Unique analytical considerations for laboratory studies identifying metabolic products of per- and polyfluoroalkyl substances (PFASs)

A Comparative Biodegradation Study to Assess the Ultimate Fate of Novel Highly Functionalized Hydrofluoroether Alcohols in Wastewater Treatment Plant Microcosms and Surface Waters

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals present in a wide range of commercial and consumer products due to their water-repellency, nonstick, or surfactant properties, resulting from their chemical and thermal stability. This stability, however, often leads to persistence in the environment when they are inevitability released. We utilized microbial microcosms from wastewater treatment plant (WWTP) sludge to determine how employing different functional groups such as heteroatom linkages, varying chain lengths, and hydrofluoroethers (HFEs) will impact the ultimate fate of these novel PFAS structures. A suite of five novel fluorosurfactant building blocks (F7 C3 OCHFCF2 SCH2 CH2 OH (FESOH), F3 COCHFCF2 SCH2 CH2 OH (MeFESOH), F7 C3 OCHFCF2 OCH2 CH2 OH (ProFdiEOH), F7 C3 OCHFCF2 CH2 OH (ProFEOH), and F3 COCHFCF2 OCH2 CH2 OH (MeFdiEOH)) and their select transformation products, were incubated in WWTP aerobic microcosms to determine structure-activity relationships. The HFE alcohol congeners with a thioether (FESOH and MeFESOH) were observed to transform faster than the ether congeners, while also producing second-generation HFE acid products (F7 C3 OCHFC(O)OH (2H-3:2 polyfluoroalkyl ether carboxylic acid [PFECA]) and F3 COCHFC(O)OH (2H-1:2 PFECA). Subsequent biodegradation experiments with 2H-1:2 PFESA and 2H-1:2 PFECA displayed no further transformation over 74 days. Surface water Photofate experiments compared 2H-1:2 PFECA, and 2H-1:2 polyfluorinated ether sulfonate (PFESA) with their fully fluorinated ether acid counterparts, and demonstrated the potential for both HFE acid species to completely mineralize over extended periods of time, a fate that highlights the value of studying novel PFAS functionalization. Environ Toxicol Chem 2024;00:1-9. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Occurrence, Fate, Human Exposure, and Toxicity of Commercial Photoinitiators

Photoinitiators (PIs) are a family of anthropogenic chemicals used in polymerization systems that generate active substances to initiate polymerization reactions under certain radiations. Although polymerization is considered a green method, its wide application in various commercial products, such as UV-curable inks, paints, and varnishes, has led to ubiquitous environmental issues caused by PIs. In this study, we present an overview of the current knowledge on the environmental occurrence, human exposure, and toxicity of PIs and provide suggestions for future research based on numerous available studies. The residual concentrations of PIs in commercial products, such as food packaging materials, are at microgram per gram levels. The migration of PIs from food packaging materials to foodstuffs has been confirmed by more than 100 reports of food contamination caused by PIs. Furthermore, more than 20 PIs have been detected in water, sediment, sewage sludge, and indoor dust collected from Asia, the United States, and Europe. Human internal exposure was also confirmed by the detection of PIs in serum. In addition, PIs were present in human breast milk, indicating that breastfeeding is an exposure pathway for infants. Among the most available studies, benzophenone is the dominant congener detected in the environment and humans. Toxicity studies of PIs reveal multiple toxic end points, such as carcinogenicity and endocrine-disrupting effects. Future investigations should focus on synergistic/antagonistic toxicity effects caused by PIs coexposure and metabolism/transformation pathways of newly identified PIs. Furthermore, future research should aim to develop "greener" PIs with high efficiency, low migration, and low toxicity.

A Review: Per- and Polyfluoroalkyl Substances-Biological Degradation

Per- and polyfluoroalkyl substances (PFASs), highly stable synthetic organic compounds with multiple carbon-fluorine bonds, are emerging as environmental contaminants, toxic, bioaccumulative, and environmentally persistent. PFASs are strongly resistant to biological and chemical degradation, and therefore PFASs present a challenge to researchers and scientists for a better understanding and application of remediation methods and biodegradation of PFASs and have become subject to strict government regulations. The review summarizes the recent knowledge of bacterial and fungal degradation of PFASs, as well as the enzymes involved in the processes of transformation/degradation of PFASs.

Taking the "F" out of forever chemicals

The right solvent mix breaks down perfluorinated organic acids.

Biotransformation of 6:2 Fluorotelomer Thioether Amido Sulfonate in Aqueous Film-Forming Foams under Nitrate-Reducing Conditions

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 nitrate-reducing 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.

Degradation of OBS (Sodium p-Perfluorous Nonenoxybenzenesulfonate) as a Novel Per- and Polyfluoroalkyl Substance by UV/Persulfate and UV/Sulfite: Fluorinated Intermediates and Treatability in Fluoroprotein Foam

Sodium p-perfluorous nonenoxybenzenesulfonate (OBS) is a novel fluorosurfactant used as the alternative to perfluorooctanesulfonic acid (PFOS) in several applications such as fire-fighting foams and chemical enhanced oil recovery ("EOR") in China, with the annual production capacity of about 3,500 t. Here, for the first time, we investigated the degradability of OBS under the conditions of UV/persulfate (UV/PS) and UV/sulfite (UV/SF) as typical redox processes. A higher reaction rate (1.05 min^-1) and total organic carbon (TOC) reduction (46.9%) but a low defluorination rate (27.6%) along with the formation of a series of fluorinated intermediates were found in UV/PS, while a high defluorination rate (87.7%) was realized in UV/SF. In particular, a nontargeted workflow using high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC/Q-TOF-MS) was established to detect fluorinated intermediates. Combined with the theoretical calculation, the distinctive degradation pathways in both oxidation and reduction processes were proposed. The degradation mechanism of OBS in UV/SF was proposed to be H/F exchange and subsequent HF elimination. Furthermore, the diluted OBS-based fluoroprotein (FP) foam was used to investigate the degradation of OBS, which confirms the treatability using the redox approach. This work provides insights into the degradability of OBS, fluorinated intermediate search, and proper treatment of related contamination.

Widening the Lens on PFASs: Direct Human Exposure to Perfluoroalkyl Acid Precursors (pre-PFAAs)

Determining health risks associated with per-/polyfluoroalkyl substances (PFASs) is a highly complex problem requiring massive efforts for scientists, risk assessors, and regulators. Among the most poorly understood pressing questions is the relative importance of pre-PFAAs, which are PFASs that degrade to highly persistent perfluoroalkyl acids. How many of the vast number of existing pre-PFAAs are relevant for direct human exposure, and what are the predominant exposure pathways? What evidence of direct exposure to pre-PFAAs is provided by human biomonitoring studies? How important are pre-PFAAs and their biotransformation products for human health risk assessment? This article outlines recent progress and recommendations toward widening the lens on human PFAS exposure to include the pre-PFAA subclass.

A novel analytical strategy for the determination of perfluoroalkyl acids in various food matrices using a home-made functionalized fluorine interaction SPME in combination with LC-MS/MS

In this study, a fluorine-fluorine interaction approach through fluoridating boron nitride nanosheets (BNNs) for sensing perfluoroalkyl acids (PFAAs) in multiple food matrices was developed. Through a facile hydrothermal fluorination modification, the BNNs were transferred into homogeneous fluorinated boron nitride nanoparticles (F-BNNs) with robust networks and specific surface area. After morphological modification, the particles displayed strong adsorption and sensing capabilities on PFAAs in both solid and liquid food matrix. Under the evaluation of mass spectrometry, F-BNNs based microextraction approach exhibited low method detection limits (MDLs) in the ranges of 0.9-3.9 pg mL^-1 and 3.6-15.8 pg g^-1 for milk and meat matrices, respectively, with satisfactory repeatability (RSD% <13.5%) and recoveries (77.7-110.5%). This work not only depicted a facile approach for preparing F-BNNs based SPME fiber, but also provided a routine analysis protocol for monitoring PFAAs in food systems.

Synthetic Phenolic Antioxidants: A Review of Environmental Occurrence, Fate, Human Exposure, and Toxicity

Synthetic phenolic antioxidants (SPAs) are widely used in various industrial and commercial products to retard oxidative reactions and lengthen product shelf life. In recent years, numerous studies have been conducted on the environmental occurrence, human exposure, and toxicity of SPAs. Here, we summarize the current understanding of these issues and provide recommendations for future research directions. SPAs have been detected in various environmental matrices including indoor dust, outdoor air particulates, sea sediment, and river water. Recent studies have also observed the occurrence of SPAs, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and 2,4-di-tert-butyl-phenol (DBP), in humans (fat tissues, serum, urine, breast milk, and fingernails). In addition to these parent compounds, some transformation products have also been detected both in the environment and in humans. Human exposure pathways include food intake, dust ingestion, and use of personal care products. For breastfeeding infants, breast milk may be an important exposure pathway. Toxicity studies suggest some SPAs may cause hepatic toxicity, have endocrine disrupting effects, or even be carcinogenic. The toxicity effects of some transformation products are likely worse than those of the parent compound. For example, 2,6-di-tert-butyl-p-benzoquinone (BHT-Q) can cause DNA damage at low concentrations. Future studies should investigate the contamination and environmental behaviors of novel high molecular weight SPAs, toxicity effects of coexposure to several SPAs, and toxicity effects on infants. Future studies should also develop novel SPAs with low toxicity and low migration ability, decreasing the potential for environmental pollution.

Elemental Fluorine Detection by Dielectric Barrier Discharge Coupled to Nanoelectrospray Ionization Mass Spectrometry for Nontargeted Analysis of Fluorinated Compounds

The growing use of fluorochemicals has elevated the need for nontargeted detection of unknown fluorinated compounds and transformation products. Elemental mass spectrometry (MS) coupled to chromatography offers a facile approach for such analyses by using fluorine as an elemental tag. However, efficient ionization of fluorine has been an ongoing challenge. Here, we demonstrate a novel atmospheric-pressure elemental ionization method where fluorinated compounds separated by gas chromatography (GC) are converted to Na₂F⁺ for nontargeted detection. The compounds are first introduced into a helium dielectric barrier discharge (DBD) for breakdown. The plasma products are subsequently ionized by interaction with a nanoelectrospray ionization (nano-ESI) plume of sodium-containing aqueous electrolytes. Our studies point to HF as the main plasma product contributing to Na₂F⁺ formation. Moreover, the results reveal that Na₂F⁺ is largely formed by the ion-neutral reaction between HF and Na₂A(NaA)_n⁺, gas-phase reagent ions produced by nano-ESI where A represents the anion of the electrolyte. Near-uniform fluorine response factors are obtained for a wide range of compounds, highlighting good efficiency of HF formation by DBD regardless of the chemical structure of the compounds. Detection limits of 3.5-19.4 pg of fluorine on-column are obtained using the reported GC-DBD-nano-ESI-MS. As an example of nontargeted screening, extractions from oil-and-water-repellent fabrics are analyzed via monitoring Na₂F⁺, resulting in detection of a fluorinated compound on a clothing item. Notably, facile switching of the ion source to atmospheric-pressure chemical ionization with the exact same chromatographic method allows identification of the detected compound at the flagged retention time.

Bioaccumulation of Novel Per- and Polyfluoroalkyl Substances in Mice Dosed with an Aqueous Film-Forming Foam

Per- and polyfluoroalkyl substances (PFASs) are widespread in the blood of the general human population, and their bioaccumulation is of considerable scientific and regulatory interest. PFAS exposure resulting from aqueous film-forming foam (AFFF) ingestion is poorly understood due to the complexity of AFFF mixtures and the presence of polyfluorinated substances that may undergo metabolic transformation. C57BL/6 mice were dosed with an AFFF primarily containing electrochemically fluorinated PFASs for 10 days, followed by a 6 day depuration. Urine was collected throughout the study and serum was collected post-depuration. Samples were analyzed via high-resolution mass spectrometry. Relative to the dosing solution, C6 and C7 perfluoroalkyl sulfonates (PFSAs) were enriched in dosed mouse serum, suggesting in vivo transformation of sulfonamide precursors. Some substituted C8 PFSAs [keto-perfluorooctane sulfonate (PFOS), hydrogen-PFOS, and unsaturated PFOS] appeared to be more bioaccumulative than linear PFOS, or were formed in vivo from unidentified precursors. A series of seven peaks in dosed mouse serum was tentatively identified as sulfonimide dimers that were either a minor component of the AFFF or were formed via metabolism of other AFFF components. This work highlights the importance of sulfonamide precursors in contributing to bioaccumulation of AFFF-associated PFSAs and identifies several classes of potentially bioaccumulative novel PFASs that warrant further investigation.