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==Contaminated Sediment Risk Assessment==
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==  
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[[Contaminated Sediments - Introduction | Contaminated sediments]] in rivers and streams, lakes, coastal harbors, and estuaries have the potential to pose ecological and human health risks. The goals of risk assessment applied to contaminated sediments are to characterize the nature and magnitude of the current and potential threats to human health, wildlife and ecosystem functioning posed by contamination; identify the key factors contributing to the potential health and ecological risks; evaluate how implementation of one or more remedy actions will mitigate the risks in the short and long term; and evaluate the risks and impacts from sediment management, both during and after any dredging or other remedy construction activities.  
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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.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
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*[[Contaminated Sediments - Introduction]]
 
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
 
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*[[Sediment Capping]]
 
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*[[Passive Sampling of Sediments]]
 
  
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'''Contributor(s):'''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*Richard J. Wenning
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*[[PFAS Ex Situ Water Treatment]]
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*Sabine E. Apitz
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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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* Contaminated Sediment Remediation Guidance for Hazardous Waste Sites<ref name="USEPA2005">United States Environmental Protection Agency (USEPA), 2005. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites. Office of Solid Waste and Emergency Response, Washington, D.C. EPA-540-R-05-012. OSWER 9355.0-85.  Free download from: [https://semspub.epa.gov/work/HQ/174471.pdf USEPA]&nbsp;&nbsp; [[Media: EPA-540-R-05-012.pdf | Report.pdf]]</ref>
 
  
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* Principles for Environmental Risk Assessment of the Sediment Compartment<ref name="Tarazona2014">Tarazona, J.V., Versonnen, B., Janssen, C., De Laender, F., Vangheluwe, M. and Knight, D., 2014. Principles for Environmental Risk Assessment of the Sediment Compartment: Proceedings of the Topical Scientific Workshop. 7-8 May 2013. European Chemicals Agency, Helsinki. Document ECHA-14-R-13-EN. Free download from: [https://echa.europa.eu/documents/10162/22816050/environmental_risk_assessment_final_en.pdf/3515b685-6601-40ce-bd48-3f8d5332c0f8 European Chemicals Agency]&nbsp;&nbsp; [[Media: ECHA-14-R-13-EN.pdf | Report.pdf]]</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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* Assessing and managing contaminated sediments:
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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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:: Part I, Developing an Effective Investigation and Risk Evaluation Strategy<ref name="Apitz2005a">Apitz, S.E., Davis, J.W., Finkelstein, K., Hohreiter, D.W., Hoke, R., Jensen, R.H., Jersak, J., Kirtay, V.J., Mack, E.E., Magar, V.S. and Moore, D., 2005. Assessing and Managing Contaminated Sediments: Part I, Developing an Effective Investigation and Risk Evaluation Strategy. Integrated Environmental Assessment and Management, 1(1), pp. 2-8. [https://doi.org/10.1897/IEAM_2004a-002.1 DOI: 10.1897/IEAM_2004a-002.1] Free access article from: [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1897/IEAM_2004a-002.1 Society of Environmental Toxicology and Chemistry]&nbsp;&nbsp; [[Media: Apitz2005a.pdf | Report.pdf]]</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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:: Part II, Evaluating Risk and Monitoring Sediment Remedy Effectiveness<ref name="Apitz2005b">Apitz, S.E., Davis, J.W., Finkelstein, K., Hohreiter, D.W., Hoke, R., Jensen, R.H., Jersak, J., Kirtay, V.J., Mack, E.E., Magar, V.S. and Moore, D., 2005b. Assessing and Managing Contaminated Sediments: Part II, Evaluating Risk and Monitoring Sediment Remedy Effectiveness. Integrated Environmental Assessment and Management, 1(1), pp.e1-e14. [https://doi.org/10.1897/IEAM_2004a-002e.1 DOI: 10.1897/IEAM_2004a-002e.1]</ref>
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*EradiFluor<sup>TM</sup><ref name="EradiFluor"/>
  
 
==Introduction==
 
==Introduction==
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Improving the management of [[Contaminated Sediments - Introduction | contaminated sediments]] is of growing concern globally. Sediment processes in both marine and freshwater environments are important to the function of aquatic ecosystems<ref name="Apitz2012">Apitz, S.E., 2012. Conceptualizing the role of sediment in sustaining ecosystem services: Sediment-Ecosystem Regional Assessment (SEcoRA), Science of the Total Environment, 415, pp. 9-30. [https://doi.org/10.1016/j.scitotenv.2011.05.060 DOI:10.1016/j.scitotenv.2011.05.060] Free download from: [https://d1wqtxts1xzle7.cloudfront.net/7588577/Apitz_SEcoRA%202012.pdf?1326618388=&response-content-disposition=inline%3B+filename%3DConceptualizing_the_role_of_sediment_in.pdf&Expires=1637094311&Signature=c2wczG59XxkitPjmBhc9PaODHJ8Vufg3gyzdG8tqGD6~mIVhLoz30E7eQNIghfMlH~jbch3KTVxMqD2AQFMQCSeXghIwqH~lXjGrEP07MJXCEgntzSW-V8Gws~33it5pEm9Ied64fSOvMLJR-PUXVr2OVTsVHQJHurHdGrtEmhUd90bKrC0NNlD28YLGQpkVUOlqa75e0K4sjPngwPUwUxhq18NAH6-1Uc3fQU5g5AjXwGph-VNe7EwzT-0do5OD056AsG-Eg8xIZi0ABJqMsg1wb92tIPpmmNy6ntdklHeN6tq~3IJFB7Tg8XYntQ-CGT8pYV9S7Kz14GhXVm9OQA__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>, and many organisms rely on certain sediment quality and quantity characteristics for their life cycle<ref name="Hauer2018">Hauer, C., Leitner, P., Unfer, G., Pulg, U., Habersack, H. and Graf, W., 2018. The Role of Sediment and Sediment Dynamics in the Aquatic Environment. In: Schmutz S., Sendzimir J. (ed.s) Riverine Ecosystem Management. Aquatic Ecology Series, vol. 8, pp. 151-169. Springer. [https://doi.org/10.1007/978-3-319-73250-3_8 DOI: 10.1007/978-3-319-73250-3_8]  Open access book from: [https://library.oapen.org/bitstream/handle/20.500.12657/27726/1002280.pdf?seque#page=153 SpringerOpen]</ref>. Human health can also be affected by sediment conditions, either via direct contact, as a result of sediment impacts on water quality, or because of the strong influence sediments can have on the quality of fish and shellfish consumed by people<ref name="Greenfield2015">Greenfield, B.K., Melwani, A.R. and Bay, S.M., 2015. A Tiered Assessment Framework to Evaluate Human Health Risk of Contaminated Sediment. Integrated Environmental Assessment and Management, 11(3), pp. 459-473.  [https://doi.org/10.1002/ieam.1610 DOI: 10.1002/ieam.1610]</ref>. A common approach to achieving the explicit management goals inherent in different sediment assessment frameworks in North America and elsewhere is the use of the ecological risk assessment (ERA)<ref name="USEPA1997a">US Environmental Protection Agency (USEPA), 1997. The Incidence and Severity of Sediment Contamination in Surface Waters of the United States: Volume 1, National Sediment Quality Survey. EPA-823R-97-006. Washington, DC.  [[Media: EPA-823-R-97-006.pdf | Report.pdf]]</ref>. An ERA “evaluates the likelihood and magnitude of adverse effects from exposure to a chemical for organisms, such as animals, plants, or microbes, in the environment”<ref name="SETAC2018">Society of Environmental Toxicology and Chemistry (SETAC), 2018. Technical Issue Paper: Environmental Risk Assessment of Chemicals. SETAC, Pensacola, FL. 5 pp. Free download from: [https://cdn.ymaws.com/www.setac.org/resource/resmgr/publications_and_resources/setac_tip_era.pdf SETAC]&nbsp;&nbsp; [[Media: setac_tip_era2018.pdf | Report.pdf]]</ref>. An ERA provides information relevant to the management decision-making process<ref name="Stahl2001">Stahl, R.G., Bachman, R., Barton, A., Clark, J., deFur, P., Ells, S., Pittinger, C., Slimak, M., Wentsel, R., 2001. Risk Management: Ecological Risk-Based Decision Making. SETAC Press, Pensacola, FL, 222 pp.  ISBN: 978-1-880611-26-5</ref>. It should be performed in a scientifically based, defensible manner that is cost-effective and protective of human health and the environment<ref name="CNO1999">Chief of Naval Operations (CNO), 1999. Navy Policy for Conducting Ecological Risk Assessments, Letter 5090, Ser N453E/9U595355, dated 05 April 99. Department of the Navy, Washington, DC. Free download from: [https://www.navfac.navy.mil/content/dam/navfac/Specialty%20Centers/Engineering%20and%20Expeditionary%20Warfare%20Center/Environmental/Restoration/er_pdfs/gpr/cno-ev-pol-era-19990405.pdf the US Navy]&nbsp;&nbsp; [[Media: CNO1999.pdf | Report.pdf]]</ref>. Therefore, science-based methods for assessing sediment quality and use of risk-based decision-making in sediment management are important for identifying conditions suspected to adversely affect ecological and human services provided by sediments, and predicting the likely consequences of different sediment management actions<ref name="Bridges2006">Bridges, T.S., Apitz, S.E., Evison, L., Keckler, K., Logan, M., Nadeau, S. and Wenning, R.J., 2006. Risk‐Based Decision Making to Manage Contaminated Sediments. Integrated Environmental Assessment and Management, 2(1), pp. 51-58.  [https://doi.org/10.1002/ieam.5630020110 DOI: 10.1002/ieam.5630020110]  Free access article from: [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.5630020110 SETAC]</ref><ref name="Apitz2011">Apitz, S.E., 2011. Integrated Risk Assessments for the Management of Contaminated Sediments in Estuaries and Coastal Systems. In: Wolanski, E. and McLusky, D.S. (eds.) Treatise on Estuarine and Coastal Science, Vol 4, pp. 311–338. Waltham: Academic Press. ISBN: 9780123747112</ref>.
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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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Sediment risk assessment is increasingly used by governmental agencies to support sediment management in freshwater, estuarine, and marine environments. Strategies for sediment management encompass a wide variety of actions, from removal, capping or treatment of contaminated sediment to the monitoring of natural processes, including sedimentation, binding, and bio- and photo-degradation that serve to reduce the potential threat to aquatic life over time. It is not uncommon to revisit a sediment risk assessment periodically to check how changed environmental conditions reflected in sediment and biotic sampling work has either reduced or exacerbated the threats identified in the initial assessment.
 
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At present, several countries lack common recommendations specific to conducting risk assessment of contaminated sediments<ref name="Bruce2020">Bruce, P., Sobek, A., Ohlsson, Y. and Bradshaw, C., 2020. Risk assessments of contaminated sediments from the perspective of weight of evidence strategies – a Swedish case study. Human and Ecological Risk Assessment, 27(5), pp. 1366-1387.  [https://doi.org/10.1080/10807039.2020.1848414 DOI: 10.1080/10807039.2020.1848414]&nbsp;&nbsp; [https://www.tandfonline.com/doi/full/10.1080/10807039.2020.1848414 Website]</ref>. In the European Union, sediment has played a secondary role in the Water Framework Directive (WFD), with most quality standards being focused on water with the option for the development of national standards for sediment and biota for bioaccumulative compounds. The Common Implementation Strategy (CIS) in 2010 provided guidance on the monitoring of contaminants in sediments and biota, but not on risk-based decision-making<ref name="EC2010">European Commission, 2010. Common Implementation Strategy For The Water Framework Directive (2000/60/EC), Technical Report - 2010 – 041; Guidance document No. 25 On Chemical Monitoring Of Sediment And Biota Under The Water Framework Directive. 82pp. ISBN 978-92-79-16224-4.  [https://op.europa.eu/en/publication-detail/-/publication/5ff7a8ec-995b-4d90-a140-0cc9b4bf980d  Free download]</ref>. There are efforts underway to incorporate guidance for management of contaminated sediment in the Common Implementation Strategy in 2021<ref name="Brils2020">Brils, J., 2020. Including sediment in European River Basin Management Plans: Twenty years of work by SedNet. Journal of Soils and Sediments, 20(12), pp.4229-4237. [https://doi.org/10.1007/s11368-020-02782-1 DOI: 10.1007/s11368-020-02782-1]&nbsp;&nbsp; [https://link.springer.com/content/pdf/10.1007/s11368-020-02782-1.pdf Open Access Article]</ref>. Sediment risk assessment guidance from Norway, Canada, the Netherlands, and the US are most often referenced when assessing the risks from contaminated sediments<ref name="Bruce2020"/><ref name="Birch2018">Birch, G.F., 2018. A review of chemical-based sediment quality assessment methodologies for the marine environment. Marine Pollution Bulletin, 133, pp.218-232.  [https://doi.org/10.1016/j.marpolbul.2018.05.039 DOI: 10.1016/j.marpolbul.2018.05.039]</ref><ref name="Kwok2014">Kwok, K.W., Batley, G.E., Wenning, R.J., Zhu, L., Vangheluwe, M. and Lee, S., 2014. Sediment quality guidelines: challenges and opportunities for improving sediment management. Environmental Science and Pollution Research, 21(1), pp. 17-27.  [https://doi.org/10.1007/s11356-013-1778-7 DOI: 10.1007/s11356-013-1778-7] Free download from: [https://www.researchgate.net/profile/Graeme-Batley/publication/236836992_Sediment_quality_guidelines_Challenges_and_opportunities_for_improving_sediment_management/links/0c96052b8a8f5ad0c6000000/Sediment-quality-guidelines-Challenges-and-opportunities-for-improving-sediment-management.pdf ResearchGate]</ref>. Some European countries, such as Norway, have focused their risk assessment guidance on the assessment of sediment conditions relative to general chemical thresholds, while in North America, risk assessment guidance focuses on site- or region-specific conditions<ref name="Apitz2008">Apitz, S.E., 2008. Is risk-based, sustainable sediment management consistent with European policy?. Journal of Soils and Sediments, 8(6), p.461-466.  [https://doi.org/10.1007/s11368-008-0039-8 DOI: 10.1007/s11368-008-0039-8]&nbsp;&nbsp; Free download from: [https://d1wqtxts1xzle7.cloudfront.net/7081664/apitz%20jss%20risk-based%20europe-with-cover-page-v2.pdf?Expires=1637274548&Signature=KqIoYyQ6VPAFN7lKHJMVC3bbn00RRMCR68bsQNBGrFJ9kbX5BnI-aucFCqRgVUNUb1lu0Q4tzUkCjPXJRGBsTA3OnbH8Ol9sNoXZ001aOwG7tKuV8qEblGiqtQUHh9GdiNAPQsm50f~E1iozL9a6imApWjqK8oFCfdUbcUd1oaW7PCDu28KWN-k5ddefWNZBAzGIdaWt3mBJ1EYeKRrp4F6Codlny3pWCT5MpA~c4c0IKq8L7Uj~-VxH5LXjFDd7cm07JeOY8S5rlxgF1zMoTIggMo5v2M3AS3CO2SAqy7yR3HC-IjUx3RsMqKa5eS2jT1ADiXcqeVygCdCCXza05g__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>.
 
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There is general consensus from a regulatory perspective, globally, on the importance of sediment risk assessment. Technical guidance documents prepared by Canada<ref name="Fletcher2008">Fletcher, R., Welsh, P. and Fletcher, T., 2008. Guidelines for Identifying, Assessing, and Managing Contaminated Sediments in Ontario. Ontario Ministry of the Environment. PIBS6658e. [http://www.ene.gov.on.ca/publications/6658e Website]</ref><ref name="HealthCanada2017">Health Canada, 2017. Supplemental Guidance on Human Health Risk Assessment of Contaminated Sediments: Direct Contact Pathway, Federal Contaminated Site Risk Assessment in Canada. ISBN: 978-0-660-07989-9. Cat.: H144-41/2017E-PDF. Pub. 160382. Free download from: [https://publications.gc.ca/collections/collection_2018/sc-hc/H144-41-2017-eng.pdf Health Canada]&nbsp;&nbsp; [[Media: HealthCanada2117.pdf | Report.pdf]]</ref> , the European Union<ref name="Tarazona2014"/>, and the United States Environmental Protection Agency (USEPA)<ref name="USEPA2005"/> advise a flexible, tiered approach for sediment risk assessment. Sediment quality guidelines in many countries reflect the scientific importance of including certain sediment-specific measurement and biotic assessment endpoints, as well as certain physical sediment processes and chemical transformation processes potentially affecting biotic responses to contaminant exposure in the sediment<ref name="Wenning2005">Wenning, R.J. Batley, G.E., Ingersoll, C.G., and Moore, D.W., (eds), 2005. Use Of Sediment Quality Guidelines And Related Tools For The Assessment Of Contaminated Sediments. SETAC, Pensacola, FL. 815 pp.  ISBN 1-880611-71-6.</ref>. New risk assessment methods continue to emerge in the scientific literature<ref name="Benson2018">Benson, N.U., Adedapo, A.E., Fred-Ahmadu, O.H., Williams, A.B., Udosen, E.D., Ayejuyo, O.O. and Olajire, A.A., 2018. A new method for assessment of sediment-associated contamination risks using multivariate statistical approach. MethodsX, 5, pp. 268-276.  [https://doi.org/10.1016/j.mex.2018.03.005 DOI: 10.1016/j.mex.2018.03.005]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S2215016118300438/pdfft?md5=85b8a3a1062310e4c7c4a06e670e66c4&pid=1-s2.0-S2215016118300438-main.pdf  Free Access Article]&nbsp;&nbsp; [[Media: Benson2018.pdf | Report.pdf]]</ref><ref name="Saeedi2015">Saeedi, M. and Jamshidi-Zanjani, A., 2015. Development of a new aggregative index to assess potential effect of metals pollution in aquatic sediments. Ecological Indicators, 58, pp. 235-243.  [https://doi.org/10.1016/j.ecolind.2015.05.047 DOI: 10.1016/j.ecolind.2015.05.047]  Free download from: [https://www.academia.edu/download/49801572/mRAC_published.pdf Academis.edu]</ref><ref name="Vaananen2018">Väänänen, K., Leppänen, M.T., Chen, X. and Akkanen, J., 2018. Metal bioavailability in ecological risk assessment of freshwater ecosystems: from science to environmental management. Ecotoxicology and Environmental Safety, 147, pp. 430-446.  [https://doi.org/10.1016/j.ecoenv.2017.08.064 DOI: 10.1016/j.ecoenv.2017.08.064]</ref>. These new methods, however, are likely to be considered supplemental to the more generalized framework shared globally.
 
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==Fundamentals of Sediment Risk Assessment==
 
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[[File: SedRiskFig1.PNG | thumb |700px|Figure 1. Schematic of the sediment risk assessment process]]
 
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Whereas there is strong evidence of anthropogenic impacts on the benthic community at many sediment sites, the degree of toxicity (or even its presence or absence) cannot be predicted with absolute certainty using contaminant concentrations alone<ref name="Apitz2011"/>. A sediment ERA should include lines of evidence (LOEs) derived from several different investigations<ref name="Wenning2005"/>. One common approach to develop several of these LOEs in a decision framework is the triad approach. Triad-based assessment frameworks require evidence based on sediment chemistry, toxicity, and benthic community structure (possibly including evidence of bioaccumulation) to designate sediment as toxic and requiring management or control<ref name="Chapman1996">Chapman, P.M., Paine, M.D., Arthur, A.D., Taylor, L.A., 1996. A triad study of sediment quality associated with a major, relatively untreated marine sewage discharge. Marine Pollution Bulletin 32(1), pp. 47–64.  [https://doi.org/10.1016/0025-326X(95)00108-Y DOI: 10.1016/0025-326X(95)00108-Y]</ref>. In some decision frameworks, particularly those used to establish and rank risks in national or regional programs, all components of the triad are carried out simultaneously, with the various LOEs combined to support weight of evidence (WOE) decision making. In other frameworks, LOEs are tiered to minimize costs by collecting only the data required to make a decision and leaving some potential consequences and uncertainties unresolved.
 
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Figure 1 provides an overview of a sediment risk assessment process. The first step, and a fundamental requirement, in sediment risk assessment, involves scoping and planning prior to undertaking work. This is important for optimizing the available assessment resource and conducting an assessment at the appropriate level of detail that is transparent and free, to the extent possible, of any bias or preconceived beliefs concerning the outcome<ref name="Hill2000">Hill, R.A., Chapman, P.M., Mann, G.S. and Lawrence, G.S., 2000. Level of Detail in Ecological Risk Assessments. Marine Pollution Bulletin, 40(6), pp. 471-477. [https://doi.org/10.1016/S0025-326X(00)00036-9 DOI: 10.1016/S0025-326X(00)00036-9]</ref>.
 
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===Screening-Level Risk Assessment (SLRA)===
 
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Technical guidance in many countries strongly encourages sediment risk assessment to begin with a Screening-Level Risk Assessment (SLRA)<ref name="USEPA2005"/><ref name="Tarazona2014"/><ref name="Fletcher2008"/>. The SLRA is a simplified risk assessment conducted using limited data and often assuming certain, generally conservative and generic, sediment characteristics, sediment contaminant levels, and exposure parameters in the absence of sufficient readily available information<ref name="Hope2006">Hope, B.K., 2006. An examination of ecological risk assessment and management practices. Environment International, 32(8), pp. 983-995.  [https://doi.org/10.1016/j.envint.2006.06.005 DOI: 10.1016/j.envint.2006.06.005]</ref><ref name="Weinstein2010">Weinstein, J.E., Crawford, K.D., Garner, T.R. and Flemming, A.J., 2010. Screening-level ecological and human health risk assessment of polycyclic aromatic hydrocarbons in stormwater detention pond sediments of Coastal South Carolina, USA. Journal of Hazardous Materials, 178(1-3), pp. 906-916.  [https://doi.org/10.1016/j.jhazmat.2010.02.024 DOI: 10.1016/j.jhazmat.2010.02.024]</ref><ref name="Rak2008">Rak, A., Maly, M.E., Tracey, G., 2008. A Guide to Screening Level Ecological Risk Assessment, TG-090801. Tri-Services Ecological Risk Assessment Working Group (TSERAWG), U.S. Army Biological Technical Assistance Group (BTAG), Aberdeen Proving Ground, MD. 26 pp.  [https://usaphcapps.amedd.army.mil/erawg/SLERA.pdf Free Download]&nbsp;&nbsp; [[Media: Rak2008.pdf | Report.pdf]]</ref><ref name="USEPA2001">US Environmental Protection Agency (USEPA), 2001. ECO Update. The Role of Screening-Level Risk Assessments and Refining Contaminants of Concern in Baseline Ecological Risk Assessments. EPA 540/F-01/014. Washington, D.C. [https://www.epa.gov/sites/default/files/2015-09/documents/slera0601.pdf  Website]&nbsp;&nbsp; [[Media: EPA 540_F-01_014.pdf  | Report.pdf]]</ref>.
 
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The analysis is often semi-quantitative, and typically includes comparisons of various chemical and physical sediment conditions to threshold limits established in national or international regulations or by generally accepted scientific interpretations. US technical guidance encourages the comparison of contaminant measurements in water, sediment, or soil to National Oceanographic and Atmospheric Administration (NOAA) sediment screening quick reference tables, or SQuiRT cards, which list quality guidelines from a range of sources, based on differing narrative intent<ref name="Buchman2008">Buchman, M.F., 2008. Screening Quick Reference Tables (SQuiRTs), NOAA OR&R Report 08-1. National Oceanographic and Atmospheric Administration (NOAA), Coastal Protection and Restoration Protection Division. 34 pp. [https://repository.library.noaa.gov/view/noaa/9327  website]&nbsp;&nbsp; [[Media: SQuiRTs2008.pdf | Report.pdf]]</ref>.
 
−
 
 
−
The screening level approach is intended to minimize the chances of concluding that there is no risk when, in fact, risk may exist. Thus, the results of an SLRA may indicate contaminants or sediments in certain locations in the original study area initially thought to be of concern are acceptable (i.e., contaminant levels are below threshold levels), or that contaminant levels are high enough to indicate immediate action without further assessment (e.g., contaminant levels are well above probable-effects guidelines). In other cases, or at other locations, SLRA may indicate the need for further examination. Further study may apply site-specific, rather than generic and conservative assumptions, to reduce uncertainty.  
 
  
−
===Detailed Risk Assessment===
+
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):
−
Detailed sediment risk assessment is conducted when SLRA results indicate one or more sediment contaminants exceed background conditions or regulatory threshold limits. For some contaminants, such as the dioxins and other persistent, bioaccumulative, and toxic substances (PBTs), technical guidance may mandate further examination, regardless of whether threshold levels are exceeded<ref name="Solomon2013">Solomon, K., Matthies, M., and Vighi, M., 2013. Assessment of PBTs in the European Union: a critical assessment of the proposed evaluation scheme with reference to plant protection products. Environmental Sciences Europe, 25(1), pp. 1-17.  [https://doi.org/10.1186/2190-4715-25-10 DOI: 10.1186/2190-4715-25-10]&nbsp;&nbsp; [https://enveurope.springeropen.com/articles/10.1186/2190-4715-25-10 Open Access Article]</ref><ref name="Matthies2016">Matthies, M., Solomon, K., Vighi, M., Gilman, A. and Tarazona, J.V., 2016. The origin and evolution of assessment criteria for persistent, bioaccumulative and toxic (PBT) chemicals and persistent organic pollutants (POPs). Environmental Science: Processes and Impacts, 18(9), pp. 1114-1128.  [https://doi.org/10.1039/C6EM00311G DOI: 10.1039/C6EM00311G]</ref>. Detailed sediment risk assessment typically follows a three-step framework similar to that described for ecological risk assessment - problem formulation, exposure analysis, and risk characterization<ref name="Suter2008">Suter, G.W., 2008. Ecological Risk Assessment in the United States Environmental Protection Agency: A Historical Overview. Integrated Environmental Assessment And Management, 4(3), pp. 285-289.  [https://doi.org/10.1897/IEAM_2007-062.1 DOI: 10.1897/IEAM_2007-062.1]&nbsp;&nbsp; Free download from: [https://bioone.org/journals/integrated-environmental-assessment-and-management/volume-4/issue-3/IEAM_2007-062.1/Ecological-Risk-Assessment-in-the-United-States-Environmental-Protection-Agency/10.1897/IEAM_2007-062.1.pdf?casa_token=ieq3Cnc-YdIAAAAA:_MH-gpnwpJKvZSV2Qew43Y4ocdgADq1HvugpvmrblcGONMJgvIjYB52zQnXn_oAUW0gTy5GAkfY BioOne]</ref>.
+
</br>
 +
::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
−
US sediment management guidance describes a detailed risk assessment process similar to that followed for US ecological risk assessment<ref name="USEPA2005"/>. The first step is problem formulation. It involves defining chemical and physical conditions, delineating the spatial footprint of the sediment area to be examined, and identifying the human uses and ecological features of the sediment. Historical data are included in this initial step to better understand the results of biota, sediment, and water sampling as well as laboratory toxicity testing results. The SLRA is often included as a part of problem formulation.
+
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"/>.
  
−
The second step is exposure analysis. This step includes the identification of pathways by which human and aquatic organisms might directly or indirectly contact contaminants in the sediment. The exposure route (i.e., ingestion, dermal, or inhalation of particulates or gaseous emissions) and both the frequency and duration of contact (i.e., hourly, daily, or seasonally) are determined for each contaminant exposure pathway and human and ecological receptor. The environmental fate of the contaminant, factors affecting uptake, and the overall exposure dose are included in the calculation of the level of contaminant exposure. The exposure analysis also includes an effects assessment, whereby the biological response and associated level required to manifest different biological responses are determined for each contaminant.
+
==Process Description==
 +
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"/>
  
−
The third step is risk-characterization. It involves calculating the risks for each human and ecological receptor posed by each sediment contaminant, as well as the cumulative risk associated with the combined exposure to all contaminants exerting similar biological effects. An uncertainty analysis is often included in this step of the risk assessment to convey where knowledge or data are lacking regarding the presence of the contaminant in the sediment, the biological response associated with exposure to the contaminant, or the behavior of the receptor with respect to contact with the sediment. A sensitivity analysis also may be conducted to convey the range of exposures (lowest, typical, and worst-case) and risks associated with changes in key assumptions and parameter values used in the exposure calculations and effects assessment.
+
==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 ''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:
−
==Key Considerations==
+
*'''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)]].
 +
*'''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>.
 +
*'''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>.
  
−
==Cap Design and Materials for Habitat Restoration==
+
==Limitations==
−
In addition to providing chemical isolation and containment, a cap can also be used to provide improvements for organisms by enhancing the habitat characteristics of the bottom substrate<ref name="Yozzo2004">Yozzo, D.J., Wilber, P. and Will, R.J., 2004. Beneficial use of dredged material for habitat creation, enhancement, and restoration in New York–New Jersey Harbor. Journal of Environmental Management, 73(1), pp. 39-52.  [https://doi.org/10.1016/j.jenvman.2004.05.008 DOI: 10.1016/j.jenvman.2004.05.008]</ref><ref name="Zhang2016">Zhang, C., Zhu, M.Y., Zeng, G.M., Yu, Z.G., Cui, F., Yang, Z.Z. and Shen, L.Q., 2016. Active capping technology: a new environmental remediation of contaminated sediment. Environmental Science and Pollution Research, 23(5), pp.4370-4386.  [https://doi.org/10.1007/s11356-016-6076-8 DOI: 10.1007/s11356-016-6076-8]</ref><ref name="Vlassopoulos2017"/>.  Often, contaminated sediment environments are degraded for a variety of reasons in addition to the toxic constituents. One way to overcome this is to provide both a habitat layer and chemical isolation or contaminant capping layer. Figure 2 illustrates just such a design providing a more appropriate habitat enhancing substrate, in this case by incorporation additional organic material, vegetation and debris, which is often used by fish species for protection, into the surface layer. In a high energy environment, it should be recognized that it may not be possible to keep a suitable habitat layer in place during high flow events.  This would be true of suitable habitat that had developed naturally as well as a constructed habitat layer and it is presumed that if such a habitat is the normal condition of the waterbody that it will recover over time between such high flow events.
+
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 [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonate (PFBS)]] exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.
  
−
==Summary==
+
==State of the Practice==
−
Clean substrate can be placed at the sediment-water interface for the purposes of reducing exposure to and risk from contaminants in the sediments. The cap can consist of simple materials such as sand designed to physically stabilize contaminated sediments and separate the benthic community from those contaminants or may include other materials designed to sequester contaminants even under adverse conditions including strong groundwater upwelling or highly mobile contaminants.  The surface of a cap may be designed of coarse material such as gravel or cobble to be stable under high flow events or designed to be more appropriate habitat for benthic and aquatic organisms. As a result of its flexibility, simplicity and low cost relative to its effectiveness, capping is one of the most prevalent remedial technologies for sediments.  
+
[[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.]]
 +
[[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.]]  
 +
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.
 +
*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.
 +
*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).
  
 
==References==
 
==References==

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
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  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
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  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

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