Modified clays reduce leaching of per‐ and polyfluoroalkyl substances from AFFF‐contaminated soils

Abstract

Technologies applicable at a field scale to mitigate soil and groundwater pollution by per-and polyfluoroalkyl substances (PFAS) due to the release of aqueous film-forming foams are urgently needed. We demonstrate that modified bentonite clays as soil amendments can effectively reduce the leaching of PFAS from impacted soils. In batch experiments, the significant decrease (95%-99%) of leachable anionic PFAS, including perfluorooctane sulfonate, perfluorohexane sulfonate, and perfluorooctane carboxylate, was achieved in 1-4 days at a clay dosage as low as 0.5% w/w. A significant decline of leachable cationic and zwitterionic PFAS (70%-99%) was also observed. The clays performed the best in immobilizing PFAS anions, while granular activated carbon was effective in preventing PFAS cation leaching. Hardwood biochar had minor or negligible effects on any PFAS. The study provides strong evidence to support using modified clays as part of mitigation or remediation strategies to prevent PFAS from mobilizing on a field scale. K E Y W O R D Saqueous film-forming foams (AFFFs), groundwater remediation, modified clays, per-and polyfluoroalkyl substances (PFAS)

PFAS are forever? The state of the science and research needs for analyzing and treating PFAS‐laden water

“…Combustion ion chromatography (CIC) has been a valuable tool to determine total fluorine or total organic fluorine of environmental samples, but such a system is not commonly available. In this topical collection, Wang, Abusallout, et al (2021), Wang, Yan, et al (2021) tested the idea of modifying a total organic carbon analyzer—an instrument common in laboratories across disciplines—as an alternative approach. The modified system can serve as a screening technique or allow for a fluorine mass balance evaluation to help determine overall treatment or percent mineralization for destruction technologies.…”

“…River water and wastewater have similar recoveries to those spiked in deionized water. Wang, Abusallout, et al (2021), Wang, Yan, et al (2021) identified some previously unknown limitations of CIC methods: possible variable recoveries across PFAS of different chain lengths or structures, and inorganic fluorine loss during combustion. The study emphasizes that suitable extraction and inorganic fluoride removal techniques are essential in this analysis to best define whether it is total, organic, or adsorbable organic fluorine.…”

“…Adsorbent treatment schemes are employed in treatment plants to produce potable water, but they are also used in the subsurface to control the migration of contaminants. Wang, Yan, et al (2021) show through batch experiments that modified bentonite clays and GAC can help minimize PFAS leaching from contaminated soils, which are long‐term PFAS sources to groundwater and surface water. The modified clay is shown to perform the best in immobilizing many anionic PFAS whereas GAC is demonstrated to be most effective in preventing leaching of select cationic PFAS.…”

PFAS Experts Symposium 2: Statements on available in situ remediation technologies

“…Stabilization/solidification (S/S) technology utilizes conventional soilmixing equipment to distribute stabilizing amendments (with or without solidifying amendments like Portland cement) to immobilize PFAS within the source area. There are multiple bench-scale demonstrations (Barth et al, 2021;Braunig et al, 2021;Hale et al, 2017;Kabiri & McLaughlin, 2021;Kupryianchyk et al, 2016;Sorengard et al, 2019Sorengard et al, , 2021Wang et al, 2021)…”

“…A full-scale application of S/S in Canada is currently underway and is using approximately 2% FluoroSorb ® Adsorbent by dry soil weight based on predesign treatability testing. Both bench-scale (Marshall, 2019;Wang et al, 2021;Yan et al, 2020Yan et al, , 2021…”