Chemical oxidization of some AFFFs leads to the formation of 6:2FTS and 8:2FTS

pKa prediction of per- and polyfluoroalkyl acids in water using in silico gas phase stretching vibrational frequencies and infrared intensities

To successfully understand and model the environmental fate of per- and polyfluoroalkyl substances (PFAS), it is necessary to know key physicochemical properties (PChPs) such as pKa; however, measured PChPs of PFAS are scarce and of uncertain reliability. In this study, quantitative structure-activity relationships (QSARs) were developed by correlating calculated (M062-X/aug-cc-pVDZ) vibrational frequencies (VF) and corresponding infrared intensities (IRInt) to the pKa of carboxylic acids, sulfonic acids, phosphonic acids, sulfonamides, betaines, and alcohols. Antisymmetric stretching VF of the anionic species were used for all subclasses except for alcohols where the OH stretching VF performed better. The individual QSARs predicted the pKa for each subclass mostly within 0.5 pKa units from the experimental values. The inclusion of IRInt as a pKa predictor for carboxylic acids improved the results by decreasing the root-mean-square error from 0.35 to 0.25 (n > 100). Application of the developed QSARs to estimate the pKa of PFAS within each subclass revealed that the length of the perfluoroalkyl chain has minimal effect on the pKa, consistent with other models but in stark contrast with the limited experimental data available.

Behavior of Per- and polyfluoroalkyl substances (PFAS) in Pilot-Scale vertical flow constructed wetlands treating landfill leachate

This study investigated the behavior of per- and polyfluoroalkyl substances (PFAS) in multiple pilot-scale vertical flow constructed wetlands (VFCW) treating landfill leachate. Eight pilot-scale VFCW columns planted with Typha latifolia or Scirpus Californicus were fed untreated municipal solid waste (MSW) landfill leachate that was diluted with potable water at a 1:10 ratio (1 part leachate to 10 parts total) at a fixed daily hydraulic loading rate of 0.525 m d^-1. Ninety-two PFAS were examined and 18 PFAS were detected at quantifiable concentrations (7 precursor species and 11 terminal species). The average concentration of Σ₉₂ PFAS in the influent was 3,100 ng L^-1, which corresponded with minimal reduction in the effluents from the four VFCW (decreases ranged from 1% to 12% on average for Σ₁₈ PFAS); however, precursors 6:3 FTCA, 7:3 FTCA, N-MeFOSAA, and N-EtFOSAA concentrations decreased significantly in the VFCW effluents, and significant decreases in the concentrations of these PFAA-precursors were concurrent with a significant increase in concentrations of five PFAAs (PFBA, PFNA, PFBS, PFOS, and PFOSI). This trend indicates that from a regulatory perspective, standalone VFCWs are likely to produce an apparent PFAS increase, which may also be true for many other leachate treatment processes incorporating aerobic biological treatment. Additional treatment to address PFAS should be integrated prior to the use of any system, including VFCWs, for the treatment of constituents of concern in MSW landfill leachate.

Occurrence, spatial distribution, and sources of PFASs in the water and sediment from lakes in the Tibetan Plateau

Per-and polyfluoroalkyl substances (PFASs) are omnipresent globally and received increasing attention recently. However, there are limited data on PFASs in the Tibetan Plateau (TP), a remote high-altitude mountain region, which is regard as an important indicator region to study long-range transport behaviors of contaminants. This study investigates the occurrence, distribution, partitioning behavior, and sources of 26 PFASs in water and sediments from the four lakes of TP. The ΣPFAS concentrations ranged from 338 to 9766 pg L^-1 in water, and 12.2-414 pg g^-1 dry weight in sediments. Perfluorobutanonic acid (PFBA) and perfluorooctane sulfonate (PFOS) were detected in all samples. Qinghai Lake had the highest ΣPFAS concentrations in both water and sediments, while the Ranwu Lake had the lowest. The functional groups and CF₂ moiety units were investigated as essential factors influencing the partition behavior. Principal component analysis (PCA) combined back-trajectory was used to infer possible sources of PFASs. The results suggested that the main source of PFASs in Yamdrok Lake, Namco Lake, and Ranwu Lake on southern TP were mainly originated from South Asia via long-range atmospheric transport (LRAT); while for the Qinghai Lake of northern TP, LRAT, local emissions, and tourism activities were the primary sources of PFASs.

Removal of PFAS from aqueous solution using PbO2 from lead-acid battery

Whilst advanced electrochemical oxidation can break down per- and polyfluoroalkyl substances (PFAS), the requirement for expensive electrode materials usually prevents its widespread application. Here we use an industrial material of lead peroxide (PbO₂) from a lead-acid battery to break down PFAS including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and 1H,1H,2H,2H-perfluorooctanesulfonic acid (6:2 FTS). By optimising the PbO₂ panel (activating and doping) and working conditions including supporting electrolyte (1 L 10 mM Na₂SO₄), initial concentration (10 μM), temperature (room temperature), current density (5 A for a 10 cm × 10 cm PbO₂ panel) etc., we successfully remove > 99% PFAS (individual PFAS monitored via HPLC-MS) whilst mineralising ∼59% PFOA (defluorination, F^- released and monitored via F-ISE, fluoride-ion selective electrode). By studying the pseudo-first-order kinetics of the PFAS breakdown (0.0028-0.007 min^-1) and defluorination (0.84-5.9 × 10^-8 min^-1), we assign the difference to the adsorption of PFAS on the PbO₂ panel and the appearance of intermediates before the full defluorination. The leaked HF gas (∼10^-5 M, collected using 0.25 L 0.1 M NaOH) and Pb²⁺ (∼12 μM, or ∼ 2.5 ppm) are also confirmed. This study employs an economic industrial material, highlights the contribution of adsorption towards the PFAS removal and breakdown, and identifies the possible leakage of secondary contaminants.

Smartphone app-based/portable sensor for the detection of fluoro-surfactant PFOA

We developed a smartphone app-based monitoring tool for the detection of anionic surfactants (AS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Akin to the methylene blue active substances (MBAS), liquid-phase extraction (LPE) is employed to extract the hydrophobic ion-pair of dye (ethyl violet)-AS to an organic phase (ethyl acetate). The colour (RGB) of the organic phase is read using a smartphone camera with the help of a reading kit. The value of RGB is carefully corrected and linked to the concentration of ASs with a standard deviation of <10% in the 10-1000 ppb (part per billion) range. In order to avoid the interference arising from inorganic anions (such as those found in tap water and groundwater), the water sample is pre-treated either by solid-phase extraction (SPE), which takes ∼30 min, or by dual liquid-phase extraction (dual-LPE, developed by us), which takes ∼5 min. In the latter case, the organic phase of the first LPE (equilibrium with water sample) is transferred and subjected to a second LPE (equilibrium with Milli-Q water) to remove any potential background interference. In the meantime, SPE can also pre-concentrate ASs at 100-1000 times (in volume) to benefit the sensitivity. Consequently, our smartphone app can detect PFOA spiked in tap/groundwater with an LOD of 10 ppb (∼12 nM, dual-LPE of ∼5 min), or 0.5 ppb (∼1.2 nM, SPE of ∼3 h), suggesting that it has the potential to succeed as a pre-screening tool for on-site application and in common laboratory tests.

Discovery of novel per- and polyfluoroalkyl substances (PFASs) at a fire fighting training ground and preliminary investigation of their fate and mobility

Aqueous film forming foams (AFFFs) have been released at fire training facilities for several decades resulting in the contamination of soil and groundwater by per- and polyfluoroalkyl substances (PFASs). AFFF compositions are proprietary and may contain a broad range of PFASs for which the chemical structures and degradation products are not known. In this study, high resolution quadrupole-time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS) in combination with data processing using filtering strategies was applied to characterize and elucidate the PFASs present in concrete extracts collected at a fire training ground after the historical use of various AFFF formulations. Twelve different fluorochemical classes, representing more than 60 chemicals, were detected and identified in the concrete extracts. Novel PFASs homologues, unmonitored before in environmental samples such as chlorinated PFSAs, ketone PFSAs, dichlorinated PFSAs and perfluoroalkane sulphonamides (FASAs) were detected in soil samples collected in the vicinity of the fire training ground. Their detection in the soil cores (from 0 to 2 m) give an insight on the potential mobility of these newly identified PFASs.

Surface-enhanced Raman scattering (SERS) detection of fluorosurfactants in firefighting foams

We demonstrated SERS (surface-enhanced Raman scattering) detection of fluorosurfactants (FSs), which are commonly formulated in aqueous firefighting foams (AFFFs), by increasing their loading affinity and boosting their Raman activity.