PFOS (Perfluorooctane Sulfonic Acid)

How It Works

PFOS was widely used in aqueous film-forming foam (AFFF) for firefighting, particularly at military bases and airports. Its use in firefighting training exercises contaminated groundwater near hundreds of military installations and civilian airports across the United States. 3M, the primary manufacturer, voluntarily phased out PFOS production in 2002 after discovering the chemical was accumulating in the blood of the general population. Like PFOA, PFOS does not break down in the environment and bioaccumulates in humans. The EPA set an MCL of 4 ppt in 2024 — the same stringent level as PFOA. Military base communities are among the most affected.

Related Terms

• PFAS (Forever Chemicals) — Per- and polyfluoroalkyl substances — a class of thousands of synthetic chemicals that don't break down in the environment, accumulate in the human body, and are linked to cancer, immune disorders, and developmental problems.
• PFOA (Perfluorooctanoic Acid) — A specific PFAS compound formerly used in Teflon manufacturing — linked to kidney cancer, testicular cancer, thyroid disease, and high cholesterol. The EPA set a drinking water limit of 4 parts per trillion.
• Maximum Contaminant Level (MCL) — The highest level of a contaminant allowed in drinking water — set by the EPA and enforceable by law. Exceeding the MCL triggers a health-based violation.