4:2FTS
1H,1H,2H,2H-perfluorohexanesulfonic acid (4:2 FTS)
- EPA federal limit
- No federal limit
- Detected in
- 10,289 systems
- Regulatory status
- Unregulated (UCMR 5)
What is 4:2FTS?
1H,1H,2H,2H-perfluorohexanesulfonic acid, known as 4:2FTS, is a man-made chemical belonging to the PFAS family, a group of thousands of synthetic compounds often called "forever chemicals." Like other PFAS, 4:2FTS contains very strong chemical bonds that make it extremely resistant to breaking down in the environment or in the human body. This means it can build up over time in water, soil, and living things.
Where does it come from?
4:2FTS is released mainly through industrial processes and shows up in a range of consumer products. It is associated with the production of fluorotelomer-based coatings, which are used to make products like stain-resistant fabrics, water-repellent clothing, food packaging, and some cleaning products. It can also enter the environment through industrial wastewater and the breakdown of other related PFAS compounds.
Health concerns
Research on 4:2FTS in humans is still very limited, so scientists do not yet have a clear picture of its health effects. Some animal studies have associated it with effects on the liver and immune system, but these findings have not been fully confirmed in human populations. Because the evidence is early-stage, no major health agency has formally classified its risk to humans. If you have specific health concerns, consult a healthcare provider.
EPA standard
The EPA has not established a Maximum Contaminant Level (MCL) — a legal limit for how much of a chemical is allowed in public drinking water — for 4:2FTS. Without a federal limit, public water systems are not required to test for or remove it. This means there is currently no regulatory safety net for this specific compound.
What you can do
If 4:2FTS is detected in your water, consider using a certified reverse osmosis filter or a granular activated carbon filter, both of which research studies suggest can reduce PFAS levels. Remember that boiling water does not remove PFAS — it can actually concentrate them. Contact your local water utility for testing information and consult a healthcare provider with any health-related questions.
About this summary: Narrative text on this page was drafted by an AI model (claude-sonnet-4-6) from EPA UCMR 5 data and reviewed before publication. The numeric data above is reported by water utilities directly to the EPA. If you spot an error, email data@checkyourwater.org.