Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7014, SE-750 07 Uppsala, Sweden.
Swedish Geotechnical Institute (SGI), SE-581 93 Linköping, Sweden.
Environ Sci Technol. 2020 Dec 15;54(24):15722-15730. doi: 10.1021/acs.est.0c01646. Epub 2020 Nov 27.
An improved quantitative and qualitative understanding of the interaction of per- and polyfluoroalkyl substances (PFASs) and short-range ordered Fe (hydr)oxides is crucial for environmental risk assessment in environments low in natural organic matter. Here, we present data on the pH-dependent sorption behavior of 12 PFASs onto ferrihydrite. The nature of the binding mechanisms was investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and by phosphate competition experiments. Sulfur K-edge XANES spectroscopy showed that the sulfur atom of the head group of the sulfonated PFASs retained an oxidation state of +V after adsorption. Furthermore, the XANES spectra did not indicate any involvement of inner-sphere surface complexes in the sorption process. Adsorption was inversely related to pH ( < 0.05) for all PFASs (i.e., C-C and C-C perfluorocarboxylates, C, C, and C perfluorosulfonates, perfluorooctane sulfonamide, and 6:2 and 8:2 fluorotelomer sulfonates). This was attributed to the pH-dependent charge of the ferrihydrite surface, as reflected in the decrease of surface ζ-potential with increasing pH. The importance of surface charge for PFAS adsorption was further corroborated by the observation that the adsorption of PFASs decreased upon phosphate adsorption in a way that was consistent with the decrease in ferrihydrite ζ-potential. The results show that ferrihydrite can be an important sorbent for PFASs with six or more perfluorinated carbons in acid environments (pH ≤ 5), particularly when phosphate and other competitors are present in relatively low concentrations.
提高对持久性和多氟烷基物质 (PFASs) 与短程有序铁 (氢) 氧化物相互作用的定量和定性理解，对于低天然有机质环境中的环境风险评估至关重要。在这里，我们提供了关于 12 种 PFASs 在铁氢氧化物上的 pH 依赖性吸附行为的数据。通过硫 K 边 X 射线吸收近边结构 (XANES) 光谱和磷酸盐竞争实验研究了结合机制的性质。硫 K 边 XANES 光谱表明，磺化 PFASs 的头基硫原子在吸附后保持 +V 氧化态。此外，XANES 光谱并未表明吸附过程中涉及内球表面络合物。所有 PFASs（即 C-C 和 C-C 全氟羧酸酯、C、C 和 C 全氟磺酸酯、全氟辛烷磺酰胺以及 6:2 和 8:2 氟代聚醚磺酸盐）的吸附均与 pH 呈负相关（<0.05）。这归因于铁氢氧化物表面电荷随 pH 变化，表面 ζ 电位随 pH 升高而降低。表面电荷对 PFAS 吸附的重要性还通过观察到在磷酸盐吸附的情况下 PFASs 的吸附减少得到进一步证实，这与铁氢氧化物 ζ 电位的降低一致。结果表明，铁氢氧化物在酸性环境（pH ≤ 5）中可以成为具有六个或更多全氟碳原子的 PFASs 的重要吸附剂，特别是当磷酸盐和其他竞争物的浓度相对较低时。
