Measuring the Hidden PFAS: Assessing Measurement Techniques and Adsorptive Treatment Efficiencies

Abstract

Per- and poly-fluoroalkyl compounds (PFAS) are emerging contaminants due to their ubiquitous presence in the environment. Owing to their extreme resistance to heat and chemical degradation, they are widely used across consumer goods and industries. Although these technical properties make PFAS desirable as industrial chemicals, they also contribute to their accumulation in the environment and living organisms. Growing concern about the toxicity, recalcitrance, and bioaccumulation potential of some PFAS compounds, has prompted the EPA to set enforceable maximum contaminant levels (MCLs) as low as 4-10 ng/L for 5 PFAS commonly detected in drinking water resources, and other PFAS compounds are receiving increasing regulatory scrutiny.The PFAS family consists of more than 8,000 chemicals. Yet, the standard liquid chromatography mass spectrometry (LC-MS/MS) method currently used to analyze PFAS only targets a small subset of these chemicals (< 1%). Hence, targeted LC-MS/MS analysis often fails to quantify uncharacterized “hidden” PFAS and does not provide an accurate estimate of the total concentration of PFAS present in contaminated water. Eleven different groundwater samples were collected from drinking water sources and near two contaminated military sites in different sites in Arizona and Pennsylvania, including locations nearby Air Force Bases. The concentration of PFAS in these samples was measured using three different analytical techniques, including standard LC-MS/MS, the total oxidizable precursor (TOP-LC-MS/MS), and total organic fluorine combustion with ion chromatography (TOF-CIC) analysis. The LC-MS/MS EPA method targeted 25 well known PFAS compounds, whereas the TOP-LC-MS/MS and TOF-CIC techniques provided a measure of the concentration of “hidden” 13 (uncharacterized) PFAS. The TOF concentration determined in the various water samples was 0.3 to 20 times higher compared to the PFAS concentration quantified in the targeted LC-MS/MS assay, whereas the TOP-LC-MS/MS analysis revealed 0.9 to 4.5 times higher PFAS levels than the LC-MS/MS method alone. In some samples, PFAS were only detected after the TOP assay, indicating the presence of “hidden” precursors. These results highlight the need to employ more comprehensive techniques than the standard LC-MS/MS method to analyze PFAS more rigorously. Furthermore, four adsorbents, including crushed granular activated carbon (CAC), anion exchange resin (IX), polyaniline (PANI), and poly-o-toluidine (POT), were tested for their ability to remove PFAS from contaminated water. PFAS analysis using three different analytical methods (i.e., LC-MS/MS, TOP-LC-MS/MS and TOF-CIC) revealed that ‘hidden’ PFAS were not effectively removed by the adsorbents tested. The adsorptive materials utilized in this study have been optimized to remove anionic, long chain PFAS targeted by existing environmental regulations. Therefore, we anticipate that the PFAS fraction resisting adsorption might consist of short-chain PFAS and neutral, cationic and/or zwitterionic PFAS. Taken together, these results indicate the need to employ better methods to quantify the ”hidden” PFAS and to develop effective remediation techniques to remove this PFAS fraction from contaminated water.