Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, ON K7K 7B4, Canada.
Australian Nuclear Science and Technology Organisation, Australia.
Sci Total Environ. 2022 Aug 1;832:154941. doi: 10.1016/j.scitotenv.2022.154941. Epub 2022 Mar 30.
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/CHOH exchanged PFAS and n - 1 PFCA, amongst others. Given the reactive species present (hydroxyl radicals (·OH), hydrogen radicals (·H) and aqueous electrons (e)), 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.
全氟和多氟烷基物质（PFAS）由于缺乏可用的破坏性修复技术，是一类具有挑战性的环境污染物。了解 PFAS 降解的基本机制是开发现场可扩展和原位破坏性修复技术的关键。本研究旨在通过一系列受控的伽马辐照研究阐明和完善水中 PFAS 降解机制的现有认识。在澳大利亚核科学与技术组织，使用钴-60 源在批处理辐照中对 PFAS 进行伽马辐照，辐照剂量高达 80 kGy。全氟辛酸（PFOA）、全氟辛烷磺酸（PFOS）、6:2 氟代醇磺酸盐（6:2 FTS）以及十三种不同的 PFAS（包括 C4-C12 PFCAs、C4、C6、C8 PFSAs 和 FOSA）被辐照，以研究降解、pH 值、链长和转化的影响。高分辨率质谱用于在整个降解实验中鉴定 80 多种氟化转化产物。这些包括-F/+H、-F/+OH、-F/CHOH 交换的 PFAS 和 n-1 PFCAs 等。鉴于存在的反应性物质（羟基自由基（·OH）、氢自由基（·H）和水合电子（e））以及形成的降解产物，可以表明水合电子是负责初始 PFAS 降解的关键反应性物质。最重要的是，根据降解产物的形成，我们发现 -F/+H 不一定必须发生在α-氟化物（最接近官能团头基）上，而是发生在整个链长上，导致比以前假设的更复杂的降解途径。虽然我们的结果支持文献中提出的一些反应步骤，但我们已经开发了一个由实验观察支持的统一的 16 步和 3 途径降解示意图。
