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==PFAS Soil Remediation Technologies==
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==Remediation of Stormwater Runoff Contaminated by Munition Constituents==  
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] are mobile in the subsurface and highly resistant to natural degradation processes, therefore soil source areas can be ongoing sources of groundwater contamination. The United States Environmental Protection Agency (US EPA) has not promulgated soil standards for any PFAS, although a handful of states have for select compounds. Soil standards issued for protection of groundwater are in the single digit part per billion range, which is a very low threshold for soil impacts. Well developed soil treatment technologies are limited to capping, excavation with incineration or disposal, and soil stabilization with sorptive amendments. At present, no in situ destructive soil treatment technologies have been demonstrated.
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Past and ongoing military operations have resulted in contamination of surface soil with [[Munitions Constituents | munition constituents (MC)]], which have human and environmental health impacts.  These compounds can be transported off site via stormwater runoff during precipitation events. Technologies to “trap and treat” surface runoff before it enters downstream receiving bodies (e.g., streams, rivers, ponds) (see Figure 1), and which are compatible with ongoing range activities are needed. This article describes a passive and sustainable approach for effective management of munition constituents in stormwater runoff.
 
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'''Related Article(s):'''
 
'''Related Article(s):'''
  
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*[[Munitions Constituents]]
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* [[PFAS Transport and Fate]]
 
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* [[PFAS Sources]]
 
  
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'''Contributor(s):''' [[Jim Hatton]] and [[Bill DiGuiseppi]]
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'''Contributor:''' Mark E. Fuller
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
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*SERDP Project ER19-1106: Development of Innovative Passive and Sustainable Treatment Technologies for Energetic Compounds in Surface Runoff on Active Ranges
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==Background==
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===Surface Runoff Characteristics and Treatment Approaches===
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[[File: FullerFig1.png | thumb | 300 px | Figure 1. Conceptual model of passive trap and treat approach for MC removal from stormwater runoff]]
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During large precipitation events the rate of water deposition exceeds the rate of water infiltration, resulting in surface runoff (also called stormwater runoff). Surface characteristics including soil texture, presence of impermeable surfaces (natural and artificial), slope, and density and type of vegetation all influence the amount of surface runoff from a given land area. The use of passive systems such as retention ponds and biofiltration cells for treatment of surface runoff is well established for urban and roadway runoff. Treatment in those cases is typically achieved by directing runoff into and through a small constructed wetland, often at the outlet of a retention basin, or via filtration by directing runoff through a more highly engineered channel or vault containing the treatment materials. Filtration based technologies have proven to be effective for the removal of metals, organics, and suspended solids<ref>Sansalone, J.J., 1999. In-situ performance of a passive treatment system for metal source control. Water Science and Technology, 39(2), pp. 193-200. [https://doi.org/10.1016/S0273-1223(99)00023-2 doi: 10.1016/S0273-1223(99)00023-2]</ref><ref>Deletic, A., Fletcher, T.D., 2006. Performance of grass filters used for stormwater treatment—A field and modelling study. Journal of Hydrology, 317(3-4), pp. 261-275. [http://dx.doi.org/10.1016/j.jhydrol.2005.05.021 doi: 10.1016/j.jhydrol.2005.05.021]</ref><ref>Grebel, J.E., Charbonnet, J.A., Sedlak, D.L., 2016. Oxidation of organic contaminants by manganese oxide geomedia for passive urban stormwater treatment systems. Water Research, 88, pp. 481-491. [http://dx.doi.org/10.1016/j.watres.2015.10.019 doi: 10.1016/j.watres.2015.10.019]</ref><ref>Seelsaen, N., McLaughlan, R., Moore, S., Ball, J.E., Stuetz, R.M., 2006. Pollutant removal efficiency of alternative filtration media in stormwater treatment. Water Science and Technology, 54(6-7), pp. 299-305. [https://doi.org/10.2166/wst.2006.617 doi: 10.2166/wst.2006.617]</ref>.
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===Surface Runoff on Ranges===
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Surface runoff represents a major potential mechanism through which energetics residues and related materials are transported off site from range soils to groundwater and surface water receptors (Figure 2). This process is particularly important for energetics that are water soluble (e.g., [[Wikipedia: Nitrotriazolone | NTO]] and [[Wikipedia: Nitroguanidine | NQ]]) or generate soluble daughter products (e.g., [[Wikipedia: 2,4-Dinitroanisole | DNAN]] and [[Wikipedia: TNT | TNT]]). While traditional MC such as [[Wikipedia: RDX | RDX]] and [[Wikipedia: HMX | HMX]] have limited aqueous solubility, they also exhibit recalcitrance to degrade under most natural conditions. RDX and [[Wikipedia: Perchlorate | perchlorate]] are frequent groundwater contaminants on military training ranges. While actual field measurements of energetics in surface runoff are limited, laboratory experiments have been performed to predict mobile energetics contamination levels based on soil mass loadings<ref>Cubello, F., Polyakov, V., Meding, S.M., Kadoya, W., Beal, S., Dontsova, K., 2024. Movement of TNT and RDX from composition B detonation residues in solution and sediment during runoff. Chemosphere, 350, Article 141023. [https://doi.org/10.1016/j.chemosphere.2023.141023 doi: 10.1016/j.chemosphere.2023.141023]</ref><ref>Karls, B., Meding, S.M., Li, L., Polyakov, V., Kadoya, W., Beal, S., Dontsova, K., 2023. A laboratory rill study of IMX-104 transport in overland flow. Chemosphere, 310, Article 136866. [https://doi.org/10.1016/j.chemosphere.2022.136866 doi: 10.1016/j.chemosphere.2022.136866]&nbsp; [[Media: KarlsEtAl2023.pdf | Open Access Article]]</ref>.
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==Toxicological Effects of PFAS==
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The characterization of toxicological effects in human health risk assessments is based on toxicological studies of mammalian exposures to per- and polyfluoroalkyl substances (PFAS), primarily studies involving [[Wikipedia:Perfluorooctanesulfonic acid | perfluorooctanesulfonic acid (PFOS)]] and [[Wikipedia:Perfluorooctanoic acid|perfluorooctanoic acid (PFOA)]]. The most sensitive noncancer adverse effects involve the liver and kidney, immune system, and various developmental and reproductive endpoints<ref name="USEPA2024b">United States Environmental Protection Agency (USEPA), 2024. Per- and Polyfluoroalkyl Substances (PFAS) Final PFAS National Primary Drinking Water Regulation. [https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas Website]</ref>. A select number of PFAS have been evaluated for carcinogenicity, primarily using epidemiological data. Only PFOS and PFOA (and their derivatives) have sufficient data for USEPA to characterize as ''Likely to Be Carcinogenic to Humans'' via the oral route of exposure. Epidemiological studies provided evidence of bladder, prostate, liver, kidney, and breast cancers in humans related to PFOS exposure, as well as kidney and testicular cancer in humans and limited evidence of breast cancer related to PFOA exposure<ref name="USEPA2024b"/><ref name="USEPA2016a">United States Environmental Protection Agency (USEPA), 2016. Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS). Office of Water, EPA 822-R-16-004. [https://www.epa.gov/sites/production/files/2016-05/documents/pfos_health_advisory_final-plain.pdf  Free Download]&nbsp; [[Media: USEPA-2016-pfos_health_advisory_final-plain.pdf | Report.pdf]]</ref><ref name="USEPA2016b">United States Environmental Protection Agency (USEPA), 2016b. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA). Office of Water, EPA 822-R-16-005. [https://www.epa.gov/sites/production/files/2016-05/documents/pfoa_health_advisory_final_508.pdf Free Download]&nbsp; [[Media: pfoa_EPA 822-R-16-005.pdf | Report.pdf]]</ref>.
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USEPA’s Integrated Risk Management System (IRIS) Program is developing Toxicological Reviews to improve understanding of the toxicity of several additional PFAS (i.e., not solely PFOA and PFOS). Toxicological Reviews provide an overview of cancer and noncancer health effects based on current literature and, where data are sufficient, derive human health toxicity criteria (i.e., human health oral reference doses and cancer slope factors) that form the basis for risk-based decision making. For risk assessors, these documents provide USEPA reference doses and cancer slope factors that can be used with exposure information and other considerations to assess human health risk. Final Toxicological Reviews have been completed for the following PFAS:
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*Perfluorooctanesulfonic acid (PFOS)
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*Perfluorooctanoic acid (PFOA)
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*Perfluorobutanoic acid (PFBA)
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*Perfluorohexanoic acid (PFHxA)
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*Perfluorobutane sulfonic acid (PFBS)
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*Perfluoropropionic acid (PFPrA)
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*Perfluorohexane sulfonic acid (PFHxS)
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*Lithium bis[(trifluoromethyl)sulfonyl]azanide (HQ-115)
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*Hexafluoropropylene oxide dimer acid (HFPO DA) and its Ammonium Salt
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Toxicity assessments are ongoing for the following PFAS:
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*Perfluorononanoic acid (PFNA)
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*Perfluorodecanoic acid (PFDA)
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It is important to note human health toxicity criteria for inhalation of PFAS are not included in the Final Toxicological Reviews and are not currently available.
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In addition to IRIS, state agencies have developed peer-reviewed provisional toxicity values that have been incorporated into USEPA’s RSLs, which are updated biannually. These values have not been reviewed by or incorporated into IRIS.
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With respect to ecological toxicity, effects on reproduction, growth, and development of avian and mammalian wildlife have been documented in controlled laboratory studies of exposures of standard toxicological test species (e.g., mice, quail) to PFAS. Many of these studies have been reviewed<ref name="ConderEtAl2020"> Conder, J., Arblaster, J., Larson, E., Brown, J., Higgins, C., 2020. Guidance for Assessing the Ecological Risks of PFAS to Threatened and Endangered Species at Aqueous Film Forming Foam-Impacted Sites. Strategic Environmental Research and Development Program (SERDP) Project ER 18-1614. [https://serdp-estcp.mil/projects/details/3f890c9b-7f72-4303-8d2e-52a89613b5f6 Project Website]&nbsp; [[Media: ER18-1614_Guidance.pdf | Guidance Document]]</ref><ref name="GobasEtAl2020">Gobas, F.A.P.C., Kelly, B.C., Kim, J.J., 2020. Final Report: A Framework for Assessing Bioaccumulation and Exposure Risks of PFAS in Threatened and Endangered Species on AFFF-Impacted Sites. SERDP Project ER18-1502. [https://serdp-estcp.mil/projects/details/09c93894-bc73-404a-8282-51196c4be163 Project Website]&nbsp; [[Media: ER18-1502_Final.pdf | Final Report]]</ref><ref name="Suski2020">Suski, J.G., 2020. Investigating Potential Risk to Threatened and Endangered Species from Per- and Polyfluoroalkyl Substances (PFAS) on Department of Defense (DoD) Sites. SERDP Project ER18-1626. [https://serdp-estcp.mil/projects/details/c328f8e3-95a4-4820-a0d4-ef5835134636 Project Website]&nbsp; [[Media: ER18-1626_Final.pdf | Report.pdf]]</ref><ref name="ZodrowEtAl2021a">Zodrow, J.M., Frenchmeyer, M., Dally, K., Osborn, E., Anderson, P. and Divine, C., 2021. Development of Per and Polyfluoroalkyl Substances Ecological Risk-Based Screening Levels. Environmental Toxicology and Chemistry, 40(3), pp. 921-936. [https://doi.org/10.1002/etc.4975 doi: 10.1002/etc.4975]&nbsp;&nbsp; [[Media: ZodrowEtAl2021a.pdf | Open Access Article]]</ref> to derive ecological Toxicity Reference Values (TRVs). TRVs can be used alongside exposure information and other considerations to assess ecological risk. Avian and mammalian wildlife receptors are generally expected to have the highest risks due to PFAS exposure. Direct toxicity to aquatic life, such as fish and invertebrates, from exposure to sediment and surface water also occurs, though concentrations in water associated with adverse effects to aquatic life are generally higher than those that could result in adverse effects to aquatic-dependent wildlife. Soil invertebrates and plants are less sensitive to PFAS when compared to terrestrial wildlife, with risk-based PFAS concentrations in soil being much higher than those associated with potential effects to terrestrial wildlife<ref name="ZodrowEtAl2021a"/>.
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==PFAS Screening Levels for Human Health and Ecological Risk Assessments==
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===Human Health Screening Levels===
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Human health screening levels for PFAS have been modified multiple times over the last decade and, in the United States, are currently available for drinking water and soil exposures as Maximum Contaminant Levels (MCLs) and USEPA Regional Screening Levels (RSLs). USEPA finalized a National Primary Drinking Water Regulation (NPDWR) for six PFAS<ref name="USEPA2024b"/>:
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*Perfluorooctanoic acid (PFOA)
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*Perfluorooctane sulfonic acid (PFOS)
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*Perfluorohexane sulfonic acid (PFHxS)
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*Perfluorononanoic acid (PFNA)
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*Hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX chemicals)
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*Perfluorobutane sulfonic acid (PFBS)
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MCLs are enforceable drinking water standards based on the most recently available toxicity information that consider available treatment technologies and costs. The MCLs for PFAS include a Hazard Index of 1 for combined exposures to four PFAS. RSLs are developed for use in risk assessments and include soil and tap water screening levels for multiple PFAS. Soil RSLs are based on residential/unrestricted and commercial/industrial land uses, and calculations of site-specific RSLs are available. 
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Internationally, Canada and the European Union have also promulgated drinking water standards for select PFAS. However, large discrepancies exist among the various regulatory organizations, largely due to the different effect endpoints and exposure doses being used to calculate risk-based levels. The PFAS guidance from the Interstate Technology and Regulatory Council (ITRC) in the US includes a regularly updated compilation of screening values for PFAS and is available on their PFAS website<ref name="ITRC2023">Interstate Technology and Regulatory Council (ITRC) 2023. PFAS Technical and Regulatory Guidance Document. [https://pfas-1.itrcweb.org/ ITRC PFAS Website]</ref>: https://pfas-1.itrcweb.org.
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===Ecological Screening Levels===
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Most peer-reviewed literature and regulatory-based environmental quality benchmarks have been developed using data for PFOS and PFOA; however, other select PFAAs have been evaluated for potential effects to aquatic receptors<ref name="ITRC2023"/><ref name="ZodrowEtAl2021a"/><ref name="ConderEtAl2020"/>. USEPA has developed water quality criteria for aquatic life<ref name="USEPA2022"> United States Environmental Protection Agency (USEPA), 2022. Fact Sheet: Draft 2022 Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS)). Office of Water, EPA 842-D-22-005. [[Media: USEPA2022.pdf | Fact Sheet]]</ref><ref name="USEPA2024c">United States Environmental Protection Agency (USEPA), 2024. Final Freshwater Aquatic Life Ambient Water Quality Criteria and Acute Saltwater Aquatic Life Benchmark for Perfluorooctanoic Acid (PFOA). Office of Water, EPA-842-R-24-002. [[Media: USEPA2024c.pdf | Report.pdf]]</ref><ref name="USEPA2024d">United States Environmental Protection Agency (USEPA), 2024. Final Freshwater Aquatic Life Ambient Water Quality Criteria and Acute Saltwater Aquatic Life Benchmark for Perfluorooctane Sulfonate (PFOS). Office of Water, EPA-842-R-24-003. [[Media: USEPA2024d.pdf | Report.pdf]]</ref> for PFOA and PFOS. Following extensive reviews of the peer-reviewed literature, Zodrow ''et al.''<ref name="ZodrowEtAl2021a"/> used the USEPA Great Lakes Initiative methodology<ref>United States Environmental Protection Agency (USEPA), 2012. Water Quality Guidance for the Great Lakes System. Part 132. [https://www.govinfo.gov/app/details/CFR-2013-title40-vol23/CFR-2013-title40-vol23-part132 Government Website]&nbsp; [[Media: CFR-2013-title40-vol23-part132.pdf | Part132.pdf]]</ref> to calculate acute and chronic screening levels for aquatic life for 23 PFAS. The Argonne National Laboratory has also developed Ecological Screening Levels for multiple PFAS<ref name="GrippoEtAl2024">Grippo, M., Hayse, J., Hlohowskyj, I., Picel, K., 2024. Derivation of PFAS Ecological Screening Values - Update. Argonne National Laboratory Environmental Science Division. [[Media: GrippoEtAl2024.pdf | Report.pdf]]</ref>. In contrast to surface water aquatic life benchmarks, sediment benchmark values are limited. For terrestrial systems, screening levels for direct exposure of soil plants and invertebrates to PFAS in soils have been developed for multiple AFFF-related PFAS<ref name="ConderEtAl2020"/><ref name="ZodrowEtAl2021a"/>, and the Canadian Council of Ministers of Environment developed several draft thresholds protective of direct toxicity of PFOS in soil<ref>Canadian Council of Ministers of the Environment (CCME), 2021. Canadian Soil and Groundwater Quality Guidelines for the Protection of Environmental and Human Health, Perfluorooctane Sulfonate (PFOS). [[Media: CCME2018.pdf | Open Access Government Document]]</ref>.
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Wildlife screening levels for abiotic media are back-calculated from food web models developed for representative receptors. Both Zodrow ''et al.''<ref name="ZodrowEtAl2021a"/> and Grippo ''et al.''<ref name="GrippoEtAl2024"/> include the development of risk-based screening levels for wildlife. The Michigan Department of Community Health<ref>Dykema, L.D., 2015. Michigan Department of Community Health Final Report, USEPA Great Lakes Restoration Initiative (GLRI) Project, Measuring Perfluorinated Compounds in Michigan Surface Waters and Fish. Grant GL-00E01122. [https://www.michigan.gov/documents/mdch/MDCH_GL-00E01122-0_Final_Report_493494_7.pdf Free Download]&nbsp; [[Media: MDCH_Geart_Lakes_PFAS.pdf | Report.pdf]]</ref> derived a provisional PFOS surface water value for avian and mammalian wildlife. In California, the San Francisco Bay Regional Water Quality Control Board developed terrestrial habitat soil ecological screening levels based on values developed in Zodrow ''et al.''<ref name="ZodrowEtAl2021a"/>. For PFOS only, a dietary screening level (i.e. applicable to the concentration of PFAS measured in dietary items) has been developed for mammals at 4.6 micrograms per kilogram (μg/kg) wet weight (ww), and for avians at 8.2 μg/kg ww<ref>Environment and Climate Change Canada, 2018. Federal Environmental Quality Guidelines, Perfluorooctane Sulfonate (PFOS). [[Media: ECCC2018.pdf | Repoprt.pdf]]</ref>.
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==Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Human Health==
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Exposure pathways and effects for select PFAS are well understood, such that standard human health risk assessment approaches can be used to quantify risks for populations relevant to a site. Human health exposures via drinking water have been the focus in risk assessments and investigations at PFAS sites<ref>Post, G.B., Cohn, P.D., Cooper, K.R., 2012. Perfluorooctanoic acid (PFOA), an emerging drinking water contaminant: A critical review of recent literature. Environmental Research, 116, pp. 93-117. [https://doi.org/10.1016/j.envres.2012.03.007 doi: 10.1016/j.envres.2012.03.007]</ref><ref>Guelfo, J.L., Marlow, T., Klein, D.M., Savitz, D.A., Frickel, S., Crimi, M., Suuberg, E.M., 2018. Evaluation and Management Strategies for Per- and Polyfluoroalkyl Substances (PFASs) in Drinking Water Aquifers: Perspectives from Impacted U.S. Northeast Communities. Environmental Health Perspectives,126(6), 13 pages. [https://doi.org/10.1289/EHP2727 doi: 10.1289/EHP2727]&nbsp; [[Media: GuelfoEtAl2018.pdf | Open Access Article]]</ref>. Risk assessment approaches for PFAS in drinking water follow typical, well-established drinking water risk assessment approaches for chemicals as detailed in regulatory guidance documents for various jurisdictions.
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Incidental exposures to soil and dusts for PFAS can occur during a variety of soil disturbance activities, such as gardening and digging, hand-to-mouth activities, and intrusive groundwork by industrial or construction workers. As detailed by the ITRC<ref name="ITRC2023"/>, many US states and USEPA have calculated risk-based screening levels for these soil and drinking water pathways (and many also include dermal exposures to soils) using well-established risk assessment guidance.
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Field and laboratory studies have shown that some PFCAs and PFSAs bioaccumulate in fish and other aquatic life at rates that could result in relevant dietary PFAS exposures for consumers of fish and other seafood<ref>Martin, J.W., Mabury, S.A., Solomon, K.R., Muir, D.C., 2003. Dietary accumulation of perfluorinated acids in juvenile rainbow trout (Oncorhynchus mykiss). Environmental Toxicology and Chemistry, 22(1), pp.189-195. [https://doi.org/10.1002/etc.5620220125 doi: 10.1002/etc.5620220125]</ref><ref>Martin, J.W., Mabury, S.A., Solomon, K.R., Muir, D.C., 2003. Bioconcentration and tissue distribution of perfluorinated acids in rainbow trout (Oncorhynchus mykiss). Environmental Toxicology and Chemistry, 22(1), pp.196-204. [https://doi.org/10.1002/etc.5620220126 doi: 10.1002/etc.5620220126]</ref><ref>Chen, F., Gong, Z., Kelly, B.C., 2016. Bioavailability and bioconcentration potential of perfluoroalkyl-phosphinic and -phosphonic acids in zebrafish (Danio rerio): Comparison to perfluorocarboxylates and perfluorosulfonates. Science of The Total Environment, 568, pp. 33-41. [https://doi.org/10.1016/j.scitotenv.2016.05.215 doi: 10.1016/j.scitotenv.2016.05.215]</ref><ref>Fang, S., Zhang, Y., Zhao, S., Qiang, L., Chen, M., Zhu, L., 2016. Bioaccumulation of per fluoroalkyl acids including the isomers of perfluorooctane sulfonate in carp (Cyprinus carpio) in a sediment/water microcosm. Environmental Toxicology and Chemistry, 35(12), pp. 3005-3013. [https://doi.org/10.1002/etc.3483 doi: 10.1002/etc.3483]</ref><ref>Bertin, D., Ferrari, B.J.D. Labadie, P., Sapin, A., Garric, J., Budzinski, H., Houde, M., Babut, M., 2014. Bioaccumulation of perfluoroalkyl compounds in midge (Chironomus riparius) larvae exposed to sediment. Environmental Pollution, 189, pp. 27-34. [https://doi.org/10.1016/j.envpol.2014.02.018  doi: 10.1016/j.envpol.2014.02.018]</ref><ref>Bertin, D., Labadie, P., Ferrari, B.J.D., Sapin, A., Garric, J., Geffard, O., Budzinski, H., Babut. M., 2016. Potential exposure routes and accumulation kinetics for poly- and perfluorinated alkyl compounds for a freshwater amphipod: Gammarus spp. (Crustacea). Chemosphere, 155, pp. 380-387. [https://doi.org/10.1016/j.chemosphere.2016.04.006 doi: 10.1016/j.chemosphere.2016.04.006]</ref><ref>Dai, Z., Xia, X., Guo, J., Jiang, X., 2013. Bioaccumulation and uptake routes of perfluoroalkyl acids in Daphnia magna. Chemosphere, 90(5), pp.1589-1596. [https://doi.org/10.1016/j.chemosphere.2012.08.026 doi: 10.1016/j.chemosphere.2012.08.026]</ref><ref>Prosser, R.S., Mahon, K., Sibley, P.K., Poirier, D., Watson-Leung, T. 2016. Bioaccumulation of perfluorinated carboxylates and sulfonates and polychlorinated biphenyls in laboratory-cultured Hexagenia spp., Lumbriculus variegatus and Pimephales promelas from field-collected sediments. Science of The Total Environment, 543(A), pp. 715-726. [https://doi.org/10.1016/j.scitotenv.2015.11.062 doi: 10.1016/j.scitotenv.2015.11.062]</ref><ref>Rich, C.D., Blaine, A.C., Hundal, L., Higgins, C., 2015. Bioaccumulation of Perfluoroalkyl Acids by Earthworms (Eisenia fetida) Exposed to Contaminated Soils. Environmental Science and Technology, 49(2) pp. 881-888. [https://doi.org/10.1021/es504152d doi: 10.1021/es504152d]</ref><ref>Muller, C.E., De Silva, A.O., Small, J., Williamson, M., Wang, X., Morris, A., Katz, S., Gamberg, M., Muir, D.C.G., 2011. Biomagnification of Perfluorinated Compounds in a Remote Terrestrial Food Chain: Lichen–Caribou–Wolf. Environmental Science and Technology, 45(20), pp. 8665-8673. [https://doi.org/10.1021/es201353v doi: 10.1021/es201353v]</ref>. In addition to fish, terrestrial wildlife can accumulate contaminants from impacted sites, resulting in potential exposures to consumers of wild game<ref name="ConderEtAl2021"/>. Additionally, exposures can occur though consumption of homegrown produce or agricultural products that originate from areas irrigated with PFAS-impacted groundwater, or that are amended with biosolids that contain PFAS, or that contain soils that were directly affected by PFAS releases<ref>Brown, J.B, Conder, J.M., Arblaster, J.A., Higgins, C.P.,  2020. Assessing Human Health Risks from Per- and Polyfluoroalkyl Substance (PFAS)-Impacted Vegetable Consumption: A Tiered Modeling Approach. Environmental Science and Technology, 54(23), pp. 15202-15214. [https://doi.org/10.1021/acs.est.0c03411 doi: 10.1021/acs.est.0c03411]&nbsp; [[Media: BrownEtAl2020.pdf | Open Access Article]]</ref>. Multiple studies have found PFAS can be taken up by plants from soil porewater<ref>Blaine, A.C., Rich, C.D., Hundal, L.S., Lau, C., Mills, M.A., Harris, K.M., Higgins, C.P., 2013. Uptake of Perfluoroalkyl Acids into Edible Crops via Land Applied Biosolids: Field and Greenhouse Studies. Environmental Science and Technology, 47(24), pp. 14062-14069. [https://doi.org/10.1021/es403094q doi: 10.1021/es403094q]&nbsp; [https://www.epa.gov/sites/production/files/2019-11/documents/508_pfascropuptake.pdf Free Download from epa.gov]</ref><ref>Blaine, A.C., Rich, C.D., Sedlacko, E.M., Hyland, K.C., Stushnoff, C., Dickenson, E.R.V., Higgins, C.P., 2014. Perfluoroalkyl Acid Uptake in Lettuce (Lactuca sativa) and Strawberry (Fragaria ananassa) Irrigated with Reclaimed Water. Environmental Science and Technology, 48(24), pp. 14361-14368. [https://doi.org/10.1021/es504150h doi: 10.1021/es504150h]</ref><ref>Ghisi, R., Vamerali, T., Manzetti, S., 2019. Accumulation of perfluorinated alkyl substances (PFAS) in agricultural plants: A review. Environmental Research, 169, pp. 326-341. [https://doi.org/10.1016/j.envres.2018.10.023 doi: 10.1016/j.envres.2018.10.023]</ref>, and livestock can accumulate PFAS from drinking water and/or feed<ref>van Asselt, E.D., Kowalczyk, J., van Eijkeren, J.C.H., Zeilmaker, M.J., Ehlers, S., Furst, P., Lahrssen-Wiederhold, M., van der Fels-Klerx, H.J., 2013. Transfer of perfluorooctane sulfonic acid (PFOS) from contaminated feed to dairy milk. Food Chemistry, 141(2), pp.1489-1495. [https://doi.org/10.1016/j.foodchem.2013.04.035 doi: 10.1016/j.foodchem.2013.04.035]</ref>. Thus, when PFAS are present in surface water bodies where fishing or shellfish harvesting occurs or terrestrial areas where produce is grown or game is hunted, the bioaccumulation of PFAS into dietary items can be an important pathway for human exposure.
  
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*[https://pfas-1.itrcweb.org/12-treatment-technologies/ ITRC Fact Sheet: Treatment Technologies, PFAS – Per- and Polyfluoroalkyl Substances]<ref name="ITRC2020">Interstate Technology and Regulatory Council (ITRC), 2020. PFAS Technical and Regulatory Guidance Document and Fact Sheets, PFAS-1. PFAS Team, Washington, DC. [https://pfas-1.itrcweb.org/ Website]&nbsp;&nbsp; [[Media: ITRC_PFAS-1.pdf | Report.pdf]]</ref>.
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PFAAs such as PFOA and PFOS are not expected to volatilize from PFAS-impacted environmental media<ref name="USEPA2016a"/><ref name="USEPA2016b"/> such as soil and groundwater, which are the primary focus of most site-specific risk assessments. In contrast to non-volatile PFAAs, fluorotelomer alcohols (FTOHs) are among the more widely studied of the volatile PFAS. FTOHs are transient in the atmosphere with a lifetime of 20 days<ref>Ellis, D.A., Martin, J.W., De Silva, A.O., Mabury, S.A., Hurley, M.D., Sulbaek Andersen, M.P., Wallington, T.J., 2004. Degradation of Fluorotelomer Alcohols:  A Likely Atmospheric Source of Perfluorinated Carboxylic Acids. Environmental Science and Technology, 38(12), pp. 3316-3321. [https://doi.org/10.1021/es049860w doi: 10.1021/es049860w]</ref>. At most AFFF sites under evaluation, AFFF releases have occurred many years before such that FTOH may no longer be present. As such, the current assumption is that volatile PFAS, such as FTOHs historically released at the site, will have transformed to stable, low-volatility PFAS, such as PFAAs in soil or groundwater, or will they have diffused to the outdoor atmosphere. There is no evidence that FTOHs or other volatile PFAS are persistent in groundwater or soils such that they present an indoor vapor intrusion pathway risk concern as observed for chlorinated solvents. Ongoing research continues for the vapor pathway<ref name="ITRC2023"/>.
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*Persistence of Perfluoroalkyl Acid Precursors in AFFF-Impacted Groundwater and Soil<ref name="Houtz2013">Houtz, E.F., Higgins, C.P., Field, J.A., and Sedlak, D.L., 2013. Persistence of Perfluoroalkyl Acid Precursors in AFFF-Impacted Groundwater and Soil. Environmental Science and Technology, 47(15), pp. 8187−8195. [https://doi.org/10.1021/es4018877 DOI: 10.1021/es4018877]</ref>.
 
  
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==Introduction==
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General and site-specific human health exposure pathways and risk assessment methods as outlined by USEPA<ref>United States Environmental Protection Agency (USEPA), 1989. Risk Assessment Guidance for Superfund: Volume I, Human Health Evaluation Manual (Part A). Office of Solid Waste and Emergency Response, EPA/540/1-89/002. [https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=10001FQY.txt Free Download]&nbsp; [[Media: USEPA1989.pdf | Report.pdf]]</ref><ref name="USEPA1997">United States Environmental Protection Agency (USEPA), 1997. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments, Interim Final. Office of Solid Waste and Emergency Response, EPA 540-R-97-006. [http://semspub.epa.gov/src/document/HQ/157941 Free Download]&nbsp; [[Media: EPA540-R-97-006.pdf | Report.pdf]]</ref> can be applied to PFAS risk assessments for which human health toxicity values have been developed. Additionally, for risk assessments with dietary exposures of PFAS, standard risk assessment food web modeling can be used to develop initial estimates of dietary concentrations which can be confirmed with site-specific tissue sampling programs.
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PFAS are a class of highly fluorinated compounds including perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and many other compounds with a variety of industrial and consumer uses.  These compounds are often highly resistant to treatment<ref name="Kissa2001">Kissa, Erik, 2001. Fluorinated Surfactants and Repellents: Second Edition. Surfactant Science Series, Volume 97. Marcel Dekker, Inc., CRC Press, New York. 640 pages.  ISBN 978-0824704728</ref> and the more mobile compounds are often problematic in groundwater systems<ref name="Backe2013">Backe, W.J., Day, T.C., and Field, J.A., 2013. Zwitterionic, Cationic, and Anionic Fluorinated Chemicals in Aqueous Film Forming Foam Formulations and Groundwater from U.S. Military Bases by Nonaqueous Large-Volume Injection HPLC-MS/MS. Environmental Science and Technology, 47(10), pp. 5226-5234. [https://doi.org/10.1021/es3034999 DOI: 10.1021/es3034999]</ref>. The US EPA has published lifetime drinking water health advisories for the combined concentration of 70 nanograms per liter (ng/L) for two common and recalcitrant PFAS: PFOS, a perfluoroalkyl sulfonic acid (PFSA), and PFOA, a perfluoroalkyl carboxylic acid (PFCA)<ref name="EPApfos2016">US Environmental Protection Agency (EPA), 2016. Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS), EPA 822-R-16-004. Office of Water, Health and Ecological Criteria Division, Washington, DC. [https://www.epa.gov/sites/production/files/2016-05/documents/pfos_health_advisory_final-plain.pdf Free download from US EPA]&nbsp;&nbsp; [[Media: USEPA-2016-pfos_health_advisory_final-plain.pdf | Report.pdf]]</ref><ref name="EPApfoa2016">US Environmental Protection Agency (EPA), 2016. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA), EPA 822-R-16-005. Office of Water, Health and Ecological Criteria Division, Washington, DC. [https://www.epa.gov/sites/production/files/2016-05/documents/pfoa_health_advisory_final-plain.pdf Free download from US EPA] &nbsp;&nbsp; [[Media: USEPA-2016-pfoa_health_advisory_final-plain.pdf | Report.pdf]]</ref>.(See [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] for nomenclature.)
 
  
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While many of the earliest sites where these compounds were detected in groundwater were manufacturing sites, some recent detections have been attributed to fire training activities associated with aqueous film-forming foams (AFFF).  AFFF is the US Department of Defense (DoD) designation for Class B firefighting foam containing PFAS, which is required for fighting fires involving petroleum liquids. Fire training areas and other source areas where AFFF was released at the surface have the potential to be ongoing sources of groundwater contamination<ref name="Houtz2013"/>. (See also [[PFAS Sources]].)
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==Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Ecological==
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Information available currently on exposures and effects of PFAS in ecological receptors indicate that the PFAS ecological risk issues at most sites are primarily associated with risks to vertebrate wildlife.  Avian and mammalian wildlife are relatively sensitive to PFAS, and dietary intake via bioaccumulation in terrestrial and aquatic food webs can result in exposures that are dominated by the more accumulative PFAS<ref name="LarsonEtAl2018">Larson, E.S., Conder, J.M., Arblaster, J.A., 2018. Modeling avian exposures to perfluoroalkyl substances in aquatic habitats impacted by historical aqueous film forming foam releases. Chemosphere, 201, pp. 335-341. [https://doi.org/10.1016/j.chemosphere.2018.03.004 doi: 10.1016/j.chemosphere.2018.03.004]</ref><ref name="ConderEtAl2020"/><ref name="ZodrowEtAl2021a"/>. Direct toxicity to aquatic life (e.g., fish, pelagic life, benthic invertebrates, and aquatic plants) can occur from exposure to sediment and surface water at effected sites.  For larger areas, surface water concentrations associated with adverse effects to aquatic life are generally higher than those that could result in adverse effects to aquatic-dependent wildlife. Soil invertebrates and plants are generally less sensitive, with risk-based concentrations in soil being much higher than those associated with potential effects to terrestrial wildlife<ref name="ZodrowEtAl2021a"/>.
  
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No national soil cleanup standards have been promulgated by the US EPA, although Regional Screening Levels (RSLs) have been calculated and published for perfluorobutane sulfonate (PFBS)<ref name="EPA2020">US Environmental Protection Agency (EPA), 2020. Regional Screening Levels (RSLs) – User's Guide. Washington, DC.  [https://www.epa.gov/risk/regional-screening-levels-rsls-users-guide Website]</ref> and data are available to calculate RSLs for PFOA and PFOS<ref name="ITRCwNs2020">Interstate Technology Regulatory Council (ITRC), 2020. PFAS Water and Soil Values Table. PFAS – Per- and Polyfluoroalkyl Substances: PFAS Fact Sheets. [https://pfas-1.itrcweb.org/wp-content/uploads/2020/12/ITRCPFASWaterandSoilValuesTables_NOV-2020-FINAL.xlsx Free download.]&nbsp;&nbsp; [[Media: ITRCPFASWaterandSoilTables2020.xlsx | 2020 Water and Soil Tables (excel file)]]</ref>. Several states have promulgated standards<ref name="AKDEC2020">Alaska Department of Environmental Conservation (AK DEC), 2020. 18 AAC 75, Oil and Other Hazardous Substances Pollution Control. Anchorage, AK.  [https://dec.alaska.gov/media/1055/18-aac-75.pdf Free download.]&nbsp;&nbsp; [[Media: AKDEC2020_18aac75.pdf | Report.pdf]]</ref> or screening levels<ref name="MEDEP2018">Maine Department of Environmental Protection (ME DEP), 2018. Maine Remedial Action Guidelines (RAGs) for Sites Contaminated with Hazardous Substances. Augusta, ME.  [https://www.maine.gov/dep/spills/publications/guidance/rags/ME-Remedial-Action-Guidelines-10-19-18cc.pdf Free download.]&nbsp;&nbsp; [[Media: MEDEP2018.pdf | Report.pdf]]</ref><ref name="EGLE2020">Michigan Department of Environment, Great Lakes, and Energy (EGLE), 2020. Cleanup Criteria Requirements for Response Activity (Formerly the Part 201 Generic Cleanup Criteria and Screening Levels). Remediation and Redevelopment Division, Lansing, MI. [https://www.michigan.gov/egle/0,9429,7-135-3311_4109_9846-251790--,00.html Website]</ref><ref name="NEDEE2018">Nebraska Department of Energy and Environment (NE DEE), 2018. Voluntary Cleanup Program Remedial Goals, Table A-1: Groundwater and Soil Remediation Goals. Lincoln, NE.  [http://www.deq.state.ne.us/Publica.nsf/xsp/.ibmmodres/domino/OpenAttachment/Publica.nsf/D243C2B56E34EA8486256F2700698997/Body/Attach%202-6%20Table%20A-1%20VCP%20LUT%20Sept%202018.pdf Free download.]&nbsp;&nbsp; [[Media: NDEE2018.pdf | Report.pdf]]</ref><ref name="NCDEQ2020">North Carolina Department of Environmental Quality (NC DEQ), 2020. Preliminary Soil Remediation Goals (PSRG) Table. Raleigh, NC.  [https://files.nc.gov/ncdeq/risk-based-remediation/1.Combined-Notes-PSRGs.pdf Free download.]&nbsp;&nbsp; [[Media: NCDEQ2020.pdf | Report.pdf]]</ref><ref name="TCEQ2021">Texas Commission on Environmental Quality (TCEQ), 2021. Texas Risk Reduction Program (TRRP), Tier 1 Protective Concentration Levels (PCL) Tables.  [http://www.tceq.texas.gov/assets/public/remediation/trrp/2021PCL%20Tables.xlsx Free Download.]&nbsp;&nbsp; [[Media: TRRP2021PCLTables.xlsx | 2021 PCL Tables (excel file)]]</ref> for soil concentrations protective of groundwater, which are several orders of magnitude lower than direct dermal exposure guidelines. These single-digit part per billion criteria will likely drive remedial actions in PFAS source areas in the future.  At present, the lack of federally promulgated standards and uncertainty about future standards causes temporary stockpiling of PFAS-impacted soils on sites with soil generated from construction or investigation activities.
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Aquatic life are exposed to PFAS through direct exposure in surface water and sediment. Ecological risk assessment approaches for PFAS for aquatic life follow standard risk assessment approaches. The evaluation of potential risks for aquatic life with direct exposure to PFAS in environmental media relies on comparing concentrations in external exposure media to protective, media-specific benchmarks, including the aquatic life risk-based screening levels discussed above<ref name="ZodrowEtAl2021a"/><ref name="USEPA2024a">United States Environmental Protection Agency (USEPA), 2024. National Recommended Water Quality Criteria - Aquatic Life Criteria Table. [https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table USEPA Website]</ref>.
  
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==Soil Treatment==
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When an area at the point of PFAS release is an industrial setting which does not feature favorable habitats for terrestrial and aquatic-dependent wildlife, the transport mechanisms may allow PFAS to travel offsite. If offsite or downgradient areas contain ecological habitat, then PFAS transported to these areas are expected to pose the highest risk potential to wildlife, particularly those areas that feature aquatic habitat<ref>Ahrens, L., Bundschuh, M., 2014. Fate and effects of poly- and perfluoroalkyl substances in the aquatic environment: A review. Environmental Toxicology and Chemistry, 33(9), pp. 1921-1929. [https://doi.org/10.1002/etc.2663 doi: 10.1002/etc.2663]&nbsp; [[Media: AhrensBundschuh2014.pdf | Open Access Article]]</ref><ref name="LarsonEtAl2018"/>.
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[[File: DiGuiseppi1w2Fig1.PNG |thumb|600px| Figure 1. A full scale PFAS-impacted soil stabilization project at a military base in Australia. Image courtesy of RemBind&trade;.]]
 
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Addressing recalcitrant contaminants in soil has traditionally been done through containment/capping or excavation and off-site disposal or treatment.  Containment/capping may be an acceptable solution for PFAS in some locations. However, containment/capping is not considered ideal given the history of releases from engineered landfills and restrictions on use of land containing capped soils. Innovative treatment approaches for PFAS include stabilization with amendments and thermal treatment.
 
  
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===Excavation and Disposal===
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Wildlife receptors, specifically birds and mammals, are typically exposed to PFAS through uptake from dietary sources such as plants and invertebrates, along with direct soil ingestion during foraging activities. Dietary intake modeling typical for ecological risk assessments is the recommended approach for an evaluation of potential risks to wildlife species where PFAS exposure occurs primarily via dietary uptake from bioaccumulation pathways. Dietary intake modeling uses relevant exposure factors for each receptor group (terrestrial birds, terrestrial mammals, aquatic-dependent birds, and aquatic mammals) to determine a total daily intake (TDI) of PFAS via all potential exposure pathways. This approach requires determination of concentrations of PFAS in dietary items, which can be obtained by measuring PFAS in biota at sites or by using food web models to predict concentrations in biota using measured concentrations of PFAS in soil, sediment, or surface water. Food web models use bioaccumulation metrics such as bioaccumulation factors (BAFs) and biomagnification factors (BMFs) with measurements of PFAS in abiotic media to estimate concentrations in dietary items, including plants and benthic or pelagic invertebrates, to model wildlife exposure and calculate TDI. Once site-specific TDI values are calculated, they are compared to known TRVs identified from toxicity data with exposure doses associated with a lack of adverse effects (termed no observed adverse effect level [NOAEL]) or low adverse effects (termed lowest observed adverse effect level [LOAEL]), per standard risk assessment practice<ref name="USEPA1997"/>.
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Excavation and off-site disposal or treatment of PFAS-impacted soils is the only well-developed treatment technology option and may be acceptable for small quantities of soil, such as those generated during characterization activities (i.e., investigation derived waste, IDW). Disposal in non-hazardous landfills is allowable in most states. However, some landfill operators are choosing to restrict acceptance of PFAS-containing waste and soils as a protection against future liability. In addition, the US EPA and some states are considering or have designated PFOA and PFOS as hazardous substances,  which would reduce the number of facilities where disposal of PFAS-contaminated soil would be allowed<ref name="EPA2019">US Environmental Protection Agency (EPA), 2019. EPA’s Per- and Polyfluoroalkyl Substances (PFAS) Action Plan: EPA 823R18004. Washington, DC.  [https://www.epa.gov/pfas/epas-pfas-action-plan Website]&nbsp;&nbsp; [[Media: EPA823R18004.pdf | Report.pdf]]&nbsp;&nbsp; [[Media: EPA100K20002.pdf | 2020 Update]]</ref>. Treatment of excavated soils is commonly performed using incineration or other high temperature thermal methods<ref name="ITRC2020"/>. Recent negative publicity regarding incomplete combustion of PFAS in incinerators<ref name="Hogue2020">Cheryl Hogue, 2020. Incineration may spread, not break down PFAS. Chemical and Engineering News, American Chemical Society.  [https://cen.acs.org/environment/persistent-pollutants/Incincerators-spread-break-down-PFAS/98/web/2020/04 Website]&nbsp;&nbsp; [[Media: Hogue2020.pdf | Report.pdf]]</ref> has caused some states to ban PFAS incineration<ref name="NYSS2020">New York State Senate, 2020. An ACT prohibiting the incineration of aqueous film-forming foam containing perfluoroalkyl and polyfluoroalkyl substances in certain cities. [https://www.nysenate.gov/legislation/bills/2019/s7880/amendment/b Website]&nbsp;&nbsp; [[Media: NYsenate2020.pdf | Report.pdf]]</ref>.
 
  
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===Stabilization===
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Recently, Conder ''et al.''<ref name="ConderEtAl2020"/>, Gobas ''et al.''<ref name="GobasEtAl2020"/>, and Zodrow ''et al.''<ref name="ZodrowEtAl2021a"/> compiled bioaccumulation modeling parameters and approaches for terrestrial and aquatic food web modeling of a variety of commonly detected PFAS at AFFF sites. There are also several sources of TRVs which can be relied upon for estimating TDI values<ref name="ConderEtAl2020"/><ref name="GobasEtAl2020"/><ref name="ZodrowEtAl2021a"/><ref>Newsted, J.L., Jones, P.D., Coady, K., Giesy, J.P., 2005. Avian Toxicity Reference Values for Perfluorooctane Sulfonate. Environmental Science and Technology, 39(23), pp. 9357-9362. [https://doi.org/10.1021/es050989v doi: 10.1021/es050989v]</ref><ref name="Suski2020"/>. In general, the highest risk for PFAS is expected for smaller insectivore and omnivore receptors (e.g., shrews and other small rodents, small nonmigratory birds), which tend to be lower in trophic level and spend more time foraging in small areas similar to or smaller in size than the impacted area. Compared to smaller, lower-trophic level organisms, larger mammalian and avian carnivores are expected to have lower exposures from site-specific PFAS sources because they forage over larger areas that may include areas that are not impacted, as compared to small organisms with small home ranges<ref name="LarsonEtAl2018"/><ref name="ConderEtAl2020"/><ref name="GobasEtAl2020"/><ref name="Suski2020"/><ref name="ZodrowEtAl2021a"/>.
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[[File:DiGuiseppi1w2Fig2.PNG|thumb|600px| Figure 2. A portable infrared thermal treatment unit for PFAS-impacted soils<ref name="DiGuiseppi2019"/>.]]
 
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Various amendments have been manufactured to sorb PFAS to reduce leaching from soil.  Although this is a non-destructive approach, stabilization can reduce mass flux from a source area or allow soils to be placed in landfills with reduced potential for leaching. Amendments sorb PFAS through hydrophobic and electrostatic interactions and are applied to soil through ''in situ'' soil mixing or ''ex situ'' stabilization (Figure 1). Effectiveness of amendments varies depending on site conditions, PFAS types present, and mixing conditions<ref name="ITRCwNs2020"/>. Good results have been observed in bench and field scale tests with a variety of cationic clays (natural or chemically modified) and zeolites<ref name="OchoaHerrera2008">Ochoa-Herrera, V., and Sierra-Alvarez, R., 2008. Removal of perfluorinated surfactants by sorption onto granular activated carbon, zeolites and sludge. Chemosphere, 72(10), pp. 1588-1593.  [https://doi.org/10.1016/j.chemosphere.2008.04.029 DOI: 10.1016/j.chemosphere.2008.04.029]</ref><ref name="Rattanaoudom2012">Rattanaoudom, R., Visvanathan, C., and Boontanon, S.K., 2012. Removal of Concentrated PFOS and PFOA in Synthetic Industrial Wastewater by Powder Activated Carbon and Hydrotalcite. Journal of Water Sustainability, 2(4), pp. 245-248.  [http://www.jwsponline.com/uploadpic/Magazine/pp%20245-258.pdf Open access article.]&nbsp;&nbsp; [[Media: Rattanaoudom2012.pdf | Report.pdf]]</ref><ref name="Ziltek2017">Ziltek, 2017. RemBind: Frequently Asked Questions.  [https://static1.squarespace.com/static/5c5503db4d546e22f6d2feb2/t/5c733787f9619ae6c84674c9/1551054727451/RemBind+FAQs.pdf Free download]&nbsp;&nbsp; [[Media: RemBind2017.pdf | Report.pdf]]</ref>. Bench-scale tests have shown that activated carbon sorbents reduce leachability of PFAS from soils<ref name="Du2014">Du, Z., Deng, S., Bei, Y., Huang, Q., Wang, B., Huang, J. and Yu, G., 2014. Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents – A review. Journal of Hazardous Materials, 274, pp. 443-454. [https://doi.org/10.1016/j.jhazmat.2014.04.038 DOI: 10.1016/j.jhazmat.2014.04.038]</ref><ref name="Yu2009">Yu, Q., Zhang, R., Deng, S., Huang, J. and Yu, G., 2009. Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: Kinetic and isotherm study. Water Research, 43(4), pp. 1150-1158.  [https://doi.org/10.1016/j.watres.2008.12.001 DOI: 10.1016/j.watres.2008.12.001]</ref><ref name="Szabo2017">Szabo, J., Hall, J., Magnuson, M., Panguluri, S., and Meiners, G., 2017. Treatment of Perfluorinated Alkyl Substances in Wash Water Using Granular Activated Carbon and Mixed Media, EPA/600/R-17/175. US Environmental Protection Agency (EPA), Washington, DC.  [https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=NHSRC&direntryid=337098 Website]&nbsp;&nbsp; [[Media: EPA600R17175.PDF | Report.pdf]]</ref>.  A commercial product developed in Australia ([https://rembind.com/ RemBind&trade;]) combines the cation exchange binding capability of clays, the hydrophobic sorption and [[Wikipedia: Van der Waals force | van der Waals]] attraction of organic material, and the electrostatic interactions of aluminum hydroxide to create a highly effective soil stabilizer.  This material has been mixed into soil at 1 to 5% ratio by weight in ''ex situ'' applications and been demonstrated to reduce leachability by greater than 99 percent<ref name="Nolan2015">Nolan, A., Anderson, P., McKay, D., Cartwright, L., and McLean, C., 2015. Treatment of PFCs in Soils, Sediments and Water, WC35. Program and Proceedings, CleanUp Conference 2015. Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC Care), Melbourne, Australia. pp. 374-375.  [https://www.crccare.com/files/dmfile/CLEANUP_2015_PROCEEDINGS-web.pdf Free download]&nbsp;&nbsp; [[Media: CRCCare2015.pdf | Report.pdf]]</ref>.
 
  
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===Thermal Treatment===
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Available information regarding PFAS exposure pathways and effects in aquatic life, terrestrial invertebrates and plants, as well as aquatic and terrestrial wildlife allow ecological risk assessment methods to be applied as outlined by USEPA<ref name="USEPA1997"/> to site-specific PFAS risk assessments. Additionally, food web modeling can be used in site-specific PFAS risk assessment to develop initial estimates of dietary concentrations for aquatic and terrestrial wildlife, which can be confirmed with tissue sampling programs at a site.
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[[File:DiGuiseppi1w2Fig3.PNG|thumb|600px| Figure 3. A full scale PFAS-impacted soil washing plant at a military base in Australia<ref name="Grimison2020"/>.]]
 
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''Incineration:'' Incineration is a well-developed technology for organics destruction, including PFAS-impacted soils. Incineration is generally defined as high temperature (>1,100&deg;C) thermal destruction of waste, and PFAS are thought to mineralize at high temperatures.  Generally, incinerators treat off-gasses by thermal oxidation with temperatures as high as 1,400&deg;C, and vaporized combustion products can be captured using condensation and wet scrubbing<ref name="ITRCwNs2020"/>. Some regulatory officials have expressed concern about possible PFAS emissions in off-gas from these incinerators, and the authors are not aware of any published evidence demonstrating complete mineralization of multiple PFAS in incinerators at the time of this posting.  In general, incineration is designed to provide “5 nines of destruction” – destruction of 99.999% of the contaminants, although incinerators are not designed to specifically treat PFAS to this standard. In the absence of approved industry standard test methods, the US EPA is developing off-gas/stack testing procedures capable of detecting PFAS at the levels considered to be harmful<ref name="EPA2018">US Environmental Protection Agency (EPA), 2018. PFAS Research and Development, Community Engagement in Fayetteville, North Carolina.  [https://www.epa.gov/pfas/pfas-community-engagement-north-carolina-meeting-materials Website]&nbsp;&nbsp; [[Media: EPAFayetteville2018.pdf | Report.pdf]]</ref>.  
 
  
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''Thermal Desorption:'' Thermal Desorption of PFAS from soil has been demonstrated at the field scale in Australia and the US (Alaska)<ref name="Nolan2015"/> using a rotary kiln operating at temperatures in the range of 900&deg;C or less with treatment times of 10-15 minutes<ref name="Burke2015">Burke, Jill, 2019. Fairbanks incinerator shows promise for cleaning toxic soil. Channel 2-KTUU, October 8.  [https://www.ktuu.com/content/news/Fairbanks-incinerator-shows-promise-for-cleaning-toxic-soil-562593631.html Website]</ref>. At these temperatures, some PFAS are mineralized, releasing fluorine that must be captured in off-gas treatment systems. Some PFAS would not be destroyed at these temperatures and therefore must be captured in off-gas treatment systems.  Several bench-scale tests have been performed that have narrowed down the optimal temperature for desorption to between 350&deg;C and 400&deg;C<ref name="Hatton2019">Hatton, J., Dasu, K., Richter, R., Fitzpatrick, T., and Higgins, C., 2019. Field Demonstration of Infrared Thermal Treatment of PFAS-impacted Soils from Subsurface Investigations. Strategic Environmental Research and Development Program (SERDP), Project ER18-1603, Alexandria, VA.  [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER18-1603 Website]&nbsp;&nbsp; [[Media: SERDP ER18-1603.pdf | Report.pdf]]</ref><ref name="DiGuiseppi2019">DiGuiseppi, W., Richter, R., and Riggle, M., 2019. Low Temperature Desorption of Per- and Polyfluoroalkyl Substances. The Military Engineer, 111(719), pp. 52-53. Society of American Military Engineers, Washington, DC.  [http://online.fliphtml5.com/fedq/sdoo/#p=54 Open access article.]&nbsp;&nbsp; [[Media: DiGuiseppi2019.pdf | Report.pdf]]</ref>. A US Department of Defense (DoD) Strategic Environmental Research and Development Program (SERDP) field-scale demonstration was performed in Oregon, where thermal desorption was conducted at 400&deg;C over several days, and the PFAS were captured on vapor-phase activated carbon and incinerated<ref name="Hatton2019"/>. An ''in situ'' thermal desorption project has been funded under the US DoD’s Environmental Security Technology Certification Program (ESTCP) to demonstrate that vadose zone soil can be heated to the requisite 350&deg;C and held there for the appropriate length of time to desorb and capture PFAS from soil source areas<ref name="Iery2020">Iery, R., 2020. In Situ Thermal Treatment of PFAS in the Vadose Zone. US Department of Defense, Environmental Security Technology Certification Program (ESTCP), Project ER20-5250.  [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/Emerging-Issues/ER20-5250 Website]</ref>.
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==PFAS Risk Assessment Data Gaps==
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There are a number of data gaps currently associated with PFAS risk assessment including the following:
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*'''Unmeasured PFAS:''' There are a number of additional PFAS that we know little about and many PFAS that we are unable to quantify in the environment. The approach to dealing with the lack of information on the overwhelming number of PFAS is being debated; in the meantime, however, PFAS beyond PFOS and PFOA are being studied more, and this information will result in improved characterization of risks for other PFAS.   
  
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===Soil Washing===
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*'''Mixtures:''' Another major challenge in effects assessment for PFAS, for both human health risk assessments and environmental risk assessments, is understanding the potential importance of mixtures of PFAS. Considering the limited human health and ecological toxicity data available for just a few PFAS, the understanding of the relative toxicity, additivity, or synergistic effects of PFAS in mixtures is just beginning.
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Soil washing has been applied to PFAS in a handful of pilot projects<ref name="Torneman2012">Torneman, N., 2012. Remedial Methods and Strategies for PFCs. Fourth Joint Nordic Meeting on Remediation of Contaminated Sites, NORDROCS 2012, Oslo, Norway.  [http://nordrocs.org/wp-content/uploads/2012/09/Session-VI-torsdag-1-Torneman-short-paper.pdf Free download.]&nbsp;&nbsp; [[Media: Torneman2012.pdf | Report.pdf]]</ref><ref name="Toase2018">Toase, D., 2018. Application of enhanced soil washing techniques to PFAS contaminated source zones. Emerging Contaminants Summit 2018, Westminster, Colorado.</ref><ref name="Grimison2018">Grimison, C., Barthelme, S., Nolan, A., Cole, J., Morrell, C., 2018. Integrated Soil and Water System for Treatment of PFAS Impacted Source Areas, 18E138P. Australasian Land and Groundwater Association (ALGA), Sydney, Australia.  [https://landandgroundwater.com/media/18E138P_-_Charles_Grimison.pdf Free download.]&nbsp;&nbsp; [[Media: Grimison2018.pdf | Report.pdf]]</ref> and one full-scale implementation in Australia. This approach requires a large-scale engineered plant to handle the various liquid and solid waste streams generated. Soil washing is less suitable for clay-rich soils, where aggregation of the particulates occurs and is difficult to prevent or mitigate. Treatment of the liquid rinse water waste stream is required, which would then rely on conventional water treatment technologies such as granular activated carbon (GAC) or ion exchange. Additionally, in some cases flocculated sludge is generated, which would require treatment or disposal offsite. At present, the only full-scale soil washing demonstration is occurring in Australia, where a vendor has constructed and is operating a 10 million AUD$ treatment plant in anticipation of future treatment of soils generated from remedial actions at Australian Defence installations. Some Australian installations are stockpiling soils due to the lack of cost-effective soil treatment options. According to the vendor, this system generates no solid waste, instead feeding any solids back into the front end of the process for further removal of PFAS<ref name="Grimison2020">Grimison, C., Brookman, I., Hunt, J., and Lucas, J., 2020. Remediation of PFAS-related impacts – ongoing scrutiny and review, Ventia Submission to PFAS Subcommittee of the Joint Standing Committee on Foreign Affairs, Defence and Trade, Australia. [https://www.aph.gov.au/DocumentStore.ashx?id=a209e924-2b7e-4727-bccf-30bef5304bba&subId=691428  Free download.]&nbsp;&nbsp; [[Media: Grimison2020.pdf | Report.pdf]]</ref>.
 
  
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==Conclusions==
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*'''Toxicity Data Gaps:''' For environmental risk assessments, some organisms such as reptiles and benthic invertebrates do not have toxicity data available. Benchmark or threshold concentrations of PFAS in environmental media intended to be protective of wildlife and aquatic organisms suffer from significant uncertainty in their derivation due to the limited number of species for which data are available. As species-specific data becomes available for more types of organisms, the accuracy of environmental risk assessments is likely to improve.  
−
Several well-developed remedial technologies have been applied to address soil contaminated with PFAS.  Unfortunately, none of the available techniques are ideal, with some reducing leachability but leaving the PFAS-impacted soil in place, while others result in destruction of the contaminants but require high energy inputs with associated high cost.  
 
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==References==
 
==References==
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==See Also==
 
==See Also==
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[https://www.atsdr.cdc.gov/pfas/health-studies/index.html Agency for Toxic Substances and Disease Registry (ATSDR) PFAS Health Studies]

Latest revision as of 18:26, 15 October 2025

Remediation of Stormwater Runoff Contaminated by Munition Constituents

Past and ongoing military operations have resulted in contamination of surface soil with munition constituents (MC), which have human and environmental health impacts. These compounds can be transported off site via stormwater runoff during precipitation events. Technologies to “trap and treat” surface runoff before it enters downstream receiving bodies (e.g., streams, rivers, ponds) (see Figure 1), and which are compatible with ongoing range activities are needed. This article describes a passive and sustainable approach for effective management of munition constituents in stormwater runoff.

Related Article(s):


Contributor: Mark E. Fuller

Key Resource(s):

  • SERDP Project ER19-1106: Development of Innovative Passive and Sustainable Treatment Technologies for Energetic Compounds in Surface Runoff on Active Ranges

Background

Surface Runoff Characteristics and Treatment Approaches

File:FullerFig1.png
Figure 1. Conceptual model of passive trap and treat approach for MC removal from stormwater runoff

During large precipitation events the rate of water deposition exceeds the rate of water infiltration, resulting in surface runoff (also called stormwater runoff). Surface characteristics including soil texture, presence of impermeable surfaces (natural and artificial), slope, and density and type of vegetation all influence the amount of surface runoff from a given land area. The use of passive systems such as retention ponds and biofiltration cells for treatment of surface runoff is well established for urban and roadway runoff. Treatment in those cases is typically achieved by directing runoff into and through a small constructed wetland, often at the outlet of a retention basin, or via filtration by directing runoff through a more highly engineered channel or vault containing the treatment materials. Filtration based technologies have proven to be effective for the removal of metals, organics, and suspended solids[1][2][3][4].

Surface Runoff on Ranges

Surface runoff represents a major potential mechanism through which energetics residues and related materials are transported off site from range soils to groundwater and surface water receptors (Figure 2). This process is particularly important for energetics that are water soluble (e.g., NTO and NQ) or generate soluble daughter products (e.g., DNAN and TNT). While traditional MC such as RDX and HMX have limited aqueous solubility, they also exhibit recalcitrance to degrade under most natural conditions. RDX and perchlorate are frequent groundwater contaminants on military training ranges. While actual field measurements of energetics in surface runoff are limited, laboratory experiments have been performed to predict mobile energetics contamination levels based on soil mass loadings[5][6].

Toxicological Effects of PFAS

The characterization of toxicological effects in human health risk assessments is based on toxicological studies of mammalian exposures to per- and polyfluoroalkyl substances (PFAS), primarily studies involving perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The most sensitive noncancer adverse effects involve the liver and kidney, immune system, and various developmental and reproductive endpoints[7]. A select number of PFAS have been evaluated for carcinogenicity, primarily using epidemiological data. Only PFOS and PFOA (and their derivatives) have sufficient data for USEPA to characterize as Likely to Be Carcinogenic to Humans via the oral route of exposure. Epidemiological studies provided evidence of bladder, prostate, liver, kidney, and breast cancers in humans related to PFOS exposure, as well as kidney and testicular cancer in humans and limited evidence of breast cancer related to PFOA exposure[7][8][9].

USEPA’s Integrated Risk Management System (IRIS) Program is developing Toxicological Reviews to improve understanding of the toxicity of several additional PFAS (i.e., not solely PFOA and PFOS). Toxicological Reviews provide an overview of cancer and noncancer health effects based on current literature and, where data are sufficient, derive human health toxicity criteria (i.e., human health oral reference doses and cancer slope factors) that form the basis for risk-based decision making. For risk assessors, these documents provide USEPA reference doses and cancer slope factors that can be used with exposure information and other considerations to assess human health risk. Final Toxicological Reviews have been completed for the following PFAS:

  • Perfluorooctanesulfonic acid (PFOS)
  • Perfluorooctanoic acid (PFOA)
  • Perfluorobutanoic acid (PFBA)
  • Perfluorohexanoic acid (PFHxA)
  • Perfluorobutane sulfonic acid (PFBS)
  • Perfluoropropionic acid (PFPrA)
  • Perfluorohexane sulfonic acid (PFHxS)
  • Lithium bis[(trifluoromethyl)sulfonyl]azanide (HQ-115)
  • Hexafluoropropylene oxide dimer acid (HFPO DA) and its Ammonium Salt

Toxicity assessments are ongoing for the following PFAS:

  • Perfluorononanoic acid (PFNA)
  • Perfluorodecanoic acid (PFDA)

It is important to note human health toxicity criteria for inhalation of PFAS are not included in the Final Toxicological Reviews and are not currently available. In addition to IRIS, state agencies have developed peer-reviewed provisional toxicity values that have been incorporated into USEPA’s RSLs, which are updated biannually. These values have not been reviewed by or incorporated into IRIS.

With respect to ecological toxicity, effects on reproduction, growth, and development of avian and mammalian wildlife have been documented in controlled laboratory studies of exposures of standard toxicological test species (e.g., mice, quail) to PFAS. Many of these studies have been reviewed[10][11][12][13] to derive ecological Toxicity Reference Values (TRVs). TRVs can be used alongside exposure information and other considerations to assess ecological risk. Avian and mammalian wildlife receptors are generally expected to have the highest risks due to PFAS exposure. Direct toxicity to aquatic life, such as fish and invertebrates, from exposure to sediment and surface water also occurs, though concentrations in water associated with adverse effects to aquatic life are generally higher than those that could result in adverse effects to aquatic-dependent wildlife. Soil invertebrates and plants are less sensitive to PFAS when compared to terrestrial wildlife, with risk-based PFAS concentrations in soil being much higher than those associated with potential effects to terrestrial wildlife[13].

PFAS Screening Levels for Human Health and Ecological Risk Assessments

Human Health Screening Levels

Human health screening levels for PFAS have been modified multiple times over the last decade and, in the United States, are currently available for drinking water and soil exposures as Maximum Contaminant Levels (MCLs) and USEPA Regional Screening Levels (RSLs). USEPA finalized a National Primary Drinking Water Regulation (NPDWR) for six PFAS[7]:

  • Perfluorooctanoic acid (PFOA)
  • Perfluorooctane sulfonic acid (PFOS)
  • Perfluorohexane sulfonic acid (PFHxS)
  • Perfluorononanoic acid (PFNA)
  • Hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX chemicals)
  • Perfluorobutane sulfonic acid (PFBS)

MCLs are enforceable drinking water standards based on the most recently available toxicity information that consider available treatment technologies and costs. The MCLs for PFAS include a Hazard Index of 1 for combined exposures to four PFAS. RSLs are developed for use in risk assessments and include soil and tap water screening levels for multiple PFAS. Soil RSLs are based on residential/unrestricted and commercial/industrial land uses, and calculations of site-specific RSLs are available.

Internationally, Canada and the European Union have also promulgated drinking water standards for select PFAS. However, large discrepancies exist among the various regulatory organizations, largely due to the different effect endpoints and exposure doses being used to calculate risk-based levels. The PFAS guidance from the Interstate Technology and Regulatory Council (ITRC) in the US includes a regularly updated compilation of screening values for PFAS and is available on their PFAS website[14]: https://pfas-1.itrcweb.org.

Ecological Screening Levels

Most peer-reviewed literature and regulatory-based environmental quality benchmarks have been developed using data for PFOS and PFOA; however, other select PFAAs have been evaluated for potential effects to aquatic receptors[14][13][10]. USEPA has developed water quality criteria for aquatic life[15][16][17] for PFOA and PFOS. Following extensive reviews of the peer-reviewed literature, Zodrow et al.[13] used the USEPA Great Lakes Initiative methodology[18] to calculate acute and chronic screening levels for aquatic life for 23 PFAS. The Argonne National Laboratory has also developed Ecological Screening Levels for multiple PFAS[19]. In contrast to surface water aquatic life benchmarks, sediment benchmark values are limited. For terrestrial systems, screening levels for direct exposure of soil plants and invertebrates to PFAS in soils have been developed for multiple AFFF-related PFAS[10][13], and the Canadian Council of Ministers of Environment developed several draft thresholds protective of direct toxicity of PFOS in soil[20].

Wildlife screening levels for abiotic media are back-calculated from food web models developed for representative receptors. Both Zodrow et al.[13] and Grippo et al.[19] include the development of risk-based screening levels for wildlife. The Michigan Department of Community Health[21] derived a provisional PFOS surface water value for avian and mammalian wildlife. In California, the San Francisco Bay Regional Water Quality Control Board developed terrestrial habitat soil ecological screening levels based on values developed in Zodrow et al.[13]. For PFOS only, a dietary screening level (i.e. applicable to the concentration of PFAS measured in dietary items) has been developed for mammals at 4.6 micrograms per kilogram (μg/kg) wet weight (ww), and for avians at 8.2 μg/kg ww[22].

Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Human Health

Exposure pathways and effects for select PFAS are well understood, such that standard human health risk assessment approaches can be used to quantify risks for populations relevant to a site. Human health exposures via drinking water have been the focus in risk assessments and investigations at PFAS sites[23][24]. Risk assessment approaches for PFAS in drinking water follow typical, well-established drinking water risk assessment approaches for chemicals as detailed in regulatory guidance documents for various jurisdictions.

Incidental exposures to soil and dusts for PFAS can occur during a variety of soil disturbance activities, such as gardening and digging, hand-to-mouth activities, and intrusive groundwork by industrial or construction workers. As detailed by the ITRC[14], many US states and USEPA have calculated risk-based screening levels for these soil and drinking water pathways (and many also include dermal exposures to soils) using well-established risk assessment guidance.

Field and laboratory studies have shown that some PFCAs and PFSAs bioaccumulate in fish and other aquatic life at rates that could result in relevant dietary PFAS exposures for consumers of fish and other seafood[25][26][27][28][29][30][31][32][33][34]. In addition to fish, terrestrial wildlife can accumulate contaminants from impacted sites, resulting in potential exposures to consumers of wild game[35]. Additionally, exposures can occur though consumption of homegrown produce or agricultural products that originate from areas irrigated with PFAS-impacted groundwater, or that are amended with biosolids that contain PFAS, or that contain soils that were directly affected by PFAS releases[36]. Multiple studies have found PFAS can be taken up by plants from soil porewater[37][38][39], and livestock can accumulate PFAS from drinking water and/or feed[40]. Thus, when PFAS are present in surface water bodies where fishing or shellfish harvesting occurs or terrestrial areas where produce is grown or game is hunted, the bioaccumulation of PFAS into dietary items can be an important pathway for human exposure.

PFAAs such as PFOA and PFOS are not expected to volatilize from PFAS-impacted environmental media[8][9] such as soil and groundwater, which are the primary focus of most site-specific risk assessments. In contrast to non-volatile PFAAs, fluorotelomer alcohols (FTOHs) are among the more widely studied of the volatile PFAS. FTOHs are transient in the atmosphere with a lifetime of 20 days[41]. At most AFFF sites under evaluation, AFFF releases have occurred many years before such that FTOH may no longer be present. As such, the current assumption is that volatile PFAS, such as FTOHs historically released at the site, will have transformed to stable, low-volatility PFAS, such as PFAAs in soil or groundwater, or will they have diffused to the outdoor atmosphere. There is no evidence that FTOHs or other volatile PFAS are persistent in groundwater or soils such that they present an indoor vapor intrusion pathway risk concern as observed for chlorinated solvents. Ongoing research continues for the vapor pathway[14].

General and site-specific human health exposure pathways and risk assessment methods as outlined by USEPA[42][43] can be applied to PFAS risk assessments for which human health toxicity values have been developed. Additionally, for risk assessments with dietary exposures of PFAS, standard risk assessment food web modeling can be used to develop initial estimates of dietary concentrations which can be confirmed with site-specific tissue sampling programs.

Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Ecological

Information available currently on exposures and effects of PFAS in ecological receptors indicate that the PFAS ecological risk issues at most sites are primarily associated with risks to vertebrate wildlife. Avian and mammalian wildlife are relatively sensitive to PFAS, and dietary intake via bioaccumulation in terrestrial and aquatic food webs can result in exposures that are dominated by the more accumulative PFAS[44][10][13]. Direct toxicity to aquatic life (e.g., fish, pelagic life, benthic invertebrates, and aquatic plants) can occur from exposure to sediment and surface water at effected sites. For larger areas, surface water concentrations associated with adverse effects to aquatic life are generally higher than those that could result in adverse effects to aquatic-dependent wildlife. Soil invertebrates and plants are generally less sensitive, with risk-based concentrations in soil being much higher than those associated with potential effects to terrestrial wildlife[13].

Aquatic life are exposed to PFAS through direct exposure in surface water and sediment. Ecological risk assessment approaches for PFAS for aquatic life follow standard risk assessment approaches. The evaluation of potential risks for aquatic life with direct exposure to PFAS in environmental media relies on comparing concentrations in external exposure media to protective, media-specific benchmarks, including the aquatic life risk-based screening levels discussed above[13][45].

When an area at the point of PFAS release is an industrial setting which does not feature favorable habitats for terrestrial and aquatic-dependent wildlife, the transport mechanisms may allow PFAS to travel offsite. If offsite or downgradient areas contain ecological habitat, then PFAS transported to these areas are expected to pose the highest risk potential to wildlife, particularly those areas that feature aquatic habitat[46][44].

Wildlife receptors, specifically birds and mammals, are typically exposed to PFAS through uptake from dietary sources such as plants and invertebrates, along with direct soil ingestion during foraging activities. Dietary intake modeling typical for ecological risk assessments is the recommended approach for an evaluation of potential risks to wildlife species where PFAS exposure occurs primarily via dietary uptake from bioaccumulation pathways. Dietary intake modeling uses relevant exposure factors for each receptor group (terrestrial birds, terrestrial mammals, aquatic-dependent birds, and aquatic mammals) to determine a total daily intake (TDI) of PFAS via all potential exposure pathways. This approach requires determination of concentrations of PFAS in dietary items, which can be obtained by measuring PFAS in biota at sites or by using food web models to predict concentrations in biota using measured concentrations of PFAS in soil, sediment, or surface water. Food web models use bioaccumulation metrics such as bioaccumulation factors (BAFs) and biomagnification factors (BMFs) with measurements of PFAS in abiotic media to estimate concentrations in dietary items, including plants and benthic or pelagic invertebrates, to model wildlife exposure and calculate TDI. Once site-specific TDI values are calculated, they are compared to known TRVs identified from toxicity data with exposure doses associated with a lack of adverse effects (termed no observed adverse effect level [NOAEL]) or low adverse effects (termed lowest observed adverse effect level [LOAEL]), per standard risk assessment practice[43].

Recently, Conder et al.[10], Gobas et al.[11], and Zodrow et al.[13] compiled bioaccumulation modeling parameters and approaches for terrestrial and aquatic food web modeling of a variety of commonly detected PFAS at AFFF sites. There are also several sources of TRVs which can be relied upon for estimating TDI values[10][11][13][47][12]. In general, the highest risk for PFAS is expected for smaller insectivore and omnivore receptors (e.g., shrews and other small rodents, small nonmigratory birds), which tend to be lower in trophic level and spend more time foraging in small areas similar to or smaller in size than the impacted area. Compared to smaller, lower-trophic level organisms, larger mammalian and avian carnivores are expected to have lower exposures from site-specific PFAS sources because they forage over larger areas that may include areas that are not impacted, as compared to small organisms with small home ranges[44][10][11][12][13].

Available information regarding PFAS exposure pathways and effects in aquatic life, terrestrial invertebrates and plants, as well as aquatic and terrestrial wildlife allow ecological risk assessment methods to be applied as outlined by USEPA[43] to site-specific PFAS risk assessments. Additionally, food web modeling can be used in site-specific PFAS risk assessment to develop initial estimates of dietary concentrations for aquatic and terrestrial wildlife, which can be confirmed with tissue sampling programs at a site.

PFAS Risk Assessment Data Gaps

There are a number of data gaps currently associated with PFAS risk assessment including the following:

  • Unmeasured PFAS: There are a number of additional PFAS that we know little about and many PFAS that we are unable to quantify in the environment. The approach to dealing with the lack of information on the overwhelming number of PFAS is being debated; in the meantime, however, PFAS beyond PFOS and PFOA are being studied more, and this information will result in improved characterization of risks for other PFAS.
  • Mixtures: Another major challenge in effects assessment for PFAS, for both human health risk assessments and environmental risk assessments, is understanding the potential importance of mixtures of PFAS. Considering the limited human health and ecological toxicity data available for just a few PFAS, the understanding of the relative toxicity, additivity, or synergistic effects of PFAS in mixtures is just beginning.
  • Toxicity Data Gaps: For environmental risk assessments, some organisms such as reptiles and benthic invertebrates do not have toxicity data available. Benchmark or threshold concentrations of PFAS in environmental media intended to be protective of wildlife and aquatic organisms suffer from significant uncertainty in their derivation due to the limited number of species for which data are available. As species-specific data becomes available for more types of organisms, the accuracy of environmental risk assessments is likely to improve.

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See Also

Agency for Toxic Substances and Disease Registry (ATSDR) PFAS Health Studies

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