Advancing PFAS characterization: Development and optimization of a UV-H2O2-TOP assay for improved PFCA chain length preservation and organic matter tolerance.

As per- and polyfluoroalkyl substances (PFAS) infiltrate the environment via industrial, commercial, and domestic sources, the demand for robust, cost-effective, and straightforward analytical assays intensifies to enhance PFAS characterization and quantification. To address this demand, this study introduces a novel UV-H2O2-TOP assay, identifying optimal parameters such as pH (5-9), oxidant concentration (500 mM H2O2), activation rate (63 mM H2O2 h-1), and an acceptable total organic carbon (TOC) limit (~1000 mg/L TOC) to achieve maximum PFAA precursor conversion. Additional work was performed further optimizing the UV-TOP assay, by confirming its superiority to heat activation, identifying the effectiveness of different persulfate salts, and investigating different concentrations of sodium persulfate and sodium hydroxide at a 1:2.5 ratio on PFCA yield. Our investigation concluded by applying the UV-H2O2-TOP assay, using sodium persulfate as the TOP assay oxidant, to 6:2 FTS and five different AFFF samples. High-resolution mass spectrometry and an expanded analytical suite support sample analysis, facilitating direct quantification of ultra-short chain perfluoroalkyl carboxylates (PFCAs) and common fluorotelomer compounds including 5:3/5:1:2 fluorotelomer betaine and 6:2 fluorotelomer sulfonamido betaine. Results highlight several advantages of this tandem UV-activated method, including enhanced preservation of perfluoroalkyl chains (post-oxidation of 6:2 fluorotelomer sulfonate resulted in 28 % PFHpA, 47 % PFHxA, 25 % C3-C5 PFCA), capacity to handle high TOC limits (1000 mg/L TOC), and ability to incorporate higher persulfate concentrations in a single oxidation cycle.

Mechanochemical degradation of per- and polyfluoroalkyl substances in soil using an industrial-scale horizontal ball mill with comparisons of key operational metrics.

Horizontal ball mills (HBMs) have been proven capable of remediating per- and polyfluoroalkyl substances (PFAS) in soil. Industrial-sized HBMs, which could easily be transported to impacted locations for on-site, ex-situ remediation, are readily available. This study examined PFAS degradation using an industrial-scale, 267 L cylinder HBM. This is the typical scale used in the industry before field application. Near-complete destruction of 6:2 fluorotelomer sulfonate (6:2 FTS), as well as the non-target PFAS in a modern fluorotelomer-based aqueous film forming foam (AFFF), was achieved when spiked onto nepheline syenite sand (NSS) and using potassium hydroxide (KOH) as a co-milling reagent. Perfluorooctanesulfonate (PFOS) showed much better and more consistent results with scale-up regardless of KOH. Perfluorooctanoate (PFOA) was examined for the first time using a HBM and behaved similarly to PFOS. Highly challenging field soils from a former firefighting training area (FFTA) were purposefully used to test the limits of the HBM. To quantify the effectiveness, free fluoride analysis was used; changes between unmilled and milled soil were measured up to 7.8 mg/kg, which is the equivalent of 12 mg/kg PFOS. Notably, this does not factor in insoluble fluoride complexes that may form in milled soils, so the actual amount of PFAS destroyed may be higher. Soil health, evaluated through the assessment of key microbial and associated plant health parameters, was not significantly affected as a result of milling, although it was characterized as poor to begin with. Leachability reached 100 % in milled soil with KOH, but already ranged from 81 to 96 % in unmilled soil. A limited assessment of the hazards associated with the inhalation of PFAS-impacted dust from ball-milling, as well as the cross-contamination potential to the environment, showed that the risk was low in both cases; however, precautions should always be taken.

Forever no more: Complete mineralization of per- and polyfluoroalkyl substances (PFAS) using an optimized UV/sulfite/iodide system.

As the global issue of PFAS contamination in water continues to grow there exists a need for technologies capable of fully mineralizing PFAS in water, with destruction being measured as both a loss of the initial PFAS and a quantitative recovery of the resultant fluoride ions. This study investigates the use of sulfite and iodide in a bicarbonate-buffered alkaline system activated with ultraviolet (UV) light to destroy PFAS. The UV/sulfite/iodide system creates a reductive environment through the generation of aqueous electrons, which can degrade PFAS. The extent of degradation and defluorination was explored for perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), 6:2 fluorotelomer sulfonic acid (6:2 FTS), and perfluorobutane sulfonic acid (PFBS). An initial UV/sulfite/iodide system achieved 100 % degradation and > 90 % defluorination for PFOS, PFOA, and 6:2 FTS, but was not capable of completely degrading PFBS. Transformation product elucidation experiments were performed for PFOS under different UV systems, and 6:2 FtSaB using the initial UV/sulfite/iodide system. Several transformation products were identified including -nF/+nH PFOS (n = 1-13), -F/+H shorter-chain PFSAs, 6:2 fluorotelomer sulfonamidoamine (6:2 FtSaAm), 6:2 fluorotelomer sulfonamide, and 6:2 fluorotelomer unsaturated sulfonamide. Novel identification of -F/+H perfluoropropane sulfonic acid (PFPS) and -F/+H perfluoroethane sulfonic acid (PFES) following degradation of PFOS confirms CC bond cleavage, and different isomers of -F/+H PFOS confirms the potential for CF bond cleavage to occur throughout the perfluoroalkyl chain. Additional optimization experiments were performed aiming to fully degrade PFBS. The optimal protocol found in this study involved an elevated initial sulfite concentration and adding additional sulfite at regular intervals during UV-activation, achieving >99.9 % destruction and complete quantitative defluorination of PFBS.

Parsimonious methodology for synthesis of silver and copper functionalized cellulose.

Metal nanomaterials, such as silver and copper, are often incorporated into commercial textiles to take advantage of their Antibacterial and antiviral properties. The goal of this study was to identify the most parsimonious method for the synthesis of silver, copper, or silver/copper bimetallic treated textiles. To accomplish this eight different methods were employed to synthesize silver, copper, and silver/copper functionalized cotton batting textiles. Using silver and copper nitrate as precursors, different reagents were used to initiate/catalyze the deposition of metal, including: (1) no additive, (2) sodium bicarbonate, (3) green tea, (4) sodium hydroxide, (5) ammonia, (6, 7) sodium hydroxide/ammonia at a 1:2 and 1:4 ratio, and (8) sodium borohydride. The use of sodium bicarbonate as a reagent to reduce silver onto cotton has not been used previously in literature and was compared to established methods. All synthesis methods were performed at 80 °C for one hour following textile addition to the solutions. The products were characterized by x-ray fluorescence (XRF) analysis for quantitative determination of the metal content and x-ray absorption near edge structure (XANES) analysis for silver and copper speciation on the textile. Scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) and size distribution inductively coupled plasma mass spectrometry (ICP-MS) were used to further characterize the products of the sodium bicarbonate, sodium hydroxide, and sodium borohydride synthesis methods following ashing of the textile. For the silver treatment methods (1 mM Ag +), sodium bicarbonate and sodium hydroxide resulted in the highest amounts of silver on the textile (8900 mg Ag/kg textile and 7600 mg Ag/kg textile) and for copper treatment (1 mM Cu +) the sodium hydroxide and sodium hydroxide/ammonium hydroxide resulted in the highest amounts of copper on the textile (3800 mg Ag/kg textile and 2500 mg Ag/kg textile). Formation of copper oxide was dependent on the pH of the solution, with 4 mM ammonia and other high pH solutions resulting in majority of the copper on the textile existing as copper oxide, with smaller amounts of ionic-bound copper. The identified parsimonious methods will lend themselves to the efficient manufacturing of antibacterial and antiviral textiles, or the development of multifunctionalized smart textiles. Supplementary Information: The online version contains supplementary material available at 10.1007/s10570-023-05099-7.

Use of a horizontal ball mill to remediate per- and polyfluoroalkyl substances in soil.

There is a need for destructive technologies for per- and polyfluoroalkyl substances (PFAS) in soil. While planetary ball mill have been shown successful degradation of PFAS, there are issues surrounding scale up (maximum size is typically 0.5 L cylinders). While having lower energy outputs, horizontal ball mills, for which scale up is not a limiting factor, already exist at commercial/industrial sizes from the mining, metallurgic and agricultural industries, which could be re-purposed. This study evaluated the effectiveness of horizontal ball mills in degrading perfluorooctanesulfonate (PFOS), 6:2 fluorotelomer sulfonate (6:2 FTSA), and aqueous film forming foam (AFFF) spiked on nepheline syenite sand. Horizontal ball milling was also applied to two different soil types (sand dominant and clay dominant) collected from a firefighting training area (FFTA). Liquid chromatography tandem mass spectrometry was used to track 21 target PFAS throughout the milling process. High-resolution accurate mass spectrometry was also used to identify the presence and degradation of 19 non-target fluorotelomer substances, including 6:2 fluorotelomer sulfonamido betaine (FtSaB), 7:3 fluorotelomer betaine (FtB), and 6:2 fluorotelomer thioether amido sulfonate (FtTAoS). In the presence of potassium hydroxide (KOH), used as a co-milling reagent, PFOS, 6:2 FTSA, and the non-target fluorotelomer substances in the AFFF were found to undergo upwards of 81%, 97%, and 100% degradation, respectively. Despite the inherent added complexity associated with field soils, better PFAS degradation was observed on the FFTA soils over the spiked NSS, and more specifically, on the FFTA clay over the FFTA sand. These results held through scale-up, going from the 1 L to the 25 L cylinders. The results of this study support further scale-up in preparation for on-site pilot tests.

Elucidating degradation mechanisms for a range of per- and polyfluoroalkyl substances (PFAS) via controlled irradiation studies.

Per- and polyfluoroalkyl substances (PFAS) are a challenging class of environmental pollutants due to a lack of available destructive remediation technologies. Understanding the fundamental mechanisms for degradation of PFAS is key for the development of field scalable and in-situ destructive based remediation technologies. This study aimed to elucidate and refine the current understanding of PFAS degradation mechanisms in water through a series of controlled gamma irradiation studies. Gamma irradiation of PFAS was performed using a cobalt-60 source in a batch irradiation up to 80 kGy at the Australian Nuclear Science and Technology Organisation. Perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), 6:2 fluorotelomer sulfonate (6:2 FTS), and a suite of thirteen different PFAS (including C4-C12 PFCAs, C4, C6, C8 PFSAs, and FOSA) were irradiated to investigate degradation, influence of pH, chain length, and transformation. High resolution mass spectrometry was used to identify more than 80 fluorinated transformation products throughout the degradation experiments. These included the -F/+H, -F/+OH, -F/CH2OH exchanged PFAS and n - 1 PFCA, amongst others. Given the reactive species present (hydroxyl radicals (·OH), hydrogen radicals (·H) and aqueous electrons (e-aq)), and the degradation products formed it was shown that aqueous electrons were the key reactive species responsible for initial PFAS degradation. Most importantly, based on degradation product formation, we found that the initial -F/+H does not have to occur at the α-fluoride (nearest the functional head group), rather occurring throughout the chain length leading to more complex degradation pathways than previously postulated. While our results support some of the reaction steps postulated in the literature, we have developed a unified 16 step and 3 pathway schematic of degradation supported by experimental observations.