Bold claim first: PFAS isomer stories aren’t the same across ecosystems, and that difference could change how we regulate these stubborn pollutants. New UB research shows that tracking forever chemicals reveals uneven distributions of PFOS isomers as they move through water, fish, and birds, with important implications for exposure and policy.
When UB chemists tested water, fish, and bird eggs, they expected to find PFAS in many places—these “forever chemicals” are ubiquitous in the environment. What surprised them was the distinct pattern of PFOS isomers depending on the sample type. PFOS is one of the most hazardous PFAS and has a couple of structural forms called isomers. In wastewater and in supermarket fish, branched PFOS isomers—those that are more spherical and water-loving—made up the majority. In contrast, the egg yolks of fish-eating birds contained almost exclusively linear PFOS isomers—elongated forms that tend to bind to proteins and linger longer in tissues.
These observations suggest that as PFOS travels through the food web—from water to fish to birds—the balance shifts toward the linear form. Diana Aga, SUNY Distinguished Professor and corresponding author, notes that this pattern could reflect how isomers behave differently once they enter living systems and move through ecosystems.
Isomers share the same chemical formula, but their different arrangements can drive very different behaviors. A simple analogy: two versions of the same molecule can have dramatically different biological or regulatory implications, much like one isomer of methamphetamine is controlled while another is used in consumer products like nasal sprays.
Despite these differences, current U.S. and European regulations often lump all PFOS isomers together when measuring PFAS, overlooking potentially meaningful variation in bioaccumulation and toxicity.
This study adds to the growing evidence that PFAS isomers don’t accumulate at the same rates and shouldn’t be treated as identical. The work spans two studies and was funded by the National Science Foundation and the Environmental Protection Agency.
Separating isomers requires advanced separation techniques. The researchers used cyclic ion mobility spectrometry, which sorts isomers by the shape-related differences that affect how they move through a gas-filled tube. Imagine dropping two sheets of paper—one flat and one crumpled—from the same height. They share material and weight, but the crumpled sheet lands first because its shape changes how air resistance acts on it. Similarly, branched PFOS isomers, with their compact shapes, travel through the drift tube at different speeds than the elongated linear isomers.
Using this technology, the UB team analyzed seven unfrozen supermarket fish samples, including bottom-dwellers like blue catfish, cod, and haddock, as well as pelagic species such as rainbow trout, salmon, and tilapia. Their findings appeared in the Journal of Agriculture and Food Chemistry.
Aga’s results show a trend: benthic (bottom-dwelling) fish harbor more variety of branched PFOS isomers than pelagic fish, and in total, benthic fish carry higher PFOS concentrations. They also tend to contain longer-chain PFAS such as PFOA and PFNA (eight and nine carbon atoms, respectively). Mindula Wijayahena, a PhD student and the study’s first author, notes that frequent consumers of bottom-dwelling species may have higher PFAS exposure.
In a separate study, the team examined PFOS isomers in municipal wastewater and in double-crested cormorant eggs collected near the Buffalo Harbor. Wastewater samples showed more than half of PFOS as branched isomers, whereas the cormorant eggs were overwhelmingly linear—nearly 90%.
Jenise Paddayuman, a PhD student and the first author on that project, remarks that linear isomers accumulate more in tissues, but the reasons behind the eggs’ strong tilt toward linear PFOS warrant further study. The results nonetheless illuminate how PFOS moves through the environment and persists in ways that depend on isomer type.
Looking ahead, Aga suggests it may be time to investigate whether the toxicological effects differ between isomers. If branched isomers are less prone to bioaccumulation, there could be a case for designing future PFAS with branched structures to reduce persistence. Whatever the path, this research highlights the need for more nuanced regulation that considers isomer-specific behavior and health implications.
