Ongoing measurement of PFAS in fish is critical to understanding human dietary exposure and ecosystem health. A timely study coming out of the U.S. EPA’s National Rivers and Streams Assessment (NRSA) 2018–2019 featuring SGS measurement of PFAS adds some real clarity to a complicated picture. The latest study, published in Science of the Total Environment, builds on work from the 2013–2014 NRSA and provides a valuable look at PFAS patterns across freshwater fish from major rivers across the U.S.
Our expert team at SGS supported this research through the analysis of fish tissue samples using a PFAS method that was the basis of EPA 1633. Our nearly 25 years’ worth of PFAS experience have allowed us to hone a set of best practices around isotope dilution, careful fish homogenization, interference mitigation and more. The data speaks volumes, and the methods used helped make it possible.
Here’s what we learned.
The EPA looked at 290 composite fish tissue samples from the 2018–2019 survey and compared them to 353 samples from 2013–2014. In both studies, over 90% of samples contained detectable PFAS, but this time around, additional compounds were found in more combinations reflecting target list expansion from 13 to 33. On average, each sample contained 5 target PFAS in 2018–2019, with over a third of samples containing seven or more.
Among the PFAS detected, PFOS, along with PFUnA, PFDA, PFDoA, and PFTrDA, were consistently present. In fact, nine different PFAS were found in more than 20% of the fish tested.
Figure reproduced from Wathen and Babuena (2025)
In good news, the concentrations of measured PFAS are declining. Compared to the previous survey, PFOS dropped by 57%, PFDA by 41%, PFUnA by 32%, and PFDoA by 20% reflecting the move away from use of longer-chain PFAS. That’s good news. But as always with PFAS, the story is in the details. The authors find that percentage declines correlated inversely with chain length, that is, C8 (PFOS) declined much more than C11 (PFDoA) reflecting lower water solubility and greater propensity for accumulation in tissue for longer-chain compounds.
This project is a great example of long-term longitudinal monitoring by governmental agencies and we’re proud to have played a part.
References
John B Wathen and Andrea C. Contreras Balbuena (2025) ‘Patterns of per – and polyfluoroalkyl substance occurrence in fish in the 2018–2019 U.S. EPA National Rivers and Streams Assessment’, Science of the Total Environment [Preprint]. Available at: https://doi.org/10.1016/j.scitotenv.2025.179216.
More about SGS and PFAS
At SGS, we’ve been supporting this kind of work for a long time. From drinking water to biosolids to fish tissue and beyond, our labs provide analytical support for regulatory programs across North America. Our methods continue to evolve alongside the science, and when you’re performing complex projects such as measuring PFAS in fish, choosing the right measurement partner is critical. To find out more, email PFAS@sgs.com
