Major Source
Industrial manufacturing
Chemical plants producing or using PFAS in coating, plating, and semiconductor manufacturing discharge into waterways and groundwater. Major historic polluters include 3M, DuPont, and Chemours facilities.
PFAS Guide
What are PFAS forever chemicals?
PFAS (per- and polyfluoroalkyl substances) are a family of over 12,000 synthetic chemicals characterized by extremely strong carbon-fluorine bonds — the strongest in organic chemistry. This bond is what makes them "forever chemicals": they don't break down naturally in the environment or in your body.
The EPA's UCMR 5 program (2023–2025) tested US public water systems for 29 specific PFAS compounds plus lithium. Five of those compounds now have enforceable Maximum Contaminant Levels (MCLs).
Understanding "ppt" — parts per trillion
4 ppt is equivalent to 4 drops of water in 250 Olympic-sized swimming pools.
These levels sound impossibly small, but PFAS compounds are biologically active at extremely low concentrations and accumulate in the body over a lifetime of daily exposure. Even trace levels matter.
Why It Matters
What the research has linked PFAS to
PFAS exposure is cumulative — it builds up over years, not hours. The conditions below have been associated with higher long-term PFAS exposure in peer-reviewed studies. Reducing exposure where it's easy is a reasonable precaution; panic isn't.
- Cancer
- Kidney cancer · Testicular cancer · Breast cancer (emerging)
- Thyroid & hormones
- Thyroid disease · Hormone disruption · Metabolic disorders
- Immune system
- Weakened vaccine response · Increased infections · Autoimmune conditions
- Child development
- Low birth weight · Developmental delays · Earlier puberty onset
Sources: EPA · NIH National Toxicology Program · ATSDR · peer-reviewed studies in Environmental Health Perspectives
Regulated PFAS
EPA MCL in EffectThe five with enforceable limits
These five compounds have federally enforceable Maximum Contaminant Levels. Water systems must test for them and take action if limits are exceeded.
PFOA →
Perfluorooctanoic acid
EPA Limit (MCL)
4 ppt
Health Effects
- Kidney cancer
- Testicular cancer
- Thyroid disease
- Immune suppression
- High cholesterol
- Pregnancy-induced hypertension
Organs Affected
Kidneys, liver, thyroid, immune system
Where It Comes From
Teflon/non-stick cookware manufacturing, food packaging, stain-resistant coatings. DuPont's Washington Works plant in WV was a major historical source.
PFOS →
Perfluorooctane sulfonic acid
EPA Limit (MCL)
4 ppt
Health Effects
- Kidney cancer
- Thyroid disease
- Developmental harm in children
- Immune suppression
- High cholesterol
- Liver damage
Organs Affected
Kidneys, thyroid, liver, immune system
Where It Comes From
Firefighting foam (AFFF) at military bases and airports. Scotchgard fabric protector (3M). Banned in the US in 2002 but persists in the environment.
HFPO-DA →
Hexafluoropropylene oxide dimer acid (GenX)
EPA Limit (MCL)
10 ppt
Health Effects
- Classified possible human carcinogen
- Kidney toxicity
- Liver damage
- Developmental toxicity
- Immune effects
Organs Affected
Kidneys, liver, thyroid
Where It Comes From
Manufactured by Chemours as a PFOA replacement at the Fayetteville Works plant in NC. Heavily contaminates the Cape Fear River basin.
PFHxS →
Perfluorohexane sulfonic acid
EPA Limit (MCL)
10 ppt
Health Effects
- Thyroid disease
- Developmental harm
- Liver toxicity
- Neurodevelopmental effects in children
- Immune suppression
Organs Affected
Thyroid, liver, brain (developmental)
Where It Comes From
Used as a PFOS replacement in firefighting foam and stain-resistant products. Found in groundwater near industrial sites and military bases.
PFNA →
Perfluorononanoic acid
EPA Limit (MCL)
10 ppt
Health Effects
- Thyroid disruption
- Immune suppression
- Liver toxicity
- Reproductive toxicity
- Low birth weight
Organs Affected
Thyroid, liver, reproductive system
Where It Comes From
Fluoropolymer manufacturing byproduct. Found near plants in NJ, NC, and TX. Less common than PFOA/PFOS but frequently detected together.
Monitored but Unregulated PFAS
The other twenty-four
These compounds were measured in UCMR 5 but currently have no federal MCL. Absence of a legal limit does not mean absence of risk — many are under active EPA review.
PFBS
Short-chain (C4) No federal limit
PFBS
Perfluorobutane sulfonic acid
Health Effects
- Thyroid disruption
- Reproductive toxicity
- Kidney effects
- Developmental harm in animal studies
Organs Affected
Thyroid, kidneys, reproductive system
Where It Comes From
Used as a replacement for PFOS in industrial applications. Found in Scotchgard reformulations, firefighting foam alternatives, and semiconductor manufacturing wastewater.
Regulatory Status
EPA issued a health advisory of 2,000 ppt in 2022. Minnesota set a state MCL of 100 ppt. Under active EPA review for federal regulation.
PFHxA
Short-chain (C6) No federal limit
PFHxA
Perfluorohexanoic acid
Health Effects
- Liver toxicity
- Developmental effects
- Reduced body weight in offspring
- Thyroid hormone changes
Organs Affected
Liver, thyroid, developing fetus
Where It Comes From
Common degradation product of fluorotelomer-based chemistry. Found in food packaging, stain-resistant treatments, and as a breakdown product of longer-chain PFAS in the environment.
Regulatory Status
Not federally regulated. Under EPA review. Detected in over 70% of UCMR 5 sampled systems with any PFAS detection, making it the most frequently detected unregulated compound.
PFBA
Short-chain (C4) No federal limit
PFBA
Perfluorobutanoic acid
Health Effects
- Liver enlargement
- Thyroid effects
- Developmental toxicity
- Reduced litter size in animal studies
Organs Affected
Liver, thyroid
Where It Comes From
Replacement chemical for PFOA in manufacturing. Also a breakdown product of many longer-chain PFAS. Found near fluorochemical plants and in wastewater treatment effluent.
Regulatory Status
Not federally regulated. Michigan set a health-based value of 420,000 ppt — orders of magnitude above the EPA's PFOA limit, reflecting PFBA's much shorter biological half-life.
PFDA
Long-chain (C10) No federal limit
PFDA
Perfluorodecanoic acid
Health Effects
- Liver damage
- Immune suppression
- Thyroid disruption
- Reproductive toxicity
- Potential carcinogen
Organs Affected
Liver, immune system, thyroid, reproductive system
Where It Comes From
Byproduct of fluoropolymer manufacturing. Often found alongside PFOA and PFOS at contaminated sites. Present in some food packaging and industrial coatings.
Regulatory Status
Not federally regulated, but bioaccumulates more than PFOA and is frequently detected in human blood samples. Likely candidate for future EPA regulation.
PFUnA
Long-chain (C11) No federal limit
PFUnA
Perfluoroundecanoic acid
Health Effects
- Liver toxicity
- Immune effects
- Developmental harm
- Increased cholesterol
Organs Affected
Liver, immune system
Where It Comes From
Byproduct of fluoropolymer production. Found in contaminated fish, particularly in the Great Lakes region. Present in food packaging leachate.
Regulatory Status
Not federally regulated. One of the longest-chain PFAS monitored in UCMR 5. Frequently used as a marker of fluoropolymer manufacturing emissions.
PFPeA
Short-chain (C5) No federal limit
PFPeA
Perfluoropentanoic acid
Health Effects
- Liver effects
- Limited toxicological data available
- Thyroid hormone disruption in animal studies
Organs Affected
Liver, thyroid
Where It Comes From
Degradation product of fluorotelomer alcohols. Found in landfill leachate, wastewater effluent, and as a breakdown product of consumer product coatings.
Regulatory Status
Not federally regulated and lacks a federal health advisory level. Very mobile in groundwater due to short chain length.
PFHpA
Medium-chain (C7) No federal limit
PFHpA
Perfluoroheptanoic acid
Health Effects
- Liver toxicity
- Thyroid disruption
- Developmental effects
- Reduced body weight
Organs Affected
Liver, thyroid
Where It Comes From
Impurity and degradation product in PFOA manufacturing. Found at legacy industrial sites and in landfill leachate. Also present in some food contact materials.
Regulatory Status
Not federally regulated. Falls just below the C8 threshold that defines long-chain PFAS for most regulatory purposes.
6:2 FTS
Fluorotelomer (C6-based) No federal limit
6:2 FTS
6:2 Fluorotelomer sulfonic acid
Health Effects
- Liver effects
- Thyroid disruption
- Kidney toxicity
- Potential developmental effects
Organs Affected
Liver, thyroid, kidneys
Where It Comes From
Major component of modern AFFF firefighting foams. Found at high concentrations around military bases, airports, and fire training sites. Also used in chrome plating.
Regulatory Status
Not federally regulated. The Department of Defense is phasing out fluorinated AFFF for civilian airport firefighting, but 6:2 FTS-based foams remain in use at some military installations.
8:2 FTS
Fluorotelomer (C8-based) No federal limit
8:2 FTS
8:2 Fluorotelomer sulfonic acid
Health Effects
- Liver toxicity
- Potential carcinogen (transforms to PFOA)
- Endocrine disruption
Organs Affected
Liver, endocrine system
Where It Comes From
Found in older-generation AFFF foams and some industrial surfactant applications. Less common than 6:2 FTS but found at legacy contamination sites.
Regulatory Status
Not federally regulated. Being phased out in newer AFFF formulations but persists at legacy AFFF release sites.
NMeFOSAA
PFOS precursor (C8-based) No federal limit
NMeFOSAA
N-methyl perfluorooctane sulfonamido acetic acid
Health Effects
- Liver toxicity
- Elevated cholesterol
- Immune effects
- Developmental toxicity
Organs Affected
Liver, immune system
Where It Comes From
Metabolite of N-methyl PFOS-based compounds used historically in food packaging, carpet treatments, and 3M's Scotchgard products.
Regulatory Status
Not federally regulated. Transforms into PFOS in the body, so detection effectively contributes to PFOS exposure.
NEtFOSAA
PFOS precursor (C8-based) No federal limit
NEtFOSAA
N-ethyl perfluorooctane sulfonamido acetic acid
Health Effects
- Liver toxicity
- Elevated cholesterol
- Thyroid effects
- Immune suppression
Organs Affected
Liver, thyroid, immune system
Where It Comes From
Metabolite of N-ethyl PFOS-based chemicals. Used in insecticide formulations (sulfluramid) and historical pesticide applications in the southern US and Latin America.
Regulatory Status
Not federally regulated. Like NMeFOSAA, transforms into PFOS in the human body.
FOSA
PFOS precursor (C8) No federal limit
FOSA
Perfluorooctane sulfonamide
Health Effects
- Neurological effects
- Liver toxicity
- Developmental harm
- Transforms to PFOS in the body
Organs Affected
Brain, liver, developing fetus
Where It Comes From
Intermediate in the production and environmental degradation of PFOS-based compounds. Found in contaminated fish and wildlife, particularly marine mammals.
Regulatory Status
Not federally regulated. Can cross the blood-brain barrier more readily than PFOS itself; bioaccumulates in fatty tissue.
ADONA
Ether-based (C7) No federal limit
ADONA
4,8-Dioxa-3H-perfluorononanoic acid
Health Effects
- Liver enlargement
- Kidney effects
- Limited human toxicological data
Organs Affected
Liver, kidneys
Where It Comes From
Manufactured by 3M/Dyneon as a PFOA replacement in fluoropolymer production. Primary contamination source is the Gendorf chemical complex in Germany; detected in US water near fluoropolymer plants.
Regulatory Status
Not federally regulated. Not widely detected in UCMR 5, suggesting limited US contamination compared to other PFAS.
PFEESA
Ether sulfonate (C4-based) No federal limit
PFEESA
Perfluoro(2-ethoxyethane)sulfonic acid
Health Effects
- Thyroid disruption
- Liver effects
- Limited toxicological data available
Organs Affected
Thyroid, liver
Where It Comes From
Used as a replacement for PFBS in some industrial applications, particularly in China. Detected in drinking water downstream of fluorochemical manufacturing facilities.
Regulatory Status
Not federally regulated. Emerging replacement PFAS with very limited health research.
How to Remove PFAS from Drinking Water
What actually works at the tap
Most effective
90–99.9%
Reverse osmosis
RO systems force water through a semi-permeable membrane that physically blocks PFAS molecules. Look for NSF/ANSI 58 or NSF P473 certification. Under-sink units range $150–$600; countertop RO systems are also available with no installation required.
Effective
Long-chain
Activated carbon
High-quality granular activated carbon (GAC) or carbon block removes PFOA and PFOS effectively but is less reliable for short-chain PFAS. Look for NSF/ANSI 53 certification. Available in pitcher form ($30–$100) and under-sink units ($100–$300).
Does NOT work
Brita · PUR
Standard pitcher filters
Basic Brita, PUR, and similar filters using standard carbon are not certified for PFAS removal. If PFAS above the MCL is detected in your water, you need a filter specifically certified for PFAS under NSF/ANSI 58 or NSF P473.
How PFAS Gets Into Drinking Water
Contamination sources
PFAS reach public water supplies through several well-documented pathways. Knowing the source helps explain why contamination is concentrated in certain areas.
Major Source
Military bases & airports
Aqueous film-forming foam (AFFF) used in fire suppression training contains high concentrations of PFOS and PFOA. Decades of use at over 700 military installations have contaminated surrounding groundwater.
Diffuse Source
Consumer products & landfills
Non-stick cookware, waterproof clothing, food packaging, and stain-resistant carpets slowly release PFAS. Landfill leachate from disposed products is a growing contamination pathway as older products break down.
Emerging Concern
Sewage sludge & biosolids
Wastewater treatment concentrates PFAS in sewage sludge. When that sludge is applied to agricultural land as fertilizer, PFAS leach into groundwater and surface water — spreading contamination far from the original source.
Glossary
Acronyms, decoded
The most common acronyms below. For the full glossary including NSF/ANSI standards, IARC, ATSDR, GAC, RO, AFFF and 15+ more terms, see the dedicated Glossary page.
- MCL — Maximum Contaminant Level
- The highest amount of a contaminant legally permitted in public drinking water, set by the EPA. Water utilities must notify customers and take corrective action if their water exceeds the MCL. PFOA and PFOS have an MCL of 4 ppt; PFNA, PFHxS, and HFPO-DA have an MCL of 10 ppt.
- ppt — Parts Per Trillion
- The unit of measurement for PFAS in water. 1 ppt = 1 nanogram per liter (ng/L). To visualize: 4 ppt is equivalent to 4 drops of water dissolved in 250 Olympic-sized swimming pools. These levels sound vanishingly small, but PFAS accumulate in the body over years.
- PFAS — Per- and Polyfluoroalkyl Substances
- An umbrella term for a family of over 12,000 synthetic chemicals. All share extremely strong carbon-fluorine bonds that resist breaking down in water, soil, or the human body — hence the nickname "forever chemicals." PFOA, PFOS, PFNA, PFHxS, and HFPO-DA (GenX) are the five with enforceable US limits.
- PFOA / PFOS
- Perfluorooctanoic acid and perfluorooctane sulfonic acid — the two most widely studied PFAS compounds. PFOA was used in Teflon and non-stick cookware manufacturing; PFOS in Scotchgard fabric protector and military firefighting foam. Both are now restricted globally and carry an EPA MCL of 4 ppt.
- UCMR 5 — Unregulated Contaminant Monitoring Rule (5th cycle)
- The EPA testing program (2023–2025) that required roughly 10,000 public water systems to test for 29 PFAS compounds. Results were published in January 2026 and form the entire data set behind CheckPFAS. "Unregulated" refers to the compounds being monitored before limits were set — most of the 29 now have or are expected to receive MCLs.
- PWS / PWSID — Public Water System / ID
- A PWS is any entity that provides drinking water to at least 25 people or 15 connections year-round. Each system is assigned a unique PWSID (Public Water System Identifier) by the EPA — a state-prefixed alphanumeric code used to track testing results across datasets.
- NSF — NSF International
- An independent organization that tests and certifies water treatment products. Relevant certifications: NSF/ANSI 58 and NSF P473 verify PFAS reduction in reverse osmosis and pitcher/point-of-use filters respectively. NSF/ANSI 53 covers general health effects (including some PFAS for long-chain compounds). NSF/ANSI 42 covers taste and odor only — not PFAS.
- RO — Reverse Osmosis
- A filtration process that forces water through a semi-permeable membrane under pressure, physically blocking PFAS molecules. The most effective consumer technology for PFAS removal: 90–99.9% reduction for all chain lengths. Available as under-sink systems ($150–$600) or countertop units.
- AFFF — Aqueous Film-Forming Foam
- A fire-suppression foam used extensively at military bases, airports, and industrial facilities. AFFF formulations contained high concentrations of PFOS and PFOA and are responsible for some of the worst PFAS groundwater contamination in the US. The DoD has identified over 700 impacted sites.
- GW / SW — Groundwater / Surface Water
- The two source water categories for public water systems. Groundwater comes from underground aquifers accessed via wells; surface water from rivers, lakes, and reservoirs. Groundwater systems near industrial facilities, military bases, or agricultural land often show higher PFAS concentrations due to soil infiltration.
Frequently Asked Questions
Does boiling water remove PFAS?
No. Boiling water does not remove PFAS — in fact, it can concentrate them by evaporating water while leaving PFAS behind. Only physical filtration (RO, activated carbon) or distillation is effective.
Is bottled water free of PFAS?
Not always. Some bottled water brands have tested positive for PFAS, and the FDA regulates bottled water less strictly than the EPA regulates tap water. Certified filtered tap water is often safer and more sustainable than bottled water.
Can I shower in PFAS-contaminated water?
The primary PFAS exposure risk is ingestion — drinking and cooking with contaminated water. Dermal absorption through bathing is generally considered low risk, though research is ongoing. If your water exceeds MCL limits, focus on filtering drinking and cooking water first.
Does the carbon filter in my refrigerator remove PFAS?
Standard refrigerator filters (NSF/ANSI 42 certified) are designed to improve taste and odor — they are not certified to remove PFAS. Look for a filter specifically certified to NSF/ANSI 53 or NSF P473 for PFAS reduction.
What is the difference between a "detection" and "exceeding the MCL"?
A detection means any measurable level of PFAS was found. Exceeding the MCL means the level surpasses the EPA's legal limit (e.g., 4 ppt for PFOA/PFOS), which requires water utilities to take action. Both are concerning, but exceeding MCL represents a higher immediate risk.
My water system says it's compliant — do I still need to worry?
Compliance means levels are below the federal MCL. However, the MCLs are set based on feasibility and economic factors, not purely on health — some scientists argue the safe level is effectively zero. If you have infants, are pregnant, or have a compromised immune system, additional filtration is prudent even at sub-MCL levels.