Per- and polyfluoroalkyl substances (PFAS) constitute a diverse group of highly fluorinated synthetic chemicals including over 7000 different substances (Buck et al. 2011; Henry et al. 2018; EPA 2019a). For over 60 years, PFAS have been used in a variety of industrial and commercial products, including stain and water repellents for textiles, paper products, and food packaging. PFAS are also found in pharmaceuticals, personal care products, non-stick coatings on cookware, surfactants, and fire-fighting foams (ITRC 2018). Some PFAS persist indefinitely in the environment and have long (e.g., several years) biological half-lives (ITRC 2018; Post 2021). Therefore, PFAS have been coined “forever chemicals.” Over the past two decades, PFAS have been detected in humans and a wide variety of wildlife, which has raised public concern. In this section, sources, environmental fate, exposure routes, toxicity, and regulations of PFAS are discussed.
H2. Background and Sources: PFAS
PFAS are classified as per- (fully, Figure 1) and poly- (partially) fluoroalkyl substances which contain at least one, fully fluorinated carbon group (Buck et al. 2011; Henry et al. 2018; ITRC 2018; Johnson et al. 2021). This class of chemicals has an array of different physical, chemical and biological properties, and their environmental fates (where they will distribute) and effects on organisms are vastly diverse (Buck et al. 2011; Henry et al. 2018; ITRC 2018). PFAS include perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which are two of the most concerning and well-studied groups (Figure 1); as well as other subclasses such as other perfluoroalkyl carboxylic acids (PFCA), other perfluoroalkyl sulfonic acids (PFSA), perfluoroalkanes, perfluoroalkyl ether, and others not yet described (Post et al. 2012; Vierke et al. 2012; Strynar et al. 2015; Sun et al. 2016; Johnson et al. 2021). All PFAS are chemically, thermally, and biologically stable which contribute to their persistence in the environment, especially those with long carbon chains like PFOA and PFOS (Buck et al. 2011).
PFAS were originally developed over 60 years ago to be used as surfactants and surface protectors for their properties of repelling water, grease, and stains (Kissa 1994). Currently, PFAS are used in non-stick coatings on cookware (e.g., “Teflon”), textiles (e.g., fabric protectors on carpets, furniture, and clothing, such as waterproof jackets), pharmaceuticals, personal care products (e.g., waterproof mascara and sunscreen), medical devices, as well as a variety of food packaging (e.g., microwave popcorn bags, take-out containers, pizza box wrappers, etc.) (Figure 2; Rao and Baker 1994; ITRC 2018;De Silva et al. 2021). In addition, PFAS are found in waxes, paints, and aqueous film-forming foams (firefighting foams) used to extinguish fires involving highly flammable liquids (Figure 2; Paul et al. 2009; Lindstrom et al. 2011; Salice et al. 2018). The same un-paralleled properties that make PFAS so beneficial in industrial and commercial applications, also make these chemicals very persistent in the environment (Johns and Stead 2000).
Industrial use of long-chain PFSAs (e.g., PFOS) and long-chain PFCAs (e.g., PFOA) has ceased, mainly due to increasing public concern about PFAS exposure and the activities of the PFOA stewardship programs in the US and Europe, and regulatory agencies (EPA 2016a; EPA 2019a; De Silva et al. 2021). PFOS production was voluntarily phased out by the primary producer 3M in 2001 (3MCompany 1999). However, many other derivatives are still in use and new ones are being developed as replacements (Schellenberger et al. 2019; De Silva et al. 2021). Additionally, it is now known that PFOS, PFOA and other legacy PFAS compounds only account for a small fraction of the total number of PFAS (EPA 2020d).
H3. PFAS in the Environment
PFAS have been released in the environment since the 1950s and are now present worldwide, with the ocean considered the final sink for these contaminants (Armitage et al. 2009a; Armitage et al. 2009b). Even though some functional groups (i.e., carbon-fluorine bonds) of PFAS are very stable, many PFAS breakdown and reform into other PFAS in the environment, presenting challenges for monitoring their presence and modeling their transport in aquatic systems (Johnson et al. 2021). The physical and chemical properties and mode of release of PFAS into the environment can affect their spatial distribution.
PFAS are released into the environment through production, use, and disposal processes (De Silva et al. 2021). PFAS concentrations are generally highest at sites near their release (Paustenbach et al. 2007; Pistocchi and Loos 2009; Hoffman et al. 2011; Shin et al. 2011; Shi et al. 2015). Global PFAS emissions predominantly occur from facilities that manufacture fluorochemicals and those that use PFAS. Even with relatively few fluoropolymer production plants worldwide (33 estimated in 2002; Prevedouros et al. 2006), emissions from these facilities can affect large geographical areas, contaminating drinking water hundreds of miles away from the source of emissions (Herrick et al. 2017; De Silva et al. 2021).
Local sources of PFAS contamination include PFAS-manufacturing and PFAS-using factories, firefighting foams, landfills, wastewater treatment plants and biosolids (Figure 3; Sinclair and Kannan 2006; Zhang et al. 2016; Coggan et al. 2019; EPA 2020g; De Silva et al. 2021). PFAS from firefighting foams used for fire suppression or training activities at fire stations and training areas, military bases, and commercial airports have resulted in widespread PFAS contamination in adjacent terrestrial and aquatic systems including soil, sediment, surface water, ground water, and drinking water (Karrman et al. 2011; Houtz et al. 2013; Anderson et al. 2016; DOD 2017; Maga et al. 2021). Additionally, PFAS-containing materials are taken to landfills, where leachate can contaminate wastewater and surface waters in surrounding areas (Huset et al. 2011; Lang et al. 2017; Masoner et al. 2020). Wastewater treatment plants treat the influent water for various contaminants, however, currently PFAS are not removed. Therefore, the effluent and biosolids from wastewater treatment plants can contain high concentrations of PFAS (Sinclair and Kannan 2006; Coggan et al. 2019). Higher concentrations of PFAS have been detected in the surface and drinking waters of aquatic systems containing high numbers of wastewater treatment plants in the US (Hu et al. 2016). Additionally, biosolids are commonly used as fertilizer on agricultural lands, and reclaimed water is used for irrigation of agricultural areas, golf courses, and residential areas in the US (De Silva et al. 2021). This may result in high concentrations of PFAS in the soil, ground water, crops, and animals in these areas (Choi et al. 2019; Coggan et al. 2019; Lazcano et al. 2019). The LSJR has many wastewater treatment plants discharging effluent, several areas utilizing reclaimed water to reduce nutrient loading into the system, and biosolids are used in agricultural areas surrounding the LSJR. The PFAS concentrations in the LSJR basin are not known and no data are currently available. Currently, there are no plans to collect PFAS on the LSJR.
H4. Biological Exposure, Toxicity, and Testing: PFAS
PFAS exposure routes include ingestion of food and water, inhalation of air and dust particles, and dermal absorption. Estimating dietary PFAS exposure to humans is calculated by measuring the PFAS concentrations in different foods and multiplying that by food consumption rates for a particular group or population (De Silva et al. 2021). There have been several challenges to accurately estimate PFAS concentrations in foods. These include obtaining PFAS data from a representative sample of a variety of foods and determining the changes in PFAS concentrations incurred when foods contact other materials and are cooked in different ways (De Silva et al. 2021). Additionally, food consumption rates can vary by geographic location, cultural customs, and age and sex of the individual (EPA 2011b). PFAS has been measured and reported in the below detection to low nanogram per gram range for milk, meat, vegetables, fruits, and bread (Ericson et al. 2007; Fromme et al. 2007; Tittlemier et al. 2007).
Besides food consumption, PFAS exposure could occur through drinking water, and PFAS have been detected in the drinking water from several locations throughout the US (EPA 2019a). In some communities like Parkersburg, West Virginia and Fayetteville, North Carolina, PFAS air emissions have contaminated drinking water sources; yet not much is known about the process of this occurrence or the extent of airborne exposure to PFAS versus ingestion of PFAS contaminated drinking water (De Silva et al. 2021).
PFOS and PFOA are found in high concentrations in dust, whereas other PFAS are more volatile (found in vapor phase; Weschler and Nazaroff 2008). Inhalation and ingestion of contaminated dust is a pernicious PFAS exposure route, particularly because most North Americans spend roughly 90% of their time indoors and PFAS are frequently utilized in products designed for indoor use (e.g., carpets, furniture, cookware, clothing, etc.; Beesoon et al. 2012). PFAS vary extensively in their physical and chemical properties and are therefore estimating indoor exposure for this group of contaminants is especially difficult (Weschler and Nazaroff 2008). Levels of PFAS in dust have been reported in the micrograms per gram range (Eriksson and Karrman 2015; Lankova et al. 2015; Winkens et al. 2018). Information is lacking on indoor PFAS exposure concentrations, partially due to analytical limitations. However, indoor PFAS air concentrations are estimated to be several orders of magnitude higher than outdoor air PFAS concentrations (Shoeib et al. 2004; Shoeib et al. 2005; Shoeib et al. 2011). PFAS levels in outdoor air are higher in urban areas than rural ones, with concentrations up to hundreds of picograms per cubic meter (Martin et al. 2002; Fromme et al. 2007; Wong et al. 2018).
PFAS concentrations in measured human blood plasma range from the part per billion (ppb; µg/L) to part per million (ppm; mg/L) range, depending on geographical location, with the highest values detected in residents near contaminated sites and occupationally exposed individuals (e.g., those working in fluorochemical production plants; Shoeib et al. 2004; Olsen et al. 2003a; Olsen et al. 2003b; Olsen et al. 2005). Sex and age of the individual and PFAS type can also influence the PFAS concentration in tissues (De Silva et al. 2021). One approach estimates external PFAS exposure (mass per kilogram of body weight) using exposure frequency and duration (De Silva et al. 2021). There are many uncertainties with all the estimation methods to date. Data are limited to individuals living near PFAS manufacturing plants or those seeking medical care for another condition, such as pregnancy (Jiang et al. 2014; Ramli et al. 2020).
The bioaccumulation of nonionic organic contaminants like PCBs and some pesticides is well known. Despite numerous research and publications over the past 10 years on PFAS, describing PFAS accumulation has been more complicated and challenging for scientists, with many noted differences among species and sex (Conder et al. 2008; Li et al. 2017; Johnson et al. 2021). Certain PFAS, including PFSA and PFCA, have been reported to bioaccumulate in humans and wildlife, have long biological half-lives (not readily excreted from the body), and have been detected in food and drinking water as discussed above (EPA 2019a). The contribution of precursor compounds which may form PFAS in the body is another important area of study in which more research is needed (Renner 2001).
Toxicity data for most PFAS are limited, with most of the studies focused on PFOA and PFOS exposure (Fenton 2020). Data collected from these studies as well as epidemiological studies have shown correlations between PFAS exposure and a myriad of health effects in humans and animals, including suppressed immune system, altered thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, alterations in reproduction and development, and cancer (Fenton 2020). Human health effects in communities with PFAS-contaminated drinking water include increased serum cholesterol and decreased antibody response to vaccinations (Post et al. 2017). Infants are particularly sensitive to PFAS toxicity from exposure through contaminated water in prepared formula or from maternal transfer of PFAS via breast milk (Choi et al. 2019; Goeden et al. 2019). Mechanisms of toxicity for studied PFAS are not well understood, and data are lacking on the effects of many other PFAS as well as the effects of PFAS mixtures on health.
Developing suitable analytical techniques for PFAS detection has also been a challenge for many scientists (De Silva et al. 2021). Initially, analytical techniques were focused on detection of PFOA and PFOS primarily, however, techniques have advanced to now include about 40 PFAS in routine measurements using liquid chromatography-tandem mass spectrometry (LC-MS/MS) (De Silva et al. 2021). Method development is progressing to detect volatile species, new PFAS compounds and total fluorine in environmental and biological samples. Total fluorine measurements provide a better estimate of total PFAS exposure; and several methods each with different pros and cons have been developed for this purpose. “Targeted” PFAS analysis is the most common approach to date, which is a very sensitive and precise LC-MS method of nonvolatile PFAS compounds. This method is used for water, airborne particulates, food, solids, and consumer products (De Silva et al. 2021). In addition, this method is used for determination of PFAS in biological samples. The availability of standards and reference materials for newer PFAS has been a limitation of analytical method development (Xiao 2017; Land et al. 2018).
H5. Regulations: PFAS
There are no national drinking water standards for PFAS in the US currently (ASDWA 2019). The US Environmental Protection Agency established nonregulatory drinking water lifetime health advisories of 70 ng/L for individual and total PFOA and PFOS in 2016 (EPA 2016b, 2016a;Post 2021). State-specific guidelines were established in nine states by May 2020, because it was concluded that the federal health advisories were insufficiently protective for PFOA and PFOS. Additionally, 10 states (excluding Florida) had developed guidelines for other PFAS (EPA 2020d; Post 2021). The guidelines for PFOA and PFOS range from 8 to 35 ng/L and 10 to 40 ng/L, respectively (Post 2021).
Seven of the nine state that developed their own drinking water guidelines, also developed Reference Doses for PFOA and PFOS (Post 2021). The US Environmental Protection Agency Reference Dose for PFOA is 20 ng/kg/day and the state Reference Doses range from 1.5 to 18 ng/kg/day. The state Reference Doses are more conservative because their guidelines are based on more sensitive toxicological effects (e.g., increased relative liver weight) than those used by the federal government (Post 2021). The US Environmental Protection Agency Reference Dose for PFOS is 20 ng/kg/day and the state Reference Doses range from 1.8 to 5 ng/kg/day, using decreased immune response as the more sensitive endpoint (Post 2021).
PFAS in fertilizers and biosolids have not been regulated and currently the US Environmental Protection Agency has not developed standards for these. The states are investigating implications for PFAS exposure in these types of applications (Post 2021).
PFAS compounds present significant environmental challenges due to their complexity, mobility, and stability, and more research is needed to elucidate the threat of these contaminants. This review highlights the current understanding about PFAS sources, exposure, and effects, and discusses knowledge gaps. Increased analytical capabilities for detecting PFAS and better understanding of the contribution of PFAS from various fluoropolymers will strengthen predictions of PFAS exposure to humans and wildlife. Field monitoring and assessment (with modern analytical techniques) of PFAS in water, sediment, and biota in aquatic systems worldwide are essential. PFAS monitoring in the environment, particularly in the LSJR, is vital. Given the uses and modes of PFAS contamination, it is likely that PFAS are present in the LSJR.