Plain-Language Definitions for Forever Chemicals Terms

This glossary covers over 50 terms used in PFAS science, policy, and regulation. Each entry is written for a general consumer audience. The category line under each term identifies whether it relates to a chemical compound, regulation, health science, treatment technology, agency, or exposure pathway.

A firefighting foam used to suppress flammable liquid fires, particularly jet fuel and petroleum. Historically formulated with PFOS and PFOA as key active ingredients. Used extensively at military bases, airports, and industrial facilities since the 1960s. AFFF use is the single largest known source of localized PFAS groundwater contamination in the United States. Fluorine-free foam (F3) alternatives are now available.
See also: PFOS, PFOA, Military Base Contamination

A federal public health agency within the U.S. Department of Health and Human Services. ATSDR publishes Minimal Risk Levels (MRLs) for toxic substances including PFAS, conducts exposure assessments in contaminated communities, and issues public health guidance. Its 2021 PFAS toxicological profile is one of the most comprehensive summaries of PFAS health evidence available.

See also: Minimal Risk Level, EPA

A water treatment technology that uses resin beads to attract and capture negatively charged PFAS molecules from water. Highly effective at removing both long-chain and short-chain PFAS, including compounds that activated carbon filters miss. More common in municipal systems than residential use but available in point-of-use units. Used by the EPA as a Best Available Technology for PFAS removal.

See also: Granular Activated Carbon, Reverse Osmosis

The process by which a substance builds up in an organism over time faster than it is eliminated. PFAS bioaccumulate in humans and animals because they bind tightly to proteins in blood, liver, and kidney tissue. Unlike fat-soluble contaminants, PFAS accumulate in protein-rich tissues. The longer the carbon-fluorine chain, the more persistent the compound and the greater the bioaccumulation potential.

See also: Half-Life, Body Burden

Solid material remaining after sewage treatment, sometimes applied to agricultural land as fertilizer. Biosolids frequently contain high concentrations of PFAS because wastewater treatment plants cannot remove PFAS from the water stream. They concentrate in the sludge instead. Agricultural application of PFAS-contaminated biosolids is a major pathway for PFAS to enter soil, groundwater, and food crops. Several states have restricted or banned biosolid application on farmland.

See also: Exposure Pathway

The total amount of a chemical present in a person’s body at a given time. For PFAS, body burden reflects cumulative lifetime exposure from all sources: water, food, products, dust, and air. The CDC measures PFAS body burden through the National Health and Nutrition Examination Survey (NHANES). Reducing ongoing exposure is the primary way to lower body burden over time.

See also: Bioaccumulation, NHANES

The defining structural feature of all PFAS. Carbon atoms bonded to fluorine atoms form one of the strongest bonds in organic chemistry, with a bond dissociation energy around 544 kJ/mol. This bond resists breakdown by water, sunlight, microbes, and most chemical reactions, which is why PFAS persist in the environment indefinitely. No known natural process breaks the carbon-fluorine bond at meaningful rates under normal environmental conditions.

See also: PFAS, Persistence

Federal law commonly known as Superfund, enacted in 1980. Authorizes the EPA to clean up contaminated sites and hold polluters financially responsible. The EPA designated PFOA and PFOS as CERCLA hazardous substances in 2024, a landmark decision that made responsible parties liable for PFAS cleanup costs at contaminated sites. Industry groups challenged the designation in court; the DOJ confirmed it would defend the rule in September 2025.

See also:EPA, Superfund, PFOA, PFOS

An annual water quality report that public water systems serving 25 or more people are required to send to customers. CCRs disclose contaminant levels detected in the water supply, the source of the water, and any violations of drinking water standards. Beginning in 2024, many systems must include PFAS monitoring results from UCMR5 in their CCRs. You can request your CCR from your water utility or find it at the EPA’s water quality portal.

See also: UCMR, MCL

The informal name for PFOA (perfluorooctanoic acid), referring to its eight-carbon chain. C8 became widely known through the DuPont contamination case in Parkersburg, West Virginia, where residents near the Washington Works plant were exposed to C8-contaminated drinking water for decades. The C8 Science Panel concluded there was a probable link between C8 exposure and six diseases: kidney cancer, testicular cancer, thyroid disease, high cholesterol, ulcerative colitis, and pregnancy-induced hypertension.

See also: PFOA, DuPont

A finish applied to textiles, particularly outdoor apparel, to make water bead and roll off the surface. Traditional DWR formulations used long-chain PFAS (C8). After regulatory pressure, the industry shifted to short-chain PFAS (C6) alternatives. PFAS-free DWR alternatives using wax or hydrocarbon-based chemistries now exist but were historically considered less durable in extreme wet conditions.

See also: Short-Chain PFAS, Long-Chain PFAS

The lowest concentration of a substance that a laboratory instrument can reliably measure. For PFAS, detection limits have improved dramatically as analytical technology has advanced. Many PFAS can now be detected at concentrations below 1 part per trillion. Lower detection limits mean contamination that previously appeared absent is now measurable.

See also: Parts Per Trillion

A chemical that interferes with the body’s hormonal system by mimicking, blocking, or altering the production or activity of hormones. PFAS act as endocrine disruptors, interfering with estrogen, androgen, and thyroid hormone signaling. Effects are most significant during critical developmental windows: fetal development, infancy, and puberty.

See also: Thyroid Disease, Reproductive Harm

The federal agency responsible for protecting human health and the environment. The EPA sets drinking water standards under the Safe Drinking Water Act, regulates toxic chemicals under TSCA, oversees Superfund cleanup under CERCLA, and runs the UCMR monitoring program. The EPA finalized the first national drinking water MCLs for six PFAS in April 2024.

See also: MCL, CERCLA, UCMR, Safe Drinking Water Act

Liquid waste or discharge released from industrial facilities, wastewater treatment plants, or other point sources into surface water. Industrial effluent is a major pathway for PFAS to enter rivers, lakes, and groundwater. Wastewater treatment plants that process PFAS-contaminated water release PFAS in their effluent because standard treatment technologies do not remove PFAS.

See also: Biosolids, Exposure Pathway

A class of synthetic polymers that contain fluorine atoms bonded to carbon in their molecular structure. Fluoropolymers include PTFE (polytetrafluoroethylene, sold as Teflon), PVDF, and FEP. They are used in non-stick cookware, wire insulation, medical devices, and industrial equipment. Fluoropolymers are a subset of PFAS but are considered more chemically stable than many other PFAS compounds.

See also: PTFE, PFAS

Firefighting foam formulated without any fluorinated chemicals. Developed as a replacement for AFFF, which contains PFOS and PFOA. F3 foams use hydrocarbon-based surfactants and can be effective on Class B fires. Adoption has been driven by regulatory pressure and AFFF phase-out timelines.

See also: AFFF, PFOS, PFOA

A water treatment medium made of carbon processed to have a highly porous surface area. GAC adsorbs PFAS by attracting the molecules to its surface through chemical bonding. Most effective at removing long-chain PFAS like PFOA and PFOS. Less effective for short-chain compounds. Filters must be replaced on schedule or they can release accumulated PFAS back into water.

See also: Reverse Osmosis, Anion Exchange

A class of short-chain PFAS developed by DuPont’s spinoff Chemours as a replacement for PFOA. GenX was marketed as a safer alternative, but studies showed it causes kidney, liver, and immune system effects in animals. It has contaminated the Cape Fear River in North Carolina, affecting drinking water for hundreds of thousands of people. The EPA set an MCL of 10 ppt for GenX in April 2024.

See also: Short-Chain PFAS, PFOA, MCL

The time it takes for the concentration of a substance to decrease by half. PFOS has an estimated serum half-life of approximately 5 years in the human body. PFOA is approximately 3 to 4 years. In the environment, PFAS do not have a meaningful half-life under normal conditions because they do not break down.

See also: Bioaccumulation, Body Burden

A method EPA uses to evaluate health risk from exposure to a mixture of chemicals with similar effects. The HI is calculated as the sum of individual fractions comparing the measured level of each PFAS to its health-based reference concentration. A Hazard Index above 1.0 indicates a mixture of concern. The EPA set an HI-based MCL in April 2024 for mixtures of two or more of PFNA, PFHxS, HFPO-DA, and PFBS.

See also: MCL, PFAS Mixture

Hexafluoropropylene oxide-dimer acid, also known by the trade name GenX. A short-chain PFAS used as a processing aid in fluoropolymer manufacturing. Detected at high levels in the Cape Fear River watershed in North Carolina. The EPA established an MCL of 10 ppt for HFPO-DA in April 2024.

See also: GenX, MCL

A water treatment process in which ions in solution are exchanged with ions attached to a resin material. Anion exchange resins are particularly effective at capturing negatively charged PFAS molecules. Highly effective for short-chain PFAS that activated carbon filters may miss. Listed as a Best Available Technology by the EPA for PFAS removal.

See also: Anion Exchange, GAC, Reverse Osmosis

PFAS with carbon chains of eight or more carbons. PFOA (C8), PFOS (C8), PFNA (C9), and PFDA (C10) are long-chain compounds. Long-chain PFAS bioaccumulate more readily than short-chain compounds and have the strongest body of evidence linking them to adverse health effects.

See also: Short-Chain PFAS, PFOA, PFOS

Liquid that has percolated through solid waste in a landfill, picking up dissolved or suspended materials as it passes. Landfill leachate frequently contains high concentrations of PFAS from disposed products, packaging, and industrial waste. Leachate can contaminate groundwater when landfill liner systems fail or are inadequate.

See also: Exposure Pathway, Groundwater

The highest level of a contaminant that is legally allowed in drinking water supplied by public water systems. MCLs are set as close to the MCLG as technically and economically feasible. They are enforceable standards. The EPA set the first national MCLs for PFAS in April 2024: 4 ppt for PFOA and PFOS, and 10 ppt for PFNA, PFHxS, and HFPO-DA.

See also: MCLG, Safe Drinking Water Act, EPA

The level of a contaminant in drinking water at which no known or expected health risk occurs, with an adequate margin of safety. MCLGs are non-enforceable health goals. When a contaminant is a known or probable carcinogen, the MCLG is set at zero. The EPA set MCLGs of zero for both PFOA and PFOS in April 2024.

See also: MCL, EPA

An estimate of daily human exposure to a hazardous substance below which non-cancer health effects are unlikely. MRLs are set by ATSDR for acute, intermediate, and chronic exposure durations. ATSDR MRLs for PFAS are often more stringent than EPA MCLs.

See also: ATSDR, MCL

An ongoing CDC program that monitors the health and nutritional status of adults and children in the United States. NHANES includes blood sampling for PFAS, providing national-level data on PFAS body burden. NHANES data consistently shows detectable levels of PFAS in most Americans tested.

See also: Body Burden, CDC

A certification standard for point-of-use reverse osmosis drinking water treatment systems. Systems certified under Standard 58 have been independently tested and verified to reduce specific contaminants including PFAS. Verify certifications at nsf.org.

See also: NSF/ANSI Standard 53, Reverse Osmosis

A certification standard for point-of-use and point-of-entry water treatment systems that reduce health-related contaminants. Some activated carbon filters certified under Standard 53 include PFAS reduction claims. Not all Standard 53 certified filters are tested for PFAS; check the specific contaminant reduction claims on the certification.

See also: NSF/ANSI Standard 58, GAC

A family of more than 12,000 synthetic chemicals defined by the presence of carbon-fluorine bonds. The prefix “per” means all hydrogen atoms on the carbon chain have been replaced by fluorine; “poly” means some but not all have been replaced. PFAS are used in hundreds of industrial and consumer applications for their resistance to water, oil, and heat. They are persistent in the environment and in the human body because the carbon-fluorine bond does not break down under normal conditions.

See also: Carbon-Fluorine Bond, PFOA, PFOS, Fluoropolymer

A short-chain PFAS with a four-carbon chain, developed as a replacement for PFOS. PFBS is less bioaccumulative than PFOS but highly mobile in the environment. It is included in the EPA’s Hazard Index MCL for PFAS mixtures.

See also: Short-Chain PFAS, PFOS, Hazard Index

An eight-carbon PFAS used as a processing aid in the manufacture of fluoropolymers including Teflon. Classified by the EPA as a human carcinogen. Linked to kidney cancer, testicular cancer, and other serious conditions. Voluntarily phased out of U.S. production by 2015. The EPA set an MCL of 4 ppt for PFOA in April 2024, with an MCLG of zero.

See also: C8, DuPont, MCL, MCLG

An eight-carbon PFAS used in stain-resistant products (Scotchgard), AFFF firefighting foam, and industrial applications. 3M was the primary manufacturer. Listed as a persistent organic pollutant under the Stockholm Convention. Has a serum half-life of approximately five years in humans. 3M voluntarily phased out PFOS production in 2000. The EPA set an MCL of 4 ppt for PFOS in April 2024, with an MCLG of zero.

See also: AFFF, 3M, MCL, Stockholm Convention

A nine-carbon long-chain PFAS found in food packaging, stain-resistant textiles, and as a breakdown product of other fluorinated compounds. Linked to thyroid disruption, immune effects, and developmental harm. The EPA set an MCL of 10 ppt for PFNA in April 2024, currently under legal challenge.

See also: Long-Chain PFAS, MCL

A six-carbon PFAS used as a replacement for PFOS. Has an estimated biological half-life of approximately 8 years in humans. Linked to thyroid effects. The EPA set an MCL of 10 ppt for PFHxS in April 2024, currently under legal challenge.

See also: PFOS, Short-Chain PFAS, MCL

The tendency of a substance to remain in the environment without breaking down. PFAS resist degradation by sunlight, water, heat, and microbial activity. A contaminated aquifer may remain contaminated for decades or centuries without active remediation.

See also: Half-Life, Carbon-Fluorine Bond

A water treatment system installed where water enters a building, treating all water used in the home. Whole-house PFAS treatment systems using reverse osmosis or GAC are available but significantly more expensive than point-of-use systems.

See also: Point of Use, Reverse Osmosis, GAC

A water treatment system installed at a single outlet, such as a kitchen faucet or under the sink. For PFAS, an NSF/ANSI Standard 58 certified reverse osmosis system at the primary drinking and cooking tap is the most common and cost-effective residential approach.

See also: Point of Entry, NSF/ANSI Standard 58

A unit of concentration equal to one microgram per liter. One ppt is equivalent to one drop of liquid in 20 Olympic-size swimming pools. The EPA’s MCLs for PFOA and PFOS are set at 4 ppt. Modern laboratory instruments can detect PFAS at concentrations below 1 ppt.

See also: MCL, Detection Limit

A unit of concentration equal to one milligram per liter, or 1,000 ppt. Some older PFAS guidance is expressed in ppb. The 2024 federal PFAS MCLs are expressed in ppt because the limits are set at such low concentrations (4 ppt = 0.004 ppb).

See also: PPT, MCL

A fluoropolymer best known by the DuPont trade name Teflon. Used as a non-stick coating on cookware and in many industrial applications. Begins to degrade above approximately 500 degrees Fahrenheit, releasing fluorinated gases. Scratched or worn PTFE coatings can fragment into food. Minnesota banned PFAS in cookware including PTFE as of January 1, 2025.

See also: Fluoropolymer, Non-Stick Cookware

A water purification technology that forces water under pressure through a semi-permeable membrane, removing dissolved solids including PFAS. RO removes 90 to 99 percent of most PFAS. The most effective residential treatment option. Under-sink systems cost $150 to $600. Look for NSF/ANSI Standard 58 certification.

See also: NSF/ANSI Standard 58, GAC, Anion Exchange

The process of cleaning up environmental contamination. PFAS remediation is technically challenging because the chemicals are extremely mobile in groundwater and resistant to standard treatment. Common approaches include pump-and-treat systems, soil excavation, and in-situ treatment using activated carbon. No cost-effective technology currently destroys PFAS completely at contaminated sites.

See also: CERCLA, Superfunds

The federal law that authorizes the EPA to set drinking water standards and regulate public water systems. The SDWA applies only to public water systems; private wells are not covered. The April 2024 PFAS MCL rule was the first time the EPA used SDWA authority to set enforceable limits for PFAS.

See also: MCL, MCLG, EPA

PFAS with carbon chains shorter than eight carbons. Developed as replacements for long-chain PFAS like PFOA and PFOS. Generally have shorter biological half-lives in the human body but are highly mobile in the environment and more readily penetrate water treatment systems. GenX and PFBS are examples.

See also: Long-Chain PFAS, GenX, PFBS

An international treaty adopted in 2001 to eliminate or restrict persistent organic pollutants. Both PFOS and PFOA are listed under the Stockholm Convention, requiring signatory countries to eliminate or restrict their production and use. The United States signed but has not ratified the Convention.

See also: PFOS, PFOA, Persistence

The common name for CERCLA, the federal law that funds and governs cleanup of the nation’s most contaminated sites. Following the 2024 CERCLA designation of PFOA and PFOS as hazardous substances, sites with PFAS contamination became subject to Superfund liability for cleanup costs.

See also: CERCLA, EPA, PFOA, PFOS

The primary federal law governing the manufacture, import, use, and disposal of chemical substances in the United States. In late 2024, the EPA strengthened its TSCA review process for PFAS and other persistent substances, removing exemptions that had allowed certain PFAS to bypass full review.

See also: EPA

A screening measurement that detects all fluorine-containing organic compounds in a sample, including PFAS. Some state laws use a 100 ppm TOF threshold to screen food packaging for PFAS. TOF testing is faster and less expensive than testing for individual PFAS compounds.

See also: Detection Limit, PPT

An EPA program under the Safe Drinking Water Act that requires public water systems to monitor for contaminants not yet regulated but suspected of occurring in drinking water. UCMR5 required monitoring for 29 PFAS between 2023 and 2025, providing the most comprehensive picture yet of PFAS contamination in U.S. public water systems.

See also: Safe Drinking Water Act, EPA, MCL

A DuPont chemical manufacturing plant in Parkersburg, West Virginia, where PFOA was used in the production of Teflon for decades. Contamination of surrounding drinking water affected the community for years. The case led to a class-action lawsuit, the C8 Science Panel, and ultimately to DuPont’s 2015 PFOA phase-out. The story was the subject of the film Dark Waters (2019).

See also: PFOA, C8, DuPont