The environmental fate of per- and polyfluoroalkyl substances
(PFAS)
in aqueous film-forming foams (AFFFs) remains largely unknown, especially
under the conditions representative of natural subsurface systems.
In this study, the biotransformation of 8:2 fluorotelomer alcohol
(8:2 FTOH), a component of new-generation AFFF formulations and a
byproduct in fluorotelomer-based AFFFs, was investigated under nitrate-,
iron-, and sulfate-reducing conditions in microcosms prepared with
AFFF-impacted soils. Liquid chromatography–tandem mass spectrometry
(LC–MS/MS) and high-resolution mass spectrometry (HRMS) were
employed to identify biotransformation products. The biotransformation
was much slower under sulfate- and iron-reducing conditions with >60
mol % of initial 8:2 FTOH remaining after ∼400 days compared
to a half-life ranging from 12.5 to 36.5 days under nitrate-reducing
conditions. Transformation products 8:2 fluorotelomer saturated and
unsaturated carboxylic acids (8:2 FTCA and 8:2 FTUA) were detected
under all redox conditions, while 7:2 secondary fluorotelomer alcohol
(7:2 sFTOH) and perfluorooctanoic acid (PFOA) were only observed as
transformation products under nitrate-reducing conditions. In addition,
1H-perfluoroheptane (F(CF2)6CF2H)
and 3-F-7:3 acid (F(CF2)7CFHCH2COOH)
were identified for the first time during 8:2 FTOH biotransformation.
Comprehensive biotransformation pathways for 8:2 FTOH are presented,
which highlight the importance of accounting for redox condition and
the related microbial community in the assessment of PFAS transformations
in natural environments.
Humans are exposed to a broad range of organic chemicals. Although targeted gas chromatography mass spectrometry techniques are used to quantify a limited number of persistent organic pollutants and trace organic contaminants in biological samples, nontargeted, high-resolution mass spectrometry (HRMS) methods assess the human exposome more extensively. We present a QuEChERS extraction for targeted and nontargeted analysis of trace organic contaminants using HRMS and compare this method to a traditional, cartridge-based solid-phase extraction (SPE). Following validation using reference and spiked serum samples, the method was applied to plasma samples (n = 75) from the Prospective investigation of Obesity, Energy, and Metabolism (POEM) study. We quantified 44 analytes using targeted analysis and 6247 peaks were detected using the nontargeted approach. Over 90% of targeted analytes were at least 90% recovered using the QuEChERS method in spiked serum samples. In nontargeted analysis, 84% of the peaks were above the method detection limit with area counts up to 3.0 × 105 times greater using the QuEChERS method. Of the targeted compounds, 88% were also identified in the nontargeted analysis. We categorized the 4212 chemicals assigned an identity in using EPA’s CompTox Dashboard and 1076 chemicals were found in at least one list. The category with the highest number of chemicals was “androgen or estrogen receptor activity.” The findings demonstrate that a QuEChERS technique is suitable for both targeted and nontargeted analysis of trace organic contaminants in biological samples.
Omics-based technologies have enabled comprehensive characterization of our exposure to environmental chemicals (chemical exposome) as well as assessment of the corresponding biological responses at the molecular level. Systematically measuring exposures and linking these stimuli to biological perturbations can determine specific chemical exposures of concern, mechanisms and biomarkers of toxicity, and interventions. However, advancement of exposomics is limited by a lack of harmonization of gas chromatography high-resolution mass spectrometry (GC-HRMS) methods used for data acquisition and approaches for assigning confidence to chemical annotations. Here we discuss the major pieces of evidence provided by GC-HRMS workflows, including retention time and retention index, electron ionization, positive chemical ionization, electron capture negative ionization, and atmospheric pressure chemical ionization spectral matching, molecular ion, accurate mass, isotopic patterns, database occurrence, and occurrence in blanks. We then provide a qualitative framework for incorporating these various lines of evidence for communicating confidence in GC-HRMS data by adapting the Schymanski scoring schema developed for reporting confidence levels by liquid chromatography high-resolution mass spectrometry (LC-HRMS). Validation of our framework is presented using standards spiked in plasma, and confident annotations in outdoor and indoor air samples, showing a false positive rate of 12% for suspect screening for chemical identifications assigned as Level 2 (when structurally similar isomers are not considered false positives). This framework is easily adaptable to various workflows and provides a concise means to communicate confidence in annotations. Further validation, refinements, and adoption of this framework will ideally lead to harmonization across the field, helping to improve the quality and interpretability of compound annotations obtained in GC-HRMS.
Quinones function as electron transport cofactors in photosynthesis and cellular respiration. The versatility and functional diversity of quinones is primarily due to the diverse midpoint potentials that are tuned by the substituent effects and interactions with surrounding amino acid residues in the binding site in the protein. In the present study, a library of substituted 1,4-naphthoquinones are analyzed by cyclic voltammetry in both protic and aprotic solvents to determine effects of substituent groups and hydrogen bonds on the midpoint potential. We use continuous-wave electron paramagnetic resonance (EPR) spectroscopy to determine the influence of substituent groups on the electronic properties of the 1,4-naphthoquinone models in an aprotic solvent. The results establish a correlation between the presence of substituent group(s) and the modification of electronic properties and a corresponding shift in the midpoint potential of the naphthoquinone models. Further, we use pulsed EPR spectroscopy to determine the effect of substituent groups on the strength and planarity of the hydrogen bonds of naphthoquinone models in a protic solvent. This study provides support for the tuning of the electronic properties of quinone cofactors by the influence of substituent groups and hydrogen bonding interactions.
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