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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

@@ Line 1: / Line 1: @@
-==Hydrothermal Alkaline Treatment (HALT)==
+==Remediation of Stormwater Runoff Contaminated by Munition Constituents==
-Hydrothermal alkaline treatment (HALT) is a thermochemical processing technology effective at destroying and defluorinating [[Wikipedia: Halogenation | halogenated]] organic compounds such as [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]]. HALT is highly effective at destroying and defluorinating all types of PFAS that have been evaluated. The HALT technology enables end-to-end treatment and destruction of PFAS from a variety of matrices when integrated into a suitable treatment train.
+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.
 <div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 '''Related Article(s):'''
-*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
+*[[Munitions Constituents]]
-*[[PFAS Ex Situ Water Treatment]]
-*[[PFAS Sources]]
-*[[PFAS Transport and Fate]]
-'''Contributors:''' Dr. Brian Pinkard, [[Dr. Timothy J. Strathmann | Dr. Timothy Strathmann]], Dr. Shilai Hao
+'''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 | 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>.
+===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>.
+==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
+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.
-*Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Impacted by PFAS<ref name="Strathmann2023">Strathmann, T.J., 2023. Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Impacted by PFAS. Project number ER18-1501, Strategic Environmental Research and Development Program (SERDP).</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"/>.
-*Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam<ref name="HaoEtAl2021">Hao, S., Choi, Y.J., Wu, B., Higgins, C.P., Deeb, R., Strathmann, T.J., 2021. Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam. Environmental Science and Technology, 55(5), pp. 3283-3295.&nbsp; [https://doi.org/10.1021/acs.est.0c06906 doi: 10.1021/acs.est.0c06906]</ref>
+==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)
-*[[Media: PinkardEtAl-2024a.pdf | Degradation and Defluorination of Ultra Short-, Short-, and Long-Chain PFASs in High Total Dissolved Solids Solutions by Hydrothermal Alkaline Treatment ─ Closing the Fluorine Mass Balance]]<ref name="PinkardEtAl2024a">Pinkard, B., Smith, S.M., Vorarath, P., Smrz, T., Schmick, S., Dressel, L., Bryan, C., Czerski, M., de Marne, A., Halevi, A., Thomsen, C., Woodruff, C., 2024. Degradation and Defluorination of Ultra Short-, Short-, and Long-Chain PFASs in High Total Dissolved Solids Solutions by Hydrothermal Alkaline Treatment─Closing the Fluorine Mass Balance. ACS ES&T Engineering, 4(11), pp. 2810-2818.&nbsp; [https://doi.org/10.1021/acsestengg.4c00378 doi: 10.1021/acsestengg.4c00378]&nbsp; [[Media: PinkardEtAl-2024a.pdf | Open Access Report.pdf]]</ref>
+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.
-==Introduction==
+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.
-[[File:PinkardFig1.png|thumb|300px|Figure 1. HALT refers to the subcritical water region on the pressure–temperature phase diagram of water]]
-Hydrothermal alkaline treatment (HALT) is a thermochemical processing technology effective at destroying and defluorinating halogenated organic compounds such as per- and polyfluoroalkyl substances (PFAS). HALT is also known as “[[Wikipedia: Hydrolysis#Alkaline_hydrolysis |alkaline hydrolysis]],” and is very similar to processing technologies such as [[Wikipedia: Hydrothermal liquefaction | hydrothermal liquefaction (HTL)]] which have been developed and investigated for organic waste-to-energy applications.
-HALT processing subjects PFAS in an aqueous solution to high pressure, high temperature, and high pH conditions. The required operating conditions are dependent on the specific target PFAS being destroyed, as [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] such as [[Wikipedia: Trifluoroacetic acid |trifluoroacetic acid (TFA)]] can be destroyed under mild conditions (e.g., P ~ 2 MPa, T ~ 200 °C, pH ~ 13)<ref name="AustinEtAl2024">Austin, C., Purohit, A., Thomsen, C., Pinkard, B.R., Strathmann, T.J., Novosselov, I.V., 2024. Hydrothermal Destruction and Defluorination of Trifluoroacetic Acid (TFA). Environmental Science and Technology, 58(18), pp. 8076-8085.&nbsp; [https://doi.org/10.1021/acs.est.3c09404 doi: 10.1021/acs.est.3c09404]</ref>, whereas [[Wikipedia: Perfluorosulfonic acids | perfluorosulfonic acids (PFSAs)]] such as [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonic acid (PFBS)]] require more aggressive processing conditions (e.g., P ~ 25 MPa, T ~ 350 °C, pH ~ 14.7) [5] (Figure 1) . HALT is capable of facilitating complete “mineralization” of PFAS, defined as the conversion of organic fluorine to dissolved inorganic fluoride. The treatment time for HALT is relatively shorter (<2 hours) compared to most other PFAS destructive technologies. For instance, treatment of two-fold diluted [[Wikipedia: Firefighting foam | aqueous film-forming foams (AFFFs)]] using HALT in batch mode achieved nearly complete defluorination in just 30 minutes under conditions of 350 °C and 5 M NaOH<ref name="HaoEtAl2021"/>. PFCAs can be destroyed with even faster kinetics at milder conditions; for example, >90% destruction and defluorination of [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] was achieved within 40 min at 200 °C<ref name="AustinEtAl2024"/>. Kinetic rate constants for individual PFAS compounds in HALT environments have been proposed in several studies<ref name="AustinEtAl2024"/><ref name="WuEtAl2019">Wu, B., Hao, S., Choi, Y.J., Higgins, C.P., Deeb, R., Strathmann, T.J., 2019. Rapid Destruction and Defluorination of Perfluorooctanesulfonate by Alkaline Hydrothermal Reaction. Environmental Science and Technology Letters, 6(10), pp. 630-636.&nbsp; [https://doi.org/10.1021/acs.estlett.9b00506 doi: 10.1021/acs.estlett.9b00506]</ref>. Several studies have also investigated the fluorine mass balance during HALT processing, showing near-stoichiometric conversion of organic fluorine to inorganic fluoride under optimal conditions<ref name="PinkardEtAl2024a"/>.
+===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>.
-From a practical perspective, HALT is best suited for destroying PFAS in concentrated liquids such as liquid concentrate streams produced as byproducts of other water treatment processes (e.g., [[PFAS Treatment by Anion Exchange | regenerable ion exchange]], foam fractionation). Previous publications demonstrate that complex sample matrices, including high concentrations of inorganic salts (e.g., 83 g/L chloride) and dissolved organic carbon (e.g., 13 g/L), do not inhibit the degradation rate of PFAS compared to a clean matrix, such as groundwater<ref name="HaoEtAl2022">Hao, S., Choi, Y.J,. Deeb, R.A., Strathmann, T.J., Higgins, C.P., 2022. Application of Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Contaminated Groundwater and Soil. Environmental Science and Technology, 56(10), pp. 6647-6657.&nbsp; [https://doi.org/10.1021/acs.est.2c00654 doi: 10.1021/acs.est.2c00654]</ref><ref name="HaoEtAl2023">Hao, S., Reardon, P.N., Choi, Y.J., Zhang, C., Sanchez, J.M., Higgins, C.P., Strathmann, T.J., 2023. Hydrothermal Alkaline Treatment (HALT) of Foam Fractionation Concentrate Derived from PFAS-Contaminated Groundwater. Environmental Science and Technology 57(44), pp. 17154-17165.&nbsp; [https://doi.org/10.1021/acs.est.3c05140 doi: 10.1021/acs.est.3c05140]</ref>. Moreover, several field demonstrations of HALT have been performed successfully, and the technology is scalable for commercialization.
+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>.
-==Reaction Mechanisms and Treatment Efficacy==
+==Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Human Health==
-[[File:PinkardFig2.png|thumb|300px|Figure 2. Representative classes of PFAS structures among 148 PFASs demonstrated complete degradation during HALT<ref name="HaoEtAl2021"/>]]
+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.
-[[File:PinkardFig3.png|thumb|300px|Figure 3. The degradation of representative classes of PFAS during HALT of 1-to-1000 diluted AFFF under conditions of 1 M NaOH, 350 °C, and a reaction time of 60 minutes<ref name="HaoEtAl2021"/>.]]
-Laboratory scale batch experiments have shown that the full suite of PFAS detected in aqueous film-forming foams (AFFFs) through targeted [[Wikipedia: Liquid chromatography–mass spectrometry | LC-MS/MS and LC-HRMS]] suspect screening analysis are degraded and defluorinated by HALT<ref name="HaoEtAl2021"/>. Figure 2 presents representative classes of PFAS structures among 148 PFAS demonstrating complete degradation during HALT. Figure 3 illustrates the degradation during HALT of representative classes of PFAS detected in an AFFF. The extent of destruction for all PFAS is highly temperature dependent, but results show that some subclasses of PFAS degrade in the absence of alkali amendments (e.g., PFCAs)<ref name="AustinEtAl2024"/>, whereas other subclasses require strong alkali in addition to near-critical reaction temperatures (e.g., PFSAs)<ref name="Strathmann2023"/><ref name="HaoEtAl2021"/><ref name="WuEtAl2019"/>.  This is attributed to different mechanisms that initiate the destruction of the individual PFAS subclasses. Degradation of PFCAs is initiated by thermally driven decarboxylation reactions<ref name="AustinEtAl2024"/>, whereas PFSA degradation, in the temperature range of HALT reactors, is proposed to be initiated via attack by the strong nucleophile OH-.<ref name="HaoEtAl2021"/>
-A mechanistic understanding of the HALT process for PFAS destruction needs further evaluation to optimize the process and reduce the consumption of chemicals and energy. While the studies of neat compounds are relatively straightforward, one of the major challenges is to address the effect of co-contaminants and apply the process to real-world operating scenarios. Recent laboratory studies with batch reactors conducted at the Colorado School of Mines (CSM) have extended the application of HALT for the destruction of PFAS in a variety of contaminated matrices, including groundwater and soils<ref name="HaoEtAl2022"/> and foam fractionation-derived liquid concentrate<ref name="HaoEtAl2023"/>. Apparent rates for the transformation of individual PFAS have been found to be largely insensitive to the type of media<ref name="HaoEtAl2023"/>, but there is a need to account for any reactions with the media that consume OH· (e.g., OH· reactions with silica-containing soil minerals)<ref name="HaoEtAl2022"/> Notably, while alkali is not required to degrade PFCAs, it is still necessary to convert the organically bound fluorine to inorganic F<sup>-</sup>. Austin ''et. al.''<ref name="AustinEtAl2024"/> showed that TFA, a C<sub>1</sub> PFCA, degrades at similar rates in the absence and presence of NaOH, but mineralization to F<sup>-</sup> and CO<sub>3</sub><sup>2-</sup> only occurs when NaOH is added; otherwise fluoroform (CHF<sub>3</sub>) is the terminal product when no NaOH is added to the reaction solution.
+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.
-HALT can also be applied to destroy other fluorinated compounds, for example, hydrofluorocarbon (HFC) refrigerants. HFC refrigerants are known to decompose into PFAS such as TFA in the atmosphere and thereby subsequently appear in concerning concentrations in rainwater. By themselves, HFCs are resistant to thermal degradation; however, in the presence of alkali (e.g., NaOH), alkaline hydrolysis can occur at T < 150˚C<ref name="AustinEtAl2024"/>.
+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.
-==State of the Art==
+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"/>.
-[[File:PinkardFig4.png | thumb |300px| Figure 4: HALT field demonstration at Fairbanks International Airport (FAI) in August 2023]]
-Recently, several field demonstrations of pilot-scale HALT systems were performed by commercial HALT provider Aquagga, Inc. These have focused on treating PFAS-rich liquids, including industrial wastewater at a 3M Company facility (April 2024)<ref name="PinkardEtAl2024b">Pinkard, B.R., Smith, S.M., Bryan, C., 2024. PFAS Degradation and Defluorination of High TDS Wastewater via Continuous Hydrothermal Alkaline Treatment (HALT). In: (Proceedings of the) 85th Annual International Water Conference (IWC 2024), Volume 1, pp. 359-374. Engineers Society of Western Pennsylvania. ISBN: 979-8-3313-1299-2</ref>, foam fractionate from a fire training pit in Fairbanks, AK (August 2023), foam fractionate from groundwater at Beale Air Force Base, CA (May 2024), and AFFF (May 2024). For all field demonstrations, a containerized HALT system was mobilized to the site and operated for up to several weeks. The systems were typically operated at a throughput between 5 and 10 gallons per hour (gph). Since 2019, HALT has progressed from small-scale batch reactors to successful field demonstration of pilot-scale systems. This technology maturation attests to strong technical and regulatory tailwinds. Effort is still needed to demonstrate the technology at full scale and in complex treatment scenarios. Long-term operation of the systems will allow for further optimization of the systems and provide data on the applicability of HALT for the treatment of industrial and environmental PFAS-contaminated waste streams.
-Pilot-scale HALT systems are typically continuous flow tubular reactor systems, consisting of a single high-temperature, high-pressure fluid path. In commercial HALT systems offered by Aquagga, Inc., chemical dosing for pH adjustment is achieved via an automated chemical dosing and mixing system. The high pH feedstock is then introduced to the high-pressure reactor via a high-pressure metering pump. Pressure is controlled via a back-pressure device downstream of the high-temperature reactor zone. The pressurized reactants are brought to reaction temperatures via a recuperative heat exchanger followed by electric resistive heaters. The reactor vessel contains the reactants at the necessary temperature and pressure and for a sufficient residence time to facilitate the destruction reactions. The product stream is then cooled through a recuperative heat exchanger, before being throttled to ambient pressure through the back-pressure device. Pressure transducers, flow meters, and thermocouples are used to monitor the reactor operations at various points in the system. All reactor components are typically housed within a shipping container, for ease of system transport and to provide secondary chemical containment.
+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.
-==Practical Applications==
+==Approaches for Evaluating Exposures and Effects in AFFF Site Environmental Risk Assessment: Ecological==
-[[File:PinkardFig5.png | thumb |300px| Figure 5: An on-site HALT pilot demonstration at a 3M Company wastewater treatment facility]]
+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 ideal use case for HALT is treating PFAS-rich liquid matrices. PFAS concentrations are high enough for HALT to be directly applicable primarily in the cases of AFFF treatment or industrial process water treatment. In the majority of use cases, it is more practical to apply a separation and concentration technology prior to HALT, to reduce the volume of liquid requiring HALT treatment while increasing PFAS concentrations in that liquid. These concentration technologies may include regenerable sorbents, membranes, or foam fractionation, all of which produce a liquid byproduct amenable for HALT.
-===Destruction of PFAS in Ion Exchange Regeneration Brine===
+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>.
-One of the most promising applications of HALT is for treating PFAS-rich ion exchange (IX) regeneration brines, either in site remediation applications (e.g., groundwater treatment<ref name="Pinkard2024">Pinkard, B.R., 2024. Hydrothermal Alkaline Treatment for a Closed-Loop, On-Site PFAS Treatment Solution. Project Number ER23-8400, Environmental Security Technology Certification Program (ESTCP).&nbsp; [https://serdp-estcp.mil/projects/details/a4c6918a-fe3b-43d2-95cb-fa3dfa3a50a2 Project Website]</ref>) or industrial wastewater treatment applications<ref name="PinkardEtAl2024a"/>. IX capture and regeneration involve sorbing PFAS to an IX resin, followed by chemical desorption of PFAS from the resin, typically with a solvent and/or salt wash solution. The IX regeneration technology is commercially mature and available from several vendors.
-A treatment train of IX followed by HALT shows promise for several reasons. One reason is that the HALT process is highly compatible with the liquid matrix produced through the IX regeneration. Typically, IX regeneration brine (a.k.a. “still bottoms”) contains high levels of dissolved solids such as sodium chloride, which can cause practical processing challenges with other liquid treatment technologies. However, high levels of TDS do not appear to cause processing challenges with HALT<ref name="PinkardEtAl2024a"/>. Another reason is that IX regeneration brines often contain ultra short- and short-chain PFAS, which are amenable to destructive treatment with HALT.
+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"/>.
-In 2022, commercial HALT provider Aquagga performed a bench study in partnership with the 3M Company, demonstrating PFAS destruction performance for HALT processing of a synthetic IX regeneration brine<ref name="PinkardEtAl2024a"/>. Seven treatment conditions were tested, and fluorine mass balance closure was demonstrated for most conditions using a range of analytical techniques. In 2024, Aquagga performed an on-site demonstration in partnership with the 3M Company treating IX regeneration brine produced from active wastewater treatment activities<ref name="PinkardEtAl2024b"/>.
+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"/>.
-===Foam Fractionate Treatment===
+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"/>.
-Foam fractionation is a technology that concentrates PFAS in liquids by taking advantage of the hydrophobic/interface-partitioning behavior exhibited by many types of PFAS. Foam fractionation is seeing broad adoption for challenging liquid matrices such as landfill leachate and groundwater. Long-chain PFAS are known to partition to interfaces much more readily than short-chain PFAS, and foam fractionation is correspondingly much more effective at removing long-chain PFAS from liquids. When coupled with HALT, foam fractionation can remove and destroy a high fraction of PFAS from challenging liquid matrices<ref name="HaoEtAl2023"/>.
-===Destruction of PFAS in AFFF===
+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.
-Legacy AFFF contains high levels of PFAS (typically 0.1 to 6 wt%) in a liquid matrix. Several studies at lab and pilot scales have demonstrated that HALT can destroy PFAS in AFFF with minimal dilution<ref name="HaoEtAl2021"/>. While the treatment is effective, the wide variety of AFFF formulations make this a challenging application.
-==Advantages and Drawbacks==
+==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.
 ==References==
@@ Line 68: / Line 99: @@
 ==See Also==
-*[https://vimeo.com/809180171/c276c1873a Peeper Deployment Video]
+[https://www.atsdr.cdc.gov/pfas/health-studies/index.html Agency for Toxic Substances and Disease Registry (ATSDR) PFAS Health Studies]
-*[https://vimeo.com/811073634/303edf2693 Peeper Retrieval Video]
-*[https://vimeo.com/811328715/aea3073540 Peeper Processing Video]
-*[https://sepub-prod-0001-124733793621-us-gov-west-1.s3.us-gov-west-1.amazonaws.com/s3fs-public/2024-09/ER20-5261%20Fact%20Sheet.pdf?VersionId=malAixSQQM3mWCRiaVaxY8wLdI0jE1PX Fact Sheet]

Difference between revisions of "User:Jhurley/sandbox"

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

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