PFOS (Perfluorooctane Sulfonic Acid)
A long-chain PFAS compound historically used in Scotchgard and AFFF firefighting foam.
Perfluorooctane sulfonic acid (PFOS) was a key ingredient in 3M's Scotchgard fabric protector and aqueous film-forming foam (AFFF) used at military bases and airports. PFOS bioaccumulates in blood and organs, with a half-life of 4-5 years in humans. The EPA MCL for PFOS is 4 parts per trillion.