PFOS

What is PFOS?

Perfluorooctanesulfonic acid, or PFOS, is a man-made chemical that belongs to a large family of substances known as PFAS, often called "forever chemicals." These chemicals earned that nickname because they break down extremely slowly and can build up in the environment and in the human body over time. PFOS was widely used in industrial and consumer products for decades before concerns about its safety led to major restrictions on its production.

Where does it come from?

PFOS was used in a wide range of products, including stain-resistant coatings on carpets and upholstery, water-repellent treatments on clothing, food packaging, and certain cleaning products. It was also a key ingredient in aqueous film-forming foam (AFFF), a type of firefighting foam used heavily at military bases and airports. Although most U.S. manufacturers phased out PFOS production in the early 2000s, it can still be found in older products and contaminated soil and water near industrial or military sites.

Health concerns

Research studies have linked PFOS exposure to several health concerns, including effects on the immune system, thyroid function, and liver health. Some studies have associated it with increased cholesterol levels and changes in hormone activity. Animal studies have also suggested possible links to certain cancers, though the evidence in humans is still limited. If you have specific health questions related to PFOS exposure, consult a healthcare provider.

EPA standard

The EPA set a maximum contaminant level (MCL) of 4 parts per trillion (ppt) for PFOS in drinking water in 2024. An MCL is the highest amount of a contaminant legally allowed in public drinking water. This limit means water utilities must test for PFOS and take action if levels exceed 4 ppt.

What you can do

If PFOS is detected in your water, consider using a certified reverse osmosis filter or a granular activated carbon filter, both of which the EPA recognizes as effective at reducing PFAS levels. Do not rely on boiling your water — boiling does not remove PFAS and can actually concentrate it. Contact your local water utility for testing results and guidance.