis. Guillette’s study showed differences in spatial distribution between controls and stabilized soil cores for PFOA, PFOS and PFHxS. A higher abundance of features was found in stabilized soil cores by NTA, which will be further identified.

To better understand the impact and levels of past PFAS releases to the environment, Michaela Cashman, USEPA, employed targeted and non-targeted analysis to reconstruct timelines of PFAS deposition from a sediment core collected near a former textile mill at the Pawtuxet River in Rhode Island. Age depth models were done by Cs137 and Pb210 isotopes and chlorinated pesticides down core analysis. The targeted analysis demonstrated the predominance of long-chain perfluoroalkyl carboxylic acids (C10, C12 and C13 PFCAs) and perfluorosulfonic acids (C8 and C10 PFSAs). TOP and EOF analysis demonstrated that <6% of fluorine was initially detected by targeted analysis, with higher levels at bottom of the core (dated 1936). Additional PFAS compounds, including unsaturated and H-substituted longer-chain PFCAs, FTCAs and other fluorinated compounds (e.g., triflamizole), were identified by NTA using FluoroMatch software. Higher inputs of PFAS were observed between 1970–1980 dominated by PFCAs until the 1990s. Ongoing research will use these data to track the transport of contaminated sediments from legacy sites in the aquatic environment. With toxicological data available to only a small fraction of the thousands of known PFAS, the study presented by Denise McMillan, USEPA, shows new approach methods to evaluate potential toxicity using in vivo and in vitro dosimetry and metabolic biotransformation studies of the hexafluoropropylene oxide homologue perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoic acid (HFPO-TeA) in Sprague Dawley rats. Evidence of chronic toxicity included thinning hair, hunching, weight loss, abnormal breathing, lethargy and lethality (>17 mg/kg/day) were observed in life observations, with potential sex-dependency. NTA identified potential biotransformation products of HFPO-TeA, which included a perfluoro alcohol (dealkylation product), and perfluoro-2,5-trimethyl-3,6-dioxanonanoic acid (HFPO-TA) oligomer. Further elucidation of transformation products and evaluations of tissue PFAS distributions, cross-species and cross-sex of in vitro hepatocyte clearance and plasma protein binding is underway.

Most PFAS are not regularly monitored at water treatment plants, which leads to a very small number of PFAS being analyzed compared with what is being produced and does not consider metabolites and transformation products. Yong-Lai Feng, Health Canada, has shown an NTA tool for mapping PFAS in drinking water using HRMS combined with a retention time prediction to increase confidence in PFAS identification. This rapid PFAS diagnostic ion search tool was able to differentiate between treated and source water and can be used to evaluate the efficiency of the water treatment.

Xuerong Li, Florida International University, presented online on the NTA assessment of PFAS in drinking and surface water from South Florida environments (Biscayne Bay canals, Key West, and Everglades canals). PFAS identification compared results obtained by Compound Discoverer 3.3 and FluoroMatch 2.0 with specific criteria proposed for data reduction and higher confidence of identification. More than 500 PFAS were tentatively identified with little overlap between different water sources. Ultimately, a semi-quantitation approach was proposed based on a global calibration curve using the averaged response factor of a mixture of native standards and internal standards.

Author's contact information: Natalia Quinete, nsoaresq@fiu.edu

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