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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.

1 Remediation of Stormwater Runoff Contaminated by Munition Constituents
2 Background
- 2.1 Surface Runoff Characteristics and Treatment Approaches
- 2.2 Surface Runoff on Ranges
3 Toxicological Effects of PFAS
4 PFAS Screening Levels for Human Health and Ecological Risk Assessments
- 4.1 Human Health Screening Levels
- 4.2 Ecological Screening Levels
5 Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Human Health
6 Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Ecological
7 PFAS Risk Assessment Data Gaps
8 References
9 See Also

Related Article(s):

Munitions Constituents

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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^ ^44.0 ^44.1 ^44.2 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. doi: 10.1016/j.chemosphere.2018.03.004
^ United States Environmental Protection Agency (USEPA), 2024. National Recommended Water Quality Criteria - Aquatic Life Criteria Table. USEPA Website
^ 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. doi: 10.1002/etc.2663 Open Access Article
^ 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. doi: 10.1021/es050989v

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Latest revision as of 18:26, 15 October 2025

Remediation of Stormwater Runoff Contaminated by Munition Constituents

Contents

Background

Surface Runoff Characteristics and Treatment Approaches

Surface Runoff on Ranges

Toxicological Effects of PFAS

PFAS Screening Levels for Human Health and Ecological Risk Assessments

Human Health Screening Levels

Ecological Screening Levels

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

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

PFAS Risk Assessment Data Gaps

References

See Also

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-==PFAS Treatment by Anion Exchange==
+==Remediation of Stormwater Runoff Contaminated by Munition Constituents==
-<center>
+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.
-{| id="mp-upper" style="margin: auto; width: 95%; margin-top:3px; border-spacing: 0px; "
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-| style="padding:2px; width:100%" |<h2 id="mp-otd-h2" style="margin:3px; background:#cedff2; font-family:inherit; font-size:120%; font-weight:bold; border:1px solid #a3b0bf; text-align:left; color:#000; padding:0.2em 0.4em;">Editorial Board</h2>
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-<!-- {| style="margin: left; text-align:left;" -->
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-| colspan="3" |<span style="line-height: 1em;">'''Editor-in-Chief'''<br /><span style="line-height: 1.2em;">[[Dr. Robert Borden, P.E.|Robert C. Borden, PhD, PE]]
-|-
-| colspan="3" |
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-|}
-{|
-|-
-||'''Editors'''
-| style="width:40px;" | ||
-|-
-||<span style="line-height: 1.1em;">[[Dr. Jason Barnes|Jason Barnes, PhD]]<br />Cascadia College || ||[[Dr. Samuel Beal|Samuel Beal, PhD]]<br />CRREL Research and Development Center
-|-
-|| || ||
-|-
-||<span style="line-height: 1.1em;">[[Craig E. Divine, Ph.D., PG|Craig E. Divine, PhD, PG]]<br />Arcadis || ||[[Dr. Kevin Finneran|Kevin Finneran, PhD]]<br />Finneran Environmental, LLC
-|-
-|| || ||
-|-
-||<span style="line-height: 1.1em;">[[Dr. Upal Ghosh|Upal Ghosh, PhD]]<br />University of Maryland, Baltimore County || ||[[Dr. Rao Kotamarthi| Rao Kotamarthi, PhD]]<br />Argonne National Lab
-|-
-|| || ||
-|-
-||<span style="line-height: 1.1em;">[[Kim Matthews| Kim Matthews]]<br />RTI International || ||[[Dr. Charles Newell, P.E.|Charles Newell, PhD, PE]]<br />GSI Environmental
-|-
-|| || ||
-|-
-||<span style="line-height: 1.1em;"> [[Dr. Alexandra Salter-Blanc|Alexandra Salter-Blanc, PhD]]<br />Jacobs || ||[[Dr. John Wilson|John Wilson, PhD]]<br />Scissortail Environmental Solutions, LLC
-|}
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-{| id="mp-left" style="width:100%; margin:4px 0 0 0; background:none; border-spacing: 0px;"
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-{| id="mp-left" style="width:100%; vertical-align:top; background:#f5faff;"
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-| style="padding:2px; width:100%" |<h2 id="mp-otd-h2_2" style="margin:3px; background:#cedff2; font-family:inherit; font-size:120%; font-weight:bold; border:1px solid #a3b0bf; text-align:left; color:#000; padding:0.2em 0.4em;">Development Team</h2>
-|-
-|
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-|-
-|'''Executive Editor'''
-|-
-|Bilgen Yuncu, PhD, PE
-|-
-|TRC, Cary NC
-|-
-|
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-|-
-||
-|-
-||
-|-
-|''Technical Editor''
-|-
-|Jim Hurley, MS, EIT
-|-
-|TRC, Cary NC
-|-
-||
-|-
-||
-|-
-|''Administrative Assistant''
-|-
-|Debra Tabron
-|-
-|TRC, Cary NC
-|}
-|}
-|}
-|}
-</center>
-[[Wikipedia: Ion exchange | Anion exchange]] has emerged as one of the most effective and economical technologies for treatment of water contaminated by [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]]. Anion exchange resins (AERs) are polymer beads (0.5–1 mm diameter) incorporating cationic adsorption sites that attract anionic PFAS by a combination of electrostatic and hydrophobic mechanisms. Both regenerable and single-use resin treatment systems are being investigated, and results from pilot-scale studies show that AERs can treat much greater volumes of PFAS-contaminated water than comparable amounts of [[Wikipedia: Activated carbon | granular activated carbon (GAC)]] adsorbent media. Life cycle treatment costs and environmental impacts of anion exchange and other adsorbent technologies are highly dependent upon the treatment criteria selected by site managers to determine when media is exhausted and requires replacement or regeneration.
 <div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 '''Related Article(s):'''
-*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
+*[[Munitions Constituents]]
-*[[PFAS Sources]]
-*[[PFAS Transport and Fate]]
-*[[PFAS Ex Situ Water Treatment]]
-*[[Supercritical Water Oxidation (SCWO)]]
-*[[PFAS Treatment by Electrical Discharge Plasma]]
-'''Contributor(s):'''
-*Dr. Timothy J. Strathmann
+'''Contributor:''' Mark E. Fuller
-*Dr. Anderson Ellis
-*Dr. Treavor H. Boyer
 '''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 | thumb | 300 px | 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<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>.
-*Anion Exchange Resin Removal of Per- and Polyfluoroalkyl Substances (PFAS) from Impacted Water: A Critical Review<ref name="BoyerEtAl2021a">Boyer, T.H., Fang, Y., Ellis, A., Dietz, R., Choi, Y.J., Schaefer, C.E., Higgins, C.P., Strathmann, T.J., 2021. Anion Exchange Resin Removal of Per- and Polyfluoroalkyl Substances (PFAS) from Impacted Water: A Critical Review. Water Research, 200, Article 117244. [https://doi.org/10.1016/j.watres.2021.117244 doi: 10.1016/j.watres.2021.117244]&nbsp;&nbsp; [[Special:FilePath/BoyerEtAl2021a.pdf| Open Access Manuscript.pdf]]</ref>
+===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., [[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>.
-*Regenerable Resin Sorbent Technologies with Regenerant Solution Recycling for Sustainable Treatment of PFAS; SERDP Project ER18-1063 Final Report<ref>Strathmann, T.J., Higgins, C.P., Boyer, T., Schaefer, C., Ellis, A., Fang, Y., del Moral, L., Dietz, R., Kassar, C., Graham, C, 2023. Regenerable Resin Sorbent Technologies with Regenerant Solution Recycling for Sustainable Treatment of PFAS; SERDP Project ER18-1063 Final Report. 285 pages. [https://serdp-estcp.org/projects/details/d3ede38b-9f24-4b22-91c9-1ad634aa5384 Project Website]&nbsp;&nbsp; [[Special:FilePath/ER18-1063.pdf| Report.pdf]]</ref>
+==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 [[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>.
+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
-==Introduction==
+Toxicity assessments are ongoing for the following PFAS:
-[[File:StrathmannFig1.png | thumb |300px|Figure 1. Illustration of PFAS adsorption by anion exchange resins (AERs). Incorporation of longer alkyl group side chains on the cationic quaternary amine functional groups leads to PFAS-resin hydrophobic interactions that increase resin selectivity for PFAS over inorganic anions like Cl<sup>-</sup>.]]
+*Perfluorononanoic acid (PFNA)
+*Perfluorodecanoic acid (PFDA)
-[[File:StrathmannFig2.png | thumb | 300px| Figure 2. Effect of perfluoroalkyl carbon chain length on the estimated bed volumes (BVs) to 50% breakthrough of PFCAs and PFSAs observed in a pilot study<ref name="StrathmannEtAl2020">Strathmann, T.J., Higgins, C., Deeb, R., 2020. Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Impacted by PFAS, Final Report - Phase I. SERDP Project ER18-1501. [https://serdp-estcp.mil/projects/details/b34d6396-6b6d-44d0-a89e-6b22522e6e9c Project Website]&nbsp;&nbsp; [[Special:FilePath/ER18-1501.pdf| Report.pdf]]</ref> treating PFAS-contaminated groundwater with the PFAS-selective AER (Purolite PFA694E) ]]
+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.
-Anion exchange is an adsorptive treatment technology that uses polymeric resin beads (0.5–1 mm diameter) that incorporate cationic adsorption sites to remove anionic pollutants from water<ref>SenGupta, A.K., 2017. Ion Exchange in Environmental Processes: Fundamentals, Applications and Sustainable Technology. Wiley. ISBN:9781119157397  [https://onlinelibrary.wiley.com/doi/book/10.1002/9781119421252 Wiley Online Library]</ref>. Anions (e.g., NO<sub>3</sub><sup>-</sup>) are adsorbed by an ion exchange reaction with anions that are initially bound to the adsorption sites (e.g., Cl<sup>-</sup>) during resin preparation. Many per- and polyfluoroalkyl substances (PFAS) of concern, including [[Wikipedia: Perfluorooctanoic acid | perfluorooctanoic acid (PFOA)]] and [[Wikipedia: Perfluorooctanesulfonic acid | perfluorooctane sulfonate (PFOS)]], are present in contaminated water as anionic species that can be adsorbed by anion exchange reactions<ref name="BoyerEtAl2021a" /><ref name="DixitEtAl2021">Dixit, F., Dutta, R., Barbeau, B., Berube, P., Mohseni, M., 2021. PFAS Removal by Ion Exchange Resins: A Review. Chemosphere, 272, Article 129777. [https://doi.org/10.1016/j.chemosphere.2021.129777 doi: 10.1016/j.chemosphere.2021.129777]</ref><ref name="RahmanEtAl2014">Rahman, M.F., Peldszus, S., Anderson, W.B., 2014. Behaviour and Fate of Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) in Drinking Water Treatment: A Review. Water Research, 50, pp. 318–340. [https://doi.org/10.1016/j.watres.2013.10.045 doi: 10.1016/j.watres.2013.10.045]</ref>.
+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"/>.
-<br>
-<center><big>Anion Exchange Reaction:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;'''PFAS<sup>-</sup>'''</big>'''<sub>(aq)</sub><big>&nbsp;+&nbsp;Cl<sup>-</sup></big><sub>(resin bound)</sub><big>&nbsp;&nbsp;&rArr;&nbsp;&nbsp;PFAS<sup>-</sup></big><sub>(resin bound)</sub><big>&nbsp;+&nbsp;Cl<sup>-</sup></big><sub>(aq)</sub>'''</center>
-Resins most commonly applied for PFAS treatment are strong base anion exchange resins (SB-AERs) that incorporate [[Wikipedia: Quaternary ammonium cation | quaternary ammonium]] cationic functional groups with hydrocarbon side chains (R-groups) that promote PFAS adsorption by a combination of electrostatic and hydrophobic mechanisms (Figure 1)<ref name="BoyerEtAl2021a" /><ref>Fuller, Mark. Ex Situ Treatment of PFAS-Impacted Groundwater Using Ion Exchange with Regeneration; ER18-1027. [https://serdp-estcp.mil/projects/details/af660326-56e0-4d3c-b80a-1d8a2d613724 Project Website].</ref>. SB-AERs maintain cationic functional groups independent of water pH. Recently introduced ‘PFAS-selective’ AERs show >1,000,000-fold greater selectivity for some PFAS over the Cl<sup>-</sup> initially loaded onto resins<ref name="FangEtAl2021">Fang, Y., Ellis, A., Choi, Y.J., Boyer, T.H., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2021. Removal of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) Using Ion-Exchange and Nonionic Resins. Environmental Science and Technology, 55(8), pp. 5001–5011. [https://doi.org/10.1021/acs.est.1c00769 doi: 10.1021/acs.est.1c00769]</ref>. These resins also show much higher adsorption capacities for PFAS (mg PFAS adsorbed per gram of adsorbent media) than granular activated carbon (GAC) adsorbents.
-PFAS of concern include a wide range of structures, including [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluoroalkyl carboxylic acids (PFCAs)]] and [[Wikipedia: Perfluorosulfonic acids | perfluoroalkyl sulfonic acids (PFSAs)]] of varying carbon chain length<ref>Interstate Technology Regulatory Council (ITRC), 2023. Technical Resources for Addressing Environmental Releases of Per- and Polyfluoroalkyl Substances (PFAS). [https://pfas-1.itrcweb.org/ ITRC PFAS Website]</ref>. As such, affinity for adsorption to AERs is heavily dependent upon PFAS structure<ref name="BoyerEtAl2021a" /><ref name="DixitEtAl2021" />. In general, it has been found that the extent of adsorption increases with increasing chain length, and that PFSAs adsorb more strongly than PFCAs of similar chain length (Figure 2)<ref name="FangEtAl2021" /><ref>Gagliano, E., Sgroi, M., Falciglia, P.P., Vagliasindi, F.G.A., Roccaro, P., 2020. Removal of Poly- and Perfluoroalkyl Substances (PFAS) from Water by Adsorption: Role of PFAS Chain Length, Effect of Organic Matter and Challenges in Adsorbent Regeneration. Water Research, 171, Article 115381. [https://doi.org/10.1016/j.watres.2019.115381 doi: 10.1016/j.watres.2019.115381]</ref>. The chain length-dependence supports the conclusion that PFAS-resin hydrophobic mechanisms contribute to adsorption. Adsorption of polyfluorinated structures also depend on structure and prevailing charge, with adsorption of zwitterionic species (containing both anionic and cationic groups in the same structure) to AERs being documented despite having a net neutral charge<ref name="FangEtAl2021" />.
+==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<ref name="USEPA2024b"/>:
+*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)
-==Reactors for Treatment of PFAS-Contaminated Water==
+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.
-Anion exchange treatment of water is accomplished by pumping contaminated water through fixed bed reactors filled with AERs (Figure 3). A common configuration involves flowing water through two reactors arranged in a lead-lag configuration<ref name="WoodardEtAl2017">Woodard, S., Berry, J., Newman, B., 2017. Ion Exchange Resin for PFAS Removal and Pilot Test Comparison to GAC. Remediation, 27(3), pp. 19–27. [https://doi.org/10.1002/rem.21515 doi: 10.1002/rem.21515]</ref>. Water flows through the pore spaces in close contact with resin beads. Sufficient contact time needs to be provided, referred to as empty bed contact time (EBCT), to allow PFAS to diffuse from the water into the resin structure and adsorb to exchange sites. Typical EBCTs for AER treatment of PFAS are 2-5 min, shorter than contact times recommended for granular activated carbon (GAC) adsorbents (≥10 min)<ref name="LiuEtAl2022">Liu, C. J., Murray, C.C., Marshall, R.E., Strathmann, T.J., Bellona, C., 2022. Removal of Per- and Polyfluoroalkyl Substances from Contaminated Groundwater by Granular Activated Carbon and Anion Exchange Resins: A Pilot-Scale Comparative Assessment. Environmental Science: Water Research and Technology, 8(10), pp. 2245–2253. [https://doi.org/10.1039/D2EW00080F doi: 10.1039/D2EW00080F]</ref><ref>Liu, C.J., Werner, D., Bellona, C., 2019. Removal of Per- and Polyfluoroalkyl Substances (PFASs) from Contaminated Groundwater Using Granular Activated Carbon: A Pilot-Scale Study with Breakthrough Modeling. Environmental Science: Water Research and Technology, 5(11), pp. 1844–1853. [https://doi.org/10.1039/C9EW00349E doi: 10.1039/C9EW00349E]</ref>. The higher adsorption capacities and shorter EBCTs of AERs enable use of much less media and smaller vessels than GAC, reducing expected capital costs for AER treatment systems<ref name="EllisEtAl2023">Ellis, A.C., Boyer, T.H., Fang, Y., Liu, C.J., Strathmann, T.J., 2023. Life Cycle Assessment and Life Cycle Cost Analysis of Anion Exchange and Granular Activated Carbon Systems for Remediation of Groundwater Contaminated by Per- and Polyfluoroalkyl Substances (PFASs). Water Research, 243, Article 120324. [https://doi.org/10.1016/j.watres.2023.120324 doi: 10.1016/j.watres.2023.120324]</ref>.
-Like other adsorption media, PFAS will initially adsorb to media encountered near the inlet side of the reactor, but as ion exchange sites become saturated with PFAS, the active zone of adsorption will begin to migrate through the packed bed with increasing volume of water treated. Moreover, some PFAS with lower affinity for exchange sites (e.g., shorter-chain PFAS that are less hydrophobic) will be displaced by competition from other PFAS (e.g., longer-chain PFAS that are more hydrophobic) and move further along the bed to occupy open sites<ref name="EllisEtAl2022">Ellis, A.C., Liu, C.J., Fang, Y., Boyer, T.H., Schaefer, C.E., Higgins, C.P., Strathmann, T.J., 2022. Pilot Study Comparison of Regenerable and Emerging Single-Use Anion Exchange Resins for Treatment of Groundwater Contaminated by per- and Polyfluoroalkyl Substances (PFASs). Water Research, 223, Article 119019. [https://doi.org/10.1016/j.watres.2022.119019 doi: 10.1016/j.watres.2022.119019]&nbsp;&nbsp; [[Special:FilePath/EllisEtAl2022.pdf| Open Access Manuscript]]</ref>. Eventually, PFAS will start to breakthrough into the effluent from the reactor, typically beginning with the shorter-chain compounds. The initial breakthrough of shorter-chain PFAS is similar to the behavior observed for AER treatment of inorganic contaminants.
+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.
-Upon breakthrough, treatment is halted, and the exhausted resins are either replaced with fresh media or regenerated before continuing treatment. Most vendors are currently operating AER treatment systems for PFAS in single-use mode where virgin media is delivered to replace exhausted resins, which are transported off-site for disposal or incineration<ref name="BoyerEtAl2021a" />. As an alternative, some providers are developing regenerable AER treatment systems, where exhausted resins are regenerated on-site by desorbing PFAS from the resins using a combination of salt brine (typically ≥1 wt% NaCl) and cosolvent (typically ≥70 vol% methanol)<ref name="BoyerEtAl2021a" /><ref name="BoyerEtAl2021b">Boyer, T.H., Ellis, A., Fang, Y., Schaefer, C.E., Higgins, C.P., Strathmann, T.J., 2021. Life Cycle Environmental Impacts of Regeneration Options for Anion Exchange Resin Remediation of PFAS Impacted Water. Water Research, 207, Article 117798. [https://doi.org/10.1016/j.watres.2021.117798 doi: 10.1016/j.watres.2021.117798]&nbsp;&nbsp; [[Special:FilePath/BoyerEtAl2021b.pdf| Open Access Manuscript]]</ref><ref>Houtz, E., (projected completion 2025). Treatment of PFAS in Groundwater with Regenerable Anion Exchange Resin as a Bridge to PFAS Destruction, Project ER23-8391. [https://serdp-estcp.mil/projects/details/a12b603d-0d4a-4473-bf5b-069313a348ba/treatment-of-pfas-in-groundwater-with-regenerable-anion-exchange-resin-as-a-bridge-to-pfas-destruction Project Website].</ref>. This mode of operation allows for longer term use of resins before replacement, but requires more complex and extensive site infrastructure. Cosolvent in the resulting waste regenerant can be recycled by distillation, which reduces chemical inputs and lowers the volume of PFAS-contaminated still bottoms requiring further treatment or disposal<ref name="BoyerEtAl2021b" />. Currently, there is active research on various technologies for destruction of PFAS concentrates in AER still bottoms residuals<ref name="StrathmannEtAl2020">Strathmann, T.J., Higgins, C., Deeb, R., 2020. Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Impacted by PFAS, Final Report - Phase I. SERDP Project ER18-1501. [https://serdp-estcp.mil/projects/details/b34d6396-6b6d-44d0-a89e-6b22522e6e9c Project Website]&nbsp;&nbsp; [[Media: ER18-1501.pdf | Report.pdf]]</ref><ref name="HuangEtAl2021">Huang, Q., Woodard, S., Nickleson, M., Chiang, D., Liang, S., Mora, R., 2021. Electrochemical Oxidation of Perfluoroalkyl Acids in Still Bottoms from Regeneration of Ion Exchange Resins Phase I - Final Report. SERDP Project ER18-1320. [https://serdp-estcp.mil/projects/details/ccaa70c4-b40a-4520-ba17-14db2cd98e8f Project Website]&nbsp;&nbsp; [[Special:FilePath/ER18-1320.pdf| Report.pdf]]</ref>.
+===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<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>.
-==Field Demonstrations==
+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>.
-Field pilot studies are critical to demonstrating the effectiveness and expected costs of PFAS treatment technologies. A growing number of pilot studies testing the performance of commercially available AERs to treat PFAS-contaminated groundwater, including sites impacted by historical use of aqueous film-forming foam (AFFF), have been published recently (Figure 4)
+==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<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.
+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.
-In comparison to other reported PFAS destruction techniques, PRD offers several advantages:
+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.
-*Relative to UV/sodium sulfite and UV/sodium iodide systems, the fitted degradation rates in the micelle-accelerated PRD reaction system were ~18 and ~36 times higher, indicating the key role of the self-assembled micelle in creating a confined space for rapid PFAS destruction<ref name="ChenEtAl2020" />. The negatively charged hydrated electron associated with the positively charged cetyltrimethylammonium ion (CTA<sup>+</sup>) forms the surfactant micelle to trap molecules with similar structures, selectively mineralizing compounds with both hydrophobic and hydrophilic groups (e.g., PFAS).
+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"/>.
-*The PRD reaction does not require solid catalysts or electrodes, which can be expensive to acquire and difficult to regenerate or dispose.
-*The aqueous solution is not heated or pressurized, and the UV wavelength used does not cause direct water [[Wikipedia: Photodissociation | photolysis]], therefore the energy input to the system is more directly employed to destroy PFAS, resulting in greater energy efficiency.
-*Since the reaction is performed at ambient temperature and pressure, there are limited concerns regarding environmental health and safety or volatilization of PFAS compared to heated and pressurized systems.
-*Due to the reductive nature of the reaction, there is no formation of unwanted byproducts resulting from oxidative processes, such as [[Wikipedia: Perchlorate | perchlorate]]  generation during electrochemical oxidation<ref>Veciana, M., Bräunig, J., Farhat, A., Pype, M. L., Freguia, S., Carvalho, G., Keller, J., Ledezma, P., 2022. Electrochemical Oxidation Processes for PFAS Removal from Contaminated Water and Wastewater: Fundamentals, Gaps and Opportunities towards Practical Implementation. Journal of Hazardous Materials, 434, Article 128886. [https://doi.org/10.1016/j.jhazmat.2022.128886 doi: 10.1016/j.jhazmat.2022.128886]</ref><ref>Trojanowicz, M., Bojanowska-Czajka, A., Bartosiewicz, I., Kulisa, K., 2018. Advanced Oxidation/Reduction Processes Treatment for Aqueous Perfluorooctanoate (PFOA) and Perfluorooctanesulfonate (PFOS) – A Review of Recent Advances. Chemical Engineering Journal, 336, pp. 170–199. [https://doi.org/10.1016/j.cej.2017.10.153 doi: 10.1016/j.cej.2017.10.153]</ref><ref>Wanninayake, D.M., 2021. Comparison of Currently Available PFAS Remediation Technologies in Water: A Review. Journal of Environmental Management, 283, Article 111977. [https://doi.org/10.1016/j.jenvman.2021.111977 doi: 10.1016/j.jenvman.2021.111977]</ref>.
-*Aqueous fluoride ions are the primary end products of PRD, enabling real-time reaction monitoring with a fluoride [[Wikipedia: Ion-selective electrode | ion selective electrode (ISE)]], which is far less expensive and faster than relying on PFAS analytical data alone to monitor system performance.
-===Disadvantages===
+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.
-*The CTAB additive is only partially consumed during the reaction, and although CTAB is not problematic when discharged to downstream treatment processes that incorporate aerobic digestors, CTAB can be toxic to surface waters and anaerobic digestors. Therefore, disposal options for treated solutions will need to be evaluated on a site-specific basis. Possible options include removal of CTAB from solution for reuse in subsequent PRD treatments, or implementation of an oxidation reaction to degrade CTAB.
+==Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Ecological==
-*The PRD reaction rate decreases in water matrices with high levels of total dissolved solids (TDS). It is hypothesized that in high TDS solutions (e.g., ion exchange still bottoms with TDS of 200,000 ppm), the presence of ionic species inhibits the association of the electron donor with the micelle, thus decreasing the reaction rate.
+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"/>.
-*The PRD reaction rate decreases in water matrices with very low UV transmissivity. Low UV transmissivity (i.e., < 1 %) prevents the penetration of UV light into the solution, such that the utilization efficiency of UV light decreases.
-==State of the Art==
+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>.
-===Technical Performance===
+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"/>.
-[[File:WittFig2.png | thumb |400px| Figure 2. Enspired Solutions<small><sup>TM</sup></small> commercial PRD PFAS destruction equipment, the PFASigator<small><sup>TM</sup></small>. Dimensions are 8 feet long by 4 feet wide by 9 feet tall.]]
-{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
+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"/>.
-|+Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
-|-
-!Analytes
-!
-!GW
-!FF
-!AFFF<br>Rinsate
-!AFF<br>(diluted 10X)
-!IDW NF
-|-
-|&Sigma; Total PFAS<small><sup>a</sup></small> (ND=0)
-| rowspan="9" style="background-color:white;" |<p style="writing-mode: vertical-rl">% Decrease<br>(Initial Concentration, &mu;g/L)</p>
-|93%<br>(370)||96%<br>(32,000)||89%<br>(57,000)||86 %<br>(770,000)||84%<br>(82)
-|-
-|&Sigma; Total PFAS (ND=MDL)||93%<br>(400)||86%<br>(32,000)||90%<br>(59,000)||71%<br>(770,000)||88%<br>(110)
-|-
-|&Sigma; Total PFAS (ND=RL)||94%<br>(460)||96%<br>(32,000)||91%<br>(66,000)||34%<br>(770,000)||92%<br>(170)
-|-
-|&Sigma; Highly Regulated PFAS<small><sup>b</sup></small> (ND=0)||>99%<br>(180)||>99%<br>(20,000)||95%<br>(20,000)||92%<br>(390,000)||95%<br>(50)
-|-
-|&Sigma; Highly Regulated PFAS (ND=MDL)||>99%<br>(180)||98%<br>(20,000)||95%<br>(20,000)||88%<br>(390,000)||95%<br> (52)
-|-
-|&Sigma; Highly Regulated PFAS (ND=RL)||>99%<br>(190)||93%<br>(20,000)||95%<br>(20,000)||79%<br>(390,000)||95%<br>(55)
-|-
-|&Sigma; High Priority PFAS<small><sup>c</sup></small> (ND=0)||91%<br>(180)||98%<br>(20,000)||85%<br>(20,000)||82%<br>(400,000)||94%<br>(53)
-|-
-|&Sigma; High Priority PFAS (ND=MDL)||91%<br>(190)||94%<br>(20,000)||85%<br>(20,000)||79%<br>(400,000)||86%<br>(58)
-|-
-|&Sigma; High Priority PFAS (ND=RL)||92%<br>(200)||87%<br>(20,000)||86%<br>(21,000)||70%<br>(400,000)||87%<br>(65)
-|-
-|Fluorine mass balance<small><sup>d</sup></small>|| ||106%||109%||110%||65%||98%
-|-
-|Sorbed organic fluorine<small><sup>e</sup></small>|| ||4%||4%||33%||N/A||31%
-|-
-| colspan="7" style="background-color:white; text-align:left" |<small>Notes:<br>GW = groundwater<br>GW FF = groundwater foam fractionate<br>AFFF rinsate = rinsate collected from fire system decontamination<br>AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x<br>IDW NF = investigation derived waste nanofiltrate<br>ND = non-detect<br>MDL = Method Detection Limit<br>RL = Reporting Limit<br><small><sup>a</sup></small>Total PFAS = 40 analytes + unidentified PFCA precursors<br><small><sup>b</sup></small>Highly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>c</sup></small>High priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>d</sup></small>Ratio of the final to the initial organic fluorine plus inorganic fluoride concentrations<br><small><sup>e</sup></small>Percent of organic fluorine that sorbed to the reactor walls during treatment<br></small>
-|}
-<br>
-The&nbsp;PRD&nbsp;reaction&nbsp;has&nbsp;been validated at the bench scale for the destruction of PFAS in a variety of environmental samples from Department of Defense sites (Table 1). Enspired Solutions<small><sup>TM</sup></small> has designed and manufactured a fully automatic commercial-scale piece of equipment called PFASigator<small><sup>TM</sup></small>, specializing in PRD PFAS destruction (Figure 2). This equipment is modular and scalable, has a small footprint, and can be used alone or in series with existing water treatment trains. The PFASigator<small><sup>TM</sup></small> employs commercially available UV reactors and monitoring meters that have been used in the water industry for decades. The system has been tested on PRD efficiency operational parameters, and key metrics were proven to be consistent with benchtop studies.
-Bench scale PRD tests were performed for the following samples collected from Department of Defense sites: groundwater (GW), groundwater foam fractionate (FF), firefighting truck rinsate ([[Wikipedia: Firefighting foam | AFFF]] Rinsate), 3M Lightwater AFFF, investigation derived waste nanofiltrate (IDW NF), [[Wikipedia: Ion exchange | ion exchange]] still bottom (IX SB), and Ansulite AFFF. The PRD treatment was more effective in low conductivity/TDS solutions. Generally, PRD reaction rates decrease for solutions with a TDS > 10,000 ppm, with an upper limit of 30,000 ppm. Ansulite AFFF and IX SB samples showed low destruction efficiencies during initial screening tests, which was primarily attributed to their high TDS concentrations. Benchtop testing data are shown in Table 1 for the remaining five sample matrices.
+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"/>.
-During treatment, PFOS and PFOA concentrations decreased 96% to >99% and 77% to 97%, respectively. For the PFAS with proposed drinking water Maximum Contaminant Levels (MCLs) recently established by the USEPA (PFNA, PFOA, PFOS, PFHxS, PFBS, and HFPO-DA), concentrations decreased >99% for GW, 93% for FF, 95% for AFFF Rinsate and IDW NF, and 79% for AFFF (diluted 10x) during the treatment time allotted. Meanwhile, the total PFAS concentrations, including all 40 known PFAS analytes and unidentified perfluorocarboxylic acid (PFCA) precursors, decreased from 34% to 96% following treatment. All of these concentration reduction values were calculated by using reporting limits (RL) as the concentrations for non-detects.
+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.
-Excellent fluorine/fluoride mass balance was achieved. There was nearly a 1:1 conversion of organic fluorine to free inorganic fluoride ion during treatment of GW, FF and AFFF Rinsate. The 3M Lightwater AFFF (diluted 10x) achieved only 65% fluorine mass balance, but this was likely due to high adsorption of PFAS to the reactor.
+==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.
-===Application===
+*'''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.
-Due to the first-order kinetics of PRD, destruction of PFAS is most energy efficient when paired with a pre-concentration technology, such as foam fractionation (FF), nanofiltration, reverse osmosis, or resin/carbon adsorption, that remove PFAS from water. Application of the PFASigator<small><sup>TM</sup></small> is therefore proposed as a part of a PFAS treatment train that includes a pre-concentration step.
-The first pilot study with the PFASigator<small><sup>TM</sup></small> was conducted in late 2023 at an industrial facility in Michigan with PFAS-impacted groundwater. The goal of the pilot study was to treat the groundwater to below the limits for regulatory discharge permits. For the pilot demonstration, the PFASigator<small><sup>TM</sup></small> was paired with an FF unit, which pre-concentrated the PFAS into a foamate that was pumped into the PFASigator<small><sup>TM</sup></small> for batch PFAS destruction. Residual PFAS remaining after the destruction batch was treated by looping back the PFASigator<small><sup>TM</sup></small> effluent to the FF system influent. During the one-month field pilot duration, site-specific discharge limits were met, and steady state operation between the FF unit and PFASigator<small><sup>TM</sup></small> was achieved such that the PFASigator<small><sup>TM</sup></small> destroyed the required concentrated PFAS mass and no off-site disposal of PFAS contaminated waste was required.
+*'''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.
 ==References==
@@ Line 213: / Line 99: @@
 ==See Also==
+[https://www.atsdr.cdc.gov/pfas/health-studies/index.html Agency for Toxic Substances and Disease Registry (ATSDR) PFAS Health Studies]