Plasma Research Laboratory, Department of Chemical and Biomolecular Engineering , Clarkson University , Potsdam , New York 13699 , United States.
Department of Civil and Environmental Engineering , Clarkson University , Potsdam , New York 13699 , United States.
Environ Sci Technol. 2019 Mar 5;53(5):2731-2738. doi: 10.1021/acs.est.8b07031. Epub 2019 Feb 22.
Byproducts produced when treating perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) in water using a plasma treatment process intentionally operated to treat these compounds slowly to allow for byproduct accumulation were quantified. Several linear chain perfluoroalkyl carboxylic acids (PFCAs) (C4 to C7) were identified as byproducts of both PFOA and PFOS treatment. PFOA, perfluorohexanesulfonate (PFHxS), and perfluorobutanesulfonate (PFBS) were also found to be byproducts from PFOS degradation. Significant concentrations of fluoride ions, inorganic carbon, and smaller organic acids (trifluoroacetic acid, acetic acid, and formic acid) were also identified. In addition to PFCAs, PFHxS, and PFBS, trace amounts of 43 PFOA-related and 35 PFOS-related byproducts were also identified using a screening and search-based algorithm. Minor concentrations of gas-phase byproducts were also identified (<2.5% of the F originally associated with the parent molecules) some of which are reported for the first time in perfluoroalkyl substance degradation experiments including cyclic perfluoroalkanes (CF, CF, CF, CF, and CF). The short chain PFCAs detected suggest the occurrence of a stepwise reduction of the parent perfluoroalkyl substances (PFAS) molecule, followed by oxidation of intermediates, perfluoroalkyl radicals, and perfluoro alcohols/ketones. Using a fluorine mass balance, 77% of the fluorine associated with the parent PFOA and 58% of the fluorine associated with the parent PFOS were identified. The bulk of the remaining fluorine was determined to be sorbed to reactor walls and tubing using sorption experiments in which plasma was not generated.
采用等离子体处理工艺处理水中的全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS）时，会有意地将处理速度控制得非常缓慢，以允许副产物积累，从而产生了副产物。几种直链全氟烷酸（PFCAs）（C4 至 C7）被鉴定为 PFOA 和 PFOS 处理的副产物。还发现 PFOA、全氟己烷磺酸盐（PFHxS）和全氟丁烷磺酸盐（PFBS）也是 PFOS 降解的副产物。氟离子、无机碳和较小的有机酸（三氟乙酸、乙酸和甲酸）的浓度也很高。除了 PFCAs、PFHxS 和 PFBS 外，还使用筛选和基于搜索的算法鉴定出痕量的 43 种与 PFOA 相关和 35 种与 PFOS 相关的副产物。还鉴定出痕量的气相副产物（<与母体分子最初相关的氟的 2.5%），其中一些在全氟烷基物质降解实验中是首次报道，包括环状全氟烷烃（CF3、CF2、CF2、CF2 和 CF2）。检测到的短链 PFCAs 表明，母体全氟烷基物质（PFAS）分子发生了逐步还原，随后是中间体、全氟烷基自由基和全氟醇/酮的氧化。使用氟质量平衡，鉴定出与母体 PFOA 相关的氟的 77%和与母体 PFOS 相关的氟的 58%。其余大部分氟被确定为使用未产生等离子体的吸附实验吸附到反应器壁和管道上。
