Department of Civil and Environmental Engineering, University of California, Los Angeles, USA.
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, USA.
Environ Pollut. 2021 Oct 1;286:117297. doi: 10.1016/j.envpol.2021.117297. Epub 2021 May 4.
Groundwater flow through aquifer soils or packed bed systems can fluctuate for various reasons, which could affect the concentration of natural colloids and per- and polyfluoroalkyl substances (PFAS) in the pore water. In such cases, PFAS concentration could either decrease due to matrix diffusion of PFAS or increase by the detachment of colloids carrying PFAS. Yet, the effect of flow fluctuation on PFAS transport or release in porous media has not been examined. To examine the relative importance of either process, we interrupted the flow during an injection of groundwater spiked with perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and bromide as conservative tracer through clay-rich soil, so that diffusive transport would be prominent during flow interruption. After flow interruption, the PFAS concentration did not decrease indicating an insignificant contribution of matrix diffusion. The concentration increased, potentially due to enhanced release of colloid-associated PFAS. Analysis of samples before and after flow interruption by particle size analysis and SEM confirmed an increase in soil colloid concentration after the flow interruption. XRD analysis of soil and the colloids proved that PFAS were associated with specific sites of the colloids. Due to a higher affinity of PFOA to soil colloids, the total PFOA concentration in the effluent samples increased more than PFBA after the flow interruption process. The results indicate that colloids may have a disproportionally higher role in the transport of PFAS in conditions that release colloids from porous media. Thus, fluctuations in groundwater flow can increase this colloid facilitated mobility of PFAS.
地下水在流经含水层土壤或填充床系统时，可能会因各种原因而波动，这可能会影响孔隙水中天然胶体和全氟及多氟烷基物质 (PFAS) 的浓度。在这种情况下，PFAS 的浓度可能会因 PFAS 的基质扩散而降低，也可能会因携带 PFAS 的胶体脱落而增加。然而，水流波动对多孔介质中 PFAS 的迁移或释放的影响尚未得到检验。为了检验这两种过程的相对重要性，我们在向富含粘土的土壤中注入添加了全氟丁烷酸 (PFBA)、全氟辛酸 (PFOA) 和溴化物作为示踪剂的地下水时中断了水流，以便在中断水流期间，扩散迁移会很明显。中断水流后，PFAS 的浓度没有降低，表明基质扩散的贡献不大。浓度增加，可能是由于胶体结合的 PFAS 释放增强所致。通过粒径分析和 SEM 对中断前后的样品进行分析，证实中断后土壤胶体浓度增加。对土壤和胶体的 XRD 分析证明 PFAS 与胶体的特定位置有关。由于 PFOA 与土壤胶体的亲和力更高，因此在中断水流过程后，流出样品中的总 PFOA 浓度比 PFBA 增加更多。结果表明，在从多孔介质中释放胶体的条件下，胶体在 PFAS 的迁移中可能具有不成比例的更高作用。因此，地下水流动的波动会增加胶体促进 PFAS 的迁移能力。
