Understanding PFAS - What They Are, Their Impact, and What We Can Do

Per-and-polyfluoroalkyl substances (PFAS) are a collective name for a broad class of man-made chemicals of emerging concern that have recently been in the spotlight due to potential human and environmental health risks. While the public attention to PFAS is relatively new, the chemicals have been used globally since the 1940s. PFAS are considered emerging contaminants because research is ongoing to better understand the impacts they pose to human and animal health and the environment. PFAS chemicals can be complex but are often characterized by having strongly bonded carbon (C) and fluorine (F) atoms in the 'tail' and water-liking functional groups in the 'head' (Figure 1). Functional groups refer to a group of atoms within a molecule that have their own characteristic properties, for instance, a carboxylate functional group that consists of a carbonyl group (C=O) and a hydroxyl group (OH).

Figure1: Overview of the general structure of non-polymeric, perfluorinated PFAS substances

Because of the strong carbon-fluorine bonds that are hydrophobic (or water-hating) and the hydrophilic (or water-liking) functional groups on the compounds, PFAS can repel water, oil, stains, and some can remain stable even at extreme temperatures. These characteristics make PFAS compounds key ingredients in a wide range of products used in industrial, household, building and construction, textile, medical, and automotive sectors. Some common uses include aqueous film-forming firefighting foams, fireproofing, stain-proofing, surfactants, non-stick cookware, waterproof apparel, packaging, and cosmetics, among many others.

Classes of PFAS Compounds

There are thousands of PFAS chemicals. PFAS compounds have been grouped into different descriptive classifications depending on the chemical bonding characteristics such as the length of the carbon chain (i.e., number of carbon atoms) in the tail, the number of fluorine atoms bonded to carbon atoms in the tail, and the type of functional group in the head, among other characteristics. Tables 1 and 2 below detail the general classification of PFAS compounds and some common examples.

Pathways to the Environment

PFAS chemicals can enter the environment throughout the manufacture, use, and disposal cycle of products that contain PFAS. Some pathways to the environment are as follows:

Industrial emissions
Emissions from industrial manufacturing of PFAS can contribute to total PFAS detected in soil, water, and air. Emissions can occur in the form of wastewater effluents, accidental spills, and leaks among others.

Aqueous film-forming fire-extinguishing foam
Aqueous film-forming foams (AFFFs) have been used to extinguish high-hazard flammable liquid fires such as fuel fires. When applied to a fuel fire, AFFFs produce a liquid film that spreads on the surface of the fire to extinguish the flame and prevent it from reigniting. Such foams are used in training and emergency response events at airports, military bases, firefighting training facilities, chemical plants, shipyards, and refineries. While an effective fuel-fire suppressant, AFFFs contain PFAS, and the deployment of AFFFs has resulted in the release of PFAS into the soil, groundwater, and surface water (Dasu et al., 2022).

Domestic wastewater
Because of PFAS use in various consumer and household products, domestic wastewater can contain different classes of PFAS (some are shown in Tables 1 and 2). Whether domestic wastewater is treated via private on-lot systems or centralized sewage treatment plants, the removal of PFAS from wastewater is influenced by the chemical characteristics of each compound. Therefore, depending on the degree of PFAS removal during treatment, treated wastewater can be a source of PFAS in soil, groundwater, and surface water. Apart from residential areas and businesses, some sewage treatment plants may also treat wastewater from industrial manufacturing facilities. For such sewage treatment plants, concentrations in both untreated and treated wastewater can consequently be influenced by the overall PFAS levels in the wastewater they receive.

Land application of highly contaminated biosolids
Biosolids are the nutrient-rich organic materials generated as byproducts of wastewater treatment. During wastewater treatment, solids components of wastewater are separated from liquid waste through settling processes. These solids, also known as sludge, are further treated via physical and chemical processes to produce the nutrient-rich byproduct commonly referred to as biosolids. Biosolids that meet the US Environmental Protection Agency’s (US EPA) pollutant and pathogen standards can be land-applied at an agronomic rate for the purpose of nutrient addition and soil reclamation. Exceptional quality biosolids can be used in home gardens and landscaping. Biosolids that do not meet agronomic application standards are disposed of at landfills or incinerated.

During wastewater treatment, some PFAS compounds that are highly hydrophobic (water-hating) can prefer to adhere to the solid component of wastewater and can subsequently be detected in biosolids. The concentrations of PFAS in biosolids are not only influenced by the chemical properties of PFAS but also the concentrations of PFAS in the wastewater received by the sewage treatment plants and the treatment technologies used. Land application of highly contaminated biosolids from sewage treatment plants that also treat wastewater from PFAS manufacturing industries has been reported to be a source of contamination in soil, groundwater, and surface water in some states such as Maine, New Mexico, and Michigan. No such contamination has been reported in Pennsylvania.

Landfills
Landfills are used for the disposal of solid waste from residential units, commercial and industrial setups, buildings, and construction. As the waste materials break down, PFAS-containing products can slowly release different PFAS compounds into the leachate that can impact adjacent soil, groundwater, and surface water depending on the structural integrity of the landfill. Some landfills divert leachate for treatment at wastewater treatment plants.

Occurrence in the Environment and Human Exposure

Due to the use of PFAS in a wide range of products, different PFAS compounds have been detected globally in soil, groundwater, surface water, animal tissue, and even human serum. The same properties that make PFAS compounds desirable in different products also contribute to their persistence and widespread detection in the environment. The primary human exposure routes can be dietary through food and drinking water, but exposure can also occur through inhalation of PFAS-contaminated dust particles. PFAS are not readily absorbed through skin, therefore showering or bathing are considered minor exposure pathways (Agency for Toxic Substances and Disease Registry (ATDSR), 2019).

Dietary Exposure to PFAS

Drinking water

A nationwide study by US Geological Survey monitored tap water supplied by both public and private water systems for PFAS. It was estimated that ~45% of the nation’s tap water has at least one PFAS compound. If your drinking water is supplied by a public water system and you are concerned about PFAS in your drinking water, you can contact your water utility to learn more about your drinking water, find out whether they have PFAS monitoring data, or if they can provide any specific recommendations for you.

If you get your drinking water from a private well, spring, or cistern, you are responsible for your own testing and treatment of your drinking water. In Pennsylvania, the Pennsylvania Department of Environmental Protection (PA DEP) has state-accredited labs for PFAS testing in potable water that are available by visiting and searching through the PA DEP Accredited Environmental Laboratories database. PA DEP has also provided instructions on how to search Pennsylvania-accredited labs in the database. In comparison to commonly measured drinking water parameters, PFAS testing is relatively expensive, with per-sample prices in the order of hundreds of dollars. Additional information on testing can be found in this Penn State Extension article: Testing and Treating PFAS Chemicals in Pennsylvania Water Wells.

If you are concerned about the levels of PFAS detected in your water source, point of use (POU) or point of entry water treatment devices can be implemented to lower PFAS levels in drinking water. Common techniques include sorption using granular activated carbon (GAC) or ion exchange resins, as well as reverse osmosis systems. In order to function effectively, these water treatment devices need to be operated and maintained according to manufacturer guidance. US EPA has a detailed summary of the performance of POU treatment devices for PFAS removal.

Food

PFAS can enter foods via environmental contamination or through the use of PFAS-containing products in food processing and packaging. If grown in contaminated soil or water, plants can uptake PFAS and accumulate them in different parts of plant tissue. Similarly, fish in PFAS-contaminated waters can accumulate PFAS in edible tissues, and animals exposed to contaminated feed and water can also have detectable PFAS in tissues and animal by-products.

PFAS levels in fish can be linked to overall PFAS occurrence in the water source, however, there are currently no federal or state fish consumption regulations or guidelines with reference to PFAS. You can determine which waterways are of concern by paying attention to local fish consumption advisories. PA DEP posts fish consumption advisories on their website.  You can also reach out to PA DEP at 717-787-9637 for inquiries about waterways of concern and existing advisories.

PFAS used in food contact materials such as packaging and non-stick coatings can migrate into food. The Food and Drug Administration (FDA) phased out the use of PFOA and PFOS in food packaging and contact surfaces in 2016, however, shorter chain PFAS may be in use as replacements. The FDA has been conducting testing on fresh and processed food to assess overall dietary PFAS exposure. No PFAS was detected in 97% of tested foods; however, at least one PFAS type was detected in 74% of seafood samples from a 2022 targeted seafood survey. Additional testing is planned to better characterize PFAS in exposure through food.

Health Impacts

According to a review of literature conducted by the US EPA, exposure to certain PFAS at certain levels may pose some health impacts, such as reproductive effects, increased risk for cancer,  suppression of the body's immune system, and interference with the body’s hormone system. Knowledge gaps on specific human health effects exist given that there are a wide variety of PFAS chemicals in use and overall individual exposure routes and exposure durations can vary. The extent of human health impact may therefore differ between individuals due to factors including (i) PFAS exposure conditions such as dose and duration of exposure, (ii) type of PFAS compound(s) one is exposed to, and (iii) individual characteristics such as genetic predisposition, age, sex, etc. (Panieri et al., 2022). The National Health and Nutrition Examination Survey (NHANES) has measured blood PFAS levels in the U.S. population since the early 2000s. Following the phase-out of PFOS and PFOA, average blood levels in the general US population have decreased by 85% and 70%, respectively. Research is ongoing to better characterize the human health impacts due to PFAS exposure.  

Regulations

Federal Standards, Advisories, and Rules

On April 10th 2024, US EPA announced the final National Primary Drinking Water Regulations (NPDWR) for six PFAS. The drinking water maximum contaminant levels (MCL) for the six PFAS as shown below. An MCL is an enforceable legal standard that identifies the highest level of a contaminant that is allowed in public drinking water.

As an additional layer of protection, a hazard index MCL of 1 (unitless) will be used to  limit exposure to mixtures containing at least two of  the following: PFNA, HFPO-DA, PFHxS, and PFBS. While different from a typical MCL, this Hazard Index considers the different toxicities of PFNA, GenX chemicals, PFHxS, and PFBS and determines if the combined levels of these PFAS in the drinking water pose a potential risk and require action. The Hazard Index is calculated by dividing the measured concentration in drinking water by a corresponding health-based concentration of the chemical determined not to have a risk of human health effects for each of the four compounds. A total value greater than one would indicate an exceedance of the Hazard Index MCL of 1.

The final MCLs are enforceable federal drinking water standards that will require public water systems to reduce levels of the six PFAS in finished water.  Public water systems are those that regularly provide drinking water to at least 25 individuals. These public water systems will have until 2029 (5 years) to monitor their treated water and implement treatment solutions to lower PFAS levels in finished water if levels exceed the final MCLs. These MCLs do not apply to drinking water from private water systems such as private wells, springs, or cisterns.

For additional information about drinking water regulations and the final PFAS regulations in drinking water visit:

• How EPA Regulates Drinking Water Contaminants
• Per- and Polyfluoroalkyl Substances (PFAS) Final PFAS National Primary Drinking Water Regulation

In 2022, US EPA provided an interim updated lifetime health advisory level for PFOA (0.004 ppt), PFOS (0.02 ppt), GenX (10 ppt) and PFBS (2,000 ppt) (Table 4). The lifetime health advisories are calculated to offer a margin of protection considering PFAS exposure through other routes beyond drinking water. It is important to note that US EPA Health Advisories are not regulatory and are not legally enforceable.

Bottled water is regulated by the US Food and Drug Administration (FDA). However, FDA has not established standards or testing requirements for PFOA, PFOS, GenX chemicals, or PFBS in bottled water currently.

Beyond drinking water, in September 2023, US EPA finalized a rule requiring all manufacturers and importers of PFAS and PFAS-containing articles since 2011 to report information related to chemical identity, uses, volumes made and processed, byproducts, environmental and health effects, worker exposure, and disposal to EPA. This is an effort to better understand PFAS use in order to effectively research, monitor and regulate PFAS.

Pennsylvania's PFAS Rule

In January 2023, the state of Pennsylvania finalized the PFAS MCL rule for PFOA and PFOS in drinking water. The Pennsylvania rule sets an MCL of 14 ng/L or parts per trillion (ppt) for PFOA and an MCL of 18 ng/L or ppt for PFOS. The proposed federal MCLs (Table 3) are lower than the state’s PFAS rule. Since the US EPA final MCLs are more stringent than state regulations, public water systems would state guidelines by following the federal MCLs.

PFAS in Agricultural Systems

PFAS can enter agricultural systems following the beneficial reuse of biosolids if the land-applied biosolids contain elevated levels of PFAS. Depending on the PFAS compound, if biosolids have elevated levels, these compounds can be sorbed to the soil, leach to both surface and groundwater and even be taken up by plants. Farm animals consuming plants and drinking water with elevated PFAS levels may also have detectable PFAS in their systems.

As a landowner, if you are interested in investigating PFAS levels in biosolids that are applied on your property, you may contact the utility or the contracted biosolid distributer. It is likely that the utility has conducted PFAS testing and may be willing to share the concentrations with you. You can also determine PFAS levels at the farm by conducting targeted testing in the farm, i.e., soil, groundwater, surface water, plant tissue, or animal by-products.

There are no federal or state regulations on land application of biosolids with reference to PFAS levels. Biosolids that are not used as a soil amendment are typically incinerated or landfilled. In order to continue the beneficial use of biosolids and also minimize PFAS contamination in agricultural settings, the state of Michigan has developed an Interim Strategy to limit land application of biosolids that are industrially impacted. Following monitoring at sewage treatment plants, a concentration greater than 20 µg/kg of PFOS is used to mark industrially impacted biosolids in Michigan.

If testing reveals that there are elevated PFAS levels at the farm, different management options can be attempted. Research on PFAS destruction is ongoing, but there is no single comprehensive method to eliminate PFAS from all media (i.e., water, soil, plant tissue, animal products, etc.). For animal drinking water and irrigation water, water treatment technologies described earlier can be used to lower PFAS levels. There are no federal or state regulations on PFAS in agricultural soils. 

The state of Maine has established screening levels for agricultural soils. A screening level is the amount of a chemical that has been found to pose a small to no risk of health effects. If you are concerned about elevated PFAS in soil, you may consider planting in uncontaminated plots.

If elevated PFAS are detected in animal products, the initial option would be to determine if the source of contamination is in the animal feed or water. Stopping the use of contaminated feed, grazing on uncontaminated plots, or use of uncontaminated water can help lower animal exposure. Some research has indicated that the concentrations of PFAS in animal products decline when exposure to PFAS, i.e., intake of contaminated feed and water, is stopped. The amount of time, however, can vary depending on the animal (Death et al., 2021).

References

Agency for Toxic Substances and Disease Registry (ATDSR). (2019). An Overview of the Science and Guidance for Clinicians PFAS on Per-and Polyfluoroalkyl Substances (PFAS).

Buck, R. C., Franklin, J., Berger, U., Conder, J. M., Cousins, I. T., Voogt, P. De, Jensen, A. A., Kannan, K., Mabury, S. A., & van Leeuwen, S. P. J. (2011). Perfluoroalkyl and polyfluoroalkyl substances in the environment: Terminology, classification, and origins. Integrated Environmental Assessment and Management, 7(4), 513–541.

Dasu, K., Xia, X., Siriwardena, D., Klupinski, T. P., & Seay, B. (2022). Concentration profiles of per- and polyfluoroalkyl substances in major sources to the environment. In Journal of Environmental Management (Vol. 301). Academic Press. 

Death, C., Bell, C., Champness, D., Milne, C., Reichman, S., & Hagen, T. (2021). Per- and polyfluoroalkyl substances (PFAS) in livestock and game species: A review. In Science of the Total Environment (Vol. 774). Elsevier B.V. 

Panieri, E., Baralic, K., Djukic-Cosic, D., Djordjevic, A. B., & Saso, L. (2022). PFAS Molecules: A Major Concern for the Human Health and the Environment. In Toxics (Vol. 10, Issue 2). MDPI.