Edmund H. Antell

Perfluoroalkyl sulfonamides (FASAs) have been detected in aqueous film-forming foams (AFFF), municipal wastewater, and consumer products, among others. Although the compounds can be quantified directly by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS–MS), methods that are frequently used to measure poly- and perfluoroalkyl substances (PFASs) for which standards are not available, like the total oxidizable precursor (TOP) assay, 19F-NMR and nontarget analysis often employ solid-phase extraction followed by elution in a polar organic solvent, such as methanol. Volatilization of FASAs during open blowdown of polar organic solvent extracts from soil, sediment, or aqueous samples leads to underestimation of PFAS concentrations. To assess the importance of this loss mechanism, we measured recovery of three FASAs under conditions relevant to environmental analysis. Recoveries of FASAs and other neutral PFAS, including FASAAs and FTCAs, from methanol during the nitrogen blowdown step decreased as analyte concentrations decreased, with recoveries of less than 1% at 2 μg/L (i.e., a concentration corresponding to about 4 ng/L in water samples prior to solid-phase extraction). The addition of 10 mM NaOH prior to the blowdown step improved recoveries to greater than 80% for all FASAs. NaOH addition prior to blowdown also resulted in an approximately 40% increase in the concentrations of precursors detected in diluted AFFF as measured with the total oxidizable precursor (TOP) assay. The increased concentrations could not be explained by analytes for which analytical standards were available. These findings highlight that volatilization during solvent evaporation can be a significant source of analytical bias for a broader class of neutral PFAS, with FASAs serving as an important example.

Aqueous film-forming foams (AFFFs) are a major source of per- and polyfluoroalkyl substances (PFAS) contamination in groundwater and soil. Although PFAS sorption is known to depend on the properties of solid matrices, the roles of organic matter and iron (hydr)oxides remain poorly understood, especially for polyfluorinated compounds. To investigate the interplay between particulate organic matter and iron (hydr)oxides in PFAS-contaminated subsurface environments, we studied the partitioning of neutral, cationic, and anionic PFAS in AFFF to well-characterized solids using the mixed-mode solid-phase extraction (SPE) technique combined with the total oxidizable precursor (TOP) assay. Our results indicated that organic matter consistently enhanced PFAS sorption. In contrast, the effect of goethite, a representative iron-containing mineral, on PFAS sorption varied with PFAS charge. Using three different AFFFs, we found that anionic PFAS exhibited strong sorption regardless of organic matter content, while cationic and zwitterionic PFAS sorbed poorly at circumneutral pH. These trends were more pronounced for iron-coated sand, which showed higher affinity for anionic PFAS. Treatment with ascorbate, a mild reductant, released PFAS associated with iron (hydr)oxides. These findings highlight the importance of iron (hydr)oxides in the retention of anionic PFAS and could be leveraged to manage PFAS mobility through subsurface iron amendments or in situ iron (hydr)oxide formation/dissolution.

Perfluoroalkyl acid (PFAA) precursors are a diverse subclass of per- and polyfluoroalkyl substances (PFASs) that can be transformed into PFAAs of public health concern. Unlike strongly acidic PFAAs, precursors can be anionic, cationic, neutral, or zwitterionic. Precursor charge affects the environmental fate, but existing quantification techniques struggle to ascertain the abundance of compounds within each charge group. To fill this gap, we developed and validated a solid-phase extraction procedure that separates precursors by charge and quantifies the sum of the precursors in each fraction with the total oxidizable precursor (TOP) assay. Method performance was demonstrated by spiking known concentrations of ten precursors into aqueous film-forming foam (AFFF)-impacted groundwater, municipal wastewater, and soil samples. Precursor fractionation and recovery were greater in groundwater and soil samples than in wastewater. Use of the method provided results that were consistent with expectations based on precursor transport properties. In surficial soils near an AFFF source zone, anionic precursors with five or fewer perfluorinated carbons accounted for about 95% of PFASs, but less than half of PFASs in the underlying groundwater. In municipal wastewater influent, the sum of precursors exceeded the sum of PFAAs and was approximately equally distributed among all charge fractions.

Per- and polyfluoroalkyl substances (PFASs) from aqueous film forming foams (AFFFs) can hinder bioremediation of co-contaminants such as trichloroethene (TCE) and benzene, toluene, ethylbenzene, and xylene (BTEX). Anaerobic dechlorination can require bioaugmentation of Dehalococcoides, and for BTEX, oxygen is often sparged to stimulate in situ aerobic biodegradation. We tested PFAS inhibition to TCE and BTEX bioremediation by exposing an anaerobic TCE-dechlorinating coculture, an aerobic BTEX-degrading enrichment culture, and an anaerobic toluene-degrading enrichment culture to n-dimethyl perfluorohexane sulfonamido amine (AmPr-FHxSA), perfluorohexane sulfonamide (FHxSA), perfluorohexanesulfonic acid (PFHxS), or nonfluorinated surfactant sodium dodecyl sulfate (SDS). The anaerobic TCE-dechlorinating coculture was resistant to individual PFAS exposures but was inhibited by >1000× diluted AFFF. FHxSA and AmPr-FHxSA inhibited the aerobic BTEX-degrading enrichment. The anaerobic toluene-degrading enrichment was not inhibited by AFFF or individual PFASs. Increases in amino acids in the anaerobic TCE-dechlorinating coculture compared to the control indicated stress response, whereas the BTEX culture exhibited lower concentrations of all amino acids upon exposure to most surfactants (both fluorinated and nonfluorinated) compared to the control. These data suggest the main mechanisms of microbial toxicity are related to interactions with cell membrane synthesis as well as protein stress signaling.