Sites impacted by aqueous film-forming foam (AFFF) contain co-contaminants that can stimulate biotransformation of polyfluoroalkyl substances. Here, we compare how microbial enrichments from AFFF-impacted soil amended with diethyl glycol monobutyl ether (found in AFFF), aromatic hydrocarbons (present in co-released fuels), acetate, and methane (substrates used or formed during bioremediation) impact the aerobic biotransformation of an AFFF-derived six-carbon electrochemical fluorination (ECF) precursor N-dimethyl ammonio propyl perfluorohexane sulfonamide (AmPr-FHxSA). We found that methane-and acetate-oxidizing cultures resulted in the highest yields of identifiable products (38 and 30%, respectively), including perfluorohexane sulfonamide (FHxSA) and perfluorohexane sulfonic acid (PFHxS). Using these data, we propose and detail a transformation pathway. Additionally, we examined chemical oxidation products of AmPr-FHxSA and FHxSA to provide insights on remediation strategies for AmPr-FHxSA. We demonstrate mineralization of these compounds using the sulfate radical and test their transformation during the total oxidizable precursor (TOP) assay. While perfluorohexanoic acid accounted for over 95% of the products formed, we demonstrate here for the first time two ECF-based precursors, AmPr-FHxSA and FHxSA, that produce PFHxS during the TOP assay. These findings have implications for monitoring poly-and perfluoroalkyl substances during site remediation and application of the TOP assay at sites impacted by ECF-based precursors.

Despite the prevalence of nitrate reduction in groundwater, the biotransformation of per-and polyfluoroalkyl substances (PFAS) under nitrate-reducing conditions remains mostly unknown compared with aerobic or strong reducing conditions. We constructed microcosms under nitrate-reducing conditions to simulate the biotransformation occurring at groundwater sites impacted by aqueous film-forming foams (AFFFs). We investigated the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a principal PFAS constituent of several AFFF formulations using both quantitative liquid chromatography−tandem mass spectrometry (LC-MS/MS) and qualitative high-resolution mass spectrometry analyses. Our results reveal that the biotransformation rates of 6:2 FtTAoS under nitratereducing conditions were about 10 times slower than under aerobic conditions, but about 2.7 times faster than under sulfate-reducing conditions. Although minimal production of 6:2 fluorotelomer sulfonate and the terminal perfluoroalkyl carboxylate, perfluorohexanoate was observed, fluorotelomer thioether and sulfinyl compounds were identified in the aqueous samples. Evidence for the formation of volatile PFAS was obtained by mass balance analysis using the total oxidizable precursor assay and detection of 6:2 fluorotelomer thiol by gas chromatography−mass spectrometry. Our results underscore the complexity of PFAS biotransformation and the interactions between redox conditions and microbial biotransformation activities, contributing to the better elucidation of PFAS environmental fate and impact.

Per-and polyfluoroalkyl substances (PFASs) are a class of synthetic, organic chemicals that contaminate drinking water and natural ecosystems. PFAS source apportionment is challenging because there are many sources, and standard analytical methods quantify fewer than 100 of the thousands of PFASs in commerce. The total oxidizable precursor (TOP) assay augments the number of PFASs that can be quantified and is increasingly incorporated into routine site investigation. Here we examine the ability of the TOP assay to identify PFAS sources, including aqueous film-forming foam (AFFF) impacted sites, municipal wastewater treatment plants (WWTPs), and municipal solid waste landfills in 145 samples from 46 locations and three countries. The bootstrapped mean composition of PFASs from each source was dominated by precursors, particularly in samples from WWTPs where precursors that form short-chain perfluoroalkyl carboxylates during the TOP assay were most common. Compared to when TOP assay data were excluded, inclusion of TOP assay data in dimension-reducing algorithms, such as principal component analysis (PCA), improved separation among sources. We converted the PCA tool into a web application that allows users to initiate PFAS source apportionment efforts on data from sites where contaminant sources are unknown.

Fungi and laccase mediator systems (LMSs) have a proven track record of oxidizing recalcitrant organic compounds. There has been considerable interest in applying LMSs to the treatment of perfluoroalkyl acids (PFAAs), a class of ubiquitous and persistent environmental contaminants. Some laboratory experiments have indicated modest losses of PFAAs over extended periods, but there have been no clear demonstrations of a transformation mechanism or the kinetics that would be needed for remediation applications. We set out to determine if this was a question of identifying and optimizing a rate-limiting step but discovered that observed losses of PFAAs were experimental artifacts. While unable to replicate the oxidation of PFAAs, we show that interactions of the PFAA compounds with laccase and laccase mediator mixtures could cause an artifact that mimics transformation (≲60%) of PFAAs. Furthermore, we employed a surrogate compound, carbamazepine (CBZ), and electron paramagnetic resonance spectroscopy to probe the formation of the radical species that had been proposed to be responsible for contaminant oxidation. We confirmed that under conditions where sufficient radical concentrations were produced to oxidize CBZ, no PFAA removal took place.

Changing climate threatens our water systems: Droughts, fires, and floods disrupt access to safe water and no country is immune. The aging infrastructure crisis offers an opportunity to build resiliency into our future water systems with approaches like (non-)potable reuse. Such strategies require participation by end-users, which we propose can be championed by water utilities through: (1) Raising awareness of water challenges, (2) education about current water realities and opportunities, and (3) providing resources to implement and sustain water solutions.