At a glance
| Chemical family | Perfluoroalkyl sulfonic acid (4-carbon perfluoroalkyl chain — "C4 PFAS" or "short-chain perfluorosulfonate"); PFOS replacement chemistry |
| CAS number | 375-73-5 (acid form); 29420-49-3 (potassium salt, the common manufactured form) |
| Classification | Not formally evaluated by IARC as a separate compound (PFAS class-level IARC monograph reviews ongoing but PFBS-specific Group classification not established); US EPA IRIS chronic oral RfD 0.0003 mg/kg/day (300 ng/kg/day, finalized 2021); US EPA Final PFAS NPDWR April 2024 — PFBS included in Hazard Index with HBV 2,000 ng/L for drinking water; ATSDR Toxicological Profile for Perfluoroalkyls covers PFBS; no individual federal MCL (only PFOA, PFOS, PFHxS, PFNA, HFPO-DA have individual MCLs) |
| Where you encounter it | AFFF firefighting foams (PFOS-replacement "C4 foam" formulations); Scotchgard reformulation (3M post-2002 textile/carpet treatments); firefighter turnout gear water/oil repellents (some pre-2022 manufacturer specifications); grease-resistant paper food packaging; drinking water in communities downstream of 3M plants (Cottage Grove MN, Decatur AL) and fire training facilities; indoor dust from treated textiles; ambient air near specific industrial sources |
| Sleep micro environment relevance | Moderate. Treated carpet and upholstery shed PFBS into indoor dust over years of use; the dust reservoir contributes to total household PFAS exposure. For firefighter households with contaminated turnout gear stored at home, the take-home pathway documented for PFOA/PFOS applies in parallel to PFBS |
| Activated carbon capture | Not applicable for VOC-phase capture. For drinking water, granular activated carbon (GAC) with appropriate certification is effective for PFBS removal; reverse osmosis (NSF/ANSI 58) is more reliable. The residential intervention is water filtration, not air capture. Inferred from established residential PFAS water-treatment performance; the air-capture chemistry that the broader Atlas focuses on is not the relevant intervention for PFAS |
What it is
PFBS — perfluorobutanesulfonic acid, CAS 375-73-5 — is a 4-carbon perfluoroalkyl sulfonic acid. Structurally PFBS is identical to PFOS except for the chain length: PFOS has eight perfluorinated carbons (C8), PFBS has four (C4). Every carbon in the chain is fully fluorinated, which makes the PFAS class environmentally persistent — the C–F bond does not break down through environmental degradation on any human-relevant timescale. The sulfonate head group gives PFBS and PFOS their surfactant properties (fluorinated tail hydrophobic and oleophobic; sulfonate hydrophilic), which is the chemistry that made PFAS useful for everything it was historically used for.
The PFBS commercial story starts in 1999-2002, when 3M voluntarily phased out PFOS production following internal toxicokinetic studies and emerging external research linking PFOS to immune and developmental effects. The replacement chemistry was short-chain: Scotchgard, certain AFFF formulations, and food contact applications were reformulated using PFBS-based and other short-chain precursors. The "shorter chain = safer" framing rested primarily on the substantially shorter human serum half-life — approximately 25-46 days versus PFOS's 5+ years — but PFBS shares the same environmental persistence that drove the PFOS regulatory cycle to begin with.
Where you encounter it
From AFFF firefighting foams
Aqueous Film-Forming Foam (AFFF) is the firefighting foam class used for Class B (flammable liquid) fires — primarily fuel fires at airports, refineries, and military bases, and historically used routinely in fire training. AFFF formulations contained PFOS through the 2000-2002 period when 3M's phase-out forced reformulation. The replacement chemistry at many fire training facilities, civilian airports, and Department of Defense installations was short-chain PFAS including PFBS-based systems. Decades of training-area soil and groundwater contamination at these sites has been documented — the US EPA, US DoD, and multiple state environmental agencies maintain inventories of AFFF-contaminated sites with PFOS, PFOA, PFBS, and other PFAS persisting in groundwater plumes. Even where C4 PFBS chemistry replaced C8 PFOS chemistry post-2002, the historical PFOS contamination persists in the same soil and water matrices.
The DoD has been transitioning toward fluorine-free firefighting foams since the late 2010s under congressional mandate; the National Defense Authorization Act of 2020 set a 2024 deadline for DoD to publish a military specification for fluorine-free AFFF alternatives. The transition is incomplete as of 2026, and substantial PFBS-containing AFFF inventory remains at civilian operational and training facilities not subject to the DoD mandate.
From firefighter turnout gear
PFAS-treated outer shell fabric in firefighter turnout gear historically used C8 chemistry through approximately 2015, when manufacturer reformulations shifted toward C6 (PFHxA-based) and C4 (PFBS-based) durable water repellent (DWR) systems. Specific gear models, manufacture years, and treatment chemistry vary — there is no single "PFBS gear" specification, but the post-2015 reformulation cycle introduced PFBS-based DWR into a fraction of the manufactured turnout gear inventory. PFAS-free turnout gear certification programs have emerged since 2022 (Honeywell, MSA, Globe, and others have introduced lines), but most active-service gear was treated under earlier specifications and continues to carry PFAS chemistry through its useful life.
The take-home contamination pathway documented for PFOA and PFOS in firefighter populations applies in parallel to PFBS: contaminated gear stored in or near sleeping areas releases PFAS into household dust over time. The same mitigation framework applies — separate work-clothing storage, change at the station rather than at home, washing PPE separately from household laundry (where the manufacturer's care instructions permit washing).
From Scotchgard and textile treatments
3M's Scotchgard product line was the commercial origin of much consumer PFAS exposure. The original Scotchgard chemistry (1962 through 2000-2002) was C8 perfluorosulfonate. Following the PFOS phase-out, 3M reformulated Scotchgard using short-chain chemistry including PFBS-based precursors. Treated carpet, upholstery, and clothing manufactured under the post-2002 chemistry contains PFBS-related compounds at low residual concentrations. The compound migrates from treated fabric into indoor dust over years of use. Karásková and colleagues 2016 documented short-chain PFAS in indoor dust from multiple countries. Peer-reviewed
From food packaging
Grease-resistant paper food packaging — fast food wrappers, microwave popcorn bags, pizza boxes, paper bowls for hot foods, French fry sleeves — historically used long-chain PFAS for the oil-repellent property. The FDA voluntary phase-out of long-chain PFAS food contact substances during 2020-2024 led many manufacturers to switch to short-chain alternatives including PFBS-precursor chemistries. Dietary PFBS exposure has been measured in the US population through CDC NHANES biomonitoring at low but detectable levels in serum.
From drinking water
The US EPA's April 10, 2024 Final PFAS National Primary Drinking Water Regulation covers PFBS via the Hazard Index calculation. Regulatory Communities downstream of historical 3M manufacturing facilities have documented PFBS contamination in drinking water — the 3M Cottage Grove, Minnesota plant area and the 3M Decatur, Alabama plant area are the two most extensively characterized US sites. Communities served by municipal water systems downstream of fire training facilities, chrome plating operations, and paper mills also show elevated PFBS in some assessments. Federal Register, April 26, 2024. Regulatory
From indoor dust
Indoor dust accumulates PFBS at measurable concentrations in homes with extensive treated-textile inventory. The dust reservoir is the dominant residential PFAS exposure pathway for non-occupational populations after dietary and drinking water — particularly for young children, whose hand-to-mouth contact rate is higher than adults. HEPA vacuuming and damp-mopping reduce the airborne re-entrainment and the surface dust load directly.
What the research says
Toxicokinetics — the short-chain framing
Olsen and colleagues 2009 in Environmental Health Perspectives reported the foundational pharmacokinetic study of PFBS in occupationally exposed 3M workers, characterizing the human serum half-life at approximately 25-46 days (vs PFOS's 5+ years and PFOA's 2-3+ years). Peer-reviewed The shorter half-life limits steady-state body burden for chronic exposures but does not change the underlying mechanism-of-action concerns for the PFAS class — PPAR-alpha activation, oxidative stress, mitochondrial effects, immune and developmental endpoints — which apply to PFBS at sufficient dose levels.
Hepatic and developmental effects
Lieder, Chang, York, Butenhoff 2009 in Toxicological Sciences reported the subchronic toxicology of potassium PFBS in rats, documenting liver weight increase, hepatocyte hypertrophy, and effects on thyroid hormone homeostasis at higher doses. Peer-reviewed The hepatic finding is consistent across the PFAS class but the PFBS-specific dose-response is documented at substantially higher concentrations than for PFOA or PFOS. Developmental toxicity in animal studies includes reduced fetal weight and increased postimplantation loss at higher dose levels.
The EPA IRIS 2021 assessment
The US EPA Integrated Risk Information System Toxicological Review of Perfluorobutanesulfonic Acid (PFBS) and Related Salts (2021) established the federal chronic oral reference dose at 0.0003 mg/kg/day (300 ng/kg/day) based on thyroid hormone effects in pregnant mice and reduced thyroxine in neonatal mice. Regulatory The 2021 IRIS finalization was a significant regulatory milestone for the PFAS replacement chemistry and underpinned the 2024 NPDWR Hazard Index inclusion. The Health-Based Value used in the HI calculation (2,000 ng/L for drinking water) is derived from this RfD using standard exposure-factor assumptions.
The 2024 PFAS NPDWR — current regulatory momentum
The April 10, 2024 EPA Final PFAS NPDWR was the federal-level inflection point for PFAS regulation in the US. Regulatory The rule established the first federally enforceable PFAS limits in drinking water and included PFBS in the four-compound Hazard Index. The HI sums the ratios of measured concentration to Health-Based Value for PFHxS (9 ng/L), PFNA (10 ng/L), HFPO-DA (10 ng/L), and PFBS (2,000 ng/L). A Hazard Index of 1 or greater exceeds the MCL. The PFOA/PFOS individual MCLs (4 ng/L each) are separate from the HI.
Human epidemiology — emerging
PFBS human epidemiology is less developed than for PFOA and PFOS — environmental monitoring started later (~2002+) and short-chain PFAS analytical methods came later. Population biomonitoring shows PFBS in CDC NHANES at lower geometric mean concentrations than PFHxS or PFOS. Disease-association studies in cohorts exposed via documented contamination events (3M Cottage Grove, Decatur) are emerging through 2024-2026 but the long-latency outcomes (cancers, cardiovascular, fertility) are not yet at the same maturity. Inferred from the general PFAS-class epidemiology timeline; PFBS-specific disease-association studies are still accumulating
What helps reduce exposure
For drinking water in known-affected areas: install certified PFAS-removal filtration. NSF/ANSI 58 (reverse osmosis) is the most thoroughly validated for PFBS; certain NSF/ANSI 53 GAC systems also work — verify the specific PFAS-reduction certification language. Generic "filtered water" without certification has variable performance.
For textiles and carpet: choose untreated or third-party-verified PFAS-free products when replacing household items. OEKO-TEX STANDARD 100 and GreenScreen Certified are reasonable certifications; generic "non-toxic" labels don't establish PFAS absence.
For firefighter households: enforce the take-home contamination protocol. Change out of turnout gear at the station, store contaminated gear in separately-ventilated space outside bedrooms, wash work clothing separately from household laundry, advocate department-level transitions to fluorine-free foams and PFAS-free turnout gear specifications.
HEPA-vacuum carpets and upholstery weekly; damp-mop hard floors. The indoor dust reservoir contains the household PFAS load that has migrated from treated textiles over years of use.
Avoid grease-resistant paper food packaging where alternatives exist. The FDA voluntary phase-out cycle 2020-2024 led some restaurants to switch to wax-only or fiber-based packaging without PFAS treatment.
What does NOT help
- Generic "filtered water" claims without PFAS-specific certification. Standard activated carbon filters without NSF certification have variable PFAS-reduction performance. The certification language is the actionable verification.
- Boiling water. Concentrates rather than removes PFAS — as water evaporates, PFAS stays in the smaller volume.
- "C4" or "short-chain" labels as safety claims. Shorter chain doesn't mean safe — PFBS is short-chain and is the subject of this page. The EPA has included PFBS in the federal Hazard Index drinking water standard specifically because it is a regulatory concern.
- "PFOA-free" or "PFOS-free" claims. Don't address C4 chemistry. Many "PFOA-free" products contain PFBS or other short-chain PFAS.
- Avoiding all carpet and upholstery as a PFAS reduction strategy. The mitigation is product choice (untreated or certified PFAS-free), not category elimination. Treated upholstery is an exposure source; untreated upholstery is not.
Open research questions
- Long-term low-dose chronic exposure effects below current EPA regulatory thresholds — the EPA IRIS 2021 RfD is based on thyroid effects in mouse studies; the human epidemiology for PFBS-specific outcomes at typical residential exposure levels is still accumulating. Speculation re: low-dose human dose-response; established at higher chronic exposures in animal studies
- Biological half-life variation across human populations — genetic and metabolic variation in PFAS handling is documented for the long-chain compounds; PFBS-specific variation has been less precisely characterized. Inferred from the broader PFAS pharmacokinetic literature
- Mixture effects with other PFAS in real-world co-exposure — the EPA's adoption of the Hazard Index regulatory approach reflects the dose-additive framework for mixed PFAS exposure, but the precise interaction terms and population-level dose-response have not been fully characterized. Speculation
Citations
- US Environmental Protection Agency (2024). PFAS National Primary Drinking Water Regulation — Final Rule. Federal Register, 89(82):32532-32757. Hazard Index includes PFBS at HBV 2,000 ng/L alongside PFHxS, PFNA, and HFPO-DA. federalregister.gov Regulatory
- US Environmental Protection Agency (2021). IRIS Toxicological Review of Perfluorobutanesulfonic Acid (PFBS) and Related Salts. EPA/635/R-20/345F. Chronic oral RfD 0.0003 mg/kg/day based on thyroid effects in pregnant mice. epa.gov/iris/pfbs Regulatory
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Perfluoroalkyls — covers PFBS section. atsdr.cdc.gov/ToxProfiles/tp200.pdf Regulatory
- Olsen GW, Chang SC, Noker PE, Gorman GS, Ehresman DJ, Lieder PH, Butenhoff JL (2009). A comparison of the pharmacokinetics of perfluorobutanesulfonate (PFBS) in rats, monkeys, and humans. Environmental Health Perspectives, 117(5):837-843. DOI 10.1289/ehp.0900920 Peer-reviewed — foundational PFBS pharmacokinetic study
- Lieder PH, Chang S-C, York RG, Butenhoff JL (2009). Toxicological evaluation of potassium perfluorobutanesulfonate in a 90-day oral gavage study with Sprague-Dawley rats. Toxicology, 255(1-2):45-52. DOI 10.1093/toxsci/kfn173 Peer-reviewed — subchronic PFBS toxicology
- Sundström M, Chang SC, Noker PE, Gorman GS, Hart JA, Ehresman DJ, Bergman Å, Butenhoff JL (2012). Comparative pharmacokinetics of perfluorohexanesulfonate (PFHxS) in rats, mice, and monkeys. Reproductive Toxicology, 33(4):441-451. DOI 10.1016/j.reprotox.2011.07.004 Peer-reviewed — methodology applicable to PFBS pharmacokinetics
- Karásková P, Venier M, Melymuk L, Bečanová J, Vojta Š, Prokeš R, Diamond ML, Klánová J (2016). Perfluorinated alkyl substances (PFASs) in household dust in Central Europe and North America. Environment International, 94:315-324. DOI 10.1016/j.envint.2016.05.031 Peer-reviewed — indoor dust PFAS exposure including PFBS
- Wang Z, Cousins IT, Scheringer M, Hungerbühler K (2013). Fluorinated alternatives to long-chain perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkane sulfonic acids (PFSAs) and their potential precursors. Environment International, 60:242-248. DOI 10.1016/j.envint.2013.08.021 Peer-reviewed — short-chain PFAS regrettable substitution framing
- Interstate Technology and Regulatory Council (ITRC) PFAS Team. PFAS Technical and Regulatory Guidance Document. pfas-1.itrcweb.org Regulatory — multi-state regulatory consortium
- US Environmental Protection Agency. Per- and Polyfluoroalkyl Substances (PFAS) — main agency PFAS page including AFFF firefighting foam regulation, drinking water rule implementation, and ongoing PFAS regulatory actions. epa.gov/sdwa/pfas Regulatory
Frequently asked questions
Is PFBS safer than PFOS?
PFBS has a substantially shorter biological half-life (~25-46 days in humans) than PFOS (~5+ years), which limits chronic body burden accumulation. That's a meaningful difference. PFBS is also environmentally persistent though — it does not biodegrade in environmental matrices on any human-relevant timescale. The EPA established PFBS as part of the Hazard Index regulatory framework for drinking water (mixed PFAS at HI ≤ 1) in the April 2024 final rule, and the EPA IRIS chronic oral reference dose for PFBS is 0.0003 mg/kg/day (300 ng/kg/day), finalized 2021. "Shorter chain" does not mean "safe" — it means a different toxicokinetic profile with its own evidence base.
What products contain PFBS?
Firefighting foams (AFFF formulations reformulated post-2002 when 3M phased out PFOS; PFBS-based "C4 foams" replaced C8 chemistry at many training and operational facilities), Scotchgard textile and carpet treatments (3M's post-2002 reformulation used short-chain PFBS chemistry), some firefighter turnout gear water/oil repellents, food packaging with grease-resistance treatments (paper food contact applications historically used long-chain PFAS; short-chain PFBS-precursor systems appeared in newer products), and various industrial applications. EPA biomonitoring detects PFBS in indoor dust and human serum at measurable concentrations.
How long does PFBS stay in the body?
The biological half-life of PFBS in humans is approximately 25 to 46 days based on Olsen and colleagues' occupational pharmacokinetic studies in 3M workers. That's substantially shorter than PFOS (5+ years) or PFOA (2-3+ years) but still slow enough that chronic exposure accumulates body burden faster than elimination clears it. Stopping exposure produces measurable reduction in serum PFBS over months — but body burden is also added to continuously by ongoing environmental and dietary exposure from a chemistry that is essentially non-degradable in environmental matrices.
Did PFBS replace PFOS in firefighting foam?
Yes — substantially. When 3M voluntarily phased out PFOS production in 2000-2002, AFFF firefighting foam manufacturers reformulated to short-chain chemistry. PFBS-based foams (so-called "C4 foams" for the 4-carbon perfluoroalkyl chain length, vs PFOS's C8) became the replacement at many fire training facilities, military bases, and civilian airport firefighting operations. Decades of pre-2002 PFOS contamination persists at training-area sites in soil and groundwater, and post-2002 PFBS contamination has been documented in the same and adjacent areas. The Department of Defense has been transitioning toward fluorine-free firefighting foams since the late 2010s but the transition is incomplete as of 2026.
Is PFBS in drinking water regulated?
Yes, through EPA's April 10, 2024 final PFAS National Primary Drinking Water Regulation. PFBS is included in the Hazard Index (HI) approach for mixed PFAS in drinking water. The HI is calculated as the sum across four PFAS — PFHxS, PFNA, HFPO-DA (GenX), and PFBS — of each compound's measured concentration divided by its health-based value. The PFBS Health-Based Value used in the HI is 2,000 ng/L. A Hazard Index of 1 or greater triggers regulatory action. Public water systems have until 2029 to comply with the rule under the originally finalized timeline; EPA proposed modifications and a compliance deadline extension in 2025 that the agency may finalize.
What is the EPA Hazard Index for PFBS?
The Hazard Index is a regulatory mathematical approach EPA finalized in the April 2024 PFAS rule to address dose-additive effects of mixed PFAS exposure. For PFBS specifically, the EPA established a Health-Based Value of 2,000 ng/L. In the HI calculation, the measured PFBS concentration is divided by 2,000 to produce that compound's contribution to the index. The same calculation is performed for PFHxS (HBV 9 ng/L), PFNA (HBV 10 ng/L), and HFPO-DA (HBV 10 ng/L). The four ratios are summed; if the total exceeds 1, the regulatory MCL for the mixture is exceeded. PFOA and PFOS have separate individual MCLs (4 ng/L each) and are not part of the Hazard Index calculation.
How can I avoid PFBS in my home?
For drinking water in known-affected areas: install NSF/ANSI 53 or NSF/ANSI 58 certified filters specifically rated for PFAS reduction (reverse osmosis systems are reliable; certain GAC systems also work — verify the specific PFAS certification language). For textiles and carpets: choose untreated or third-party-verified PFAS-free products when replacing household items. For firefighters: department-level advocacy for fluorine-free firefighting foams and PFAS-free turnout gear, plus the standard take-home contamination protocol (separate work clothing, change at the station, don't bring contaminated gear into the bedroom). For food: avoid grease-resistant paper food packaging where alternatives exist. The bedroom-specific dust pathway is reduced by regular HEPA vacuuming and damp-mopping.
Related compounds
Embr Sleep is a sleep environment company researching the chemistry of the bedroom. See the methodology page for how this Atlas tags claims by evidence strength. For broader context on PFAS exposure pathways and firefighter take-home contamination, see non-toxic bedroom and farm family sleep.
Last reviewed 2026-05-25. If you find a factual error, contact us.