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==PFAS Transport and Fate==
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==  
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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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The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) which can destroy [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor">Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. [https://www.haleyaldrich.com/about-us/applied-research-program/eradifluor/ Comercial Website]</ref>) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.
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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>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
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'''Related Article(s): '''
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'''Related Article(s):'''
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
 
  
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'''Contributor(s): '''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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Dr. Hunter Anderson and Dr. Mark L. Brusseau
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*[[PFAS Ex Situ Water Treatment]]
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*[[PFAS Sources]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[Photoactivated Reductive Defluorination - PFAS Destruction]]
  
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'''Key Resource(s): '''
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'''Contributors:''' John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu
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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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'''Key Resources:'''
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*Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management<ref name="BentelEtAl2019">Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. [https://doi.org/10.1021/acs.est.8b06648 doi: 10.1021/acs.est.8b06648]&nbsp; [[Media: BentelEtAl2019.pdf | Open Access Article]]</ref>
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*Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies<ref>Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. [https://doi.org/10.1021/acs.est.1c07608 doi: 10.1021/acs.est.1c07608]&nbsp; [[Media: LiuZEtAl2022.pdf | Open Access Article]]</ref>
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*Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment<ref>Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. [https://doi.org/10.1021/acs.est.0c00961 doi: 10.1021/acs.est.0c00961]</ref>
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*EradiFluor<sup>TM</sup><ref name="EradiFluor"/>
  
 
==Introduction==
 
==Introduction==
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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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The hydrated electron (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) can be described as an electron in solution surrounded by a small number of water molecules<ref name="BuxtonEtAl1988">Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. [https://doi.org/10.1063/1.555805 doi: 10.1063/1.555805]</ref>. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials<ref name="BuxtonEtAl1988"/>.  
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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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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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==PFAS Transport and Fate Processes==
 
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[[File:AndersonBrusseau1w2Fig1.png | thumb | 400px | Figure 1. Illustration of PFAS partitioning and transformation processes. Source: D. Adamson, GSI, used with permission.]]
 
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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]]. 
 
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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>.
 
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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==
 
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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.
 
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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.
 
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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>. 
 
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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>.
 
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==Transport and Partitioning in Aqueous Systems==
 
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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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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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Among the electron source chemicals, sulfite (SO<sub>3</sub><sup>2−</sup>) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as ''hv, SO<sub>3</sub><sup><big>'''•-'''</big></sup>'' is the sulfur trioxide radical anion):
 +
</br>
 +
::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
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[[File:AndersonBrusseau1w2Fig2.png | thumb | 400px | 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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The hydrated electron has demonstrated excellent performance in destroying PFAS such as [[Wikipedia:Perfluorooctanesulfonic acid | perfluorooctanesulfonic acid (PFOS)]], [[Wikipedia:Perfluorooctanoic acid|perfluorooctanoic acid (PFOA)]]<ref>Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. [https://doi.org/10.1016/j.scitotenv.2017.06.197 doi: 10.1016/j.scitotenv.2017.06.197]</ref> and [[Wikipedia: GenX|GenX]]<ref>Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. [https://doi.org/10.1021/acs.est.8b02172 doi: 10.1021/acs.est.8b02172]</ref>. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., [[Wikipedia: Decarboxylation | decarboxylation]], [[Wikipedia: Hydroxylation | hydroxylation]], [[Wikipedia: Elimination reaction | elimination]], and [[Wikipedia: Hydrolysis | hydrolysis]])<ref name="BentelEtAl2019"/>.
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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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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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==Process Description==
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A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a [[Wikipedia: Foam fractionation | foam fractionation]], [[PFAS Treatment by Anion Exchange | regenerable ion exchange]], or a [[Reverse Osmosis and Nanofiltration Membrane Filtration Systems for PFAS Removal | membrane filtration system]]) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1. [[File: XiongFig1.png | thumb | left | 600 px | Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream]]<br clear="left"/>
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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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==Advantages==
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[[File:AndersonBrusseau1w2Fig3.png | thumb | 400px | 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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A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by ''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'', low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:
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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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*'''High efficiency for short- and ultrashort-chain PFAS:''' While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies<ref>Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. [https://doi.org/10.1016/j.jhazmat.2020.124452 doi: 10.1016/j.jhazmat.2020.124452]</ref><ref>Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. [https://doi.org/10.1021/acs.est.0c02158 doi: 10.1021/acs.est.0c02158]</ref><ref>Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. [https://doi.org/10.1021/acsestwater.0c00170 doi: 10.1021/acsestwater.0c00170]</ref>, the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] and [[Wikipedia: Perfluoropropionic acid | perfluoropropionic acid (PFPrA)]]. 
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*'''High defluorination ratio:''' As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
 +
*'''No harmful byproducts:''' While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
 +
*'''Ambient pressure and low temperature:''' The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS. 
 +
*'''Low energy consumption:''' The electrical energy per order values for the degradation of [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., [[Supercritical Water Oxidation (SCWO) | supercritical water oxidation]])<ref>Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. [https://doi.org/10.1080/10643389.2018.1542916 doi: 10.1080/10643389.2018.1542916]</ref>.
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*'''Co-contaminant destruction:''' The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride<ref>Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. [https://doi.org/10.1016/j.jece.2015.07.026 doi: 10.1016/j.jece.2015.07.026]</ref><ref>Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. [https://doi.org/10.1016/j.cej.2012.11.086 doi: 10.1016/j.cej.2012.11.086]</ref><ref>Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. [https://doi.org/10.1021/es3008535 doi: 10.1021/es3008535]</ref><ref>Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. [https://doi.org/10.1016/j.watres.2014.05.051 doi: 10.1016/j.watres.2014.05.051]</ref>.
  
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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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==Limitations==
 +
Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.
 +
*Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
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*Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
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*The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonate (PFBS)]] exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.
  
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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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==State of the Practice==
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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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[[File: XiongFig2.png | thumb | 500 px | Figure 2. Field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.]]
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* Numerous aerobic biotransformation pathways exist with relatively rapid kinetics
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[[File: XiongFig3.png | thumb | 500 px | Figure 3. Field demonstration of a treatment train (SAFF + EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.]]  
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* All polyfluorinated precursors studied to date have the potential to aerobically biotransform to PFAAs
+
The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the [[Wikipedia: TOP Assay | total oxidizable precursor (TOP) assay]], adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.  
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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
+
*Under the [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)] [https://serdp-estcp.mil/projects/details/4c073623-e73e-4f07-a36d-e35c7acc75b6/er21-5152-project-overview Project ER21-5152], a field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an ''in situ'' foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
−
* Aerobic biotransformation of various electrochemical fluorination-derived precursors primarily results in the formation of PFAAs, including PFOS, with the conservation of chain-length
+
*Another field demonstration was completed at an Air Force base in California, where a treatment train combining [https://serdp-estcp.mil/projects/details/263f9b50-8665-4ecc-81bd-d96b74445ca2 Surface Active Foam Fractionation (SAFF)] and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).
−
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"/>.  
 
−
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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==See Also==

Latest revision as of 11:33, 29 January 2026

PFAS Destruction by Ultraviolet/Sulfite Treatment

The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (eaq- ) which can destroy PFAS in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.

Related Article(s):

Contributors: John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu

Key Resources:

  • Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management[2]
  • Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies[3]
  • Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment[4]
  • EradiFluorTM[1]

Introduction

The hydrated electron (eaq- ) can be described as an electron in solution surrounded by a small number of water molecules[5]. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials[5].

Among the electron source chemicals, sulfite (SO32−) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as hv, SO3•- is the sulfur trioxide radical anion):

Equation 1:   XiongEq1.png

The hydrated electron has demonstrated excellent performance in destroying PFAS such as perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA)[6] and GenX[7]. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., decarboxylation, hydroxylation, elimination, and hydrolysis)[2].

Process Description

A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a foam fractionation, regenerable ion exchange, or a membrane filtration system) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1.

Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream


Advantages

A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by eaq-, low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:

  • High efficiency for short- and ultrashort-chain PFAS: While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies[8][9][10], the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA).
  • High defluorination ratio: As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
  • No harmful byproducts: While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
  • Ambient pressure and low temperature: The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS.
  • Low energy consumption: The electrical energy per order values for the degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., supercritical water oxidation)[11].
  • Co-contaminant destruction: The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride[12][13][14][15].

Limitations

Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.

  • Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
  • Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
  • The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and perfluorobutanesulfonate (PFBS) exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.

State of the Practice

Figure 2. Field demonstration of EradiFluorTM[1] for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.
Figure 3. Field demonstration of a treatment train (SAFF + EradiFluorTM[1]) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluorTM[1]; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.

The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluorTM[1] system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the total oxidizable precursor (TOP) assay, adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.

  • Under the Environmental Security Technology Certification Program (ESTCP) Project ER21-5152, a field demonstration of EradiFluorTM[1] was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an in situ foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
  • Another field demonstration was completed at an Air Force base in California, where a treatment train combining Surface Active Foam Fractionation (SAFF) and EradiFluorTM[1] was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluorTM[1] was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluorTM[1]. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).

References

  1. ^ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. Comercial Website
  2. ^ 2.0 2.1 Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. doi: 10.1021/acs.est.8b06648  Open Access Article
  3. ^ Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. doi: 10.1021/acs.est.1c07608  Open Access Article
  4. ^ Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. doi: 10.1021/acs.est.0c00961
  5. ^ 5.0 5.1 Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. doi: 10.1063/1.555805
  6. ^ Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. doi: 10.1016/j.scitotenv.2017.06.197
  7. ^ Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. doi: 10.1021/acs.est.8b02172
  8. ^ Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. doi: 10.1016/j.jhazmat.2020.124452
  9. ^ Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. doi: 10.1021/acs.est.0c02158
  10. ^ Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. doi: 10.1021/acsestwater.0c00170
  11. ^ Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. doi: 10.1080/10643389.2018.1542916
  12. ^ Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. doi: 10.1016/j.jece.2015.07.026
  13. ^ Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. doi: 10.1016/j.cej.2012.11.086
  14. ^ Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. doi: 10.1021/es3008535
  15. ^ Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. doi: 10.1016/j.watres.2014.05.051

See Also

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