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==Contaminated Sediment Risk Assessment==   
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==Transition of Aqueous Film Forming Foam (AFFF) Fire Suppression Infrastructure Impacted by Per and Polyfluoroalkyl Substances (PFAS)==   
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[[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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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)|Per and polyfluoroalkyl substances (PFAS)]] contained in [[wikipedia:Firefighting foam |Class B aqueous film-forming foams (AFFFs)]] are known to accumulate on wetted surfaces of many fire suppression systems after decades of exposure<ref name="LangEtAl2022">Lang, J.R., McDonough, J., Guillette, T.C., Storch, P., Anderson, J., Liles, D., Prigge, R., Miles, J.A.L., Divine, C., 2022. Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods. Chemosphere, 308(Part 2), 136254. [https://doi.org/10.1016/j.chemosphere.2022.136254 doi: 10.1016/j.chemosphere.2022.136254]&nbsp;&nbsp;[[Media:LangEtAl2022.pdf | Open Access Article]]</ref>. When replacement PFAS-free firefighting formulations are added to existing infrastructure, PFAS can rebound from the wetted surfaces into the new formulations at high concentrations<ref name="RossStorch2020">Ross, I., and Storch, P., 2020. Foam Transition: Is It as Simple as "Foam Out / Foam In?". The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q2 Supplement, 20 pages. [[Media:Catalyst_2020_Q2_Sup.pdf | Industry Newsletter]]</ref><ref>Kappetijn, K., 2023. Replacement of fluorinated extinguishing foam: When is clean clean enough? The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q1 2023, pp. 31-33. [[Media:Catalyst_2023_Q1.pdf | Industry Newsletter]]</ref>. Effective methods are needed to properly transition to PFAS-free firefighting formulations in existing fire suppression infrastructure. Considerations in the transition process may include but are not limited to locating, identifying, and evaluating existing systems and AFFF, fire engineering evaluations, system prioritization, cost/downtime analyses, sampling and analysis, evaluation of risks and hazards to human health and the environment, transportation, and disposal.
 
<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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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]  
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
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*[[PFAS Sources]]
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*[[Sediment Capping]]
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*[[PFAS Ex Situ Water Treatment]]
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*[[Passive Sampling of Sediments]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
  
 
'''Contributor(s):'''  
 
'''Contributor(s):'''  
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*Richard J. Wenning
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*Dr. Johnsie Ray Lang
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*Sabine E. Apitz
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*Dr. Jonathan Miles
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*John Anderson
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*Dr. Theresa Guillette
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*[[Craig E. Divine, Ph.D., PG|Dr. Craig Divine]]
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*[[Dr. Stephen Richardson]]
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
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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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*Department of Defense (DoD) performance standard for PFAS-free firefighting formulation: [https://media.defense.gov/2023/Jan/12/2003144157/-1/-1/1/MILITARY-SPECIFICATION-FOR-FIRE-EXTINGUISHING-AGENT-FLUORINE-FREE-FOAM-F3-LIQUID-CONCENTRATE-FOR-LAND-BASED-FRESH-WATER-APPLICATIONS.PDF Military Specification MIL-PRF-32725]<ref name="DoD2023">US Department of Defense, 2023. Performance Specification for Fire Extinguishing Agent, Fluorine-Free Foam (F3) Liquid Concentrate for Land-Based, Fresh Water Applications. Mil-Spec MIL-PRF-32725, 18 pages. [[Media: MilSpec32725.pdf | Military Specification Document]]</ref>
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*[[Media:LangEtAl2022.pdf | Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods]]<ref name="LangEtAl2022"/>
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* 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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* Assessing and managing contaminated sediments:
 
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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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:: 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>
 
  
 
==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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[[File:LangFig1.png | thumb |400px|Figure 1. (A) Schematic of a typical PFAS molecule demonstrating the hydrophobic fluorinated tail in green and the hydrophilic charged functional group in blue, (B) a PFAS bilayer formed with the hydrophobic tails facing inward and the charged functional groups on the outside, and (C) multiple bilayers of PFAS assembled on the wetted surfaces of fire suppression piping.]]PFAS are a class of synthetic fluorinated compounds which are highly mobile and persistent within the environment<ref>Giesy, J.P., Kannan, K., 2001. Global Distribution of Perfluorooctane Sulfonate in Wildlife. Environmental Science and Technology 35(7), pp. 1339-1342. [https://doi.org/10.1021/es001834k doi: 10.1021/es001834k]</ref>. Due to the surfactant properties of PFAS, these compounds self-assemble at any solid-liquid interface forming resilient bilayers during prolonged exposure<ref>Krafft, M.P., Riess, J.G., 2015. Selected physicochemical aspects of poly- and perfluoroalkylated substances relevant to performance, environment and sustainability-Part one. Chemosphere, 129, pp. 4-19. [https://doi.org/10.1016/j.chemosphere.2014.08.039 doi: 10.1016/j.chemosphere.2014.08.039]</ref>. Solid phase accumulation of PFAS has been proposed to be influenced by both [[wikipedia: Hydrophobic effect|hydrophobic]] and electrostatic interactions with fluorinated carbon chain length as the dominant feature influencing sorption<ref>Higgins, C.P., Luthy, R.G., 2006. Sorption of Perfluorinated Surfactants on Sediments. Environmental Science and Technology, 40(23), pp. 7251-7256. [https://doi.org/10.1021/es061000n doi: 10.1021/es061000n]</ref>. While the majority of previous research into solid phase sorption typically focused on water treatment applications or subsurface porous media<ref>Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of the Total Environment, 613-614, pp. 176-185. [https://doi.org/10.1016/j.scitotenv.2017.09.065 doi: 10.1016/j.scitotenv.2017.09.065]&nbsp;&nbsp;[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693257/ Open Access Manuscript]</ref>, recently PFAS accumulations have been identified on the wetted surfaces of fire suppression infrastructure exposed to aqueous film forming foam (AFFF)<ref name="LangEtAl2022"/> (see Figure 1).
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Fire suppression systems with potential PFAS impacts include fire fighting vehicles that carried AFFF and fixed suppression systems in buildings containing large amounts of flammable materials such as aircraft hangars (Figure 2). PFAS residue on the wetted surfaces of existing infrastructure can rebound into replacement PFAS-free firefighting formulations if not removed during the transition process<ref name="RossStorch2020"/>. Simple surface rinsing with water and low-pressure washing has been proven to be inefficient for removal of surface bound PFAS from piping and tanks that contained fluorinated AFFF<ref name="RossStorch2020"/>
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[[File:LangFig2.png | thumb|left|600px|Figure 2. Fixed fire suppression system for an aircraft hangar, with storage tank on left and distribution piping on right.]]
  
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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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In&nbsp;addition&nbsp;to&nbsp;proper methods for system cleaning to remove residual PFAS, transition to PFAS-free foam may also include consideration of compliance with state and federal regulations, selection of the replacement PFAS-free firefighting formulation, a cost benefit analysis for replacement of the system components versus cleaning, and PFAS verification testing. Foam transition should be completed in a manner which minimizes the volume of waste generated as well as preventing any PFAS release into the environment.
  
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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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==PFAS Assembly on Solid Surfaces==
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The self-assembly of [[Wikipedia: Amphiphile | amphiphilic]] molecules into supramolecular bilayers is a result of their structure and how it interacts with the bulk water of a solution. Single chain hydrocarbon based amphiphiles can form [[Wikipedia: Micelle | micelles]] under relatively dilute aqueous concentrations, however for hydrocarbon based surfactants the formation of more complex organized system such as [[Wikipedia: Vesicle (biology and chemistry) | vesicles]] is rarely seen, requiring double chain amphiphiles such as [[wikipedia: Phospholipid|phospholipids]]. Associations of single chain [[wikipedia: Ion#Anions_and_cations|cationic and anionic]] hydrocarbon based amphiphiles into stable supramolecular structures such as vesicles has however been demonstrated<ref>Fukuda, H., Kawata, K., Okuda, H., 1990. Bilayer-Forming Ion-Pair Amphiphiles from Single-Chain Surfactants. Journal of the American Chemical Society, 112(4), pp. 1635-1637. [https://doi.org/10.1021/ja00160a057 doi: 10.1021/ja00160a057]</ref>, with the ion pairing of the polar head groups mimicking the a double tail situation. The behavior of single chain [[wikipedia: Per-_and_polyfluoroalkyl_substances#Fluorosurfactants|fluorosurfactant]] amphiphiles has been demonstrated to be significantly different from similar hydrocarbon based analogues. Not only are [[Wikipedia: Critical micelle concentration | critical micelle concentrations (CMC)]] of fluorosurfactants typically two orders of magnitude lower than corresponding hydrocarbon surfactants but self-assembly can occur even when fluorosurfactants are dispersed at low concentrations significantly below the CMC in water and other solvents<ref name="Krafft2006">Krafft, M.P., 2006. Highly fluorinated compounds induce phase separation in, and nanostructuration of liquid media. Possible impact on, and use in chemical reactivity control. Journal of Polymer Science Part A: Polymer Chemistry, 44(14), pp. 4251-4258. [https://doi.org/10.1002/pola.21508 doi: 10.1002/pola.21508]&nbsp;&nbsp;[[Media:Krafft2006.pdf | Open Access Article]]</ref>. The assembly of fluorinated amphiphiles structurally similar to those found in AFFF have been shown to readily form stable, complex structures including vesicles, fibers, and globules at concentrations as low as 0.5% w/v in contrast to their hydrocarbon analogues which remained fluid at 30% w/v<ref>Krafft, M.P., Guilieri, F., Riess, J.G., 1993. Can Single-Chain Perfluoroalkylated Amphiphiles Alone form Vesicles and Other Organized Supramolecular Systems? Angewandte Chemie International Edition in English, 32(5), pp. 741-743. [https://doi.org/10.1002/anie.199307411 doi: 10.1002/anie.199307411]</ref><ref name="KrafftEtAl_1994">Krafft, M.P., Guilieri, F., Riess, J.G., 1994. Supramolecular assemblies from single chain perfluoroalkylated phosphorylated amphiphiles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 84(1), pp. 113-119. [https://doi.org/10.1016/0927-7757(93)02681-4 doi: 10.1016/0927-7757(93)02681-4]</ref>.  
  
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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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Krafft found that fluorinated amphiphiles formed bilayer membranes with phospholipids, and that the resulting vesicles were more stable than those made of phospholipids alone<ref name="KrafftEtAl_1998">Krafft, M.P., Riess, J.G., 1998. Highly Fluorinated Amphiphiles and Collodial Systems, and their Applications in the Biomedical Field. A Contribution. Biochimie, 80(5-6), pp. 489-514. [https://doi.org/10.1016/S0300-9084(00)80016-4 doi: 10.1016/S0300-9084(00)80016-4]</ref>. The similarities in amphiphilic properties between phospholipids and the hydrocarbon-based surfactants in AFFF suggests that bilayer vesicles may form between these and the fluorosurfactants also present in the concentrate. Krafft demonstrated that both the permeability of resulting mixed vesicles and their propensity to fuse with each other at increasing ionic strength was reduced as a result of the creation of an inert hydrophobic and [[wikipedia: Lipophobicity|lipophobic]] film within the membrane, and also suggested that the fluorinated amphiphiles increased [[Wikipedia: van der Waals force | van der Waals interactions]] in the hydrocarbon region<ref name="KrafftEtAl_1998"/>. Thus this low permeability may allow vesicles formed by the surfactants present in AFFF to act as long term repositories of PFAS not only as part of the bilayer itself but also solvated within the vesicle. This prediction is supported by the observation that supramolecular structures formed from single chain fluorinated amphiphiles have been demonstrated to be stable at elevated temperature (15 min at 121&deg;C) and have been shown to be stable over periods of months, even increasing in size over time when stored at environmentally relevant temperatures<ref name="KrafftEtAl_1994"/>.
  
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==Fundamentals of Sediment Risk Assessment==
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Formation of complex structures at relatively low solute concentrations requires the monomer molecules to be well ordered to maintain tight packing in the supramolecular structure<ref>Ringsdorf, H., Schlarb, B., Venzmer, J., 1988. Molecular Architecture and Function of Polymeric Oriented Systems: Models for the Study of Organization, Surface Recognition, and Dynamics of Biomembranes. Angewandte Chemie International Edition in English, 27(1), pp. 113-158. [https://doi.org/10.1002/anie.198801131 doi: 10.1002/anie.198801131]</ref>. This order results from electrostatic forces, [[wikipedia: Hydrogen bond|hydrogen bonding]], and in the case of fluorinated amphiphiles, hydrophobic interactions. The geometry of the amphiphile also potentially contributes to the type of supramolecular aggregation<ref>Israelachvili, J.N., Mitchell, D.J., Ninham, B.W., 1976. Theory of Self-Assembly of Hydrocarbon Amphiphiles into Micelles and Bilayers. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 72, pp. 1525-1568. [https://doi.org/10.1039/F29767201525 doi: 10.1039/F29767201525]</ref>. Surfactants which adopt a conical shape (such as a typical hydrocarbon based surfactant with a large polar head group and a single alkyl chain as a tail) tend to form micelles more easily. Increasing the bulk of the tail makes the surfactant more cylindrically shaped which makes assembly into bilayers more likely.  
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[[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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Perfluoroalkyl chains are significantly more bulky than their hydrocarbon based analogues both in cross sectional area (28-30 Å<sup>2</sup> versus 20 Å<sup>2</sup>, respectively) and mean volume (CF<sub>2</sub> and CF<sub>3</sub> estimated as 38 Å<sup>3</sup> and 92 Å<sup>3</sup> compared to 27 Å<sup>3</sup> and 54 Å<sup>3</sup> for CH<sub>2</sub> and CH<sub>3</sub>)<ref name="KrafftEtAl_1998"/><ref name="Krafft2006"/>. Structural studies on linear PFOS have shown that the molecule adopts an unusual helical structure<ref>Erkoç, Ş., Erkoç, F., 2001. Structural and electronic properties of PFOS and LiPFOS. Journal of Molecular Structure: THEOCHEM, 549(3), pp. 289-293. [https://doi.org/10.1016/S0166-1280(01)00553-X doi:10.1016/S0166-1280(01)00553-X]</ref><ref name="TorresEtAl2009">Torres, F.J., Ochoa-Herrera, V., Blowers, P., Sierra-Alvarez, R., 2009. Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers. Chemosphere 76(8), pp. 1143-1149. [https://doi.org/10.1016/j.chemosphere.2009.04.009 doi: 10.1016/j.chemosphere.2009.04.009]</ref> in aqueous and solvent phases to alleviate [[wikipedia: Steric_effects#Steric_hindrance|steric hindrance]]. This arrangement results from the carbon chain starting in the planar all anti [[wikipedia:Conformational isomerism|conformation]] and then successively twisting all the CC-CC dihedrals by 15&deg;-20&deg; in the same direction<ref>Abbandonato, G., Catalano, D., Marini, A., 2010. Aggregation of Perfluoroctanoate Salts Studied by <sup>19</sup>F NMR and DFT Calculations: Counterion Complexation, Poly(ethylene glycol) Addition, and Conformational Effects. Langmuir 26(22), pp. 16762-16770. [https://doi.org/10.1021/la102578k  doi: 10.1021/la102578k].</ref>. The conformation also minimizes the electrostatic repulsion between fluorine atoms bonded to the same side of the carbon backbone by maximizing the interatomic distances between them<ref name="TorresEtAl2009"/>.
  
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===Screening-Level Risk Assessment (SLRA)===
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A consequence of the helical structure is that there is limited carbon-carbon bond rotation within the perfluoroalkyl chain giving them increased rigidity compared to alkyl chains<ref>Barton, S.W., Goudot, A., Bouloussa, O., Rondelez, F., Lin, B., Novak, F., Acero, A., Rice, S., 1992. Structural transitions in a monolayer of fluorinated amphiphile molecules. The Journal of Chemical Physics, 96(2), pp. 1343-1351. [https://doi.org/10.1063/1.462170 doi: 10.1063/1.462170]</ref>. The bulkiness of the perfluoroalkyl chain confers a cylindrical shape on the fluorosurfactant amphiphile and therefore favors the formation of bilayers and vesicles the aggregation of which is further assisted by the rigidity of the molecules which allow close packing in the supramolecular structure. Fluorosurfactants therefore cannot be regarded as more hydrophobic analogues of hydrogenated surfactants. Their self-assembly behavior is characterized by a strong tendency to form vesicles and lamellar phases rather than micelles, due to the bulkiness and rigidity of the perfluoroalkyl chain that tends to decrease the curvature of the aggregates they form in solution<ref>Barton, C.A., Butler, L.E., Zarzecki, C.J., Flaherty, J., Kaiser, M., 2006. Characterizing Perfluorooctanoate in Ambient Air near the Fence Line of a Manufacturing Facility: Comparing Modeled and Monitored Values. Journal of the Air and Waste Management Association, 56, pp. 48-55. [https://doi.org/10.1080/10473289.2006.10464429 doi: 10.1080/10473289.2006.10464429]&nbsp;&nbsp;[https://www.tandfonline.com/doi/epdf/10.1080/10473289.2006.10464429?needAccess=true Open Access Article]</ref>. The larger tail cross section of fluorinated compared to hydrogenated amphiphiles tends to favor the formation of aggregates with lesser surface curvature, therefore rather than micelles they form bilayer membranes, vesicles, tubules and fibers<ref>Krafft, M.P., Guilieri, F., Riess, J.G., 1993. Can Single-Chain Perfluoroalkylated Amphiphiles Alone form Vesicles and Other Organized Supramolecular Systems? Angewandte Chemie International Edition in English, 32(5), pp. 741-743. [https://doi.org/10.1002/anie.199307411 doi: 10.1002/anie.199307411]</ref><ref>Furuya, H., Moroi, Y., Kaibara, K., 1996. Solid and Solution Properties of Alkylammonium Perfluorocarboxylates. The Journal of Physical Chemistry, 100(43), pp. 17249-17254.  [https://doi.org/10.1021/jp9612801 doi: 10.1021/jp9612801]</ref><ref>Giulieri, F., Krafft, M.P., 1996. Self-organization of single-chain fluorinated amphiphiles with fluorinated alcohols. Thin Solid Films, 284-285, pp. 195-199. [https://doi.org/10.1016/S0040-6090(95)08304-9 doi: 10.1016/S0040-6090(95)08304-9]</ref><ref>Gladysz, J.A., Curran, D.P., Horvath, I.T., 2004. Handbook of Fluorous Chemistry. WILEY-VCH Verlag GmbH & Co. KGaA,, Weinheim, Germany. ISBN: 3-527-30617-X</ref>. Rojas ''et al.'' (2002) demonstrated that perfluorooctyl sulphonamide formed a contiguous bilayer at 50 mg/L with self-assembled aggregates present at concentrations as low as 10 mg/L<ref name="RojasEtAl2002">Rojas, O.J., Macakova, L., Blomberg, E., Emmer, A., and Claesson, P.M., 2002. Fluorosurfactant Self-Assembly at Solid/Liquid Interfaces. Langmuir, 18(21), pp. 8085-8095. [https://doi.org/10.1021/la025989c doi: 10.1021/la025989c]</ref>.
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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>.
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==Thermodynamics of PFAS Accumulations on Solid Surfaces==
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The thermodynamics of formation of amphiphiles into supramolecular species requires consideration of both hydrophobic and hydrophilic interactions resulting from the amphoteric nature of the molecule. The hydrophilic portions of the molecule are driven to maximize their solvation interaction with as many water molecules as possible, whereas the hydrophobic portions of the molecule are driven to aggregate together thus minimizing interaction with the bulk water. Both of these processes change the [[wikipedia:Enthalpy|enthalpy]] and [[wikipedia: Entropy|entropy]] of the system.
  
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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.  
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In aqueous solution, the hydrophilic portions of an amphiphile form hydrogen bonds (4 - 120 kJ/mol) and van der Waals interactions (<5 kJ/mol) with water molecules and surfaces, and electrostatic interactions (5 – 300 kJ/mol) can also occur where the amphiphile is ionic<ref name="LombardoEtAl2015">Lombardo, D., Kiselev, M.A., Magazù, S., Calandra, P., 2015. Amphiphiles Self-Assembly: Basic Concepts and Future Perspectives of Supramolecular Approaches. Advances in Condensed Matter Physics, vol. 2015, article ID 151683, 22 pages. [https://doi.org/10.1155/2015/151683 doi: 10.1155/2015/151683]&nbsp;&nbsp;[[Media: LombardoEtAl2015.pdf | Open Access Article]]</ref>. These interactions, although weak compared to intramolecular covalent bonds within a molecule are energetically favorable and increase the enthalpy of the combined solute-solvent system. Thus, the hydrophilic portion of an amphiphile will look to maximize enthalpic gain through hydrogen bond interactions with the bulk water.
  
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===Detailed Risk Assessment===
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The hydrophobic portion of an amphiphile cannot form hydrogen bonds with the bulk solution, and its presence disrupts the hydrogen bond interactions between individual water molecules within the bulk water matrix. This disruption lowers the entropy of the system by reducing the degrees of translational rotational freedom available to the bulk water. The [[wikipedia:Second law of thermodynamics|second law of thermodynamics]] dictates that a system will arrange itself to maximize its entropy. With hydrophobic species this can be achieved by their spontaneous aggregation, as the reduction in solution entropy of the aggregated system is less than that which would occur if the component parts were solvated individually. These hydrophobic and hydrophilic interactions are weak, and the individual entropy gain per amphiphile upon aggregation is very small. However, taken together the overall effect on the entropy of the aggregate is sufficient to maintain it in solution, and moreover these interactions make the aggregates resistant to minor perturbations while retaining the reversibility of the self-assembled structure<ref name="LombardoEtAl2015"/>.
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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>.
 
  
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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.
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==Regulatory Drivers for Transition to PFAS-Free Firefighting Formulations==
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Regulations restricting the use and release of PFAS are being proposed and promulgated worldwide, with several enacted regulations addressing the use of aqueous film forming foams (AFFF) containing PFAS<ref name="Queensland2016">Queensland (Australia) Department of Environment and Heritage Protection, 2016. Operational Policy - Environmental Management of Firefighting Foam. 16 pages. [https://environment.des.qld.gov.au/assets/documents/regulation/firefighting-foam-policy.pdf Free Download]</ref><ref>U.S. Congress, 2019. S.1790 - National Defense Authorization Act for Fiscal Year 2020. United States Library of Congress.&nbsp;&nbsp;[https://www.congress.gov/bill/116th-congress/senate-bill/1790 Text and History of Law].</ref><ref>Arizona State Legislature, 2019. Title 36, Section 1696. Firefighting foam; prohibited uses; exception; definitions. [https://www.azleg.gov/viewdocument/?docName=https://www.azleg.gov/ars/36/01696.htm Text of Law]</ref><ref>California Legislature, 2020. Senate Bill No. 1044, Chapter 308, Firefighting equipment and foam: PFAS chemicals. [https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=201920200SB1044 Text and History of Law]</ref><ref>Arkansas General Assembly, 2021. An Act Concerning the Use of Certain Chemicals in Firefighting Foam; and for Other Purposes. Act 315, State of Arkansas. [https://trackbill.com/bill/arkansas-house-bill-1351-concerning-the-use-of-certain-chemicals-in-firefighting-foam/2008913/ Text and History of Law].</ref><ref>Espinosa, Summers, Kelly, J., Statler, Hansen, Young, 2021. Amendment to Fire Prevention and Control Act. House Bill 2722. West Virginia Legislature. [https://trackbill.com/bill/west-virginia-house-bill-2722-prohibiting-the-use-of-class-b-fire-fighting-foam-for-testing-purposes-if-the-foam-contains-a-certain-class-of-fluorinated-organic-chemicals/2047674/ Text and History of Law]</ref><ref>Louisiana Legislature, 2021. Act No. 232. [https://trackbill.com/bill/louisiana-house-bill-389-fire-protect-fire-marshal-provides-relative-to-the-discharge-or-use-of-class-b-fire-fighting-foam-containing-fluorinated-organic-chemicals/2092535/  Text and History of Law]</ref><ref>Vermont Legislature, 2021b. Act No. 36, PFAS in Class B Firefighting Foam. [https://trackbill.com/bill/vermont-senate-bill-20-an-act-relating-to-restrictions-on-perfluoroalkyl-and-polyfluoroalkyl-substances-and-other-chemicals-of-concern-in-consumer-products/1978963/  History and Text of Law]</ref>. In addition to regulated usage, firefighting formulation users are transitioning to PFAS-free firefighting formulations to reduce environmental liability in the event of a release, to reduce the cost of expensive containment systems and management of generated waste streams, and to avoid reputational damage. In 2016, Queensland, Australia was one of the first governments to ban PFAS use in firefighting foam<ref name="Queensland2016"/>. The US 2020 National Defense Authorization Act specified immediate prohibition of controlled releases of AFFF containing PFAS and required the Secretary of the Navy to publish a specification for PFAS-free firefighting formulation use and ensure it is available for use by the Department of Defense (DoD) by October 1, 2023<ref>U.S. Congress, 2021. S.2792 - National Defense Authorization Act for Fiscal Year 2021. United States Library of Congress.&nbsp;&nbsp;[https://www.congress.gov/bill/117th-congress/senate-bill/2792/ Text and History of Law].</ref>. The National Fire Protection Association (NFPA) recently removed the requirement for AFFF containing PFAS from their Standard on Aircraft Hangars and added two new chapters to allow users to determine if AFFF containing PFAS is needed at their facility<ref name="NFPA2022">National Fire Protection Association (NFPA), 2022. Codes and Standards, 409: Standard on Aircraft Hangars. [https://www.nfpa.org/codes-and-standards/4/0/9/409?l=42 NFPA Website]</ref>.
  
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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.
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==Selection of Replacement PFAS-Free Firefighting Formulations==       
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Since they first entered the market in the 2000s, the operational capabilities of PFAS-free firefighting formulations have grown<ref>Allcorn, M., Bluteau, T., Corfield, J., Day, G., Cornelsen, M., Holmes, N.J.C., Klein, R.A., McDowall, J.G., Olsen, K.T., Ramsden, N., Ross, I., Schaefer, T.H., Weber, R., Whitehead, K., 2018. Fluorine-Free Firefighting Foams (3F) – Viable Alternatives to Fluorinated Aqueous Film-Forming Foams (AFFF). White Paper prepared for the IPEN by members of the IPEN F3 Panel and associates, POPRC-14, Rome. [https://ipen.org/sites/default/files/documents/IPEN_F3_Position_Paper_POPRC-14_12September2018d.pdf Free Download].</ref> and numerous companies are now manufacturing and delivering PFAS-free firefighting formulations for fixed systems and AFFF vehicles<ref>Ansul (Company), Ansul NFF-331 3%x3% Non-Fluorinated Foam Concentrate (Commercial Product). [https://docs.johnsoncontrols.com/specialhazards/api/khub/documents/1nbeVfynU1IW~eJcCOA0Bg/content Product Data Sheet].</ref><ref>BioEx (Company), Ecopol A+ (Commercial Product). [https://www.bio-ex.com/en/our-products/product/ecopol-aplus/  Website]</ref><ref>National Foam (Company), 2020. Avio F3 Green KHC 3%, Fluorine Free Foam Concentrate (Commercial Product). [https://nationalfoam.com/wp-content/uploads/sites/4/NMS515-Avio-Green-KHC-3-FF.pdf Safety Data Sheet]</ref>. Key factors in the selection of a PFAS-free firefighting formulation product are compatibility of the new formulation with the existing system (as confirmed by a fire protection engineer) and environmental certifications (i.e., verifying the absence of organic fluorine or PFAS or the absence of other non-fluorine environmental contaminants).
  
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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.
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In January 2023, the US Department of Defense (DoD) published the [https://media.defense.gov/2023/Jan/12/2003144157/-1/-1/1/MILITARY-SPECIFICATION-FOR-FIRE-EXTINGUISHING-AGENT-FLUORINE-FREE-FOAM-F3-LIQUID-CONCENTRATE-FOR-LAND-BASED-FRESH-WATER-APPLICATIONS.PDF Performance Specification for Fire Extinguishing Agent, Fluorine-Free Foam (F3) Liquid Concentrate for Land-Based, Fresh Water Applications]<ref name="DoD2023"/>. This Military Performance Specification (Mil-Spec) allows PFAS-free firefighting formulations to be certified as meeting certain standardized operational goals for use in military settings. In addition to Mil-Spec requirements, PFAS-free firefighting formulations can also be certified through Underwriters Laboratories Standard for Safety, Foam Equipment and Liquid Concentrates, UL 162, which requires the new firefighting formulations be investigated for suitability and compatibility with the specific equipment with which they are intended to be used<ref>Underwriters Laboratories Inc., 2018. UL162, UL Standard for Safety, Foam Equipment and Liquid Concentrates, 8th Edition, Revised 2022. 40 pages. [https://global.ihs.com/doc_detail.cfm?document_name=UL%20162&item_s_key=00096960 Website]</ref>. Several PFAS-free foams have been certified under various parts of EN1568, the European Standard which specifies the necessary foam properties and performance requirements<ref>European Standards, 2018. CSN EN 1568-1 ed. 2: Fire extinguishing media - Foam concentrates - Part 1: Specification for medium expansion foam concentrates for surface application to water-immiscible liquids. 48 pages. [https://www.en-standard.eu/csn-en-1568-1-ed-2-fire-extinguishing-media-foam-concentrates-part-1-specification-for-medium-expansion-foam-concentrates-for-surface-application-to-water-immiscible-liquids/ European Standards Website.]</ref>. Both [https://serdp-estcp.mil/ ESTCP and SERDP] have supported (and continue to support) the development and field validation of PFAS-free firefighting formulations (e.g. [https://serdp-estcp.mil/projects/details/baa72637-e3c8-40ee-a007-f295311c72ad WP22-7456], [https://serdp-estcp.mil/projects/details/1bed98f7-dbe6-4bdd-98d2-1f9cfeb5f3d9/wp21-3465-project-overview WP21-3465], [https://serdp-estcp.mil/projects/details/bc932800-cfc8-4e86-a212-5f8c9d27f17c WP20-1535]). Both the US Federal Aviation Administration (FAA) and National Fire Protection Association (NFPA) have performed a variety of foam certification tests on numerous PFAS-free firefighting formulations<ref>Back, G.G., Farley, J.P., 2020. Evaluation of the Fire Protection Effectiveness of Fluorine Free Firefighting Foams. National Fire Protection Association, Fire Protection Research Foundation. [https://www.iafc.org/docs/default-source/1safehealthshs/effectivenessofflourinefreefoam.pdf Free Download].</ref><ref>Casey, J., Trazzi, D., 2022. Fluorine-Free Foam Testing. Federal Aviation Administration (FAA) Final Report. [https://www.airporttech.tc.faa.gov/DesktopModules/EasyDNNNews/DocumentDownload.ashx?portalid=0&moduleid=3682&articleid=2882&documentid=3054  Open Access Article]</ref>.
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==Key Considerations==
 
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===Stakeholder Engagement===
 
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Stakeholder involvement is widely acknowledged as an important element of [[Wikipedia: Dredging | dredged]] material management<ref name="Collier2014">Collier, Z.A., Bates, M.E., Wood, M.D. and Linkov, I., 2014. Stakeholder engagement in dredged material management decisions. Science of the Total Environment, 496, pp. 248-256. [https://doi.org/10.1016/j.scitotenv.2014.07.044 DOI: 10.1016/j.scitotenv.2014.07.044]  Free download from: [https://www.researchgate.net/profile/Matthew-Bates-9/publication/264460412_Stakeholder_Engagement_in_Dredged_Material_Management_Decisions/links/5a9d50fbaca2721e3f32adea/Stakeholder-Engagement-in-Dredged-Material-Management-Decisions.pdf ResearchGate]</ref>, sediment remediation<ref name="Oen2010">Oen, A.M.P., Sparrevik, M., Barton, D.N., Nagothu, U.S., Ellen, G.J., Breedveld, G.D., Skei, J. and Slob, A., 2010. Sediment and society: an approach for assessing management of contaminated sediments and stakeholder involvement in Norway. Journal of Soils and Sediments, 10(2), pp. 202-208. [https://doi.org/10.1007/s11368-009-0182-x DOI: 10.1007/s11368-009-0182-x]</ref>, and other environmental and sediment related activities<ref name="Gerrits2004">Gerrits, L. and Edelenbos, J., 2004. Management of Sediments Through Stakeholder Involvement. Journal of Soils and Sediments, 4(4), pp. 239-246. [https://doi.org/10.1007/BF02991120 DOI: 10.1007/BF02991120]</ref><ref name="Braun2019">Braun, A.B., da Silva Trentin, A.W., Visentin, C. and Thomé, A., 2019. Sustainable remediation through the risk management perspective and stakeholder involvement: A systematic and bibliometric view of the literature. Environmental Pollution, 255(1), p.113221. [https://doi.org/10.1016/j.envpol.2019.113221 DOI: 10.1016/j.envpol.2019.113221]</ref>.
 
  
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Sediment management, particularly at the river basin scale, involves a wide variety of different environmental, governmental, and societal issues<ref name="Liu2018">Liu, C., Walling, D.E. and He, Y., 2018. The International Sediment Initiative case studies of sediment problems in river basins and their management. International Journal of Sediment Research, 33(2), pp. 216-219.  [https://doi.org/10.1016/j.ijsrc.2017.05.005 DOI: 10.1016/j.ijsrc.2017.05.005]  Free download from: [https://www.researchgate.net/profile/Cheng-Liu-43/publication/317032034_Review_The_International_Sediment_Initiative_Case_Studies_of_sediment_problems_in_river_basins_and_their_management/links/5f4f37d2299bf13a319703df/Review-The-International-Sediment-Initiative-Case-Studies-of-sediment-problems-in-river-basins-and-their-management.pdf ResearchGate]</ref>. Incorporating these different views, interests, and perspectives into a form that builds consensus for whatever actions and goals are in mind (e.g., commercial ports and shipping, navigation, flood protection, or habitat restoration) necessitates a formal stakeholder engagement process<ref name="Slob2008">Slob, A.F.L., Ellen, G.J. and Gerrits, L., 2008. Sediment management and stakeholder involvement. In: Sustainable Management of Sediment Resources, Vol. 4: Sediment Management at the River Basin Scale, Owens, P.N. (ed.), pp. 199-216. Elsevier.  [https://doi.org/10.1016/S1872-1990(08)80009-8 DOI: 10.1016/S1872-1990(08)80009-8]</ref>.
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==Selection of Flushing Agent==
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General industry guidance has typically recommended several rinses with water to remove PFAS from impacted equipment. Owing to the unique physical and chemical properties of PFAS, the use of room temperature water to remove PFAS from impacted equipment has not been very effective. To address these recalcitrant accumulations, companies are developing new methods to remove self-assembled PFAS bilayers from existing fire-fighting infrastructure so that it can be successfully transitioned to PFAS-free formulations. Arcadis developed a non-toxic cleaning agent, Fluoro Fighter<sup>TM</sup>, which has been demonstrated to be effective for removal of PFAS from equipment by disrupting the accumulated layers of PFAS coating the AFFF-wetted surfaces.  
  
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Results from a three-year (2008-2010) [https://www.ngi.no/eng/Projects/Sediment-and-society Sediment and Society] research project funded by the Norwegian Research Council point to three important challenges that must be resolved for successful stakeholder engagement: (1) how to include people who have important management information and local knowledge, but not much influence in the decision-making process; (2) how to secure resources to ensure participation and (3) how to engage and motivate stakeholders to participate early in the sediment remediation planning process<ref name="Oen2010"/>.
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Laboratory studies have supported the optimization of this PFAS removal method in fire suppression system piping obtained from a commercial airport hangar in Sydney, Australia<ref name="LangEtAl2022"/>. Prior to removal from the hangar, the stainless-steel pipe held PFAS-containing AFFF for more than three decades. Results indicated that Fluoro Fighter<sup>TM</sup>, as well as flushing at elevated temperatures, removed more surface associated PFAS in comparison to equivalent extractions using methanol or water at room temperature. ESTCP has supported (and continues to support) the development and field validation of best practices for methodologies to clean foam delivery systems (e.g. [https://serdp-estcp.mil/projects/details/1521652f-a8b2-4c52-9232-c1018989a6b1 ER20-5364], [https://serdp-estcp.mil/projects/details/6d0750be-f20b-4765-bdfa-872adccaf37a ER20-5361], [https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ER20-5369], [https://serdp-estcp.mil/projects/details/4fd2e4ab-ddb7-40f8-835e-e1d637c0d650 ER21-7229]).
  
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===Conceptual Site Model===
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==PFAS Verification Testing==
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The preparation of a conceptual site model (CSM) is a fundamental component of problem formulation and the first step in detailed sediment risk assessment. The CSM is a narrative and/or illustrative representation of the physical, chemical and biological processes that control the transport, migration and actual or potential impacts of sediment contamination to human and/or ecological receptors<ref name="NJDEP2019">New Jersey Department of Environmental Protection, 2019. Technical Guidance for Preparation and Submission of a Conceptual Site Model. Version 1.1. Site Remediation and Waste Management Program, Trenton, NJ. 46 pp. [https://www.nj.gov/dep/srp/guidance/srra/csm_tech_guidance.pdf Free download].</ref><ref name="USEPA2011">US Environmental Protection Agency, 2011. Guidance for the Development of Conceptual Models for a Problem Formulation Developed for Registration Review. Environmental Fate and Effects Division, Office of Pesticide Programs, Washington, D.C. [https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/guidance-development-conceptual-models-problem Website]</ref>. The CSM should include a “food web” because the aquatic food web is an important exposure pathway by which contaminants in the sediment reach humans and pelagic aquatic life<ref name="Arnot2004">Arnot, J.A. and Gobas, F.A., 2004. A Food Web Bioaccumulation Model for Organic Chemicals in Aquatic Ecosystems. Environmental Toxicology and Chemistry, 23(10), pp. 2343-2355.  [https://doi.org/10.1897/03-438 DOI: 10.1897/03-438]</ref>.
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In general, PFAS sampling techniques used to support firefighting formulation transition activities are consistent with conventional sampling techniques used in the environmental industry, but special consideration is made regarding high concentration PFAS materials, elevated detection levels, cross-contamination potential, precursor content, and matrix interferences. The analytical method selected should be appropriate for the regulatory requirements in the site area.
  
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The CSM provides an early opportunity for critical examination of the interactions between sediment and the water column and the influence of groundwater inputs, surface runoff, and hydrodynamics. For example, there are situations where impacts in the aquatic food web can be driven by ongoing inputs to the water column from upstream sources, but mistakenly connected to polluted sediments. Other considerations included in a CSM can be socio-economic and include linkages to the ecosystem services provided by sediments<ref name="Broszeit2019">Broszeit, S., Beaumont, N.J., Hooper, T.L., Somerfield, P.J. and Austen, M.C., 2019. Developing conceptual models that link multiple ecosystem services to ecological research to aid management and policy, the UK marine example. Marine Pollution Bulletin, 141, pp.236-243.  [https://doi.org/10.1016/j.marpolbul.2019.02.051 DOI: 10.1016/j.marpolbul.2019.02.051]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S0025326X19301511/pdfft?md5=34993d6c3a57b6fb18a8b6329597fcb9&pid=1-s2.0-S0025326X19301511-main.pdf Open Access Article.]</ref><ref name="Wang2021">Wang, J., Lautz, L.S., Nolte, T.M., Posthuma, L., Koopman, K.R., Leuven, R.S. and Hendriks, A.J., 2021. Towards a systematic method for assessing the impact of chemical pollution on ecosystem services of water systems. Journal of Environmental Management, 281, p. 111873. [https://doi.org/10.1016/j.jenvman.2020.111873 DOI: 10.1016/j.jenvman.2020.111873]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S0301479720317989/pdfft?md5=daff5e94f8aed44ffce6508afef2308c&pid=1-s2.0-S0301479720317989-main.pdf  Open Access Article.]</ref>, or the social, economic and environmental impacts of sediment management alternatives. In such a case, when risk assessment seeks to compare risks of various management actions (including no action), the CSM can be termed a sustainability CSM, or SustCSM<ref name="McNally2020">McNally, A.D., Fitzpatrick, A.G., Harrison, D., Busey, A., and Apitz, S.E., 2020. Tiered approach to sustainability analysis in sediment remediation decision making. Remediation Journal, 31(1), pp. 29-44.  [https://doi.org/10.1002/rem.21661 DOI: 10.1002/rem.21661]&nbsp;&nbsp; [https://onlinelibrary.wiley.com/doi/epdf/10.1002/rem.21661 Open Access Article].</ref><ref name="Holland2011">Holland, K.S., Lewis, R.E., Tipton, K., Karnis, S., Dona, C., Petrovskis, E., and Hook, C., 2011. Framework for Integrating Sustainability Into Remediation Projects. Remediation Journal, 21(3), pp. 7-38. [https://doi.org/10.1002/rem.20288 DOI: 10.1002/rem.20288].</ref>. At a minimum, however, the purpose of the CSM is to illustrate the scope of the risk assessment and guide the quantification of exposure and risk.
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==Rinsate Treatment==
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Numerous technologies for treatment of PFAS-impacted water sources, including rinsates, have been and are currently being developed. These include separation technologies such as [[PFAS Ex Situ Water Treatment|foam fractionation, nanofiltration, sorbents/flocculants, ion exchange resins, reverse osmosis, and destructive technologies such as sonolysis, electrochemical oxidation, hydrothermal alkaline treatment]], [[PFAS Treatment by Electrical Discharge Plasma |enhanced contact plasma]], and [[Supercritical Water Oxidation (SCWO) |supercritical water oxidation (SCWO)]]. Many of these technologies have rapidly developed from bench-scale (e.g., microcosms, columns, single reactors) to commercially available field-scale units capable of managing PFAS-impacted waters of varying waste volumes and PFAS compositions and concentrations. Ongoing field research continues to improve the treatment efficiency, reliability, and versatility of these technologies, both individually and as coupled treatment solutions (e.g., treatment train). ESTCP has supported (and continues to support) the development and field validation of separation and destructive technologies for treatment of PFAS-impacted water sources, including rinsates (e.g. [https://serdp-estcp.mil/projects/details/0c7af048-3a00-471f-9480-292aa78ecd4f ER20-5370], [https://serdp-estcp.mil/projects/details/0aa2fb20-b851-4b5b-ac64-e72795986b8a ER20-5369], [https://serdp-estcp.mil/projects/details/0d7c91a8-d755-4876-a8bb-c3e896feee0d ER20-5350], [https://serdp-estcp.mil/projects/details/790e2dda-1f7b-4ff5-b77e-08ed10a456b1 ER20-5355]).  
  
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===Environmental Fate===
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Remedy selection for treatment of rinsates involves several key factors. It is critical that environmental practitioners have up-to-date technical and practical knowledge on the suitability of these remedial options for different site conditions, treatment volumes, PFAS composition (e.g., presence of precursors, co-contaminants), PFAS concentrations, safety considerations, potential for undesired byproducts (e.g., perchlorate, disinfection byproducts), and treatment costs (e.g., energy demand, capital costs, operational labor).
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An important consideration in exposure analysis is the determination of the bioavailable fraction of the contaminant in the sediment. There are two considerations. First, the adverse condition may be buried deep enough in sediments to be below the biologically available zone; typically, conditions in sediment below a depth of 5 cm will not contact burrowing benthic organisms<ref name="Anderson2010">Anderson, R.H., Prues, A.G. and Kravitz, M.J., 2010. Determination of the biologically relevant sampling depth for terrestrial ecological risk assessments. Geoderma, 154(3-4), pp.336-339.  [https://doi.org/10.1016/j.geoderma.2009.11.004 DOI: 10.1016/j.geoderma.2009.11.004]</ref>. If there is no prospect for the adverse condition to come closer to the surface, then the risk assessment could conclude the risk of exposure is insignificant. The second consideration relates to chemistry and the factors involved in the binding to sediment particles or the chemical form of the substance in the sediment<ref name="Eggleton2004">Eggleton, J. and Thomas, K.V., 2004. A review of factors affecting the release and bioavailability of contaminants during sediment disturbance events. Environment International, 30(7), pp. 973-980. [https://doi.org/10.1016/j.envint.2004.03.001 DOI: 10.1016/j.envint.2004.03.001]</ref>. However, these assumptions should be examined in the context of [[Climate Change Primer | climate change]], and the likelihood of more frequent and extreme events, putting burial at risk, higher temperatures and changing biogeochemical conditions, which may alter environmental fate of contaminants, compared to historical studies.  
 
  
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The above contaminant bioavailability considerations are important factors influencing assumptions in the risk assessment about contaminant exposure<ref name="Peijnenburg2020">Peijnenburg, W.J., 2020. Implementation of bioavailability in prospective and retrospective risk assessment of chemicals in soils and sediments. In: The Handbook of Environmental Chemistry, vol 100, Bioavailability of Organic Chemicals in Soil and Sediment, Ortega-Calvo, J.J., Parsons, J.R. (ed.s), pp.391-422. Springer.  [https://doi.org/10.1007/698_2020_516 DOI: 10.1007/698_2020_516]</ref><ref name="Ortega-Calvo2015">Ortega-Calvo, J.J., Harmsen, J., Parsons, J.R., Semple, K.T., Aitken, M.D., Ajao, C., Eadsforth, C., Galay-Burgos, M., Naidu, R., Oliver, R. and Peijnenburg, W.J., 2015. From Bioavailability Science to Regulation of Organic Chemicals. Environmental Science and Technology, 49, 10255−10264. [https://doi.org/10.1021/acs.est.5b02412 DOI: 10.1021/acs.est.5b02412]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/acs.est.5b02412 Open Access Article].</ref>. There have been recent advances in the use of sorbent amendments applied to contaminated sediments that alter sediment geochemistry, increase contaminant binding, and reduce contaminant exposure risks to people and the environment<ref name="Ghosh2011">Ghosh, U., Luthy, R.G., Cornelissen, G., Werner, D. and Menzie, C.A., 2011. In-situ sorbent amendments: a new direction in contaminated sediment management. Environmental Science and Technology, 45, 4, 1163–1168.  [https://doi.org/10.1021/es102694h DOI: 10.1021/es102694h]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/es102694h Open Access Article]</ref>. [[Passive Sampling of Sediments | Passive sampling techniques]] have emerged to quantify chemical binding to sediment and determine the freely dissolved concentration that is bioavailable.
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==References==
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<references />
  
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===Assessment and Measurement Endpoints===
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==See Also==
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Assessment and measurement endpoints used in sediment risk assessment are comparable to those described in USEPA ecological risk assessment guidance<ref name="USEPA2005"/><ref name="USEPA1992">US Environmental Protection Agency (USEPA), 1992. Framework for Ecological Risk Assessment, EPA/630/R-92/001. Risk Assessment Forum, Washington DC. [[Media: EPA-630-R-92-001.pdf | Report.pdf]]</ref><ref name="USEPA1996">US Environmental Protection Agency (USEPA), 1996. Eco Update: Ecological Significance and Selection of Candidate Assessment Endpoints. EPA/540/F-95/037. Office of Solid Waste and Emergency Response, Washington DC.  [[Media: EPA 540-F-95-037.pdf | Report.pdf]]</ref><ref name="USEPA1997b">US Environmental Protection Agency (USEPA), 1997. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments - Interim Final, EPA 540/R-97/006. Office of Solid Waste and Emergency Response, Washington DC.  [[Media: EPA 540-R-97-006.pdf | Report.pdf]]</ref><ref name="USEPA1998">US Environmental Protection Agency (USEPA), 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Risk Assessment Forum, Washington DC.  [[Media: EPA 630-R-95-002F.pdf | Report.pdf]]</ref>. A sediment risk assessment, and ecological risk assessments more broadly, must have clearly defined endpoints that are socially and biologically relevant, accessible to prediction and measurement, and susceptible to the hazard being assessed<ref name="USEPA1992"/>.
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[https://portal.ct.gov/-/media/CFPC/KO/2022/Latest-News/DESPP-DEEP-AFFF-MuniFDupdate-2022-05-26.pdf   Connecticut Take-Back Program for municipal fire departments using AFFF containing PFAS]
  
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Assessment endpoints for humans include both carcinogenic and noncarcinogenic effects. Due to their assumed higher levels of exposure, human receptors used in sediment risk assessment typically include recreational, commercial, and subsistence fishermen, i.e., people who might be at increased risk from eating fish or contacting the sediment or water on a regular basis such as indigenous peoples, immigrants from fishing cultures, and subsistence fishers who rely upon fish as a major source of protein. Special considerations are given to women of child-bearing age, pregnant women and young children. Assessment endpoints for ecological receptors focus on benthic organisms, resident fish, piscivorous and other predatory birds and marine mammals. Endpoints typically include mortality, reproductive success and population susceptibility to disease or similar adverse chronic conditions.
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[https://www.arcadis.com/en-us/knowledge-hub/blog/united-states/johnsie-lang/2021/transitioning-to-pfas-free-firefighting  Arcadis blog on Fluoro Fighter<sup>TM</sup>]
  
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Measurement endpoints are related quantitatively to each assessment endpoint. Whenever practical, multiple measurement endpoints are chosen to provide additional lines of evidence for each assessment endpoint. For example, for humans, it might be possible to measure contaminant levels in both food items and human blood or tissue. For predatory fish, birds and mammals, it might be possible to measure contaminants in both prey and predator tissues. Measurement endpoints can be selected to assess non-chemical stressors as well, such as habitat alteration and water turbidity. Typically, measurement endpoints are compared to measurements at a reference site to ascertain the degree of departure from local natural or background conditions.
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[https://serdp-estcp.mil/projects/details/1521652f-a8b2-4c52-9232-c1018989a6b1  Project Summary ESTCP ER20-5634: Demonstration and Validation of Environmentally Sustainable Methods to Effectively Remove PFAS from Fire Suppression Systems]
  
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===Sediment Toxicity Testing===
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[https://serdp-estcp.org/projects/details/0d7c91a8-d755-4876-a8bb-c3e896feee0d Project Summary ESTCP ER20-5350: Supercritical Water Oxidation (SCWO) for Complete PFAS Destruction]
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Sediment bioassays are an integral part of effects characterization when assessing the risks posed by contaminated sediments and developing sediment quality guidelines<ref name="USEPA2014">US Environmental Protection Agency (USEPA), 2014. Toxicity Testing and Ecological Risk Assessment Guidance for Benthic Invertebrates. Office of Chemical Safety and Pollution Prevention, Washington DC.  [https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/toxicity-testing-and-ecological-risk-assessment Website]&nbsp;&nbsp; [[Media: USEPA2014.pdf | Report.pdf]]</ref><ref name="Simpson2016a">Simpson, S., Campana, O., Ho, K., 2016. Chapter 7, Sediment Toxicity Testing. In: J. Blasco, P.M. Chapman, O. Campana, M. Hampel (ed.s), Marine Ecotoxicology: Current Knowledge and Future Issues. Academic Press Incorporated. pp. 199-237.  [https://doi.org/10.1016/B978-0-12-803371-5.00007-2 DOI: 10.1016/B978-0-12-803371-5.00007-2]</ref>. The selection of appropriate sediment bioassays is dependent on the questions being addressed, the physical and chemical characteristics of the sediment matrix, the nature of the contaminant(s) of concern, and preferences of the supervising regulatory authority for the test method and test organisms<ref name="Amiard-Triquet2015">Amiard-Triquet, C., Amiard, J.C. and Mouneyrac, C. (ed.s), 2015. Aquatic Ecotoxicology: Advancing Tools For Dealing With Emerging Risks. Academic Press, NY. ISBN #9780128009499.  [https://doi.org/10.1016/B978-0-12-800949-9.12001-7 DOI: 10.1016/B978-0-12-800949-9.12001-7]</ref>. Bioassay procedures have been standardized in several countries, and it is not unusual for different test methods to be required in different countries for the same sediment management purpose<ref name="DelValls2004">DelValls, T.A., Andres, A., Belzunce, M.J., Buceta, J.L., Casado-Martinez, M.C., Castro, R., Riba, I., Viguri, J.R. and Blasco, J., 2004. Chemical and ecotoxicological guidelines for managing disposal of dredged material. TrAC Trends in Analytical Chemistry, 23(10-11), pp. 819-828. [https://doi.org/10.1016/j.trac.2004.07.014 DOI: 10.1016/j.trac.2004.07.014]&nbsp;&nbsp; Free download from: [https://d1wqtxts1xzle7.cloudfront.net/46085251/Chemical_and_Ecotoxicological_Guidelines20160530-23122-4fooj2-with-cover-page-v2.pdf?Expires=1637618385&Signature=aNsOfciO0HPhucL8S713nenRlvviD2dbLi8y63n93iGX~Cc7CHwyYQ2bfNlT6VnjuFJeVT83M01Xog6esr14gyvL9pmlo3hw5fQp5J9vA8gqXcT9kQfM1T2Q0Ig883yGMFmtgUrrU6p8c8V~8rh5DTKDD5ZsiL4zloGgF6Gs4F2ecEDqyFBZ17yYpXGVVBmpfm87sUpaPY0Ix9iWJ~5nxM~HF6XYl1sA1rgFSerT-Y5W8Ma7-XMljnYHQ7hW7eqMjyN66IDj7pwafG7Ox-Hnp07IuD-oMY1dHHrzTOmHpXpWgMYLn2zf1BSmy~tqIFHE6UjZn5ako93PgExuzEjEiw__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>. Guidance documents in Australia, Canada, Europe and the US cover the wide range of sediment bioassay procedures most often used in risk assessment<ref name="Bat2005">Bat, L., 2005. A Review of Sediment Toxicity Bioassays Using the Amphipods and Polychaetes. Turkish Journal of Fisheries and Aquatic Sciences, 5(2), pp. 119-139.  [https://dergipark.org.tr/en/pub/trjfas-ayrildi/issue/13287/160604 Free download]&nbsp;&nbsp; [[Media: Bat2005.pdf | Report.pdf]]</ref><ref name="Keddy1995">Keddy, C.J., Greene, J.C. and Bonnell, M.A., 1995. Review of Whole-Organism Bioassays: Soil, Freshwater Sediment, and Freshwater Assessment in Canada. Ecotoxicology and Environmental Safety, 30(3), pp. 221-251.  [https://doi.org/10.1006/eesa.1995.1027 DOI: 10.1006/eesa.1995.1027]</ref><ref name="Giesy1990">Giesy, J.P., Rosiu, C.J., Graney, R.L. and Henry, M.G., 1990. Benthic invertebrate bioassays with toxic sediment and pore water. Environmental Toxicology and Chemistry, 9(2), pp. 233-248.  [https://doi.org/10.1002/etc.5620090214 DOI: 10.1002/etc.5620090214]</ref><ref name="Simpson2016b">Simpson, S. and Batley, G. (ed.s), 2016. Sediment Quality Assessment: A Practical Guide, Second Edition. 358 pp. CSIRO Publishing, Australia. ISBN # 9781486303847.</ref><ref name="Moore2019">Moore, D.W., Farrar, D., Altman, S. and Bridges, T.S., 2019. Comparison of Acute and Chronic Toxicity Laboratory Bioassay Endpoints with Benthic Community Responses in Field‐Exposed Contaminated Sediments. Environmental Toxicology and Chemistry, 38(8), pp. 1784-1802.  [https://doi.org/10.1002/etc.4454 DOI: 10.1002/etc.4454]</ref>.
 
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In general, sediment toxicity tests focus on either (acute) lethality in whole organisms (typically benthic infaunal species such as amphipods and polychaetes) following short-term or acute exposures (<14 days) or (chronic) sublethal responses (e.g., reduced growth or reproduction or both) following longer-term exposures<ref name="Simpson2016a"/>. It is not unusual in sediment risk assessment to rely on more than one sediment bioassay. Both acute and chronic tests involving either solid-phase or pore-water sediment fractions can be useful to discern the contributions of different contaminants in whole sediment by examining the response of different endpoints in different test organisms<ref name="Keddy1995"/><ref name="Giesy1990"/>. The application of more specialized techniques such as toxicity identification evaluations (TIEs) have also proved useful to help identify contaminants or contaminant classes most likely responsible for toxicity and to exclude potentially confounding factors such as ammonia<ref name="Ho2013">Ho, K.T. and Burgess, R.M., 2013. What's causing toxicity in sediments? Results of 20 years of toxicity identification and evaluations. Environmental Toxicology and Chemistry, 32(11), pp. 2424-2432.  [https://doi.org/10.1002/etc.2359 DOI: 10.1002/etc.2359]</ref><ref name="Bailey2016">Bailey, H.C., Curran, C.A., Arth, P., Lo, B.P. and Gossett, R., 2016. Application of sediment toxicity identification evaluation techniques to a site with multiple contaminants. Environmental Toxicology and Chemistry, 35(10), pp. 2456-2465.  [https://doi.org/10.1002/etc.3488 DOI: 10.1002/etc.3488]</ref>.
 
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===Uncertainty===
 
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As part of the overall analysis of risk from exposure to certain sediment conditions, it is generally understood there is a moderate degree of uncertainty associated with sampling and the environmental fate of contaminants; an order of magnitude of uncertainty associated with ecological exposure and dose-response; and greater than an order of magnitude of uncertainty associated with the quantification of potential human health effects<ref name="DiGuardo2018">Di Guardo, A., Gouin, T., MacLeod, M. and Scheringer, M., 2018. Environmental fate and exposure models: advances and challenges in 21st century chemical risk assessment. Environmental Science: Processes and Impacts, 20(1), pp. 58-71.  [https://doi.org/10.1039/C7EM00568G DOI: 10.1039/C7EM00568G]&nbsp;&nbsp;  [https://pubs.rsc.org/en/content/articlehtml/2018/em/c7em00568g  Open access article]</ref>. The sources of uncertainty and significance to sediment risk assessment can vary widely, thereby affecting confidence in the decisions made based on risk assessment<ref name="Reckhow1994">Reckhow, K.H., 1994. Water quality simulation modeling and uncertainty analysis for risk assessment and decision making. Ecological Modelling, 72(1-2), pp.1-20.  [https://doi.org/10.1016/0304-3800(94)90143-0 DOI: 10.1016/0304-3800(94)90143-0]</ref><ref name="Chapman2002">Chapman, P.M., Ho, K.T., Munns Jr, W.R., Solomon, K. and Weinstein, M.P., 2002. Issues in sediment toxicity and ecological risk assessment. Marine Pollution Bulletin, 44(4), pp. 271-278.  [https://doi.org/10.1016/S0025-326X(01)00329-0 DOI: 10.1016/S0025-326X(01)00329-0]</ref>.
 
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Consequently, technical guidance in several countries encourages including a quantitative uncertainty analysis in sediment risk assessment<ref name="USEPA2005"/><ref name="Tarazona2014"/><ref name="Apitz2005a"/><ref name="Apitz2005b"/>. The aim of uncertainty analysis is to express either quantitatively or qualitatively the limitations inherent in predicting exposures and effects and, ultimately, the level of overall risk posed by sediment conditions<ref name="Batley2002">Batley, G.E., Burton, G.A., Chapman, P.M. and Forbes, V.E., 2002. Uncertainties in Sediment Quality Weight-of-Evidence (WOE) Assessments. Human and Ecological Risk Assessment, 8(7), pp. 1517-1547.  [https://doi.org/10.1080/20028091057466 DOI: 10.1080/20028091057466]</ref>. Sediment risk assessment increasingly relies on a weight-of-evidence process to improve the certainty of conclusions about whether or not impairment exists due to sediment contamination, and, if so, which stressors and biological species (or ecological responses) are of greatest concern<ref name="Burton2002">Burton, G.A., Batley, G.E., Chapman, P.M., Forbes, V.E., Smith, E.P., Reynoldson, T., Schlekat, C.E., Besten, P.J.D., Bailer, A.J., Green, A.S. and Dwyer, R.L., 2002. A Weight-of-Evidence Framework for Assessing Sediment (or Other) Contamination: Improving Certainty in the Decision-Making Process. Human and Ecological Risk Assessment, 8(7), pp. 1675-1696.  [https://doi.org/10.1080/20028091056854 DOI: 10.1080/20028091056854]</ref>. Recent advancements, including the use of Bayesian networks and geographic information systems, also help capture the range of variability in both measured and predicted exposures and responses<ref name="Holsman2017">Holsman, K., Samhouri, J., Cook, G., Hazen, E., Olsen, E., Dillard, M., Kasperski, S., Gaichas, S., Kelble, C.R., Fogarty, M. and Andrews, K., 2017. An ecosystem‐based approach to marine risk assessment. Ecosystem Health and Sustainability, 3(1), p. e01256.  [https://doi.org/10.1002/ehs2.1256 DOI: 10.1002/ehs2.1256]&nbsp;&nbsp; [https://www.tandfonline.com/doi/full/10.1002/ehs2.1256 Open access article]</ref><ref name="Marcot2019">Marcot, B.G. and Penman, T.D., 2019. Advances in Bayesian network modelling: Integration of modelling technologies. Environmental Modelling and Software, 111, pp. 386-393.  [https://doi.org/10.1016/j.envsoft.2018.09.016 DOI: 10.1016/j.envsoft.2018.09.016]</ref><ref name="Men2019">Men, C., Liu, R., Wang, Q., Guo, L., Miao, Y. and Shen, Z., 2019. Uncertainty analysis in source apportionment of heavy metals in road dust based on positive matrix factorization model and geographic information system. Science of The Total Environment, 652, pp. 27-39.  [https://doi.org/10.1016/j.scitotenv.2018.10.212 DOI: 10.1016/j.scitotenv.2018.10.212]</ref>. The level of sophistication applied to the uncertainty analysis is a subjective consideration and often decided by regulatory pressures, public perceptions and the likely cost (not only economic, but also social and environmental) of mitigating or removing the contamination.
 
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==Role in Sediment Management==
 
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Whether or not remediation of contaminated sediments is warranted depends on the magnitude of direct or indirect health risks to humans, ecological threats to aquatic biota, and the extent of risk reduction that can be achieved by removal or containment of the contamination<ref name="Kvasnicka2020">Kvasnicka, J., Burton Jr, G.A., Semrau, J. and Jolliet, O., 2020. Dredging Contaminated Sediments: Is it Worth the Risks? Environmental Toxicology and Chemistry, 39(3), pp. 515-516.  [https://setac.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/etc.4679 DOI: 10.1002/etc.4679]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/etc.4679 Open access article]</ref>. As all sediment management also introduces risk pathways, such as sediment re-suspension leading to contaminant release, possible impacts due to land, water and energy usage, and risk to workers, remedial decision-making should also consider the risks posed by the remedial process. There are two types of remediation risks inherent in sediment remediation - engineering and biological. Sediment remedy implementation risks are predominantly short-term engineering issues associated with applying the remedy such as worker and community health and safety, equipment failures, and accident rates<ref name="Wenning2006">Wenning, R.J., Sorensen, M. and Magar, V.S., 2006. Importance of Implementation and Residual Risk Analyses in Sediment Remediation. Integrated Environmental Assessment and Management, 2(1), pp. 59-65.  [https://doi.org/10.1002/ieam.5630020111 DOI: 10.1002/ieam.5630020111]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.5630020111 Open access article]</ref>. Sediment residual risks are predominantly longer-term changes in exposure and effects to humans, aquatic biota, and wildlife after the remedy has been implemented<ref name="Wenning2006"/>.
 
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In addition to evaluating sediment conditions prior to remediation, sediment risk assessment can be useful to understand how the engineering risks, the contaminant exposure pathways, and which human and wildlife populations are at risk might change with different remediation options<ref name="NRC2001">National Research Council (NRC), 2001. A Risk‐Management Strategy For PCB Contaminated Sediments. Committee On Remediation Of PCB‐Contaminated Sediments, Board On Environmental Studies And Toxicology. National Academies Press, Washington DC. 452 pp. ISBN: 0-309-58873-1 [https://doi.org/10.17226/10041 DOI: 10.17226/10041]&nbsp;&nbsp; Free download from: [https://www.nap.edu/catalog/10041/a-risk-management-strategy-for-pcb-contaminated-sediments The National Academies Press]</ref>. Decision tools such as multi-criteria decision analysis (MCDA), or sustainability assessment<ref name="Apitz2018">Apitz, S.E., Fitzpatrick, A., McNally, A., Harrison, D., Coughlin, C., and Edwards, D.A., 2018. Stakeholder Value-Linked Sustainability Assessment: Evaluating Remedial Alternatives for the Portland Harbor Superfund Site, Portland, Oregon, USA. Integrated Environmental Assessment and Management, 14(1), pp. 43-62. [https://doi.org/10.1002/ieam.1998 DOI: 10.1002/ieam.1998]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.1998 Open access article]</ref><ref name="Fitzpatrick2018">Fitzpatrick, A., Apitz, S.E., Harrison, D., Ruffle, B., and Edwards, D.A., 2018. The Portland Harbor Superfund Site Sustainability Project:  Introduction. Integrated Environmental Assessment and Management, 14(1), pp. 17-21.  [https://doi.org/10.1002/ieam.1997 DOI: 10.1002/ieam.197]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.1997 Open access article]</ref>, for example, incorporate elements from sediment risk assessment to support remediation decision making<ref name="Linkov2006a">Linkov, I., Satterstrom, F.K., Kiker, G., Seager, T.P., Bridges, T., Gardner, K.H., Rogers, S.H., Belluck, D.A. and Meyer, A., 2006. Multicriteria Decision Analysis: A Comprehensive Decision Approach for Management of Contaminated Sediments. Risk Analysis, 26(1), pp. 61-78.  [https://doi.org/10.1111/j.1539-6924.2006.00713.x DOI: 10.1111/j.1539-6924.2006.00713.x]&nbsp;&nbsp; Free download from: [https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1164&context=usarmyceomaha US Army Corps of Engineers]</ref>. Sediment risk assessment also plays an important role in the implementation of monitored natural recovery (MNR) as a remediation strategy<ref name="Magar2006">Magar, V.S. and Wenning, R.J., 2006. The role of monitored natural recovery in sediment remediation. Integrated Environmental Assessment and Management, 2(1), pp. 66-74.  [https://doi.org/10.1002/ieam.5630020112 DOI: 10.1002/ieam.5630020112]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.5630020112 Open access article]</ref>. Insofar as ecological recovery is affected by surface‐sediment‐contaminant concentrations, the primary recovery processes for MNR are natural sediment burial and transformation of the contaminant to less toxic forms by biological or chemical processes<ref name="Magar2009">Magar, V.S., Chadwick, D.B., Bridges, T.S., Fuchsman, P.C., Conder, J.M., Dekker, T.J., Steevens, J.A., Gustavson, K.E. and Mills, M.A., 2009. Technical Guide: Monitored Natural Recovery at Contaminated Sediment Sites. Environmental Security Technology Certification Program (ESTCP) Project ER-0622. 277 pp.  [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Sediments/In-place-Remediation/ER-200622/(language)/eng-US Website]&nbsp;&nbsp; [https://apps.dtic.mil/sti/pdfs/ADA512822.pdf Free download]</ref>.
 
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Since risk reduction is the long‐term goal of contaminated sediment management<ref name="Apitz2002">Apitz, S.E. and Power, E.A., 2002. From Risk Assessment to Sediment Management: An International Perspective. Journal of Soils and Sediments, 2(2), pp. 61-66.  [https://doi.org/10.1007/BF02987872 DOI: 10.1007/BF02987872]&nbsp;&nbsp; Free download from: [https://www.researchgate.net/profile/Sabine-Apitz/publication/225649107_From_risk_assessment_to_sediment_management_An_international_perspective/links/09e4150cb2df7c6331000000/From-risk-assessment-to-sediment-management-An-international-perspective.pdf ResearchGate]</ref>, predicting the rate at which contaminant exposures and risks are mitigated by sedimentation and degradation over time can be aided by including parameters in the risk assessment that calculate the rate of contaminant removal or decay in the sediment. Evaluating sediment management options in terms of risk reduction involves assessing risks under the diverse set of conditions that include the current state of the site as well as the conditions that would occur both during the implementation work and long after the work is complete and the ecosystem stabilizes<ref name="Linkov2006b">Linkov, I., Satterstrom, F.K., Kiker, G.A., Bridges, T.S., Benjamin, S.L. and Belluck, D.A., 2006. From Optimization to Adaptation: Shifting Paradigms in Environmental Management and Their Application to Remedial Decisions. Integrated Environmental Assessment and Management, 2(1), pp. 92-98.  [https://doi.org/10.1002/ieam.5630020116 DOI: 10.1002/ieam.5630020116]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.5630020116 Open access article]</ref><ref name="Reible2003">Reible, D., Hayes, D., Lue-Hing, C., Patterson, J., Bhowmik, N., Johnson, M. and Teal, J., 2003. Comparison of the Long-Term Risks of Removal and In Situ Management of Contaminated Sediments in the Fox River. Soil and Sediment Contamination, 12(3), pp. 325-344.  [https://doi.org/10.1080/713610975 DOI: 10.1080/713610975]</ref>.
 
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==Summary==
 
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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.
 
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==References==
 
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<references />
 
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==See Also==
 

Revision as of 14:04, 29 March 2024

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

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

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Introduction

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

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

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

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

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

PFAS Assembly on Solid Surfaces

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

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

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

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

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

Thermodynamics of PFAS Accumulations on Solid Surfaces

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

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

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

Regulatory Drivers for Transition to PFAS-Free Firefighting Formulations

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

Selection of Replacement PFAS-Free Firefighting Formulations

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

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

Selection of Flushing Agent

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

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

PFAS Verification Testing

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

Rinsate Treatment

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

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

References

  1. ^ 1.0 1.1 1.2 1.3 Lang, J.R., McDonough, J., Guillette, T.C., Storch, P., Anderson, J., Liles, D., Prigge, R., Miles, J.A.L., Divine, C., 2022. Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods. Chemosphere, 308(Part 2), 136254. doi: 10.1016/j.chemosphere.2022.136254   Open Access Article
  2. ^ 2.0 2.1 2.2 Ross, I., and Storch, P., 2020. Foam Transition: Is It as Simple as "Foam Out / Foam In?". The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q2 Supplement, 20 pages. Industry Newsletter
  3. ^ Kappetijn, K., 2023. Replacement of fluorinated extinguishing foam: When is clean clean enough? The Catalyst (Journal of JOIFF, The International Organization for Industrial Emergency Services Management), Q1 2023, pp. 31-33. Industry Newsletter
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See Also

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

Arcadis blog on Fluoro FighterTM

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

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

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