PFOS is a man-made chemical used in various products. It persists in the environment and can contaminate water sources through industrial activities. PFOS accumulates in the body over time.

PFOS (Perfluorooctane sulfonate) is part of the PFAS family of chemicals. It was widely used in products like firefighting foams and stain repellents since the 1950s. PFOS can contaminate water through industrial discharge and firefighting activities. Its presence in water is measured in parts per trillion (ppt). Due to its persistence, PFOS has been phased out in many countries, but it remains in the environment and can still be detected in water sources worldwide.