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==PFAS Transport and Fate==
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==Transition of Aqueous Film Forming Foam (AFFF) Fire Suppression Infrastructure Impacted by Per and Polyfluoroalkyl Substances (PFAS)==  
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The transport and fate of Per- and Polyfluoroalkyl Substances (PFAS) in the environment is controlled by the nature of the PFAS source, characteristics of the individual PFAS, and environmental conditions where the PFAS are present. Transport, partitioning, and transformation are the primary processes controlling PFAS fate in the environment. PFAS compounds can also be taken up by both plants and animals, and in some cases, bioaccumulate through the food chain.
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)|Per and polyfluoroalkyl substances (PFAS)]] contained in [[wikipedia:Firefighting foam |Class B aqueous film-forming foams (AFFFs)]] are known to accumulate on wetted surfaces of many fire suppression systems after decades of exposure<ref name="LangEtAl2022">Lang, J.R., McDonough, J., Guillette, T.C., Storch, P., Anderson, J., Liles, D., Prigge, R., Miles, J.A.L., Divine, C., 2022. Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods. Chemosphere, 308(Part 2), 136254. [https://doi.org/10.1016/j.chemosphere.2022.136254 doi: 10.1016/j.chemosphere.2022.136254]&nbsp;&nbsp;[[Media:LangEtAl2022.pdf | Open Access Article]]</ref>. When replacement PFAS-free firefighting formulations are added to existing infrastructure, PFAS can rebound from the wetted surfaces into the new formulations at high concentrations<ref name="RossStorch2020">Ross, I., and Storch, P., 2020. Foam Transition: Is It as Simple as "Foam Out / Foam In?". The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q2 Supplement, 20 pages. [[Media:Catalyst_2020_Q2_Sup.pdf | Industry Newsletter]]</ref><ref>Kappetijn, K., 2023. Replacement of fluorinated extinguishing foam: When is clean clean enough? The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q1 2023, pp. 31-33. [[Media:Catalyst_2023_Q1.pdf | Industry Newsletter]]</ref>. Effective methods are needed to properly transition to PFAS-free firefighting formulations in existing fire suppression infrastructure. Considerations in the transition process may include but are not limited to locating, identifying, and evaluating existing systems and AFFF, fire engineering evaluations, system prioritization, cost/downtime analyses, sampling and analysis, evaluation of risks and hazards to human health and the environment, transportation, and disposal.
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Understanding PFAS transport and fate is necessary for evaluating the potential risk from a PFAS release and for predictions about PFAS occurrence, migration, and persistence, and about the potential vectors for exposure. This knowledge is important for site characterization, identification of potential sources of PFAS to the site, development of an appropriate conceptual site model (CSM), and selection and predicted performance of remediation strategies.  
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
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'''Related Article(s):'''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*[[PFAS Sources]]
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*[[PFAS Ex Situ Water Treatment]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
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'''Contributor(s):'''
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*Dr. Johnsie Ray Lang
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*Dr. Jonathan Miles
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*John Anderson
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*Dr. Theresa Guillette
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*[[Craig E. Divine, Ph.D., PG|Dr. Craig Divine]]
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*[[Dr. Stephen Richardson]]
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'''Key Resource(s):'''
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*Department of Defense (DoD) performance standard for PFAS-free firefighting formulation:  [https://media.defense.gov/2023/Jan/12/2003144157/-1/-1/1/MILITARY-SPECIFICATION-FOR-FIRE-EXTINGUISHING-AGENT-FLUORINE-FREE-FOAM-F3-LIQUID-CONCENTRATE-FOR-LAND-BASED-FRESH-WATER-APPLICATIONS.PDF Military Specification MIL-PRF-32725]<ref name="DoD2023">US Department of Defense, 2023. Performance Specification for Fire Extinguishing Agent, Fluorine-Free Foam (F3) Liquid Concentrate for Land-Based, Fresh Water Applications. Mil-Spec MIL-PRF-32725, 18 pages. [[Media: MilSpec32725.pdf | Military Specification Document]]</ref>
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*[[Media:LangEtAl2022.pdf | Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods]]<ref name="LangEtAl2022"/>
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==Introduction==
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[[File:LangFig1.png | thumb |400px|Figure 1. (A) Schematic of a typical PFAS molecule demonstrating the hydrophobic fluorinated tail in green and the hydrophilic charged functional group in blue, (B) a PFAS bilayer formed with the hydrophobic tails facing inward and the charged functional groups on the outside, and (C) multiple bilayers of PFAS assembled on the wetted surfaces of fire suppression piping.]]PFAS are a class of synthetic fluorinated compounds which are highly mobile and persistent within the environment<ref>Giesy, J.P., Kannan, K., 2001. Global Distribution of Perfluorooctane Sulfonate in Wildlife. Environmental Science and Technology 35(7), pp. 1339-1342. [https://doi.org/10.1021/es001834k doi: 10.1021/es001834k]</ref>. Due to the surfactant properties of PFAS, these compounds self-assemble at any solid-liquid interface forming resilient bilayers during prolonged exposure<ref>Krafft, M.P., Riess, J.G., 2015. Selected physicochemical aspects of poly- and perfluoroalkylated substances relevant to performance, environment and sustainability-Part one. Chemosphere, 129, pp. 4-19. [https://doi.org/10.1016/j.chemosphere.2014.08.039 doi: 10.1016/j.chemosphere.2014.08.039]</ref>. Solid phase accumulation of PFAS has been proposed to be influenced by both [[wikipedia: Hydrophobic effect|hydrophobic]] and electrostatic interactions with fluorinated carbon chain length as the dominant feature influencing sorption<ref>Higgins, C.P., Luthy, R.G., 2006. Sorption of Perfluorinated Surfactants on Sediments. Environmental Science and Technology, 40(23), pp. 7251-7256. [https://doi.org/10.1021/es061000n doi: 10.1021/es061000n]</ref>. While the majority of previous research into solid phase sorption typically focused on water treatment applications or subsurface porous media<ref>Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of the Total Environment, 613-614, pp. 176-185. [https://doi.org/10.1016/j.scitotenv.2017.09.065 doi: 10.1016/j.scitotenv.2017.09.065]&nbsp;&nbsp;[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693257/  Open Access Manuscript]</ref>, recently PFAS accumulations have been identified on the wetted surfaces of fire suppression infrastructure exposed to aqueous film forming foam (AFFF)<ref name="LangEtAl2022"/> (see Figure 1).
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Fire suppression systems with potential PFAS impacts include fire fighting vehicles that carried AFFF and fixed suppression systems in buildings containing large amounts of flammable materials such as aircraft hangars (Figure 2). PFAS residue on the wetted surfaces of existing infrastructure can rebound into replacement PFAS-free firefighting formulations if not removed during the transition process<ref name="RossStorch2020"/>. Simple surface rinsing with water and low-pressure washing has been proven to be inefficient for removal of surface bound PFAS from piping and tanks that contained fluorinated AFFF<ref name="RossStorch2020"/>
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[[File:LangFig2.png | thumb|left|600px|Figure 2. Fixed fire suppression system for an aircraft hangar, with storage tank on left and distribution piping on right.]]
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In&nbsp;addition&nbsp;to&nbsp;proper methods for system cleaning to remove residual PFAS, transition to PFAS-free foam may also include consideration of compliance with state and federal regulations, selection of the replacement PFAS-free firefighting formulation, a cost benefit analysis for replacement of the system components versus cleaning, and PFAS verification testing. Foam transition should be completed in a manner which minimizes the volume of waste generated as well as preventing any PFAS release into the environment.
  
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
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==PFAS Assembly on Solid Surfaces==
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</br>
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{|
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| || '''Equation&nbsp;1:'''
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|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation1r.png]]
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|-
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| Where: || ||
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|-
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| || ''C<sub>0</sub>''|| is the freely dissolved concentration of the analyte in the sediment (mg/L or &mu;g/L)
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|-
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| || ''C<sub>p,t</sub>'' || is the measured concentration of the analyte in the peeper at time of retrieval (mg/L or &mu;g/L)
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|-
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| || ''K'' || is the elimination rate of the target analyte
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|-
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| || ''t'' || is the deployment time (days)
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|}
  
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'''Related Article(s): '''
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</br>
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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{|
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| || '''Equation&nbsp;2:'''  
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|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation2r.png]]
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|-
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| Where: || ||
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|-
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| || ''K''|| is the elimination rate of the target analyte
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|-
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| || ''K<sub>tracer</sub>'' || is the elimination rate of the tracer
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|-
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| || ''D'' || is the free-water diffusion of the analyte (cm<sup>2</sup>/s)
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|-
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| || ''D<sub>tracer</sub>'' || is the free-water diffusion of the tracer (cm<sup>2</sup>/s)
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|}
  
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'''Contributor(s): '''  
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</br>
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Dr. Hunter Anderson and Dr. Mark L. Brusseau
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{|
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| || '''Equation&nbsp;3:'''  
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|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation3r2.png]]
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|-
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| Where: || ||
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|-
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| || ''K<sub>tracer</sub>'' || is the elimination rate of the tracer
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|-
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| || ''C<sub>tracer,i</sub>''|| is the measured initial concentration of the tracer in the peeper prior to deployment (mg/L or &mu;g/L)
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|-
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| || ''C<sub>tracer,t</sub>'' || is the measured final concentration of the tracer in the peeper at time of retrieval (mg/L or &mu;g/L)
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|-
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| || ''t'' || is the deployment time (days)
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|}
  
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'''Key Resource(s): '''
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The self-assembly of [[Wikipedia: Amphiphile | amphiphilic]] molecules into supramolecular bilayers is a result of their structure and how it interacts with the bulk water of a solution. Single chain hydrocarbon based amphiphiles can form [[Wikipedia: Micelle | micelles]] under relatively dilute aqueous concentrations, however for hydrocarbon based surfactants the formation of more complex organized system such as [[Wikipedia: Vesicle (biology and chemistry) | vesicles]] is rarely seen, requiring double chain amphiphiles such as [[wikipedia: Phospholipid|phospholipids]]. Associations of single chain [[wikipedia: Ion#Anions_and_cations|cationic and anionic]] hydrocarbon based amphiphiles into stable supramolecular structures such as vesicles has however been demonstrated<ref>Fukuda, H., Kawata, K., Okuda, H., 1990. Bilayer-Forming Ion-Pair Amphiphiles from Single-Chain Surfactants. Journal of the American Chemical Society, 112(4), pp. 1635-1637. [https://doi.org/10.1021/ja00160a057 doi: 10.1021/ja00160a057]</ref>, with the ion pairing of the polar head groups mimicking the a double tail situation. The behavior of single chain [[wikipedia: Per-_and_polyfluoroalkyl_substances#Fluorosurfactants|fluorosurfactant]] amphiphiles has been demonstrated to be significantly different from similar hydrocarbon based analogues. Not only are [[Wikipedia: Critical micelle concentration | critical micelle concentrations (CMC)]] of fluorosurfactants typically two orders of magnitude lower than corresponding hydrocarbon surfactants but self-assembly can occur even when fluorosurfactants are dispersed at low concentrations significantly below the CMC in water and other solvents<ref name="Krafft2006">Krafft, M.P., 2006. Highly fluorinated compounds induce phase separation in, and nanostructuration of liquid media. Possible impact on, and use in chemical reactivity control. Journal of Polymer Science Part A: Polymer Chemistry, 44(14), pp. 4251-4258. [https://doi.org/10.1002/pola.21508 doi: 10.1002/pola.21508]&nbsp;&nbsp;[[Media:Krafft2006.pdf | Open Access Article]]</ref>. The assembly of fluorinated amphiphiles structurally similar to those found in AFFF have been shown to readily form stable, complex structures including vesicles, fibers, and globules at concentrations as low as 0.5% w/v in contrast to their hydrocarbon analogues which remained fluid at 30% w/v<ref>Krafft, M.P., Guilieri, F., Riess, J.G., 1993. Can Single-Chain Perfluoroalkylated Amphiphiles Alone form Vesicles and Other Organized Supramolecular Systems? Angewandte Chemie International Edition in English, 32(5), pp. 741-743. [https://doi.org/10.1002/anie.199307411 doi: 10.1002/anie.199307411]</ref><ref name="KrafftEtAl_1994">Krafft, M.P., Guilieri, F., Riess, J.G., 1994. Supramolecular assemblies from single chain perfluoroalkylated phosphorylated amphiphiles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 84(1), pp. 113-119. [https://doi.org/10.1016/0927-7757(93)02681-4 doi: 10.1016/0927-7757(93)02681-4]</ref>.
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*[https://pfas-1.itrcweb.org/wp-content/uploads/2020/04/ITRC_PFAS_TechReg_April2020.pdf  Per- and Polyfluoroalkyl Substances (PFAS), PFAS-1. ITRC 2020.]<ref name="ITRC2020">Interstate Technology and Regulatory Council (ITRC), 2020. Technical/Regulatory Guidance: Per- and Polyfluoroalkyl Substances (PFAS), PFAS-1. ITRC, PFAS Team, Washington DC. [https://pfas-1.itrcweb.org/wp-content/uploads/2020/04/ITRC_PFAS_TechReg_April2020.pdf  Free Download from ITRC].&nbsp;&nbsp; [[Media: ITRC_PFAS-1.pdf | Report.pdf]]</ref>
 
  
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*[[Media: Brusseau2018manuscript.pdf | Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Brusseau 2018 (manuscript).]]<ref name="Brusseau2018">Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of the Total Environment, 613-614, pp. 176-185. [https://doi.org/10.1016/j.scitotenv.2017.09.065 DOI: 10.1016/j.scitotenv.2017.09.065]&nbsp;&nbsp; [[Media: Brusseau2018manuscript.pdf | Author’s Manuscript]]</ref>
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Krafft found that fluorinated amphiphiles formed bilayer membranes with phospholipids, and that the resulting vesicles were more stable than those made of phospholipids alone<ref name="KrafftEtAl_1998">Krafft, M.P., Riess, J.G., 1998. Highly Fluorinated Amphiphiles and Collodial Systems, and their Applications in the Biomedical Field. A Contribution. Biochimie, 80(5-6), pp. 489-514. [https://doi.org/10.1016/S0300-9084(00)80016-4 doi: 10.1016/S0300-9084(00)80016-4]</ref>. The similarities in amphiphilic properties between phospholipids and the hydrocarbon-based surfactants in AFFF suggests that bilayer vesicles may form between these and the fluorosurfactants also present in the concentrate. Krafft demonstrated that both the permeability of resulting mixed vesicles and their propensity to fuse with each other at increasing ionic strength was reduced as a result of the creation of an inert hydrophobic and [[wikipedia: Lipophobicity|lipophobic]] film within the membrane, and also suggested that the fluorinated amphiphiles increased [[Wikipedia: van der Waals force | van der Waals interactions]] in the hydrocarbon region<ref name="KrafftEtAl_1998"/>. Thus this low permeability may allow vesicles formed by the surfactants present in AFFF to act as long term repositories of PFAS not only as part of the bilayer itself but also solvated within the vesicle. This prediction is supported by the observation that supramolecular structures formed from single chain fluorinated amphiphiles have been demonstrated to be stable at elevated temperature (15 min at 121&deg;C) and have been shown to be stable over periods of months, even increasing in size over time when stored at environmentally relevant temperatures<ref name="KrafftEtAl_1994"/>.
  
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==Introduction==
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Formation of complex structures at relatively low solute concentrations requires the monomer molecules to be well ordered to maintain tight packing in the supramolecular structure<ref>Ringsdorf, H., Schlarb, B., Venzmer, J., 1988. Molecular Architecture and Function of Polymeric Oriented Systems: Models for the Study of Organization, Surface Recognition, and Dynamics of Biomembranes. Angewandte Chemie International Edition in English, 27(1), pp. 113-158. [https://doi.org/10.1002/anie.198801131 doi: 10.1002/anie.198801131]</ref>. This order results from electrostatic forces, [[wikipedia: Hydrogen bond|hydrogen bonding]], and in the case of fluorinated amphiphiles, hydrophobic interactions. The geometry of the amphiphile also potentially contributes to the type of supramolecular aggregation<ref>Israelachvili, J.N., Mitchell, D.J., Ninham, B.W., 1976. Theory of Self-Assembly of Hydrocarbon Amphiphiles into Micelles and Bilayers. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 72, pp. 1525-1568. [https://doi.org/10.1039/F29767201525 doi: 10.1039/F29767201525]</ref>. Surfactants which adopt a conical shape (such as a typical hydrocarbon based surfactant with a large polar head group and a single alkyl chain as a tail) tend to form micelles more easily. Increasing the bulk of the tail makes the surfactant more cylindrically shaped which makes assembly into bilayers more likely.  
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The transport and fate of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] is a rapidly evolving field of science, with many questions that are not yet resolved. Much of the currently available information is based on a few well-studied PFAS compounds. However, there is a large number and variety of PFAS with a wide range of physical and chemical characteristics that affect their behavior in the environment. The transport and fate of some PFAS could differ significantly from the compounds studied to date. Nevertheless, information about the behavior of some PFAS in the environment can be ascertained from the results of currently available research.  
 
  
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PFAS transport and fate in the environment is controlled by the nature of the PFAS source, characteristics of the individual PFAS, and environmental conditions where the PFAS are present.  Perfluoroalkyl acids (PFAAs) (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] for nomenclature) are strong acids and are anionic in the environmentally-relevant pH range.  They are extremely persistent in the environment and do not degrade or transform under typical environmental conditions. Polyfluoroalkyl substances (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] for nomenclature) include compounds that have the potential to degrade to PFAAs. These compounds are commonly referred to as PFAA precursors or just ‘precursors’. Because some polyfluoroalkyl substances can degrade into PFAA via biotic or abiotic degradation pathways, PFAAs are sometimes referred to as “terminal PFAS” or “terminal degradation products”.
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Perfluoroalkyl chains are significantly more bulky than their hydrocarbon based analogues both in cross sectional area (28-30 Å<sup>2</sup> versus 20 Å<sup>2</sup>, respectively) and mean volume (CF<sub>2</sub> and CF<sub>3</sub> estimated as 38 Å<sup>3</sup> and 92 Å<sup>3</sup> compared to 27 Å<sup>3</sup> and 54 Å<sup>3</sup> for CH<sub>2</sub> and CH<sub>3</sub>)<ref name="KrafftEtAl_1998"/><ref name="Krafft2006"/>. Structural studies on linear PFOS have shown that the molecule adopts an unusual helical structure<ref>Erkoç, Ş., Erkoç, F., 2001. Structural and electronic properties of PFOS and LiPFOS. Journal of Molecular Structure: THEOCHEM, 549(3), pp. 289-293. [https://doi.org/10.1016/S0166-1280(01)00553-X doi:10.1016/S0166-1280(01)00553-X]</ref><ref name="TorresEtAl2009">Torres, F.J., Ochoa-Herrera, V., Blowers, P., Sierra-Alvarez, R., 2009. Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers. Chemosphere 76(8), pp. 1143-1149. [https://doi.org/10.1016/j.chemosphere.2009.04.009 doi: 10.1016/j.chemosphere.2009.04.009]</ref> in aqueous and solvent phases to alleviate [[wikipedia: Steric_effects#Steric_hindrance|steric hindrance]]. This arrangement results from the carbon chain starting in the planar all anti [[wikipedia:Conformational isomerism|conformation]] and then successively twisting all the CC-CC dihedrals by 15&deg;-20&deg; in the same direction<ref>Abbandonato, G., Catalano, D., Marini, A., 2010. Aggregation of Perfluoroctanoate Salts Studied by <sup>19</sup>F NMR and DFT Calculations: Counterion Complexation, Poly(ethylene glycol) Addition, and Conformational Effects. Langmuir 26(22), pp. 16762-16770. [https://doi.org/10.1021/la102578k  doi: 10.1021/la102578k].</ref>. The conformation also minimizes the electrostatic repulsion between fluorine atoms bonded to the same side of the carbon backbone by maximizing the interatomic distances between them<ref name="TorresEtAl2009"/>.
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The most important molecular properties controlling PFAA transport are the carbon chain length and functional moieties of the headgroups (e.g., sulfonate, carboxylate). The molecular properties of PFAA precursors are more varied, with different carbon chain lengths, headgroups and ionic states<ref name="Buck2011">Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., de Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A., and van Leeuwen, S.P.J., 2011. Perfluoroalkyl and Polyfluoroalkyl Substances in the Environment: Terminology, Classification, and Origins. Integrated Environmental Assessment and Management, 7(4): pp. 513-541. [ https://doi.org/10.1002/ieam.258  DOI: 10.1002/ieam.258]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.258 Open Access Article]</ref><ref name="Wang2017">Wang, Z., DeWitt, J.C., Higgins, C.P., and Cousins, I.T., 2017. A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)? Environmental Science and Technology, 51(5), pp. 2508-2518. American Chemical Society. [https://doi.org/10.1021/acs.est.6b04806 DOI: 10.1021/acs.est.6b04806]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/acs.est.6b04806 Free Download from ACS]</ref> (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]]). All of these properties can influence transport and fate of PFAA precursors in the environment.  
 
  
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Important environmental characteristics include the nature of the source (mode of input into the environment), the length of time that the source was active, and the magnitude of the input, as well as precipitation and infiltration rates, depth to groundwater, surface water and groundwater flow rates and interactions, prevailing atmospheric conditions, the properties of the porous-media (e.g., soil and sediment) and aqueous solution, microbiological factors, and the presence of additional fluid phases such as air and non-aqueous phase liquids [[Wikipedia: Non-aqueous phase liquid | (NAPLs)]] in the vadose zone and water-saturated source. In the subsurface, soil characteristics (texture, organic carbon content, clay mineralogy, metal-oxide content, solid surface area, surface charge, and exchange capacity) and solution characteristics (pH, redox potential, major ion chemistry, and co-contaminants) can influence PFAS transport and fate.  
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A consequence of the helical structure is that there is limited carbon-carbon bond rotation within the perfluoroalkyl chain giving them increased rigidity compared to alkyl chains<ref>Barton, S.W., Goudot, A., Bouloussa, O., Rondelez, F., Lin, B., Novak, F., Acero, A., Rice, S., 1992. Structural transitions in a monolayer of fluorinated amphiphile molecules. The Journal of Chemical Physics, 96(2), pp. 1343-1351. [https://doi.org/10.1063/1.462170 doi: 10.1063/1.462170]</ref>. The bulkiness of the perfluoroalkyl chain confers a cylindrical shape on the fluorosurfactant amphiphile and therefore favors the formation of bilayers and vesicles the aggregation of which is further assisted by the rigidity of the molecules which allow close packing in the supramolecular structure. Fluorosurfactants therefore cannot be regarded as more hydrophobic analogues of hydrogenated surfactants. Their self-assembly behavior is characterized by a strong tendency to form vesicles and lamellar phases rather than micelles, due to the bulkiness and rigidity of the perfluoroalkyl chain that tends to decrease the curvature of the aggregates they form in solution<ref>Barton, C.A., Butler, L.E., Zarzecki, C.J., Flaherty, J., Kaiser, M., 2006. Characterizing Perfluorooctanoate in Ambient Air near the Fence Line of a Manufacturing Facility: Comparing Modeled and Monitored Values. Journal of the Air and Waste Management Association, 56, pp. 48-55. [https://doi.org/10.1080/10473289.2006.10464429 doi: 10.1080/10473289.2006.10464429]&nbsp;&nbsp;[https://www.tandfonline.com/doi/epdf/10.1080/10473289.2006.10464429?needAccess=true Open Access Article]</ref>. The larger tail cross section of fluorinated compared to hydrogenated amphiphiles tends to favor the formation of aggregates with lesser surface curvature, therefore rather than micelles they form bilayer membranes, vesicles, tubules and fibers<ref>Krafft, M.P., Guilieri, F., Riess, J.G., 1993. Can Single-Chain Perfluoroalkylated Amphiphiles Alone form Vesicles and Other Organized Supramolecular Systems? Angewandte Chemie International Edition in English, 32(5), pp. 741-743. [https://doi.org/10.1002/anie.199307411 doi: 10.1002/anie.199307411]</ref><ref>Furuya, H., Moroi, Y., Kaibara, K., 1996. Solid and Solution Properties of Alkylammonium Perfluorocarboxylates. The Journal of Physical Chemistry, 100(43), pp. 17249-17254.  [https://doi.org/10.1021/jp9612801 doi: 10.1021/jp9612801]</ref><ref>Giulieri, F., Krafft, M.P., 1996. Self-organization of single-chain fluorinated amphiphiles with fluorinated alcohols. Thin Solid Films, 284-285, pp. 195-199. [https://doi.org/10.1016/S0040-6090(95)08304-9 doi: 10.1016/S0040-6090(95)08304-9]</ref><ref>Gladysz, J.A., Curran, D.P., Horvath, I.T., 2004. Handbook of Fluorous Chemistry. WILEY-VCH Verlag GmbH & Co. KGaA,, Weinheim, Germany. ISBN: 3-527-30617-X</ref>. Rojas ''et al.'' (2002) demonstrated that perfluorooctyl sulphonamide formed a contiguous bilayer at 50 mg/L with self-assembled aggregates present at concentrations as low as 10 mg/L<ref name="RojasEtAl2002">Rojas, O.J., Macakova, L., Blomberg, E., Emmer, A., and Claesson, P.M., 2002. Fluorosurfactant Self-Assembly at Solid/Liquid Interfaces. Langmuir, 18(21), pp. 8085-8095. [https://doi.org/10.1021/la025989c doi: 10.1021/la025989c]</ref>.
  
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==PFAS Transport and Fate Processes==
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==Thermodynamics of PFAS Accumulations on Solid Surfaces==
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[[File:AndersonBrusseau1w2Fig1.png | thumb | 600px | Figure 1. Illustration of PFAS partitioning and transformation processes. Source: D. Adamson, GSI, used with permission.]]
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The thermodynamics of formation of amphiphiles into supramolecular species requires consideration of both hydrophobic and hydrophilic interactions resulting from the amphoteric nature of the molecule. The hydrophilic portions of the molecule are driven to maximize their solvation interaction with as many water molecules as possible, whereas the hydrophobic portions of the molecule are driven to aggregate together thus minimizing interaction with the bulk water. Both of these processes change the [[wikipedia:Enthalpy|enthalpy]] and [[wikipedia: Entropy|entropy]] of the system.
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Transport, partitioning, and transformation are the primary processes controlling PFAS fate in the environment (Figure 1). PFAS compounds can also be taken up by both plants and animals, and in some cases, bioaccumulate through the food chain. However, PFAS uptake and bioaccumulation is not discussed in this article (see “Environmental Concern” section of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]).
 
  
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* '''Transport:''' PFAS can be transported substantial distances in the atmosphere<ref name="Ahrens2012">Ahrens, L., Harner, T., Shoeib, M., Lane, D.A. and Murphy, J.G., 2012. Improved Characterization of Gas–Particle Partitioning for Per- and Polyfluoroalkyl Substances in the Atmosphere Using Annular Diffusion Denuder Samplers. Environmental Science and Technology, 46(13), pp. 7199-7206. [https://doi.org/10.1021/es300898s DOI: 10.1021/es300898s]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Tom_Harner/publication/225046057_Improved_Characterization_of_Gas-Particle_Partitioning_for_Per-_and_Polyfluoroalkyl_Substances_in_the_Atmosphere_Using_Annular_Diffusion_Denuder_Samplers/links/5cc730c4299bf12097893fdc/Improved-Characterization-of-Gas-Particle-Partitioning-for-Per-and-Polyfluoroalkyl-Substances-in-the-Atmosphere-Using-Annular-Diffusion-Denuder-Samplers.pdf ResearchGate].</ref>, surface water<ref name="Taniyasu2013">Taniyasu, S., Yamashita, N., Moon, H.B., Kwok, K.Y., Lam, P.K., Horii, Y., Petrick, G. and Kannan, K., 2013.  Does wet precipitation represent local and regional atmospheric transportation by perfluorinated alkyl substances? Environment International, 55, pp. 25-32. [https://doi.org/10.1016/j.envint.2013.02.005 DOI: 10.1016/j.envint.2013.02.005]</ref>, soil<ref name="Braunig2017">Bräunig, J., Baduel, C., Heffernan, A., Rotander, A., Donaldson, E. and Mueller, J.F., 2017. Fate and redistribution of perfluoroalkyl acids through AFFF-impacted groundwater. Science of the Total Environment, 596, pp. 360-368. [https://doi.org/10.1016/j.scitotenv.2017.04.095 DOI: 10.1016/j.scitotenv.2017.04.095]</ref>, and groundwater<ref name="Weber2017">Weber, A.K., Barber, L.B., LeBlanc, D.R., Sunderland, E.M. and Vecitis, C.D., 2017. Geochemical and Hydrologic Factors Controlling Subsurface Transport of Poly- and Perfluoroalkyl Substances, Cape Cod, Massachusetts. Environmental Science and Technology, 51(8), pp. 4269-4279. [https://doi.org/10.1021/acs.est.6b05573 DOI: 10.1021/acs.est.6b05573]&nbsp;&nbsp; [https://bgc.seas.harvard.edu/assets/weber2017_final.pdf Free Download]</ref>. The primary mechanisms controlling PFAS transport are [[Wikipedia:Advection | advection]] and [[Wikipedia:Dispersive_mass_transfer | dispersion]], similar to other dissolved compounds. For additional information on transport in groundwater, see [[Advection and Groundwater Flow]] and [[Dispersion and Diffusion]]. 
+
<center><big>Anion Exchange Reaction:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;'''PFAS<sup>-</sup></big><sub>(aq)</sub><big>&nbsp;+&nbsp;Cl<sup>-</sup></big><sub>(resin bound)</sub><big>&nbsp;&nbsp;&rArr;&nbsp;&nbsp;PFAS<sup>-</sup></big><sub>(resin bound)</sub><big>&nbsp;+&nbsp;Cl<sup>-</sup></big><sub>(aq)</sub>'''</center>
  
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* '''Partitioning:''' Partitioning of PFAS between the mobile and immobile phases is one of the most important processes controlling the rate of migration in the environment. The primary mobile phases are typically air and water.  Relatively immobile phases include stream sediments, soils, aquifer material, NAPLs, and interfaces between different phases (air-water, NAPL-water).  Partitioning of a significant portion of the PFAS mass into an immobile phase increases the amount of material stored in the system and slows the apparent rate of migration in the mobile phase – a phenomenon that has been observed in field metadata<ref name="Anderson2019">Anderson, R.H., Adamson, D.T. and Stroo, H.F., 2019. Partitioning of poly-and perfluoroalkyl substances from soil to groundwater within aqueous film-forming foam source zones. Journal of Contaminant Hydrology, 220, pp. 59-65. [https://doi.org/10.1016/j.jconhyd.2018.11.011 DOI: 10.1016/j.jconhyd.2018.11.011]&nbsp;&nbsp; Manuscript available from [https://www.researchgate.net/profile/Hans_Stroo3/publication/329227107_Partitioning_of_poly-_and_perfluoroalkyl_substances_from_soil_to_groundwater_WITHIN_aqueous_film-forming_foam_source_zones/links/5e56996b299bf1bdb83e2f69/Partitioning-of-poly-and-perfluoroalkyl-substances-from-soil-to-groundwater-WITHIN-aqueous-film-forming-foam-source-zones.pdf ResearchGate]</ref>.
+
{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
 +
|+Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
 +
|-
 +
! Analytes
 +
!
 +
! GW
 +
! FF
 +
! AFFF<br>Rinsate
 +
! AFF<br>(diluted 10X)
 +
! IDW NF
 +
|-
 +
| &Sigma; Total PFAS<small><sup>a</sup></small> (ND=0)
 +
| rowspan="9" style="background-color:white;" | <p style="writing-mode: vertical-rl">% Decrease<br>(Initial Concentration, &mu;g/L)</p>
 +
| 93%<br>(370) || 96%<br>(32,000) || 89%<br>(57,000) || 86 %<br>(770,000) || 84%<br>(82)
 +
|-
 +
| &Sigma; Total PFAS (ND=MDL) || 93%<br>(400) || 86%<br>(32,000) || 90%<br>(59,000) || 71%<br>(770,000) || 88%<br>(110)
 +
|-  
 +
| &Sigma; Total PFAS (ND=RL) || 94%<br>(460) || 96%<br>(32,000) || 91%<br>(66,000) || 34%<br>(770,000) || 92%<br>(170)
 +
|-
 +
| &Sigma; Highly Regulated PFAS<small><sup>b</sup></small> (ND=0) || >99%<br>(180) || >99%<br>(20,000) || 95%<br>(20,000) || 92%<br>(390,000) || 95%<br>(50)
 +
|-
 +
| &Sigma; Highly Regulated PFAS (ND=MDL) || >99%<br>(180) || 98%<br>(20,000) || 95%<br>(20,000) || 88%<br>(390,000) || 95%<br> (52)
 +
|-
 +
| &Sigma; Highly Regulated PFAS (ND=RL) || >99%<br>(190) || 93%<br>(20,000) || 95%<br>(20,000) || 79%<br>(390,000) || 95%<br>(55)
 +
|-
 +
| &Sigma; Priority PFAS<small><sup>c</sup></small> (ND=0) || 91%<br>(180) || 98%<br>(20,000) || 85%<br>(20,000) || 82%<br>(400,000) || 94%<br>(53)
 +
|-
 +
| &Sigma; Priority PFAS (ND=MDL) || 91%<br>(190) || 94%<br>(20,000) || 85%<br>(20,000) || 79%<br>(400,000) || 86%<br>(58)
 +
|-
 +
| &Sigma; Priority PFAS (ND=RL) || 92%<br>(200) || 87%<br>(20,000) || 86%<br>(21,000) || 70%<br>(400,000) || 87%<br>(65)
 +
|-
 +
| Fluorine mass balance<small><sup>d</sup></small> || ||106% || 109% || 110% || 65% || 98%
 +
|-
 +
| Sorbed organic fluorine<small><sup>e</sup></small> || || 4% || 4% || 33% || N/A || 31%
 +
|-
 +
| colspan="7" style="background-color:white; text-align:left" | <small>Notes:<br>GW = groundwater<br>GW FF = groundwater foam fractionate<br>AFFF rinsate = rinsate collected from fire system decontamination<br>AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x<br>IDW NF = investigation derived waste nanofiltrate<br>ND = non-detect<br>MDL = Method Detection Limit<br>RL = Reporting Limit<br><small><sup>a</sup></small>Total PFAS = 40 analytes + unidentified PFCA precursors<br><small><sup>b</sup></small>Highly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>c</sup></small>High priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>d</sup></small>Ratio of the final to the initial organic fluorine plus inorganic fluoride concentrations<br><small><sup>e</sup></small>Percent of organic fluorine that sorbed to the reactor walls during treatment<br></small>
 +
|}
  
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* '''Transformation:''' Transformation of PFAS is controlled by the molecular structure of the individual compounds.  Perfluorinated compounds, including PFAAs, are resistant to abiotic and biotic transformation reactions under typical conditions and highly persistent in the environment.  In contrast, precursors can be transformed by both abiotic and biotic processes, often resulting in the production of so-called “terminal” PFAA daughter products. 
 
  
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==Transport and Partitioning in the Atmosphere==
+
In aqueous solution, the hydrophilic portions of an amphiphile form hydrogen bonds (4 - 120 kJ/mol) and van der Waals interactions (<5 kJ/mol) with water molecules and surfaces, and electrostatic interactions (5 – 300 kJ/mol) can also occur where the amphiphile is ionic<ref name="LombardoEtAl2015">Lombardo, D., Kiselev, M.A., Magazù, S., Calandra, P., 2015. Amphiphiles Self-Assembly: Basic Concepts and Future Perspectives of Supramolecular Approaches. Advances in Condensed Matter Physics, vol. 2015, article ID 151683, 22 pages. [https://doi.org/10.1155/2015/151683 doi: 10.1155/2015/151683]&nbsp;&nbsp;[[Media: LombardoEtAl2015.pdf | Open Access Article]]</ref>. These interactions, although weak compared to intramolecular covalent bonds within a molecule are energetically favorable and increase the enthalpy of the combined solute-solvent system. Thus, the hydrophilic portion of an amphiphile will look to maximize enthalpic gain through hydrogen bond interactions with the bulk water.
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Air serves as a transport media for PFAS, particularly for uncharged polyfluorinated PFAS.  Airborne PFAS transport contributes to global distribution and can lead to localized deposition to soils and surface water in the vicinity of emission sources<ref name="Simcik2005">Simcik, M.F. and Dorweiler, K.J., 2005. Ratio of Perfluorochemical Concentrations as a Tracer of Atmospheric Deposition to Surface Waters. Environmental Science and Technology, 39(22), pp.  8678-8683. [https://doi.org/10.1021/es0511218 DOI: 10.1021/es0511218]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Matt_Simcik/publication/7444956_Ratio_of_Perfluorochemical_Concentrations_as_a_Tracer_of_Atmospheric_Deposition_to_Surface_Waters/links/5f035861299bf1881603c3be/Ratio-of-Perfluorochemical-Concentrations-as-a-Tracer-of-Atmospheric-Deposition-to-Surface-Waters.pdf ResearchGate]</ref><ref name="Prevedouros2006">Prevedouros, K., Cousins, I.T., Buck, R.C. and Korzeniowski, S.H., 2006. Sources, Fate and Transport of Perfluorocarboxylates. Environmental Science and Technology, 40(1), pp. 32-44. [https://doi.org/10.1021/es0512475 DOI: 10.1021/es0512475]&nbsp;&nbsp; Free download available from [https://d1wqtxts1xzle7.cloudfront.net/39945519/Sources_Fate_and_Transport_of_Perfluoroc20151112-1647-19vcvbf.pdf?1447365456=&response-content-disposition=inline%3B+filename%3DSources_Fate_and_Transport_of_Perfluoroc.pdf&Expires=1605023809&Signature=Z6KqgaDN6lKdAazoe6qoASoCtVystG5i~5EnrTcb~qMg3xZPz4O49Kghh62WmMzqEKE788~6EwrnlBVo9o6cM0hjf2vymFYxg4mx-eSIOEonfFjk6RonSaWp5gRbA6m~SNjwsjaKXID3OQyWIlLVpUd2LzAdI5rLGFA~gIXXtNPyCArLuGn-kbPYUIcBUg5TIkTZ6TDLXF~ujmzK9tNv~55UYabsJL4pmwIGC2sNGkEyJrYMfU577fbactdrmQXTJH7XbgpfDSfd4-xWkDZTdvVf~TypDDqUCZdtCkY8wINdpqtfe1KEzLrAj7rxxALAHUYxlVbPB45XTkLAGe5qww__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA  Academia]</ref><ref name="Ahrens2011">Ahrens, L., Shoeib, M., Harner, T., Lane, D.A., Guo, R. and Reiner, E.J., 2011. Comparison of Annular Diffusion Denuder and High Volume Air Samplers for Measuring Per- and Polyfluoroalkyl Substances in the Atmosphere." Analytical Chemistry, 83(24), pp. 9622-9628. [https://doi.org/10.1021/ac202414w DOI: 10.1021/ac202414w]&nbsp;&nbsp; Free download available from [https://www.informea.org/sites/default/files/imported-documents/UNEP-POPS-POPRC11FU-SUBM-PFOA-Canada-2-20151211.En.pdf Informea].</ref><ref name="Rauert2018">Rauert, C., Shoieb, M., Schuster, J.K., Eng, A. and Harner, T., 2018. Atmospheric concentrations and trends of poly-and perfluoroalkyl substances (PFAS) and volatile methyl siloxanes (VMS) over 7 years of sampling in the Global Atmospheric Passive Sampling (GAPS) network. Environmental Pollution, 238, pp. 94-102. [https://doi.org/10.1016/j.envpol.2018.03.017 DOI: 10.1016/j.envpol.2018.03.017]&nbsp;&nbsp; Open access article available from [https://reader.elsevier.com/reader/sd/pii/S0269749117352521?token=4C770E6E8AEDB0B3BA6A1D5B2C20ED5385F81823612551FA3380AAA1DA7A978F9CB36834AF6B7F91F35FF57E32013252 ScienceDirect]&nbsp;&nbsp; [[Media:Rauert2018.pdf | Report.pdf]]</ref>.  
 
  
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PFAAs, which are ionic and possess a negative charge under ambient environmental conditions, are far less volatile than many other groundwater contaminants.  An online database of vapor pressures and Henry’s Law constants for different PFAS, including PFAAs, is maintained by the Interstate Technology Regulatory Council<ref name="ITRC2020"/>.  In general, vapor pressures of PFAS are low and water solubilities are high, limiting partitioning from water to air<ref name="ITRC2020"/>. However, under certain conditions, particularly within industrial stack emissions, PFAS can be transported through the atmosphere in both the gas phase and associated with fugitive particulates.  In particular, volatile compounds including fluorotelomer alcohols (FTOHs) may be present in the gas phase, whereas, PFAAs can aerosolize and be transported as particulates<ref name="Ahrens2012"/>. In addition, precursors can be transformed to PFAAs in the atmosphere, which can result in PFAA deposition.
+
The hydrophobic portion of an amphiphile cannot form hydrogen bonds with the bulk solution, and its presence disrupts the hydrogen bond interactions between individual water molecules within the bulk water matrix. This disruption lowers the entropy of the system by reducing the degrees of translational rotational freedom available to the bulk water. The [[wikipedia:Second law of thermodynamics|second law of thermodynamics]] dictates that a system will arrange itself to maximize its entropy. With hydrophobic species this can be achieved by their spontaneous aggregation, as the reduction in solution entropy of the aggregated system is less than that which would occur if the component parts were solvated individually. These hydrophobic and hydrophilic interactions are weak, and the individual entropy gain per amphiphile upon aggregation is very small. However, taken together the overall effect on the entropy of the aggregate is sufficient to maintain it in solution, and moreover these interactions make the aggregates resistant to minor perturbations while retaining the reversibility of the self-assembled structure<ref name="LombardoEtAl2015"/>.
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Short-range atmospheric transport and deposition can result in PFAS contamination in terrestrial and aquatic systems near points of significant emissions, impacting soil, groundwater, and other media of concern<ref name="Fang2018">Fang, X., Wang, Q., Zhao, Z., Tang, J., Tian, C., Yao, Y., Yu, J. and Sun, H., 2018. Distribution and dry deposition of alternative and legacy perfluoroalkyl and polyfluoroalkyl substances in the air above the Bohai and Yellow Seas, China. Atmospheric Environment, 192, pp. 128-135. [https://doi.org/10.1016/j.atmosenv.2018.08.052 DOI: 10.1016/j.atmosenv.2018.08.052]</ref><ref name="Brandsma2019">Brandsma, S.H., Koekkoek, J.C., van Velzen, M.J.M. and de Boer, J., 2019.  The PFOA substitute GenX detected in the environment near a fluoropolymer manufacturing plant in the Netherlands. Chemosphere, 220, pp. 493-500. [https://doi.org/10.1016/j.chemosphere.2018.12.135 DOI: 10.1016/j.chemosphere.2018.12.135]&nbsp;&nbsp; Open access article available from [https://reader.elsevier.com/reader/sd/pii/S0045653518324706?token=E541D5C4B200C8626A86F41049FE9DCA92652BC9A8BA7D9E47832C08070AB5AF256F4872474C50B5C4908F5CA4C24947 ScienceDirect].&nbsp;&nbsp; [[Media: Brandsma2019.pdf | Report.pdf]]</ref>.  Releases of ionic PFAS from factories are likely tied to particulate matter, which settle to the ground in dry weather and are also wet-scavenged by precipitation<ref name="Barton2006">Barton, C.A., Butler, L.E., Zarzecki, C.J., Flaherty, J. and Kaiser, M., 2006. Characterizing Perfluorooctanoate in Ambient Air near the Fence Line of a Manufacturing Facility: Comparing Modeled and Monitored Values. Journal of the Air and Waste Management Association, 56(1), pp.  48-55. [https://doi.org/10.1080/10473289.2006.10464429 DOI: 10.1080/10473289.2006.10464429]&nbsp;&nbsp; Free access article available from [https://www.tandfonline.com/doi/pdf/10.1080/10473289.2006.10464429?needAccess=true Taylor and Francis Online]&nbsp;&nbsp; [[Media: Barton2006.pdf | Report.pdf]]</ref>.  The impact of other potential sources, such as combustion emissions or wind-blown fire-fighting foam from fire training and fire response sites, on the fate and transport of PFAS in air may need to be assessed.
 
  
−
Long-range transport processes are responsible for the wide distribution of neutral and ionic PFAS across the Earth as evidenced by their occurrence in biota, surface snow, ice cores, seawater, and other environmental media in regions as remote as the Arctic and Antarctic<ref name="Bossi2016">Bossi, R., Vorkamp, K. and Skov, H., 2016. Concentrations of organochlorine pesticides, polybrominated diphenyl ethers and perfluorinated compounds in the atmosphere of North Greenland. Environmental Pollution, 217, pp. 4-10. [https://doi.org/10.1016/j.envpol.2015.12.026 DOI: 10.1016/j.envpol.2015.12.026]</ref><ref name="Ahrens2010">Ahrens, L., Gerwinski, W., Theobald, N. and Ebinghaus, R., 2010. Sources of polyfluoroalkyl compounds in the North Sea, Baltic Sea and Norwegian Sea: Evidence from their spatial distribution in surface water. Marine Pollution Bulletin, 60(2), pp. 255-260. [https://doi.org/10.1016/j.marpolbul.2009.09.013 DOI: 10.1016/j.marpolbul.2009.09.013]</ref>.
+
==Regulatory Drivers for Transition to PFAS-Free Firefighting Formulations==
−
Distribution of PFAS to remote regions far removed from direct industrial input is believed to occur from both: a) long-range atmospheric transport and subsequent degradation of volatile precursors; and b) transport via ocean currents and release into the air as marine aerosols (sea spray)<ref name="DeSilva2009">De Silva, A.O., Muir, D.C. and Mabury, S.A., 2009. Distribution of perfluorocarboxylate isomers in select samples from the North American environment. Environmental Toxicology and Chemistry: An International Journal 28(9), pp. 1801-1814. [https://doi.org/10.1897/08-500.1 DOI: 10.1897/08-500.1]</ref><ref name="Armitage2009">Armitage, J.M., 2009. Modeling the global fate and transport of perfluoroalkylated substances (PFAS). Doctoral Dissertation, Institutionen för tillämpad miljövetenskap (ITM), Stockholm University. [[Media: Armitage2009.pdf | Report.pdf]]</ref>.
+
Regulations restricting the use and release of PFAS are being proposed and promulgated worldwide, with several enacted regulations addressing the use of aqueous film forming foams (AFFF) containing PFAS<ref name="Queensland2016">Queensland (Australia) Department of Environment and Heritage Protection, 2016. Operational Policy - Environmental Management of Firefighting Foam. 16 pages. [https://environment.des.qld.gov.au/assets/documents/regulation/firefighting-foam-policy.pdf Free Download]</ref><ref>U.S. Congress, 2019. S.1790 - National Defense Authorization Act for Fiscal Year 2020. United States Library of Congress.&nbsp;&nbsp;[https://www.congress.gov/bill/116th-congress/senate-bill/1790 Text and History of Law].</ref><ref>Arizona State Legislature, 2019. Title 36, Section 1696. Firefighting foam; prohibited uses; exception; definitions. [https://www.azleg.gov/viewdocument/?docName=https://www.azleg.gov/ars/36/01696.htm Text of Law]</ref><ref>California Legislature, 2020. Senate Bill No. 1044, Chapter 308, Firefighting equipment and foam: PFAS chemicals. [https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=201920200SB1044 Text and History of Law]</ref><ref>Arkansas General Assembly, 2021. An Act Concerning the Use of Certain Chemicals in Firefighting Foam; and for Other Purposes. Act 315, State of Arkansas. [https://trackbill.com/bill/arkansas-house-bill-1351-concerning-the-use-of-certain-chemicals-in-firefighting-foam/2008913/ Text and History of Law].</ref><ref>Espinosa, Summers, Kelly, J., Statler, Hansen, Young, 2021. Amendment to Fire Prevention and Control Act. House Bill 2722. West Virginia Legislature. [https://trackbill.com/bill/west-virginia-house-bill-2722-prohibiting-the-use-of-class-b-fire-fighting-foam-for-testing-purposes-if-the-foam-contains-a-certain-class-of-fluorinated-organic-chemicals/2047674/ Text and History of Law]</ref><ref>Louisiana Legislature, 2021. Act No. 232. [https://trackbill.com/bill/louisiana-house-bill-389-fire-protect-fire-marshal-provides-relative-to-the-discharge-or-use-of-class-b-fire-fighting-foam-containing-fluorinated-organic-chemicals/2092535/  Text and History of Law]</ref><ref>Vermont Legislature, 2021b. Act No. 36, PFAS in Class B Firefighting Foam. [https://trackbill.com/bill/vermont-senate-bill-20-an-act-relating-to-restrictions-on-perfluoroalkyl-and-polyfluoroalkyl-substances-and-other-chemicals-of-concern-in-consumer-products/1978963/  History and Text of Law]</ref>. In addition to regulated usage, firefighting formulation users are transitioning to PFAS-free firefighting formulations to reduce environmental liability in the event of a release, to reduce the cost of expensive containment systems and management of generated waste streams, and to avoid reputational damage. In 2016, Queensland, Australia was one of the first governments to ban PFAS use in firefighting foam<ref name="Queensland2016"/>. The US 2020 National Defense Authorization Act specified immediate prohibition of controlled releases of AFFF containing PFAS and required the Secretary of the Navy to publish a specification for PFAS-free firefighting formulation use and ensure it is available for use by the Department of Defense (DoD) by October 1, 2023<ref>U.S. Congress, 2021. S.2792 - National Defense Authorization Act for Fiscal Year 2021. United States Library of Congress.&nbsp;&nbsp;[https://www.congress.gov/bill/117th-congress/senate-bill/2792/ Text and History of Law].</ref>. The National Fire Protection Association (NFPA) recently removed the requirement for AFFF containing PFAS from their Standard on Aircraft Hangars and added two new chapters to allow users to determine if AFFF containing PFAS is needed at their facility<ref name="NFPA2022">National Fire Protection Association (NFPA), 2022. Codes and Standards, 409: Standard on Aircraft Hangars. [https://www.nfpa.org/codes-and-standards/4/0/9/409?l=42 NFPA Website]</ref>.
  
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==Transport and Partitioning in Aqueous Systems==
+
==Selection of Replacement PFAS-Free Firefighting Formulations==        
−
PFAS adsorb from water to a variety of solid materials including organic materials, clay minerals, metal oxides, and granular activated carbon<ref name="Du2014">Du, Z., Deng, S., Bei, Y., Huang, Q., Wang, B., Huang, J. and Yu, G., 2014. Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents – A review. Journal of Hazardous Materials, 274, pp. 443-454. [https://doi.org/10.1016/j.jhazmat.2014.04.038 DOI: 10.1016/j.jhazmat.2014.04.038]</ref>. This process is thought to occur through two primary mechanisms: 1) sorption to organic-carbon components of the solids; and 2) electrostatic (and other) interactions with inorganic constituents of the solids, including clay minerals and metal-oxides<ref name="Guelfo2013">Guelfo, J.L. and Higgins, C.P., 2013. Subsurface Transport Potential of Perfluoroalkyl Acids at Aqueous Film-Forming Foam (AFFF)-Impacted Sites. Environmental Science and Technology, 47(9), pp. 4164-4171. [https://doi.org/10.1021/es3048043 DOI: 10.1021/es3048043]&nbsp;&nbsp; [https://mountainscholar.org/bitstream/handle/11124/80055/Guelfo_mines_0052E_10298.pdf?sequence=1#page=64 Doctoral Dissertation]</ref><ref name="Zhao2014">Zhao, L., Bian, J., Zhang, Y., Zhu, L. and Liu, Z., 2014. Comparison of the sorption behaviors and mechanisms of perfluorosulfonates and perfluorocarboxylic acids on three kinds of clay minerals. Chemosphere, 114, pp. 51-58. [https://doi.org/10.1016/j.chemosphere.2014.03.098 DOI: 10.1016/j.chemosphere.2014.03.098]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Lixia_Zhao8/publication/262148355_Comparison_of_the_sorption_behaviors_and_mechanisms_of_perfluorosulfonates_and_perfluorocarboxylic_acids_on_three_kinds_of_clay_minerals/links/5b1be5dca6fdcca67b681a4f/Comparison-of-the-sorption-behaviors-and-mechanisms-of-perfluorosulfonates-and-perfluorocarboxylic-acids-on-three-kinds-of-clay-minerals.pdf ResearchGate].</ref>. The relative contribution of each mechanism varies depending on surface chemistry and other geochemical factors, as well as the molecular properties of the PFAS. In general, the impact of electrostatic interactions with charged soil constituents is more important for PFAS than non-polar, hydrophobic organic contaminants (e.g. hydrocarbons, chlorinated solvents). Adsorption of PFAS by solids is often nonlinear, with greater sorption at lower solute concentrations.  The impacts of adsorption kinetics and their potential reversibility on PFAS transport have not yet been examined for most PFAS compounds. 
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Since they first entered the market in the 2000s, the operational capabilities of PFAS-free firefighting formulations have grown<ref>Allcorn, M., Bluteau, T., Corfield, J., Day, G., Cornelsen, M., Holmes, N.J.C., Klein, R.A., McDowall, J.G., Olsen, K.T., Ramsden, N., Ross, I., Schaefer, T.H., Weber, R., Whitehead, K., 2018. Fluorine-Free Firefighting Foams (3F) – Viable Alternatives to Fluorinated Aqueous Film-Forming Foams (AFFF). White Paper prepared for the IPEN by members of the IPEN F3 Panel and associates, POPRC-14, Rome. [https://ipen.org/sites/default/files/documents/IPEN_F3_Position_Paper_POPRC-14_12September2018d.pdf Free Download].</ref> and numerous companies are now manufacturing and delivering PFAS-free firefighting formulations for fixed systems and AFFF vehicles<ref>Ansul (Company), Ansul NFF-331 3%x3% Non-Fluorinated Foam Concentrate (Commercial Product). [https://docs.johnsoncontrols.com/specialhazards/api/khub/documents/1nbeVfynU1IW~eJcCOA0Bg/content Product Data Sheet].</ref><ref>BioEx (Company), Ecopol A+ (Commercial Product). [https://www.bio-ex.com/en/our-products/product/ecopol-aplus/ Website]</ref><ref>National Foam (Company), 2020. Avio F3 Green KHC 3%, Fluorine Free Foam Concentrate (Commercial Product). [https://nationalfoam.com/wp-content/uploads/sites/4/NMS515-Avio-Green-KHC-3-FF.pdf Safety Data Sheet]</ref>. Key factors in the selection of a PFAS-free firefighting formulation product are compatibility of the new formulation with the existing system (as confirmed by a fire protection engineer) and environmental certifications (i.e., verifying the absence of organic fluorine or PFAS or the absence of other non-fluorine environmental contaminants).
  
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Sorption of hydrocarbons, chlorinated solvents and other hydrophobic organics is often controlled the by organic-carbon components of the solid phase (see [[Sorption of Organic Contaminants]]). However, studies of PFAS sorption to solid phase organic carbon have reported conflicting results. In a study of field sites with aqueous film-forming foam (AFFF, a type of fire-fighting foam) releases, solid phase organic carbon content was found to significantly influence PFAS soil-to-groundwater concentration ratios. Statistical modeling was then used to derive apparent organic carbon partition coefficients for 18 different PFAS<ref name="Anderson2019"/>. A recent compilation of published organic carbon partition coefficients found a good correspondence to PFAS molecular structure<ref name="Brusseau2019a">Brusseau, M.L., 2019. Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per-and poly-fluoroalkyl substances. Environmental Pollution, 254B, p. 113102. [https://doi.org/10.1016/j.envpol.2019.113102 DOI: 10.1016/j.envpol.2019.113102]</ref>. However, other studies have shown a general lack of correlation between solid phase partition coefficients and organic carbon<ref name="Li2018">Li, Y., Oliver, D.P. and Kookana, R.S., 2018. A critical analysis of published data to discern the role of soil and sediment properties in determining sorption of per and polyfluoroalkyl substances (PFASs). Science of the Total Environment, 628, pp. 110-120. [https://doi.org/10.1016/j.scitotenv.2018.01.167 DOI: 10.1016/j.scitotenv.2018.01.167]</ref>. It is possible that greater variability may be observed for broader data sets that incorporate different ranges of PFAS concentrations, different solution conditions, different measurement methods, and field-based data which often have less well-defined conditions and may also be influenced by other retention processes<ref name="Anderson2019"/><ref name="Brusseau2019a"/>.
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In January 2023, the US Department of Defense (DoD) published the [https://media.defense.gov/2023/Jan/12/2003144157/-1/-1/1/MILITARY-SPECIFICATION-FOR-FIRE-EXTINGUISHING-AGENT-FLUORINE-FREE-FOAM-F3-LIQUID-CONCENTRATE-FOR-LAND-BASED-FRESH-WATER-APPLICATIONS.PDF Performance Specification for Fire Extinguishing Agent, Fluorine-Free Foam (F3) Liquid Concentrate for Land-Based, Fresh Water Applications]<ref name="DoD2023"/>. This Military Performance Specification (Mil-Spec) allows PFAS-free firefighting formulations to be certified as meeting certain standardized operational goals for use in military settings. In addition to Mil-Spec requirements, PFAS-free firefighting formulations can also be certified through Underwriters Laboratories Standard for Safety, Foam Equipment and Liquid Concentrates, UL 162, which requires the new firefighting formulations be investigated for suitability and compatibility with the specific equipment with which they are intended to be used<ref>Underwriters Laboratories Inc., 2018. UL162, UL Standard for Safety, Foam Equipment and Liquid Concentrates, 8th Edition, Revised 2022. 40 pages. [https://global.ihs.com/doc_detail.cfm?document_name=UL%20162&item_s_key=00096960 Website]</ref>. Several PFAS-free foams have been certified under various parts of EN1568, the European Standard which specifies the necessary foam properties and performance requirements<ref>European Standards, 2018. CSN EN 1568-1 ed. 2: Fire extinguishing media - Foam concentrates - Part 1: Specification for medium expansion foam concentrates for surface application to water-immiscible liquids. 48 pages. [https://www.en-standard.eu/csn-en-1568-1-ed-2-fire-extinguishing-media-foam-concentrates-part-1-specification-for-medium-expansion-foam-concentrates-for-surface-application-to-water-immiscible-liquids/ European Standards Website.]</ref>. Both [https://serdp-estcp.mil/ ESTCP and SERDP] have supported (and continue to support) the development and field validation of PFAS-free firefighting formulations (e.g. [https://serdp-estcp.mil/projects/details/baa72637-e3c8-40ee-a007-f295311c72ad WP22-7456], [https://serdp-estcp.mil/projects/details/1bed98f7-dbe6-4bdd-98d2-1f9cfeb5f3d9/wp21-3465-project-overview WP21-3465], [https://serdp-estcp.mil/projects/details/bc932800-cfc8-4e86-a212-5f8c9d27f17c WP20-1535]). Both the US Federal Aviation Administration (FAA) and National Fire Protection Association (NFPA) have performed a variety of foam certification tests on numerous PFAS-free firefighting formulations<ref>Back, G.G., Farley, J.P., 2020. Evaluation of the Fire Protection Effectiveness of Fluorine Free Firefighting Foams. National Fire Protection Association, Fire Protection Research Foundation. [https://www.iafc.org/docs/default-source/1safehealthshs/effectivenessofflourinefreefoam.pdf Free Download].</ref><ref>Casey, J., Trazzi, D., 2022. Fluorine-Free Foam Testing. Federal Aviation Administration (FAA) Final Report. [https://www.airporttech.tc.faa.gov/DesktopModules/EasyDNNNews/DocumentDownload.ashx?portalid=0&moduleid=3682&articleid=2882&documentid=3054  Open Access Article]</ref>.
  
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[[File:AndersonBrusseau1w2Fig2.png | thumb | 500px | Figure 2. Example of expected orientation and accumulation of PFAS at air-water interface. Source: D. Adamson, GSI, used with permission.]]
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==Selection of Flushing Agent==
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Most solids present in the environment contain both fixed-charged (negative) and variably charged surfaces.  At neutral to high pH, variably charged clay minerals have a net-negative charge. As a result, negatively charged PFAAs do not strongly interact electrostatically in most soils, although as the soil pH decreases electrostatic sorption would be expected to increase in soils with variably charged clay minerals.  Cationic and zwitterionic precursors are expected to be more strongly sorbed than anionic PFAAs in most environments due to well-established cation exchange reactions. Other factors, including ionic strength, composition, and the presence of co-solutes, can affect adsorption of PFAS<ref name="Higgins2006">Higgins, C.P. and Luthy, R.G., 2006. Sorption of Perfluorinated Surfactants on Sediments. Environmental Science and Technology, 40(23), pp. 7251-7256. [https://doi.org/10.1021/es061000n DOI: 10.1021/es061000n]</ref><ref name="Chen2009">Chen, H., Chen, S., Quan, X., Zhao, Y. and Zhao, H., 2009. Sorption of perfluorooctane sulfonate (PFOS) on oil and oil-derived black carbon: Influence of solution pH and [Ca2+]. Chemosphere, 77(10), pp. 1406-1411. [https://doi.org/10.1016/j.chemosphere.2009.09.008 DOI: 10.1016/j.chemosphere.2009.09.008]</ref><ref name="Pan2009">Pan, G., Jia, C., Zhao, D., You, C., Chen, H. and Jiang, G., 2009. Effect of cationic and anionic surfactants on the sorption and desorption of perfluorooctane sulfonate (PFOS) on natural sediments. Environmental Pollution, 157(1), pp.325-330. [https://doi.org/10.1016/j.envpol.2008.06.035 DOI: 10.1016/j.envpol.2008.06.035]&nbsp;&nbsp; Free download available from [https://www.researchgate.net/profile/Gang_Pan2/publication/23189567_Effect_of_cationic_and_anionic_surfactants_on_the_sorption_and_desorption_of_perfluorooctane_sulfonate_PFOS_on_natural_sediments/links/5be19d23a6fdcc3a8dc2550d/Effect-of-cationic-and-anionic-surfactants-on-the-sorption-and-desorption-of-perfluorooctane-sulfonate-PFOS-on-natural-sediments.pdf ResearchGate]</ref><ref name="Guelfo2013"/><ref name="Zhao2014"/>.
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General industry guidance has typically recommended several rinses with water to remove PFAS from impacted equipment. Owing to the unique physical and chemical properties of PFAS, the use of room temperature water to remove PFAS from impacted equipment has not been very effective. To address these recalcitrant accumulations, companies are developing new methods to remove self-assembled PFAS bilayers from existing fire-fighting infrastructure so that it can be successfully transitioned to PFAS-free formulations. Arcadis developed a non-toxic cleaning agent, Fluoro Fighter<sup>TM</sup>, which has been demonstrated to be effective for removal of PFAS from equipment by disrupting the accumulated layers of PFAS coating the AFFF-wetted surfaces.  
  
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Most PFAS compounds act as surface-active agents (or [[Wikipedia:Surfactant | surfactants]]) due to the presence of a hydrophilic headgroup and a hydrophobic tail.  The hydrophilic headgroup will preferentially partition to the aqueous phase and the hydrophobic tail will preferentially partition to the non-aqueous phase (air or organic material).  As a result, PFAS tend to accumulate at interfaces (air-water, water-NAPL, water-solid) (Figure 2).  This tendency to accumulate at interfaces can influence transport in the atmosphere (on water droplets and hydrated aerosols), in the vadose or unsaturated zone at air-water interfaces, in the presence of NAPLs, and in wastewater treatment systems<ref name="Brusseau2018"/><ref name="Brusseau2019b">Brusseau, M.L., 2019. The Influence of Molecular Structure on the Adsorption of PFAS to Fluid-Fluid Interfaces: Using QSPR to Predict Interfacial Adsorption Coefficients. Water Research, 152, pp. 148-158.  [https://doi.org/10.1016/j.watres.2018.12.057 DOI: 10.1016/j.watres.2018.12.057]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374777/ Author’s Manuscript]</ref>.
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Laboratory studies have supported the optimization of this PFAS removal method in fire suppression system piping obtained from a commercial airport hangar in Sydney, Australia<ref name="LangEtAl2022"/>. Prior to removal from the hangar, the stainless-steel pipe held PFAS-containing AFFF for more than three decades. Results indicated that Fluoro Fighter<sup>TM</sup>, as well as flushing at elevated temperatures, removed more surface associated PFAS in comparison to equivalent extractions using methanol or water at room temperature. ESTCP has supported (and continues to support) the development and field validation of best practices for methodologies to clean foam delivery systems (e.g. [https://serdp-estcp.mil/projects/details/1521652f-a8b2-4c52-9232-c1018989a6b1 ER20-5364], [https://serdp-estcp.mil/projects/details/6d0750be-f20b-4765-bdfa-872adccaf37a ER20-5361], [https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ER20-5369], [https://serdp-estcp.mil/projects/details/4fd2e4ab-ddb7-40f8-835e-e1d637c0d650 ER21-7229]).
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In theoretical and experimental studies of transport in unsaturated porous media, adsorption at the air-water interface increased PFOS and PFOA retention<ref name="Brusseau2018"/><ref name="Lyu2018">Lyu, Y., Brusseau, M.L., Chen, W., Yan, N., Fu, X., and Lin, X., 2018.  Adsorption of PFOA at the Air-Water Interface during Transport in Unsaturated Porous Media. Environmental Science and Technology, 52(14), pp. 7745-7753. [https://doi.org/10.1021/acs.est.8b02348 DOI: 10.1021/acs.est.8b02348]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6312111/ Author’s Manuscript]</ref><ref name="BrusseauEtAl2019">Brusseau, M.L., Yan, N., Van Glubt, S., Wang, Y., Chen, W., Lyu, Y., Dungan, B., Carroll, K.C., and Holguin, F.O., 2019. Comprehensive Retention Model for PFAS Transport in Subsurface Systems. Water Research, 148, pp. 41-50.  [https://doi.org/10.1016/j.watres.2018.10.035 DOI: 10.1016/j.watres.2018.10.035]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6294326/ Author’s Manuscript]</ref>, contributing approximately 20% to 80% of total retention in sands and soil. The impact of oil-water interfacial adsorption on PFAS transport was also quantitatively characterized in recent studies and shown to contribute to total retention on a similar scale as air-water interfacial adsorption<ref name="Brusseau2018"/><ref name="BrusseauEtAl2019"/>.  These processes may result in increased PFAS mass retained in NAPL source zones, increased PFAS sorption with the resulting retardation of transport, and greater persistence of dissolved PFAS in the environment.  
 
  
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==Transformation==
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==PFAS Verification Testing==
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[[File:AndersonBrusseau1w2Fig3.png | thumb | 600px | Figure 3. Conceptual model of precursor transformation resulting in the formation of PFAAs. Source L. Trozzolo, TRC and C. Higgins, Colorado School of Mines, used with permission.]]
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In general, PFAS sampling techniques used to support firefighting formulation transition activities are consistent with conventional sampling techniques used in the environmental industry, but special consideration is made regarding high concentration PFAS materials, elevated detection levels, cross-contamination potential, precursor content, and matrix interferences. The analytical method selected should be appropriate for the regulatory requirements in the site area.
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Certain polyfluorinated substances have the potential to transform to other PFAS, with PFAAs as the typical terminal daughter products. These polyfluorinated substances are often referred to as “precursors”. The transformation potential of polyfluorinated precursors is influenced by the presence, location, and number of carbon-hydrogen (C-H) bonds and potentially carbon-oxygen (C-O) bonds throughout the carbon chain. Specifically, PFAS with C-H bonds are subject to a variety of biotic and abiotic reactions that ultimately result in the formation of PFAAs with perfluorinated carbon chains of the same length or shorter than the initial polyfluorinated precursor<ref name="Houtz2013">Houtz, E.F., Higgins, C.P., Field, J.A. and Sedlak, D.L., 2013. Persistence of perfluoroalkyl acid precursors in AFFF-impacted groundwater and soil. Environmental Science and Technology, 47(15), pp.  8187-8195.  [https://doi.org/10.1021/es4018877 DOI: 10.1021/es4018877]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Erika_Houtz/publication/252323955_Persistence_of_Perfluoroalkyl_Acid_Precursors_in_AFFF-Impacted_Groundwater_and_Soil/links/59dbddeeaca2728e2018336d/Persistence-of-Perfluoroalkyl-Acid-Precursors-in-AFFF-Impacted-Groundwater-and-Soil.pdf ReseqarchGate]</ref><ref name="McGuire2014">McGuire, M.E., Schaefer, C., Richards, T., Backe, W.J., Field, J.A., Houtz, E., Sedlak, D.L., Guelfo, J.L., Wunsch, A., and Higgins, C.P., 2014. Evidence of Remediation-Induced Alteration of Subsurface Poly- and Perfluoroalkyl Substance Distribution at a Former Firefighter Training Area. Environmental Science and Technology, 48(12) pp. 6644-6652.  [https://doi.org/10.1021/es5006187 DOI: 10.1021/es5006187]&nbsp;&nbsp; Manuscript available from [https://ir.library.oregonstate.edu/downloads/td96k706f Oregon State University]</ref><ref name="Anderson2016">Anderson, R.H., Long, G.C., Porter, R.C. and Anderson, J.K., 2016. Occurrence of select perfluoroalkyl substances at US Air Force aqueous film-forming foam release sites other than fire-training areas: Field-validation of critical fate and transport properties. Chemosphere, 150, pp. 678-685.  [https://doi.org/10.1016/j.chemosphere.2016.01.014 DOI: 10.1016/j.chemosphere.2016.01.014]</ref><ref name="Weber2017"/>.
 
  
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Transformation studies published to date have tested only a small subsample of possible precursors and, therefore, much uncertainty exists regarding 1) the extent to which precursor transformation occurs on a global scale, 2) which environmental compartments represent the majority of transformation, 3) relevant environmental conditions that affect transformation processes, and 4) transformation rates and pathways. Nevertheless, a portion of the precursors are expected to transform to PFAAs over time as shown in Figure 3.
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==Rinsate Treatment==
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Numerous technologies for treatment of PFAS-impacted water sources, including rinsates, have been and are currently being developed. These include separation technologies such as [[PFAS Ex Situ Water Treatment|foam fractionation, nanofiltration, sorbents/flocculants, ion exchange resins, reverse osmosis, and destructive technologies such as sonolysis, electrochemical oxidation, hydrothermal alkaline treatment]], [[PFAS Treatment by Electrical Discharge Plasma |enhanced contact plasma]], and [[Supercritical Water Oxidation (SCWO) |supercritical water oxidation (SCWO)]]. Many of these technologies have rapidly developed from bench-scale (e.g., microcosms, columns, single reactors) to commercially available field-scale units capable of managing PFAS-impacted waters of varying waste volumes and PFAS compositions and concentrations. Ongoing field research continues to improve the treatment efficiency, reliability, and versatility of these technologies, both individually and as coupled treatment solutions (e.g., treatment train). ESTCP has supported (and continues to support) the development and field validation of separation and destructive technologies for treatment of PFAS-impacted water sources, including rinsates (e.g. [https://serdp-estcp.mil/projects/details/0c7af048-3a00-471f-9480-292aa78ecd4f ER20-5370], [https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ER20-5369], [https://serdp-estcp.mil/projects/details/0d7c91a8-d755-4876-a8bb-c3e896feee0d ER20-5350], [https://serdp-estcp.mil/projects/details/790e2dda-1f7b-4ff5-b77e-08ed10a456b1 ER20-5355]).  
  
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Precursors can be transformed by a variety of abiotic processes including hydrolysis, photolysis, and oxidation. Hydrolysis of some precursors, followed by subsequent biotransformation, can produce perfluoroalkyl sulfonates (PFSAs).  An important example is the production of PFOS from perfluorooctane sulfonyl fluoride (POSF)<ref name="Martin2010">Martin, J.W., Asher, B.J., Beesoon, S., Benskin, J.P. and Ross, M.S., 2010. PFOS or PreFOS? Are perfluorooctane sulfonate precursors (PreFOS) important determinants of human and environmental perfluorooctane sulfonate (PFOS) exposure? Journal of Environmental Monitoring, 12(11), pp.1979-2004.  [https://doi.org/10.1039/C0EM00295J DOI: 10.1039/C0EM00295J]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Matthew_Ross3/publication/47415684_PFOS_or_PreFOS_Are_perfluorooctane_sulfonate_precursors_PreFOS_important_determinants_of_human_and_environmental_perfluorooctane_sulfonate_PFOS_exposure/links/00b7d520a6132da945000000.pdf ResearchGate]</ref>.  Other hydrolysis reactions produce perfluoroalkyl carboxylates (PFCAs). At neutral pH, the hydrolysis of fluorotelomer-derived polymeric precursors results in the formation of monomeric precursors of PFOA and other PFAAs with half-lives of 50 to 90 years)<ref name="Washington2010">Washington, J.W., Ellington, J.J., Jenkins, T.M. and Yoo, H., 2010. Response to Comments on “Degradability of an Acrylate-Linked, Fluorotelomer Polymer in Soil”. Environmental Science and Technology, 44(2), pp. 849-850. [https://doi.org/10.1021/es902672q DOI: 10.1021/es902672q]&nbsp;&nbsp;  [https://pubs.acs.org/doi/pdf/10.1021/es902672q Free Download from ACS].</ref>.  Oxidation of precursors by hydroxyl radicals can occur in natural waters, with the fluorotelomer-derived precursors being oxidized relatively rapidly<ref name="Gauthier2005">Gauthier, S.A. and Mabury, S.A., 2005. Aqueous photolysis of 8: 2 fluorotelomer alcohol. Environmental Toxicology and Chemistry, 24(8), pp.1837-1846.  [https://doi.org/10.1897/04-591R.1 DOI: 10.1897/04-591R.1]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Suzanne_Gauthier/publication/7609648_Aqueous_photolysis_of_8_2_fluorotelomer_alcohol/links/5ec16c4792851c11a86d9438/Aqueous-photolysis-of-8-2-fluorotelomer-alcohol.pdf ResearchGate].</ref><ref name="Plumlee2009">Plumlee, M.H., McNeill, K. and Reinhard, M., 2009. Indirect Photolysis of Perfluorochemicals: Hydroxyl Radical-Initiated Oxidation of N-Ethyl Perfluorooctane Sulfonamido Acetate (N-EtFOSAA) and Other Perfluoroalkanesulfonamides. Environmental Science and Technology, 43(10), pp.3662-3668.  [https://doi.org/10.1021/es803411w DOI: 10.1021/es803411w]&nbsp;&nbsp; Free download from [https://www.researchgate.net/profile/Megan_Plumlee/publication/26309488_Indirect_Photolysis_of_Perfluorochemicals_Hydroxyl_Radical-Initiated_Oxidation_of_N-Ethyl_Perfluorooctane_Sulfonamido_Acetate_N-EtFOSAA_and_Other_Perfluoroalkanesulfonamides/links/5aac0437a6fdcc1bc0b8d002/Indirect-Photolysis-of-Perfluorochemicals-Hydroxyl-Radical-Initiated-Oxidation-of-N-Ethyl-Perfluorooctane-Sulfonamido-Acetate-N-EtFOSAA-and-Other-Perfluoroalkanesulfonamides.pdf ResearchGate].</ref>.
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Remedy selection for treatment of rinsates involves several key factors. It is critical that environmental practitioners have up-to-date technical and practical knowledge on the suitability of these remedial options for different site conditions, treatment volumes, PFAS composition (e.g., presence of precursors, co-contaminants), PFAS concentrations, safety considerations, potential for undesired byproducts (e.g., perchlorate, disinfection byproducts), and treatment costs (e.g., energy demand, capital costs, operational labor).
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Evidence of aerobic biotransformation is provided from studies of PFAS composition throughout the continuum of wastewater treatments<ref name="Arvaniti2015">Arvaniti, O.S. and Stasinakis, A.S., 2015. Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment. Science of the Total Environment, 524, pp. 81-92.  [https://doi.org/10.1016/j.scitotenv.2015.04.023 DOI: 10.1016/j.scitotenv.2015.04.023]</ref>, from field studies at AFFF-impacted sites<ref name="Houtz2013"/><ref name="McGuire2014"/><ref name="Anderson2016"/><ref name="Weber2017"/>, and from microcosm experiments. In general, the literature on aerobic biotransformation collectively demonstrates or indirectly supports the following conclusions as summarized in ITRC 2020<ref name="ITRC2020"/>:
 
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* Numerous aerobic biotransformation pathways exist with relatively rapid kinetics
 
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* All polyfluorinated precursors studied to date have the potential to aerobically biotransform to PFAAs
 
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* Aerobic biotransformation of various fluorotelomer-derived precursors exclusively results in the formation of PFCAs, including PFOA, without necessarily the conservation of chain-length
 
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* Aerobic biotransformation of various electrochemical fluorination-derived precursors primarily results in the formation of PFAAs, including PFOS, with the conservation of chain-length
 
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Precursor transformation can complicate CSMs (and risk assessments) and should be considered during comprehensive site investigations. For example, atmospheric emissions of volatile precursors can result in long-range transport where subsequent transformation and deposition can result in detectable levels of PFAAs in environmental media independent of obvious point-sources<ref name="Vedagiri2018">Vedagiri, U.K., Anderson, R.H., Loso, H.M. and Schwach, C.M., 2018. Ambient levels of PFOS and PFOA in multiple environmental media. Remediation Journal, 28(2), pp. 9-51.  [https://doi.org/10.1002/rem.21548 DOI: 10.1002/rem.21548]</ref>.  With respect to site-related precursors, transformation of otherwise unmeasured PFAS into detectable PFAAs is obviously relevant to site investigations to the extent transformation occurs after initial site characterization efforts or if past remedial efforts have accelerated ''in situ'' transformation rates<ref name="McGuire2014"/>.  Additionally, differential transport rates between precursor PFAS and the corresponding terminal PFAA could also confound CSMs if transformation rates are slower than transport rates as has been suggested<ref name="Weber2017"/>. 
 
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To account for otherwise unmeasurable precursors, several surrogate analytical methods have been developed. See [[PFAS Sampling and Analytical Methods]] for additional detail.
 
  
 
==References==
 
==References==
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<references/>
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<references />
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==See Also==
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[https://portal.ct.gov/-/media/CFPC/KO/2022/Latest-News/DESPP-DEEP-AFFF-MuniFDupdate-2022-05-26.pdf  Connecticut Take-Back Program for municipal fire departments using AFFF containing PFAS]
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[https://www.arcadis.com/en-us/knowledge-hub/blog/united-states/johnsie-lang/2021/transitioning-to-pfas-free-firefighting  Arcadis blog on Fluoro Fighter<sup>TM</sup>]
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[https://serdp-estcp.mil/projects/details/1521652f-a8b2-4c52-9232-c1018989a6b1  Project Summary ESTCP ER20-5634: Demonstration and Validation of Environmentally Sustainable Methods to Effectively Remove PFAS from Fire Suppression Systems]
  
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==See Also:==
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[https://serdp-estcp.org/projects/details/0d7c91a8-d755-4876-a8bb-c3e896feee0d  Project Summary ESTCP ER20-5350: Supercritical Water Oxidation (SCWO) for Complete PFAS Destruction]

Latest revision as of 22:03, 25 April 2024

Transition of Aqueous Film Forming Foam (AFFF) Fire Suppression Infrastructure Impacted by Per and Polyfluoroalkyl Substances (PFAS)

Per and polyfluoroalkyl substances (PFAS) contained in Class B aqueous film-forming foams (AFFFs) are known to accumulate on wetted surfaces of many fire suppression systems after decades of exposure[1]. When replacement PFAS-free firefighting formulations are added to existing infrastructure, PFAS can rebound from the wetted surfaces into the new formulations at high concentrations[2][3]. Effective methods are needed to properly transition to PFAS-free firefighting formulations in existing fire suppression infrastructure. Considerations in the transition process may include but are not limited to locating, identifying, and evaluating existing systems and AFFF, fire engineering evaluations, system prioritization, cost/downtime analyses, sampling and analysis, evaluation of risks and hazards to human health and the environment, transportation, and disposal.

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Introduction

Figure 1. (A) Schematic of a typical PFAS molecule demonstrating the hydrophobic fluorinated tail in green and the hydrophilic charged functional group in blue, (B) a PFAS bilayer formed with the hydrophobic tails facing inward and the charged functional groups on the outside, and (C) multiple bilayers of PFAS assembled on the wetted surfaces of fire suppression piping.

PFAS are a class of synthetic fluorinated compounds which are highly mobile and persistent within the environment[5]. Due to the surfactant properties of PFAS, these compounds self-assemble at any solid-liquid interface forming resilient bilayers during prolonged exposure[6]. Solid phase accumulation of PFAS has been proposed to be influenced by both hydrophobic and electrostatic interactions with fluorinated carbon chain length as the dominant feature influencing sorption[7]. While the majority of previous research into solid phase sorption typically focused on water treatment applications or subsurface porous media[8], recently PFAS accumulations have been identified on the wetted surfaces of fire suppression infrastructure exposed to aqueous film forming foam (AFFF)[1] (see Figure 1).

Fire suppression systems with potential PFAS impacts include fire fighting vehicles that carried AFFF and fixed suppression systems in buildings containing large amounts of flammable materials such as aircraft hangars (Figure 2). PFAS residue on the wetted surfaces of existing infrastructure can rebound into replacement PFAS-free firefighting formulations if not removed during the transition process[2]. Simple surface rinsing with water and low-pressure washing has been proven to be inefficient for removal of surface bound PFAS from piping and tanks that contained fluorinated AFFF[2]

Figure 2. Fixed fire suppression system for an aircraft hangar, with storage tank on left and distribution piping on right.

In addition to proper methods for system cleaning to remove residual PFAS, transition to PFAS-free foam may also include consideration of compliance with state and federal regulations, selection of the replacement PFAS-free firefighting formulation, a cost benefit analysis for replacement of the system components versus cleaning, and PFAS verification testing. Foam transition should be completed in a manner which minimizes the volume of waste generated as well as preventing any PFAS release into the environment.

PFAS Assembly on Solid Surfaces


Equation 1:      Equation1r.png
Where:
C0 is the freely dissolved concentration of the analyte in the sediment (mg/L or μg/L)
Cp,t is the measured concentration of the analyte in the peeper at time of retrieval (mg/L or μg/L)
K is the elimination rate of the target analyte
t is the deployment time (days)


Equation 2:      Equation2r.png
Where:
K is the elimination rate of the target analyte
Ktracer is the elimination rate of the tracer
D is the free-water diffusion of the analyte (cm2/s)
Dtracer is the free-water diffusion of the tracer (cm2/s)


Equation 3:          Equation3r2.png
Where:
Ktracer is the elimination rate of the tracer
Ctracer,i is the measured initial concentration of the tracer in the peeper prior to deployment (mg/L or μg/L)
Ctracer,t is the measured final concentration of the tracer in the peeper at time of retrieval (mg/L or μg/L)
t is the deployment time (days)

The self-assembly of amphiphilic molecules into supramolecular bilayers is a result of their structure and how it interacts with the bulk water of a solution. Single chain hydrocarbon based amphiphiles can form micelles under relatively dilute aqueous concentrations, however for hydrocarbon based surfactants the formation of more complex organized system such as vesicles is rarely seen, requiring double chain amphiphiles such as phospholipids. Associations of single chain cationic and anionic hydrocarbon based amphiphiles into stable supramolecular structures such as vesicles has however been demonstrated[9], with the ion pairing of the polar head groups mimicking the a double tail situation. The behavior of single chain fluorosurfactant amphiphiles has been demonstrated to be significantly different from similar hydrocarbon based analogues. Not only are critical micelle concentrations (CMC) of fluorosurfactants typically two orders of magnitude lower than corresponding hydrocarbon surfactants but self-assembly can occur even when fluorosurfactants are dispersed at low concentrations significantly below the CMC in water and other solvents[10]. The assembly of fluorinated amphiphiles structurally similar to those found in AFFF have been shown to readily form stable, complex structures including vesicles, fibers, and globules at concentrations as low as 0.5% w/v in contrast to their hydrocarbon analogues which remained fluid at 30% w/v[11][12].

Krafft found that fluorinated amphiphiles formed bilayer membranes with phospholipids, and that the resulting vesicles were more stable than those made of phospholipids alone[13]. The similarities in amphiphilic properties between phospholipids and the hydrocarbon-based surfactants in AFFF suggests that bilayer vesicles may form between these and the fluorosurfactants also present in the concentrate. Krafft demonstrated that both the permeability of resulting mixed vesicles and their propensity to fuse with each other at increasing ionic strength was reduced as a result of the creation of an inert hydrophobic and lipophobic film within the membrane, and also suggested that the fluorinated amphiphiles increased van der Waals interactions in the hydrocarbon region[13]. Thus this low permeability may allow vesicles formed by the surfactants present in AFFF to act as long term repositories of PFAS not only as part of the bilayer itself but also solvated within the vesicle. This prediction is supported by the observation that supramolecular structures formed from single chain fluorinated amphiphiles have been demonstrated to be stable at elevated temperature (15 min at 121°C) and have been shown to be stable over periods of months, even increasing in size over time when stored at environmentally relevant temperatures[12].

Formation of complex structures at relatively low solute concentrations requires the monomer molecules to be well ordered to maintain tight packing in the supramolecular structure[14]. This order results from electrostatic forces, hydrogen bonding, and in the case of fluorinated amphiphiles, hydrophobic interactions. The geometry of the amphiphile also potentially contributes to the type of supramolecular aggregation[15]. Surfactants which adopt a conical shape (such as a typical hydrocarbon based surfactant with a large polar head group and a single alkyl chain as a tail) tend to form micelles more easily. Increasing the bulk of the tail makes the surfactant more cylindrically shaped which makes assembly into bilayers more likely.

Perfluoroalkyl chains are significantly more bulky than their hydrocarbon based analogues both in cross sectional area (28-30 Å2 versus 20 Å2, respectively) and mean volume (CF2 and CF3 estimated as 38 Å3 and 92 Å3 compared to 27 Å3 and 54 Å3 for CH2 and CH3)[13][10]. Structural studies on linear PFOS have shown that the molecule adopts an unusual helical structure[16][17] in aqueous and solvent phases to alleviate steric hindrance. This arrangement results from the carbon chain starting in the planar all anti conformation and then successively twisting all the CC-CC dihedrals by 15°-20° in the same direction[18]. The conformation also minimizes the electrostatic repulsion between fluorine atoms bonded to the same side of the carbon backbone by maximizing the interatomic distances between them[17].

A consequence of the helical structure is that there is limited carbon-carbon bond rotation within the perfluoroalkyl chain giving them increased rigidity compared to alkyl chains[19]. The bulkiness of the perfluoroalkyl chain confers a cylindrical shape on the fluorosurfactant amphiphile and therefore favors the formation of bilayers and vesicles the aggregation of which is further assisted by the rigidity of the molecules which allow close packing in the supramolecular structure. Fluorosurfactants therefore cannot be regarded as more hydrophobic analogues of hydrogenated surfactants. Their self-assembly behavior is characterized by a strong tendency to form vesicles and lamellar phases rather than micelles, due to the bulkiness and rigidity of the perfluoroalkyl chain that tends to decrease the curvature of the aggregates they form in solution[20]. The larger tail cross section of fluorinated compared to hydrogenated amphiphiles tends to favor the formation of aggregates with lesser surface curvature, therefore rather than micelles they form bilayer membranes, vesicles, tubules and fibers[21][22][23][24]. Rojas et al. (2002) demonstrated that perfluorooctyl sulphonamide formed a contiguous bilayer at 50 mg/L with self-assembled aggregates present at concentrations as low as 10 mg/L[25].

Thermodynamics of PFAS Accumulations on Solid Surfaces

The thermodynamics of formation of amphiphiles into supramolecular species requires consideration of both hydrophobic and hydrophilic interactions resulting from the amphoteric nature of the molecule. The hydrophilic portions of the molecule are driven to maximize their solvation interaction with as many water molecules as possible, whereas the hydrophobic portions of the molecule are driven to aggregate together thus minimizing interaction with the bulk water. Both of these processes change the enthalpy and entropy of the system.

Anion Exchange Reaction:      PFAS-(aq) + Cl-(resin bound)  ⇒  PFAS-(resin bound) + Cl-(aq)
Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
Analytes GW FF AFFF
Rinsate 		AFF
(diluted 10X) 		IDW NF
Σ Total PFASa (ND=0)

% Decrease
(Initial Concentration, μg/L)

 93%
(370)		 96%
(32,000)		 89%
(57,000)		 86 %
(770,000)		 84%
(82)
Σ Total PFAS (ND=MDL) 93%
(400)		 86%
(32,000)		 90%
(59,000)		 71%
(770,000)		 88%
(110)
Σ Total PFAS (ND=RL) 94%
(460)		 96%
(32,000)		 91%
(66,000)		 34%
(770,000)		 92%
(170)
Σ Highly Regulated PFASb (ND=0) >99%
(180)		 >99%
(20,000)		 95%
(20,000)		 92%
(390,000)		 95%
(50)
Σ Highly Regulated PFAS (ND=MDL) >99%
(180)		 98%
(20,000)		 95%
(20,000)		 88%
(390,000)		 95%
(52)
Σ Highly Regulated PFAS (ND=RL) >99%
(190)		 93%
(20,000)		 95%
(20,000)		 79%
(390,000)		 95%
(55)
Σ Priority PFASc (ND=0) 91%
(180)		 98%
(20,000)		 85%
(20,000)		 82%
(400,000)		 94%
(53)
Σ Priority PFAS (ND=MDL) 91%
(190)		 94%
(20,000)		 85%
(20,000)		 79%
(400,000)		 86%
(58)
Σ Priority PFAS (ND=RL) 92%
(200)		 87%
(20,000)		 86%
(21,000)		 70%
(400,000)		 87%
(65)
Fluorine mass balanced 106% 109% 110% 65% 98%
Sorbed organic fluorinee 4% 4% 33% N/A 31%
Notes:
GW = groundwater
GW FF = groundwater foam fractionate
AFFF rinsate = rinsate collected from fire system decontamination
AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x
IDW NF = investigation derived waste nanofiltrate
ND = non-detect
MDL = Method Detection Limit
RL = Reporting Limit
aTotal PFAS = 40 analytes + unidentified PFCA precursors
bHighly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA
cHigh priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA
dRatio of the final to the initial organic fluorine plus inorganic fluoride concentrations
ePercent of organic fluorine that sorbed to the reactor walls during treatment


In aqueous solution, the hydrophilic portions of an amphiphile form hydrogen bonds (4 - 120 kJ/mol) and van der Waals interactions (<5 kJ/mol) with water molecules and surfaces, and electrostatic interactions (5 – 300 kJ/mol) can also occur where the amphiphile is ionic[26]. These interactions, although weak compared to intramolecular covalent bonds within a molecule are energetically favorable and increase the enthalpy of the combined solute-solvent system. Thus, the hydrophilic portion of an amphiphile will look to maximize enthalpic gain through hydrogen bond interactions with the bulk water.

The hydrophobic portion of an amphiphile cannot form hydrogen bonds with the bulk solution, and its presence disrupts the hydrogen bond interactions between individual water molecules within the bulk water matrix. This disruption lowers the entropy of the system by reducing the degrees of translational rotational freedom available to the bulk water. The second law of thermodynamics dictates that a system will arrange itself to maximize its entropy. With hydrophobic species this can be achieved by their spontaneous aggregation, as the reduction in solution entropy of the aggregated system is less than that which would occur if the component parts were solvated individually. These hydrophobic and hydrophilic interactions are weak, and the individual entropy gain per amphiphile upon aggregation is very small. However, taken together the overall effect on the entropy of the aggregate is sufficient to maintain it in solution, and moreover these interactions make the aggregates resistant to minor perturbations while retaining the reversibility of the self-assembled structure[26].

Regulatory Drivers for Transition to PFAS-Free Firefighting Formulations

Regulations restricting the use and release of PFAS are being proposed and promulgated worldwide, with several enacted regulations addressing the use of aqueous film forming foams (AFFF) containing PFAS[27][28][29][30][31][32][33][34]. In addition to regulated usage, firefighting formulation users are transitioning to PFAS-free firefighting formulations to reduce environmental liability in the event of a release, to reduce the cost of expensive containment systems and management of generated waste streams, and to avoid reputational damage. In 2016, Queensland, Australia was one of the first governments to ban PFAS use in firefighting foam[27]. The US 2020 National Defense Authorization Act specified immediate prohibition of controlled releases of AFFF containing PFAS and required the Secretary of the Navy to publish a specification for PFAS-free firefighting formulation use and ensure it is available for use by the Department of Defense (DoD) by October 1, 2023[35]. The National Fire Protection Association (NFPA) recently removed the requirement for AFFF containing PFAS from their Standard on Aircraft Hangars and added two new chapters to allow users to determine if AFFF containing PFAS is needed at their facility[36].

Selection of Replacement PFAS-Free Firefighting Formulations

Since they first entered the market in the 2000s, the operational capabilities of PFAS-free firefighting formulations have grown[37] and numerous companies are now manufacturing and delivering PFAS-free firefighting formulations for fixed systems and AFFF vehicles[38][39][40]. Key factors in the selection of a PFAS-free firefighting formulation product are compatibility of the new formulation with the existing system (as confirmed by a fire protection engineer) and environmental certifications (i.e., verifying the absence of organic fluorine or PFAS or the absence of other non-fluorine environmental contaminants).

In January 2023, the US Department of Defense (DoD) published the Performance Specification for Fire Extinguishing Agent, Fluorine-Free Foam (F3) Liquid Concentrate for Land-Based, Fresh Water Applications[4]. This Military Performance Specification (Mil-Spec) allows PFAS-free firefighting formulations to be certified as meeting certain standardized operational goals for use in military settings. In addition to Mil-Spec requirements, PFAS-free firefighting formulations can also be certified through Underwriters Laboratories Standard for Safety, Foam Equipment and Liquid Concentrates, UL 162, which requires the new firefighting formulations be investigated for suitability and compatibility with the specific equipment with which they are intended to be used[41]. Several PFAS-free foams have been certified under various parts of EN1568, the European Standard which specifies the necessary foam properties and performance requirements[42]. Both ESTCP and SERDP have supported (and continue to support) the development and field validation of PFAS-free firefighting formulations (e.g. WP22-7456, WP21-3465, WP20-1535). Both the US Federal Aviation Administration (FAA) and National Fire Protection Association (NFPA) have performed a variety of foam certification tests on numerous PFAS-free firefighting formulations[43][44].

Selection of Flushing Agent

General industry guidance has typically recommended several rinses with water to remove PFAS from impacted equipment. Owing to the unique physical and chemical properties of PFAS, the use of room temperature water to remove PFAS from impacted equipment has not been very effective. To address these recalcitrant accumulations, companies are developing new methods to remove self-assembled PFAS bilayers from existing fire-fighting infrastructure so that it can be successfully transitioned to PFAS-free formulations. Arcadis developed a non-toxic cleaning agent, Fluoro FighterTM, which has been demonstrated to be effective for removal of PFAS from equipment by disrupting the accumulated layers of PFAS coating the AFFF-wetted surfaces.

Laboratory studies have supported the optimization of this PFAS removal method in fire suppression system piping obtained from a commercial airport hangar in Sydney, Australia[1]. Prior to removal from the hangar, the stainless-steel pipe held PFAS-containing AFFF for more than three decades. Results indicated that Fluoro FighterTM, as well as flushing at elevated temperatures, removed more surface associated PFAS in comparison to equivalent extractions using methanol or water at room temperature. ESTCP has supported (and continues to support) the development and field validation of best practices for methodologies to clean foam delivery systems (e.g. ER20-5364, ER20-5361, ER20-5369, ER21-7229).

PFAS Verification Testing

In general, PFAS sampling techniques used to support firefighting formulation transition activities are consistent with conventional sampling techniques used in the environmental industry, but special consideration is made regarding high concentration PFAS materials, elevated detection levels, cross-contamination potential, precursor content, and matrix interferences. The analytical method selected should be appropriate for the regulatory requirements in the site area.

Rinsate Treatment

Numerous technologies for treatment of PFAS-impacted water sources, including rinsates, have been and are currently being developed. These include separation technologies such as foam fractionation, nanofiltration, sorbents/flocculants, ion exchange resins, reverse osmosis, and destructive technologies such as sonolysis, electrochemical oxidation, hydrothermal alkaline treatment, enhanced contact plasma, and supercritical water oxidation (SCWO). Many of these technologies have rapidly developed from bench-scale (e.g., microcosms, columns, single reactors) to commercially available field-scale units capable of managing PFAS-impacted waters of varying waste volumes and PFAS compositions and concentrations. Ongoing field research continues to improve the treatment efficiency, reliability, and versatility of these technologies, both individually and as coupled treatment solutions (e.g., treatment train). ESTCP has supported (and continues to support) the development and field validation of separation and destructive technologies for treatment of PFAS-impacted water sources, including rinsates (e.g. ER20-5370, ER20-5369, ER20-5350, ER20-5355).

Remedy selection for treatment of rinsates involves several key factors. It is critical that environmental practitioners have up-to-date technical and practical knowledge on the suitability of these remedial options for different site conditions, treatment volumes, PFAS composition (e.g., presence of precursors, co-contaminants), PFAS concentrations, safety considerations, potential for undesired byproducts (e.g., perchlorate, disinfection byproducts), and treatment costs (e.g., energy demand, capital costs, operational labor).

References

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See Also

Connecticut Take-Back Program for municipal fire departments using AFFF containing PFAS

Arcadis blog on Fluoro FighterTM

Project Summary ESTCP ER20-5634: Demonstration and Validation of Environmentally Sustainable Methods to Effectively Remove PFAS from Fire Suppression Systems

Project Summary ESTCP ER20-5350: Supercritical Water Oxidation (SCWO) for Complete PFAS Destruction

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