What is Perfluorotridecanoic acid (PFTrDA) and Why Does It Matter?

Perfluorotridecanoic acid — most people call it PFTrDA — is one of the lesser-known members of the PFAS family. PFAS (per- and polyfluoroalkyl substances) are a group of thousands of man-made chemicals that don't break down in the environment or in your body. PFTrDA is a long-chain PFAS, meaning it has more carbon atoms than shorter-chain versions, which makes it especially persistent. It enters drinking water primarily through industrial discharge, the breakdown of other PFAS compounds, and runoff from sites where PFAS-containing products were manufactured or used. Firefighting foam, stain-resistant coatings, and certain industrial processes are among the most common original sources.

The health concerns around PFTrDA are serious, even at very low levels. Like other long-chain PFAS, it accumulates in the body over time — a property scientists call bioaccumulation. Research linked to PFAS exposure broadly includes disruption of the immune system, thyroid hormone interference, liver damage, and increased cancer risk (EWG). Long-chain PFAS compounds are particularly worrying because they tend to stay in the body longer than their shorter-chain counterparts. Children and pregnant women face the greatest risk, since even small exposures during critical developmental windows can have lasting effects on health.

Right now, the regulatory picture is complicated. The EPA's enforceable limit for total PFAS in drinking water — finalized in 2024 — sets a maximum of 4 parts per trillion (ppt) for PFOA and PFOS individually, but PFTrDA is not yet individually regulated at the federal level. The EWG health guideline for long-chain PFAS like PFTrDA is effectively 1 ppt, based on the most current science about health risks. The data here tells a clear story: across 34 water systems tested, 32 showed PFTrDA levels above that EWG guideline. The average detected level was 0.732 ppt, but the highest recorded level hit 12.5 ppt — more than 12 times above what EWG considers safe. That gap between regulatory action and scientific guidance leaves a lot of families unprotected.

Geographically, Massachusetts accounts for 14 of the 34 affected systems — more than any other state. New York and Alabama each show 7 affected systems, followed by Michigan with 2 and Illinois with 1. Massachusetts and New York's numbers likely reflect a combination of older industrial activity, dense population served by surface water sources, and more rigorous testing programs that catch contaminants other states might miss. Alabama's presence on this list is notable and may connect to military installations and industrial sites in the state where PFAS-containing firefighting foam was historically used. The pattern across these states suggests PFTrDA contamination isn't a regional fluke — it's a widespread industrial legacy problem showing up wherever testing is thorough enough to find it.

The good news is that effective filtration options exist. Reverse osmosis (RO) filtration removes up to 99% of PFAS compounds, including long-chain varieties like PFTrDA, according to NSF International testing data. Activated carbon filters — especially those using granular activated carbon (GAC) — also reduce PFAS levels significantly, though they're generally less effective than RO at very low concentrations. If you're in Massachusetts, New York, Alabama, or any area with known PFAS concerns, an under-sink reverse osmosis system is the most reliable choice for your drinking and cooking water. Echo Water's RO systems are independently tested to confirm PFAS reduction, so you know exactly what you're getting. Checking your annual water quality report (called a Consumer Confidence Report) is a smart first step — it tells you what your utility has tested for and at what levels. If PFTrDA or other PFAS aren't listed, that may mean your utility hasn't tested for them yet, which is reason enough to filter proactively.

Regulatory Standards for Perfluorotridecanoic acid (PFTrDA)

Cities With the Highest Perfluorotridecanoic acid (PFTrDA) Levels

States Most Affected by Perfluorotridecanoic acid (PFTrDA)

Frequently Asked Questions

Related Contaminant Guides