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Consumer and/or industrial uses of PFAS-containing materials results in the discharge of PFAS to industrial and municipal wastewater treatment plants (WWTPs). Conventional WWTP treatment processes remove less than 5% of PFAAs<ref name="Ahrens2011a"/><ref name="Schultz2006">Schultz, M.M., Higgins, C.P., Huset, C.A., Luthy, R.G., Barofsky, D.F., and Field, J.A., 2006. Fluorochemical Mass Flows in a Municipal Wastewater Treatment Facility. Environmental Science and Technology, 40(23), pp. 7350-7357.  [https://doi.org/10.1021/es061025m DOI: 10.1021/es061025m]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556954/ Author Manuscript]</ref><ref name="MWRA2019">Michigan Waste and Recycling Association (MWRA), 2019. Statewide Study on Landfill Leachate PFOA and PFOS Impact on Water Resource Recovery Facility Influent, Second Revision.  [[Media: MWRA2019.pdf | Report.pdf]]</ref>. WWTPs, particularly those that receive industrial wastewater, are possible sources of PFAS release<ref name="Bossi2008">Bossi, R., Strand, J., Sortkjær, O. and Larsen, M.M., 2008. Perfluoroalkyl compounds in Danish wastewater treatment plants and aquatic environments. Environment International, 34(4), pp. 443-450. [https://doi.org/10.1016/j.envint.2007.10.002  DOI: 10.1016/j.envint.2007.10.002]  Free download from: [https://www.academia.edu/download/43968517/Perfluoroalkyl_compounds_in_Danish_waste20160321-31116-esz4d1.pdf Academia.edu]</ref><ref name="Lin2014">Lin, A.Y.C., Panchangam, S.C., Tsai, Y.T., and Yu, T.H., 2014. Occurrence of perfluorinated compounds in the aquatic environment as found in science park effluent, river water, rainwater, sediments, and biotissues. Environmental Monitoring and Assessment, 186(5), pp. 3265-3275.  [https://doi.org/10.1007/s10661-014-3617-9 DOI: 10.1007/s10661-014-3617-9]</ref><ref name="Ahrens2009">Ahrens, L., Felizeter, S., Sturm, R., Xie, Z. and Ebinghaus, R., 2009. Polyfluorinated compounds in waste water treatment plant effluents and surface waters along the River Elbe, Germany. Marine Pollution Bulletin, 58(9), pp.1326-1333. [https://doi.org/10.1016/j.marpolbul.2009.04.028 DOI: 10.1016/j.marpolbul.2009.04.028]&nbsp;&nbsp; [[Media:Ahrens2009.pdf | Author’s manuscript]]</ref>.
 
Consumer and/or industrial uses of PFAS-containing materials results in the discharge of PFAS to industrial and municipal wastewater treatment plants (WWTPs). Conventional WWTP treatment processes remove less than 5% of PFAAs<ref name="Ahrens2011a"/><ref name="Schultz2006">Schultz, M.M., Higgins, C.P., Huset, C.A., Luthy, R.G., Barofsky, D.F., and Field, J.A., 2006. Fluorochemical Mass Flows in a Municipal Wastewater Treatment Facility. Environmental Science and Technology, 40(23), pp. 7350-7357.  [https://doi.org/10.1021/es061025m DOI: 10.1021/es061025m]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556954/ Author Manuscript]</ref><ref name="MWRA2019">Michigan Waste and Recycling Association (MWRA), 2019. Statewide Study on Landfill Leachate PFOA and PFOS Impact on Water Resource Recovery Facility Influent, Second Revision.  [[Media: MWRA2019.pdf | Report.pdf]]</ref>. WWTPs, particularly those that receive industrial wastewater, are possible sources of PFAS release<ref name="Bossi2008">Bossi, R., Strand, J., Sortkjær, O. and Larsen, M.M., 2008. Perfluoroalkyl compounds in Danish wastewater treatment plants and aquatic environments. Environment International, 34(4), pp. 443-450. [https://doi.org/10.1016/j.envint.2007.10.002  DOI: 10.1016/j.envint.2007.10.002]  Free download from: [https://www.academia.edu/download/43968517/Perfluoroalkyl_compounds_in_Danish_waste20160321-31116-esz4d1.pdf Academia.edu]</ref><ref name="Lin2014">Lin, A.Y.C., Panchangam, S.C., Tsai, Y.T., and Yu, T.H., 2014. Occurrence of perfluorinated compounds in the aquatic environment as found in science park effluent, river water, rainwater, sediments, and biotissues. Environmental Monitoring and Assessment, 186(5), pp. 3265-3275.  [https://doi.org/10.1007/s10661-014-3617-9 DOI: 10.1007/s10661-014-3617-9]</ref><ref name="Ahrens2009">Ahrens, L., Felizeter, S., Sturm, R., Xie, Z. and Ebinghaus, R., 2009. Polyfluorinated compounds in waste water treatment plant effluents and surface waters along the River Elbe, Germany. Marine Pollution Bulletin, 58(9), pp.1326-1333. [https://doi.org/10.1016/j.marpolbul.2009.04.028 DOI: 10.1016/j.marpolbul.2009.04.028]&nbsp;&nbsp; [[Media:Ahrens2009.pdf | Author’s manuscript]]</ref>.
  
Evaluation of full-scale WWTPs has indicated that conventional primary (sedimentation and clarification) and secondary (aerobic biodegradation of organic matter) treatment processes can result in changes in PFAS concentrations and classes. For example, higher concentrations of PFAAs have been observed in effluent than in influent, presumably due to transformation of precursor PFAS<ref name="Schultz2006"/>. Some data has indicated that the terminal PFAS compounds PFOS and PFOA were among the most frequently detected PFAS in wastewater<ref name="Hamid2016">Hamid, H. and Li, L., 2016. Role of wastewater treatment plant in environmental cycling of poly- and perfluoroalkyl substances. Ecocycles, 2(2), pp. 43-53. [https://doi.org/10.19040/ecocycles.v2i2.62 DOI: 10.19040/ecocycles.v2i2.62]&nbsp;&nbsp; [[Media: Hamid2016.pdf | Open access article.]]</ref>. A state-wide study in Michigan indicated that PFAS were detected in all of the samples from 42 WWTPs, including influent, effluent, and biosolids/sludge samples, and that the short-chain PFAS were more frequently detected in the liquid process flow (influent and effluent), while long-chain PFAS were more common in biosolids<ref name="EGLE2020">Michigan Department of Environment, Great Lakes and Energy (EGLE), 2020.  Summary Report: Initiatives to Evaluate the Presence of PFAS in Municipal Wastewater and Associated Residuals (Sludge/Biosolids) in Michigan. [[Media:EGLE2020.pdf | Report.pdf]]&nbsp;&nbsp;
+
Evaluation of full-scale WWTPs has indicated that conventional primary (sedimentation and clarification) and secondary (aerobic biodegradation of organic matter) treatment processes can result in changes in PFAS concentrations and classes. For example, higher concentrations of PFAAs have been observed in effluent than in influent, presumably due to transformation of precursor PFAS<ref name="Schultz2006"/>. Some data has indicated that the terminal PFAS compounds PFOS and PFOA were among the most frequently detected PFAS in wastewater<ref name="Hamid2016">Hamid, H. and Li, L., 2016. Role of wastewater treatment plant in environmental cycling of poly- and perfluoroalkyl substances. Ecocycles, 2(2), pp. 43-53. [https://doi.org/10.19040/ecocycles.v2i2.62 DOI: 10.19040/ecocycles.v2i2.62]&nbsp;&nbsp; [[Media: Hamid2016.pdf | Open access article.]]</ref>. A state-wide study in Michigan indicated that PFAS were detected in all of the samples from 42 WWTPs, including influent, effluent, and biosolids/sludge samples, and that the short-chain PFAS were more frequently detected in the liquid process flow (influent and effluent), while long-chain PFAS were more common in biosolids<ref name="EGLE2020"/>.
[https://www.michigan.gov/documents/egle/wrd-pfas-initiatives_691391_7.pdf Website]</ref>.
 
  
Multiple studies have found PFAS in municipal sewage sludge<ref name="Higgins2005">Higgins, C.P., Field, J.A., Criddle, C.S., and Luthy, R.G., 2005. Quantitative Determination of Perfluorochemicals in Sediments and Domestic Sludge. Environmental Science and Technology, 39 (11), pp. 3946 – 3956.  [https://doi.org/10.1021/es048245p DOI: 10.1021/es048245p]</ref><ref name="EGLE2020"/>. The US EPA states that more than half of the sludge produced in the United States is applied to agricultural land as biosolids, therefore there are concerns that biosolids applications may become a potential source of PFAS to the environment<ref name="USEPA2020">US Environmental Protection Agency (USEPA), 2020. Research on Per- and Polyfluoroalkyl Substances (PFAS).  [https://www.epa.gov/chemical-research/research-and-polyfluoroalkyl-substances-pfas Website]</ref>. Application of biosolids as a soil amendment can potentially result in transfer of PFAS to soil, surface water and groundwater and can possibly allow PFAS to enter the food chain<ref name="Sepulvado2011">Sepulvado, J.G., Blaine, A.C., Hundal, L.S. and Higgins, C.P., 2011. Occurrence and Fate of Perfluorochemicals in Soil Following the Land Application of Municipal Biosolids. Environmental Science and Technology, 45(19), pp.  8106-8112.  [https://doi.org/10.1021/es103903d DOI: 10.1021/es103903d]</ref><ref name="Lindstrom2011">Lindstrom, A.B., Strynar, M.J., Delinsky, A.D., Nakayama, S.F., McMillan, L., Libelo, E.L., Neill, M. and Thomas, L., 2011. Application of WWTP Biosolids and Resulting Perfluorinated Compound Contamination of Surface and Well Water in Decatur, Alabama, USA. Environmental Science and Technology, 45(19), pp. 8015-8021.  [https://doi.org/10.1021/es1039425 DOI: 10.1021/es1039425]</ref><ref name="Blaine2013">Blaine, A.C., Rich, C.D., Hundal, L.S., Lau, C., Mills, M.A., Harris, K.M. and 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;&nbsp; Free download from: [https://www.epa.gov/sites/production/files/2019-11/documents/508_pfascropuptake.pdf US EPA]</ref><ref name="Blaine2014">Blaine, A.C., Rich, C.D., Sedlacko, E.M., Hundal, L.S., Kumar, K., Lau, C., Mills, M.A., Harris, K.M. and Higgins, C.P., 2014. Perfluoroalkyl Acid Distribution in Various Plant Compartments of Edible Crops Grown in Biosolids-Amended Soils. Environmental Science and Technology, 48(14), pp. 7858-7865.  [https://doi.org/10.1021/es500016s DOI: 10.1021/es500016s] Free download from: [https://www.researchgate.net/profile/Kuldip_Kumar2/publication/263015815_Perfluoroalkyl_Acid_Distribution_in_Various_Plant_Compartments_of_Edible_Crops_Grown_in_Biosolids-Amended_soils/links/5984cb310f7e9b6c852f4f02/Perfluoroalkyl-Acid-Distribution-in-Various-Plant-Compartments-of-Edible-Crops-Grown-in-Biosolids-Amended-soils.pdf ResearchGate]</ref><ref name="Navarro2017">Navarro, I., de la Torre, A., Sanz, P., Porcel, M.Á., Pro, J., Carbonell, G. and de los Ángeles Martínez, M., 2017. Uptake of perfluoroalkyl substances and halogenated flame retardants by crop plants grown in biosolids-amended soils. Environmental Research, 152, pp. 199-206.  [https://doi.org/10.1016/j.envres.2016.10.018 DOI: 10.1016/j.envres.2016.10.018]</ref>. Limited studies have shown that PFAS concentrations can be elevated in surface and groundwater in the vicinity of agricultural fields that received PFAS contaminated biosolids for an extended period<ref name="Washington2010">Washington, J.W., Yoo, H., Ellington, J.J., Jenkins, T.M., and Libelo, E.L., 2010. Concentrations, Distribution, and Persistence of Perfluoroalkylates in Sludge-Applied Soils near Decatur, Alabama, USA. Environmental Science and Technology, 44(22), pp. 8390-8396.  [https://doi.org/10.1021/es1003846 DOI: 10.1021/es1003846]  Free download from: [https://www.researchgate.net/profile/John_Washington3/publication/47447289_Concentrations_Distribution_and_Persistence_of_Perfluoroalkylates_in_Sludge-Applied_Soils_near_Decatur_Alabama_USA/links/5e3c0184a6fdccd9658add41/Concentrations-Distribution-and-Persistence-of-Perfluoroalkylates-in-Sludge-Applied-Soils-near-Decatur-Alabama-USA.pdf ResearchGate]</ref>. The most abundant PFAS found in biosolids are the long-chain PFAS<ref name="Hamid2016"/><ref name="EGLE2020"/>. Based on the persistence and stability of long-chain PFAS and their interaction with biosolids, research is ongoing to determine PFAS leachability from biosolids and their bioavailability for uptake by plants, soil organisms, and the consumers of potentially PFAS-impacted plants and soil organisms.  
+
Multiple studies have found PFAS in municipal sewage sludge<ref name="Higgins2005">Higgins, C.P., Field, J.A., Criddle, C.S., and Luthy, R.G., 2005. Quantitative Determination of Perfluorochemicals in Sediments and Domestic Sludge. Environmental Science and Technology, 39 (11), pp. 3946 – 3956.  [https://doi.org/10.1021/es048245p DOI: 10.1021/es048245p]</ref><ref name="EGLE2020"/>. The US EPA states that more than half of the sludge produced in the United States is applied to agricultural land as biosolids, therefore there are concerns that biosolids applications may become a potential source of PFAS to the environment<ref name="USEPA2020">US Environmental Protection Agency (USEPA), 2020. Research on Per- and Polyfluoroalkyl Substances (PFAS).  [https://www.epa.gov/chemical-research/research-and-polyfluoroalkyl-substances-pfas Website]</ref>. Application of biosolids as a soil amendment can potentially result in transfer of PFAS to soil, surface water and groundwater and can possibly allow PFAS to enter the food chain<ref name="Sepulvado2011">Sepulvado, J.G., Blaine, A.C., Hundal, L.S. and Higgins, C.P., 2011. Occurrence and Fate of Perfluorochemicals in Soil Following the Land Application of Municipal Biosolids. Environmental Science and Technology, 45(19), pp.  8106-8112.  [https://doi.org/10.1021/es103903d DOI: 10.1021/es103903d]</ref><ref name="Lindstrom2011">Lindstrom, A.B., Strynar, M.J., Delinsky, A.D., Nakayama, S.F., McMillan, L., Libelo, E.L., Neill, M. and Thomas, L., 2011. Application of WWTP Biosolids and Resulting Perfluorinated Compound Contamination of Surface and Well Water in Decatur, Alabama, USA. Environmental Science and Technology, 45(19), pp. 8015-8021.  [https://doi.org/10.1021/es1039425 DOI: 10.1021/es1039425]</ref><ref name="Blaine2013">Blaine, A.C., Rich, C.D., Hundal, L.S., Lau, C., Mills, M.A., Harris, K.M. and 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;&nbsp; Free download from: [https://www.epa.gov/sites/production/files/2019-11/documents/508_pfascropuptake.pdf US EPA]</ref><ref name="Blaine2014">Blaine, A.C., Rich, C.D., Sedlacko, E.M., Hundal, L.S., Kumar, K., Lau, C., Mills, M.A., Harris, K.M. and Higgins, C.P., 2014. Perfluoroalkyl Acid Distribution in Various Plant Compartments of Edible Crops Grown in Biosolids-Amended Soils. Environmental Science and Technology, 48(14), pp. 7858-7865.  [https://doi.org/10.1021/es500016s DOI: 10.1021/es500016s] Free download from: [https://www.researchgate.net/profile/Kuldip_Kumar2/publication/263015815_Perfluoroalkyl_Acid_Distribution_in_Various_Plant_Compartments_of_Edible_Crops_Grown_in_Biosolids-Amended_soils/links/5984cb310f7e9b6c852f4f02/Perfluoroalkyl-Acid-Distribution-in-Various-Plant-Compartments-of-Edible-Crops-Grown-in-Biosolids-Amended-soils.pdf ResearchGate]</ref><ref name="Navarro2017">Navarro, I., de la Torre, A., Sanz, P., Porcel, M.Á., Pro, J., Carbonell, G. and de los Ángeles Martínez, M., 2017. Uptake of perfluoroalkyl substances and halogenated flame retardants by crop plants grown in biosolids-amended soils. Environmental Research, 152, pp. 199-206.  [https://doi.org/10.1016/j.envres.2016.10.018 DOI: 10.1016/j.envres.2016.10.018]</ref>. Limited studies have shown that PFAS concentrations can be elevated in surface and groundwater in the vicinity of agricultural fields that received PFAS contaminated biosolids for an extended period<ref name="Washington2010">Washington, J.W., Yoo, H., Ellington, J.J., Jenkins, T.M., and Libelo, E.L., 2010. Concentrations, Distribution, and Persistence of Perfluoroalkylates in Sludge-Applied Soils near Decatur, Alabama, USA. Environmental Science and Technology, 44(22), pp. 8390-8396.  [https://doi.org/10.1021/es1003846 DOI: 10.1021/es1003846]  Free download from: [https://www.researchgate.net/profile/John_Washington3/publication/47447289_Concentrations_Distribution_and_Persistence_of_Perfluoroalkylates_in_Sludge-Applied_Soils_near_Decatur_Alabama_USA/links/5e3c0184a6fdccd9658add41/Concentrations-Distribution-and-Persistence-of-Perfluoroalkylates-in-Sludge-Applied-Soils-near-Decatur-Alabama-USA.pdf ResearchGate]</ref>. The most abundant PFAS found in biosolids are the long-chain PFAS<ref name="Hamid2016"/><ref name="EGLE2020"/>. Based on the persistence and stability of long-chain PFAS and their interaction with biosolids, research is ongoing to determine PFAS leachability from biosolids and their bioavailability for uptake by plants, soil organisms, and the consumers of potentially PFAS-impacted plants and soil organisms.
  
 
==Solid Waste Management Facilities==
 
==Solid Waste Management Facilities==

Revision as of 19:41, 4 February 2021

PFAS Soil Remediation Technologies

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are mobile in the subsurface and highly resistant to natural degradation processes, therefore soil source areas can be ongoing sources of groundwater contamination. The United States Environmental Protection Agency (US EPA) has not promulgated soil standards for any PFAS, although a handful of states have for select compounds. Soil standards issued for protection of groundwater are in the single digit part per billion range, which is a very low threshold for soil impacts. Well developed soil treatment technologies are limited to capping, excavation with incineration or disposal, and soil stabilization with sorptive amendments. At present, no in situ destructive soil treatment technologies have been demonstrated.

Related Article(s):

Contributor(s): Jim Hatton and Bill DiGuiseppi

Key Resource(s):

Introduction

PFAS are a class of highly fluorinated compounds including perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and many other compounds with a variety of industrial and consumer uses. These compounds are often highly resistant to treatment[3] and the more mobile compounds are often problematic in groundwater systems[4]. The US EPA has published lifetime drinking water health advisories for the combined concentration of 70 nanograms per liter (ng/L) for two common and recalcitrant PFAS: PFOS, a perfluoroalkyl sulfonic acid (PFSA), and PFOA, a perfluoroalkyl carboxylic acid (PFCA)[5][6].(See Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) for nomenclature.)

While many of the earliest sites where these compounds were detected in groundwater were manufacturing sites, some recent detections have been attributed to fire training activities associated with aqueous film-forming foams (AFFF). AFFF is the US Department of Defense (DoD) designation for Class B firefighting foam containing PFAS, which is required for fighting fires involving petroleum liquids. Fire training areas and other source areas where AFFF was released at the surface have the potential to be ongoing sources of groundwater contamination[2]. (See also PFAS Sources.)

No national soil cleanup standards have been promulgated by the US EPA, although Regional Screening Levels (RSLs) have been calculated and published for perfluorobutane sulfonate (PFBS)[7] and data are available to calculate RSLs for PFOA and PFOS[8]. Several states have promulgated standards[9] or screening levels[10][11][12][13][14] for soil concentrations protective of groundwater, which are several orders of magnitude lower than direct dermal exposure guidelines. These single-digit part per billion criteria will likely drive remedial actions in PFAS source areas in the future. At present, the lack of federally promulgated standards and uncertainty about future standards causes temporary stockpiling of PFAS-impacted soils on sites with soil generated from construction or investigation activities.

Soil Treatment

Addressing recalcitrant contaminants in soil has traditionally been done through containment/capping or excavation and off-site disposal or treatment. Containment/capping may be an acceptable solution for PFAS in some locations. However, containment/capping is not considered ideal given the history of releases from engineered landfills and restrictions on use of land containing capped soils. Innovative treatment approaches for PFAS include stabilization with amendments and thermal treatment.

Excavation and Disposal

Excavation and off-site disposal or treatment of PFAS-impacted soils is the only well-developed treatment technology option and may be acceptable for small quantities of soil, such as those generated during characterization activities (i.e., investigation derived waste, IDW). Disposal in non-hazardous landfills is allowable in most states. However, some landfill operators are choosing to restrict acceptance of PFAS-containing waste and soils as a protection against future liability. In addition, the US EPA and some states are considering or have designated PFOA and PFOS as hazardous substances, which would reduce the number of facilities where disposal of PFAS-contaminated soil would be allowed


Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are a complex family of more than 3,000 manmade fluorinated organic chemicals[15] although not all of these are currently in use or production. PFAS are produced using several different processes. Fluorosurfactants, which include perfluoroalkyl acids (PFAAs) (see PFAS article for nomenclature) and side-chain fluorinated polymers, have been manufactured using two major processes: electrochemical fluorination (ECF) and telomerization[16]. ECF was licensed by 3M in the 1940s[17] and used by 3M until 2001. ECF produces a mixture of even and odd numbered carbon chain lengths of approximately 70% linear and 30% branched substances[18]. Telomerization was developed in the 1970s[19], and yields mainly even numbered, straight carbon chain isomers[3][20]. PFAS manufacturers have provided PFAS to secondary manufacturers for production of a vast array of industrial and consumer products.

During manufacturing, PFAS may be released into the atmosphere then redeposited on land where they can also affect surface water and groundwater, or PFAS may be discharged without treatment to wastewater treatment plants or landfills, and eventually be released into the environment by treatment systems that are not designed to mitigate PFAS (see also PFAS Transport and Fate). Industrial discharges of PFAS were unregulated for many years, but that has begun to change. In January 2016, New York became the first state in the nation to regulate PFOA as a hazardous substance followed by the regulation of PFOS in April 2016. Consumer and industrial uses of PFAS-containing products can also end up releasing PFAS into landfills and into municipal wastewater, where it may accumulate undetected in biosolids which are typically treated by land application.

Industrial Sources

PFAS are used in many industrial and consumer applications, which may have released PFAS into the environment and impacted drinking water supplies in many areas of the United States[21]. Both in the United States (US) and abroad, primary manufacturing facilities produce PFAS and secondary manufacturing facilities use PFAS to produce goods. Environmental release mechanisms associated with these facilities include air emission and dispersion, spills, and disposal of manufacturing wastes and wastewater. Potential impacts to air, soil, sediment, surface water, stormwater, and groundwater are present not only at primary release points but potentially over the surrounding area[22]. Some of the potential primary and secondary sources of PFAS releases to the environment are listed here[1]:

  • Paper products: Surface coatings to repel grease and moisture. Uses include non-food paper packaging (for example, cardboard, carbonless forms, masking papers) and food-contact materials (for example, pizza boxes, fast food wrappers, microwave popcorn bags, baking papers, pet food bags)[23][3][24][26][29][33][34][37][39]
  • Metal Plating & Etching: Corrosion prevention, mechanical wear reduction, aesthetic enhancement, surfactant, wetting agent/fume suppressant for chrome, copper, nickel and tin electroplating, and post-plating cleaner[40][41][3][27][42][34][43][16][44]
  • Industrial Surfactants, Resins, Molds, Plastics: Manufacture of plastics and fluoropolymers, rubber, and compression mold release coatings; plumbing fluxing agents; fluoroplastic coatings, composite resins, and flame retardant for polycarbonate[3][47][26][48][27][49][45][33][35][37][50]
  • Photolithography, Semiconductor Industry: Photoresists, top anti-reflective coatings, bottom anti-reflective coatings, and etchants, with other uses including surfactants, wetting agents, and photo-acid generation[51][52][25][45][34][35]

Class B Firefighting Foams

Aqueous film forming foam (AFFF) and other fluorinated Class B firefighting foams are another important source of PFAS to the environment, especially in military and aviation settings. Class B firefighting foams have been used since the 1960s to extinguish flammable liquid hydrocarbon fires and for vapor suppression. These foams contain complex and variable mixtures of PFAS that act as surfactants. Fluorinated surfactants are both hydrophobic and oleophobic (oil-repelling), as well as thermally stable, chemically stable, and highly surface active[53]. These properties make them uniquely suited to fighting hydrocarbon fuel fires. Use of fluorinated Class B foams is prevalent and is a major source of PFAS to the environment. Release to the environment typically occurs during firefighting operations, firefighter training, apparatus testing, or leakage during storage. Research into fluorine-free alternatives is underway and Congressional pressure is leading towards banning fluorinated Class B firefighting foams in the United States.

Figure 1. Types of Class B firefighting foams. Reproduced from ITRC, 2020; original figure courtesy of S. Thomas, Wood PLC, used with permission.

When discussing the relationship between firefighting foams and sources of PFAS to the environment, the emphasis is typically on AFFF; however, many different types of Class B firefighting foams exist. These may or may not be fluorinated (contain PFAS). Class B foams are used to extinguish Class B fires, that is, those involving flammable liquids. Fluorinated Class B foams spread across the surface of the flammable liquid forming a thin film and extinguish fires by (1) excluding air from the flammable vapors, (2) suppressing vapor release, (3) physically separating the flames from the fuel source, and (4) cooling the fuel surface and surrounding metal surfaces[54]. From a PFAS perspective, Class B firefighting foams can be divided into two broad categories: fluorinated foams (that contain PFAS) and fluorine-free foams (that do not contain PFAS)[1]. This distinction and examples of each type are shown in Figure 1.

AFFF was developed by the US Navy in the 1960s and in 1969, the US Department of Defense (DoD) issued military specification MIL-F-24385 listing firefighting performance requirements for all AFFF used within the US DoD[1][55][56]. These performance standards are often referred to as “Mil-Spec.” Products that meet the Mil-Spec have been added to the US DoD Qualified Product Listing (QPL). In 2006 the US Federal Aviation Administration (FAA) also began requiring that 14-CFR-139-certified commercial airports purchase Mil-Spec compliant AFFF only. Because the US DoD and FAA have been the primary purchasers of AFFF, development of AFFF product mixtures has historically been performance-driven (to comply with the Mil-Spec) rather than formula-driven (the specific PFAS mixtures utilized have varied over time and by manufacturer). Multiple manufacturers in the US and throughout the world produce or have produced AFFF concentrate[1]. AFFF concentrate is or has been available in 1%, 3%, or 6% formulations, where the percentage designates the recommended percentage of concentrate to be mixed into water during application.

The specific mixtures of PFAS found in AFFF have varied by manufacturer and over time due to differences in production processes and voluntary formula changes. AFFF formulations can generally be grouped into three categories[1]:

  • Legacy Perfluorooctane Sulfonate (PFOS) AFFF This type of AFFF was manufactured exclusively by 3M under the brand name “Lightwater” from the late 1960s until 2002 using the ECF production process. They contain PFOS and perflouroalkane sulfonates (PFSAs) such as perfluorohexane sulfonate (PFHxS)[1][4]. Legacy PFOS AFFF produced by ECF were voluntarily phased out in 2002, however, use of stockpiled product was permitted after that date[1].
  • Legacy fluorotelomer AFFF This group consists of AFFF manufactured and sold in the U.S. from the 1970s until 2016 and includes all brands that were produced using a process known as fluorotelomerization (FT). The FT manufacturing process produces polyfluorinated substances that can degrade in the environment to perfluoroalkyl substances (specifically PFAAs) including Perfluorooctanoic Acid (PFOA). Polyfluoroalkyl substances that degrade to create terminal PFAAs are referred to as “precursors” [1].
  • Modern fluorotelomer AFFF This group consists of AFFF developed in response to the USEPA 2010-2015 voluntary PFOA Stewardship Program[57], which asked companies to commit to first reducing and then eliminating the following: PFOA, precursors that can break down to PFOA, and related chemicals from facility emissions and products. In response, manufacturers began producing only short-chain fluorosurfactants targeting fluorotelomer PFAS with 6 carbons per chain (C6), rather than the traditional long-chain fluorosurfactants (8 or more carbons per chain). These short-chain PFAS do not breakdown in the environment to PFOS or PFOA[1]. Their toxicity in comparison to long-chain fluorosurfactants is a topic of current research.

In the US, AFFF users including the US DoD (predominantly the Navy and Air Force), civilian airports, oil refineries, other petrochemical industries, and municipal fire departments[58]. AFFF is used, for example, in fire fighting vehicles, in fixed fire suppression systems (including sprinklers and fixed spray systems in or at aircraft hangars, flammable liquid storage areas, engine hush houses, and fuel farms), and onboard military and commercial ships. Fluorinated Class B foams may be introduced to the environment through the following practices[1]:

  • low volume releases of foam concentrate during storage, transfer or operational requirements that mandate periodic equipment calibration
  • moderate volume discharge of foam solution for apparatus testing and episodic discharge of AFFF-containing fire suppression systems within large aircraft hangars and buildings
  • occasional, high-volume, broadcast discharge of foam solution for firefighting and fire suppression/prevention for emergency response
  • periodic, high volume, broadcast discharge for fire training
  • accidental leaks from foam distribution piping between storage and pumping locations, and from storage tanks and railcars

The DoD is currently replacing legacy, long-chain AFFF with modern, short-chain fluorotelomer AFFF and disposing of the legacy foams through incineration. While the PFAS included in modern fluorotelomer AFFF formulations are currently understood to be less toxic and less bioaccumulative than those used in legacy formulations, they are also environmentally persistent and can degrade to produce other PFAS that may pose environmental concerns[1]. While fluorine free alternatives exist, they do not meet the current Mil-Spec[56] which requires that fluorine-based compounds be used. The US DoD is working to revise the Mil-Spec to allow fluorine-free foams, and several states have passed laws prohibiting the use of fluorinated Class B foams for training and prohibiting future manufacture, sale or distribution of fluorinated foams, with limited exceptions[59] (e.g., WA Rev Code § 70.75A.005 (2019); VA § 9.1-207.1 (2019)). Additionally, a bill passed in the US Congress in 2018 directs the FAA to allow fluorine-free foams for use at commercial airports[60]. Research into the development of Mil-Spec compliant fluorine-free foams that will be compatible with existing AFFF and supporting equipment is ongoing and includes the following:

  • Novel Fluorine-Free Replacement for Aqueous Film Forming Foam (Lead investigator: Dr. Joseph Tsang, Naval Air Warfare Center Weapons Divisions) SERDP/ESTCP Project WP-2737
  • Fluorine-Free Aqueous Film Forming Foam (Lead investigator: Dr. John Payne, National Foam) SERDP/ESTCP Project WP-2738
  • Fluorine-Free Foams with Oleophobic Surfactants and Additives for Effective Pool fire Suppression (Lead investigator: Dr. Ramagopal Ananth, U.S. Naval Research Laboratory) SERDP/ESTCP Project WP-2739

Wastewater Treatment Plants

Consumer and/or industrial uses of PFAS-containing materials results in the discharge of PFAS to industrial and municipal wastewater treatment plants (WWTPs). Conventional WWTP treatment processes remove less than 5% of PFAAs[32][61][62]. WWTPs, particularly those that receive industrial wastewater, are possible sources of PFAS release[63][64][65].

Evaluation of full-scale WWTPs has indicated that conventional primary (sedimentation and clarification) and secondary (aerobic biodegradation of organic matter) treatment processes can result in changes in PFAS concentrations and classes. For example, higher concentrations of PFAAs have been observed in effluent than in influent, presumably due to transformation of precursor PFAS[61]. Some data has indicated that the terminal PFAS compounds PFOS and PFOA were among the most frequently detected PFAS in wastewater[66]. A state-wide study in Michigan indicated that PFAS were detected in all of the samples from 42 WWTPs, including influent, effluent, and biosolids/sludge samples, and that the short-chain PFAS were more frequently detected in the liquid process flow (influent and effluent), while long-chain PFAS were more common in biosolids[11].

Multiple studies have found PFAS in municipal sewage sludge[67][11]. The US EPA states that more than half of the sludge produced in the United States is applied to agricultural land as biosolids, therefore there are concerns that biosolids applications may become a potential source of PFAS to the environment[68]. Application of biosolids as a soil amendment can potentially result in transfer of PFAS to soil, surface water and groundwater and can possibly allow PFAS to enter the food chain[69][70][71][72][73]. Limited studies have shown that PFAS concentrations can be elevated in surface and groundwater in the vicinity of agricultural fields that received PFAS contaminated biosolids for an extended period[74]. The most abundant PFAS found in biosolids are the long-chain PFAS[66][11]. Based on the persistence and stability of long-chain PFAS and their interaction with biosolids, research is ongoing to determine PFAS leachability from biosolids and their bioavailability for uptake by plants, soil organisms, and the consumers of potentially PFAS-impacted plants and soil organisms.

Solid Waste Management Facilities

Industrial, commercial, and consumer products containing PFAS that have been disposed in municipal solid waste (MSW) landfills or other legacy disposal areas since the 1950s are potential sources of PFAS release to the environment. Environmental and drinking water impacts from disposal of legacy PFAS-containing industrial and consumer wastes have been documented[75][22][76].

Several studies have identified a wide variety of PFAS in MSW landfill leachates[77][78]. PFAS composition and concentration in leachates vary depending on waste age, climate, and waste composition[79][80]. The relative concentrations of various PFAS in leachate and groundwater from landfill sites is different from those found at WWTPs and AFFF-contaminated sites. In particular, 5:3 fluorotelomer carboxylic acid (FTCA) is a common and often dominant PFAS found in landfills, and has been released from carpet in model anaerobic landfill reactors. This compound could prove to be an indicator that PFAS in the environment originated from a landfill[81][80]. PFAS may also be released to the air from landfills, predominantly as fluorotelomer alcohols (FTOHs) and perfluorobutanoate (PFBA). In one study, total airborne PFAS concentrations were 5 to 30 times greater at landfills than at background reference sites[82]. PFAS release rates within landfills vary over time for a given waste mass, with climate (for example, rainfall) serving as the apparent driving factor for the variations[80][83].

Commercial and Consumer Products

PFAS are widely used in consumer products and household applications, with a diverse mixture of PFAS found in varying concentrations depending on the product[84][85][86][87][38][37][16][88]. Environmental releases associated with the commercial and consumer products are primarily related to their production. To a much lower extent, the environmental releases may be associated with the management of solid waste (for example, disposal of used items in a MSW landfill) and wastewater disposal (for example, discharge to WWTPs, private septic systems, or other subsurface disposal systems).

Studies have shown that physical degradation of some consumer products (such as PFAS-treated paper, textiles, and carpets) may release PFAS in house dust[89]. Additionally, studies have also shown that professional ski wax technicians may have significant inhalation exposures to PFAS[90] and snowmelt and surface waters near ski areas could have measurable PFAS impacts[91].

As increased environmental sampling for PFAS occurs, additional information will become available to further our understanding of the major and minor PFAS contributors to the environment.

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