What Is PFOS?

PFOS, perfluorooctyl sulfonate, is one of the PFAS, and the EPA describes it and PFOA as two of the most widely used and studied chemicals in the group. The International Agency for Research on Cancer says PFOA and PFOS have been found in products including food packaging, carpets, building materials, cosmetics, cookware, waterproof clothing and firefighting foams.

3M voluntarily phased out PFOS between 2000 and 2002, according to the EPA, which in March 2002 began requiring notice before any future manufacture or import of 13 PFAS chemicals included in that phase-out. In November 2023 IARC classified PFOS as possibly carcinogenic to humans, and PFOA as carcinogenic to humans.

The EPA’s 2024 drinking water rule set a health-based goal of zero for PFOS and an enforceable limit of 4.0 parts per trillion, and the rule took effect on June 25, 2024. On May 18, 2026 the EPA proposed keeping that limit while letting water systems request two more years, to 2031, to comply.

Sources checked September 15, 2026. Every point below links the page it came from.

The sources behind this answer

  • Government sourceThe EPA describes PFAS as a group of man-made chemicals that includes PFOA, PFOS and GenX, found in products such as cleaners, textiles, leather, paper and paints, firefighting foams and wire insulation. US EPA ↗
  • Regulatory filingIn March 2002 the EPA required notice before any future manufacture or import of 13 PFAS chemicals included in 3M’s voluntary phase-out of PFOS between 2000 and 2002. US EPA ↗
  • Government sourceIn November 2023 an IARC working group classified PFOS as possibly carcinogenic to humans (Group 2B) and PFOA as carcinogenic to humans (Group 1). IARC, World Health Organization ↗
  • Government sourceIARC says PFOA and PFOS have been found in products such as food packaging, carpets, building materials, cosmetics, cookware, waterproof clothing and firefighting foams. IARC, World Health Organization ↗
  • Regulatory filingThe EPA’s final 2024 rule set a Maximum Contaminant Level Goal of zero and an enforceable limit of 4.0 parts per trillion for PFOS and for PFOA, effective June 25, 2024. Federal Register ↗
  • Regulatory filingOn May 18, 2026 the EPA proposed keeping the PFOA and PFOS limits while letting drinking water systems request two more years, to 2031, to comply. US EPA ↗

Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.

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