Perfluorooctanoic acid (PFOA) including linear and branched isomers is one of only three PFAS included in the Stockholm convention on Persistent Organic Pollutants. Unfortunately, PFOA branched isomers have received less attention than the linear due to analytical difficulties and perceived lower environmental concentrations. In this study, we revealed a environmentally relevant pathway for the formation of branched PFOA from PFAS precursors. AFFF samples showed a doubling of branched PFOA concentrations (138 mg/L) after TOP assay oxidation (307 mg/L). These findings indicate that branched PFOA may be more pervasive in the environment than previously thought. Additionally, we investigated the reductive degradability of PFOA using vitamin B12 (VB₁₂) (a naturally occurring electron shuttle) in combination with either zero-valent zinc (ZVZ) or zero-valent iron (ZVI). Linear PFOA, as well as two branched isomers (3-methyl PFOA and 5,5-dimethyl PFOA), resisted reductive defluorination under the experimental conditions. However, all other branched isomers degraded within 10 days in the ZVZ-VB₁₂ system. The experimental rate constants for specific PFOA isomers generally correlate with their calculated reduction potentials, except for 6-methyl PFOA. A potential defluorination pathway was proposed based on high-resolution mass spectrometry (LC-Orbitrap) and density functional theory (DFT) studies.

中文翻译：

---

PFAS 前体中 PFOA 异构体的表征及其还原脱氟


全氟辛酸 （PFOA） 包括直链异构体和支链异构体，是《关于持久性有机污染物的斯德哥尔摩公约》中仅有的三种 PFAS 之一。遗憾的是，由于分析困难和感知到的环境浓度较低，PFOA 支链异构体受到的关注低于线性异构体。在这项研究中，我们揭示了从 PFAS 前体形成支链 PFOA 的环境相关途径。AFFF 样品显示，在 TOP 分析氧化 （138 mg/L） 后，支链 PFOA 浓度 （307 mg/L） 增加了一倍。这些发现表明，支链 PFOA 在环境中的分布可能比以前认为的更普遍。此外，我们还使用维生素 B12 （VB₁₂）（一种天然存在的电子穿梭）与零价锌 （ZVZ） 或零价铁 （ZVI） 结合使用研究了 PFOA 的还原性。线性 PFOA 以及两种支链异构体（3-甲基 PFOA 和 5,5-二甲基 PFOA）在实验条件下抵抗还原脱氟。然而，所有其他支链异构体在 ZVZ-VB_{12 系统中都在 10} 天内降解。特定 PFOA 异构体的实验速率常数通常与其计算的还原电位相关，但 6-甲基 PFOA 除外。基于高分辨率质谱 （LC-Orbitrap） 和密度泛函理论 （DFT） 研究，提出了一种潜在的脱氟途径。