Citation:

Zhang, C., Z. Hopkins, J. McCord, M. Strynar, AND D. Knappe. Fate of Per- and Polyfluoroalkyl Ether Acids in the Total Oxidizable Precursor Assay and Implications for the Analysis of Impacted Water. Environmental Science & Technology Letters. American Chemical Society, Washington, DC, 6(11):662-668, (2019). https://doi.org/10.1021/acs.estlett.9b00525

Impact/Purpose:

The traditional total oxidizeable precurssor (TOP) assay is intended to provide a “total” summary of PFAS compounds that may transform into chemicals of concern. This study identified new end products of the assay that are not on the standard list, implying that the long standing assay panel does not successfully capture all PFAS species that may be of relevance in a sample impacted by emerging PFAS. PFAS standards were spiked into aqueous samples and subjected to oxidative conditions in accordance with the TOP assay to convert oxidizable PFAS materials to stable end-products. Oxidized PFAS standards were subjected to targeted and non-targeted analysis to identify transformation products (if any) and quantify the PFAS species. Historical water samples from locations on the Cape Fear River (Huske Lock & Damn and Lock & Dam #1) from 2014, 2015, and 2018 were analyzed by the TOP assay and quantified using an expanded analyte panel to demonstrate the impact of emerging contaminants on estimated “total” PFAS load. This study identified new end products of the assay that are not on the standard list, implying that the assay does not successfully capture all PFAS species that may be of relevance in a sample. This is of importance to partners who examine total PFAS content via TOP assay or similar transformative assays to determine total PFAS.

Description:

Per- and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. The PFAS class includes almost 5000 registered compounds, but analytical methods are lacking for most PFASs. The total oxidizable precursor (TOP) assay was developed to indirectly quantify unknown PFASs that are precursors to commonly measured perfluoroalkyl acids. To understand the behavior of recently identified per- and polyfluoroalkyl ether acids (PFEAs), including fluorinated replacements and manufacturing byproducts, we determined the fate of 15 PFEAs in the TOP assay. Ten perfluoroalkyl ether acids and a chlorinated polyfluoroalkyl ether acid (F-53B) were stable in the TOP assay and represent terminal products that are likely as persistent as historically used PFASs. Adding perfluoroalkyl ether acids and F-53B to the target analyte list for the TOP assay is recommended to capture a higher percentage of the total PFAS concentration in environmental samples. In contrast, polyfluoroalkyl ether acids with a -O-CFH- moiety were oxidized, typically to products that could not be identified by liquid chromatography and high-resolution mass spectrometry. Application of the TOP assay in its proposed enhanced form revealed high levels of PFEAs, the presence of precursors that form perfluoroalkyl carboxylic acids, and the absence of precursors that form PFEAs in surface water impacted by PFAS-containing wastewater discharges.

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