EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
No guideline
Science-based, stricter target
Health effects
Toxicological data on 4:2 FTS is limited. Fluorotelomer compounds can degrade to shorter-chain perfluorocarboxylic acids in the environment. Short-chain FTS compounds are highly water-soluble and mobile, contributing to widespread low-level exposure. Health effects at drinking water concentrations are not well characterised.
Where it comes from
Used in AFFF firefighting foam and surface-treatment products. Detected near military installations, airports, and industrial sites with AFFF use history. Also found in areas with fluorinated biosolids application.
How it's regulated
No federal EPA MCL. Not regulated under the 2024 PFAS NPDWR. Monitored under UCMR5. No EWG health guideline established due to limited toxicological data.
How to filter 4:2 fts
Not all filters address 4:2 fts. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is 4:2 fts?
4:2 FTS is a four-carbon fluorotelomer sulfonic acid. Fluorotelomer sulfonates are used in firefighting foam (AFFF), surface coatings, and industrial applications. The "4:2" designation refers to four perfluorinated carbons and two non-fluorinated carbons. It is the shortest-chain FTS compound monitored under UCMR5.
What are the health effects of 4:2 fts?
Toxicological data on 4:2 FTS is limited. Fluorotelomer compounds can degrade to shorter-chain perfluorocarboxylic acids in the environment. Short-chain FTS compounds are highly water-soluble and mobile, contributing to widespread low-level exposure. Health effects at drinking water concentrations are not well characterised.
Is 4:2 fts regulated in drinking water?
No federal EPA MCL. Not regulated under the 2024 PFAS NPDWR. Monitored under UCMR5. No EWG health guideline established due to limited toxicological data.
Where does 4:2 fts come from?
Used in AFFF firefighting foam and surface-treatment products. Detected near military installations, airports, and industrial sites with AFFF use history. Also found in areas with fluorinated biosolids application.
How do I remove 4:2 fts from tap water?
The most effective methods for removing 4:2 fts are: Reverse osmosis (RO), NSF 58 certified RO system, Activated carbon block filter. Look for NSF-certified systems—independent certification confirms removal claims have been verified.
Is 4:2 fts in your water?
Enter your ZIP code to see the measured level in your specific utility.