PFOS (Perfluorooctane Sulfonate)

What is PFOS (Perfluorooctane Sulfonate)?

PFOS is a PFAS "forever chemical" that labs measure in blood serum.

PFOS repels water, grease, and soil, which is why it ended up in protectants for paper and cardboard packaging, carpets, leather, and textiles, and in firefighting foam. ATSDR also lists it as a processing aid in fluoropolymer manufacturing. 3M, the manufacturer, ended production after talks with EPA. EPA dates that voluntary phase-out to between 2000 and 2002, and in 2002 it issued two rules requiring notice before anyone made or imported 13, then 75, related PFAS. Production stopped, but PFOS doesn't leave quickly. A Swedish study followed 106 people in Ronneby after firefighting-foam-contaminated drinking water was replaced with clean water. It estimated a PFOS half-life of 3.4 years (95% CI 3.1 to 3.7), with faster elimination in women. ATSDR's toxicological profile gives a range of 3.3 to 27 years across studies. The national numbers followed the phase-out. In CDC's NHANES survey, geometric mean serum PFOS for people age 12 and older fell from 30.3 µg/L in 1999-2000 to 3.93 µg/L in 2017-March 2020, a drop of 87%, and the authors tie it to the production changes that began in 2000-2002. Even so, PFOS was detected in 98.97% to 100% of participants in every cycle. (µg/L is the same unit as ng/mL.) In July 2022, a National Academies of Sciences, Engineering, and Medicine (NASEM) committee published the clinical framework that other PFAS pages on this site point to. It's written for clinicians, and for a specific group: patients likely to have a history of elevated exposure. That means people who worked with fluorochemicals or served as firefighters, lived in communities with documented PFAS contamination, or lived near facilities, military bases, or airports that use fluorochemicals. For them, the report says testing should be an informed, shared decision between clinician and patient. The drawbacks it lists include difficulty interpreting results and decreased property values after contamination is identified. The framework doesn't use a PFOS number by itself. It uses the simple sum of seven PFAS: MeFOSAA, PFHxS, PFOA, PFDA, PFUnDA, PFOS, and PFNA, counting the linear and branched forms of PFOA and PFOS. That's why a commercial panel can print nine rows and then add them. The report also warns that a laboratory may not report every one of the seven. Quest's panel, for example, adds 0.07 ng/mL for any analyte not detected at its 0.10 ng/mL cutoff, so the sum reflects the lab's rules as well as the blood sample. The PFUnDA (Perfluoroundecanoic Acid) page covers how labs report results below the detection limit. The report sorts the sum into three bands (see the table below). For the middle band, it tells clinicians to encourage reduced exposure and to prioritize screening for dyslipidemia and hypertensive pregnancy disorders, plus age-appropriate breast cancer screening. For the top band, it adds thyroid function testing and assessment for kidney cancer, testicular cancer, and ulcerative colitis at wellness visits. Those are instructions to clinicians. Longetic doesn't assign a band to anyone. That's a conversation for you and your clinician. The cutoffs have a narrow basis, and NASEM says so. They come from the German Human Biomonitoring Commission's HBM-I and HBM-II values (HBM-I: 2 ng/mL for PFOA and 5 ng/mL for PFOS in plasma; HBM-II: 10 ng/mL for PFOA and 20 ng/mL for PFOS), combined by weight-based dose additivity. The committee wrote that the values "were derived from epidemiological studies evaluating associations at the population level, and the relevance of these values to interpret risk in individuals is uncertain." It also said testing "cannot indicate or predict the likelihood that an individual will end up with a particular condition." ATSDR goes further. As of its July 2026 review, it hasn't developed health-based screening based on PFAS blood levels, and it says results don't provide information for treatment or predict future health problems. A classification isn't a level, either. IARC rated PFOS Group 2B, possibly carcinogenic to humans, in November 2023, on strong mechanistic evidence, limited animal evidence, and inadequate human cancer evidence. And the EPA's drinking-water limit for PFOS, 4.0 ng/L as of EPA's May 2026 page, is a limit for public water systems, not a blood level. The PFOA (Perfluorooctanoic Acid) page covers that rule.

Typical reference context

No clinical reference interval exists for PFOS alone. The first table is what NASEM published for clinicians, using the sum of seven PFAS. The second shows how measured values are distributed in US surveys. A population distribution isn't a health threshold.

The bands are guidance for clinicians, not a diagnostic threshold, and the report says it should be updated as more information becomes available. The NHANES rows describe groups of people, not any one person's result.

What changed recently

In November 2023, IARC classified PFOS as Group 2B and PFOA as Group 1 (Monographs Volume 135). The two decisions rest on different evidence, and the PFOA (Perfluorooctanoic Acid) page covers the Group 1 call.

In 2024, ATSDR published its clinician materials (factsheet updated January 18, 2024). The online version was reviewed July 7, 2026, and still states that ATSDR hasn't developed health-based screening based on blood levels. That's a different position from the NASEM bands, and worth knowing if a clinician cites one and not the other.

In September 2024, Quest Diagnostics scientists published the assay behind a commercial NASEM-sum panel. In 1,023 specimens from 2023-2024, the median sum was 4.65 ng/mL, against 7.74 ng/mL in NHANES 2017-2020. These were lab samples, not a representative survey, so the two medians aren't a like-for-like trend.

In January 2025, CDC scientists extended the NHANES PFOS series through March 2020 and reported the 87% decline since 1999-2000. In May 2026, EPA proposed keeping the PFOA and PFOS drinking-water limits while rescinding the limits for four other PFAS. No update to the NASEM bands appears in any source we reviewed as of October 2026.

Tests often checked alongside this

The NASEM sum includes six other analytes: PFOA (Perfluorooctanoic Acid), PFHxS (Perfluorohexane Sulfonate), PFNA (Perfluorononanoic Acid), PFDA (Perfluorodecanoic Acid), PFUnDA (Perfluoroundecanoic Acid), and Me-PFOSA-AcOH, which labs may also print as MeFOSAA. NASEM tells clinicians to prioritize dyslipidemia screening in both upper bands, which is done with a lipid panel, and it names thyroid function testing for the top band.

What can affect this marker

ATSDR lists the routes by which people take in PFAS: living near sites with contaminated air, soil, or drinking water, eating food grown or raised near such places, eating fish or wild game contaminated by PFAS (notably PFOS), food packaged in PFAS-containing material, stain-resistant carpet and water-repellent clothing, and inhaling PFAS from manufacturing or firefighting foam. Babies can be exposed before birth, through breastfeeding, and through formula mixed with contaminated water. Time matters too. With a half-life of years, a result today can reflect exposure from years ago, and in the Ronneby study women cleared PFOS faster than men.

Reading PFOS results across lab reports

Reports differ in ways that matter when you line them up. Check the units (ng/mL and µg/L are the same), whether PFOS appears once or as linear and branched rows, whether the lab printed the NASEM sum or only separate analytes, and which of the seven it measured. Check the collection date and the reporting limit printed beside each result. A blood PFOS result is a snapshot of one draw at one lab. Keeping reports together, with the lab and date attached, lets you and your clinician compare like with like.

What to ask your doctor

• Does my exposure history, such as my work, my water supply, or where I've lived, fit the group NASEM wrote its testing guidance for?
• Which PFAS did this lab measure, and did it report the NASEM sum of seven or separate analytes?
• How did the lab handle results below its reporting limit when it added them up?
• Given that ATSDR says blood results don't inform treatment, what would we do differently with this number?

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