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But here’s where it gets controversial: PFAS isomers aren’t just academic curiosities—how we read their patterns could reshape food safety and regulatory policy. And this is the part most people miss: the same molecule can behave very differently depending on its structural form, which may influence exposure assessments and cleanup strategies.
Tracking PFAS diversity in the food web reveals that not all isomers distribute equally.
A symbolic image represents the concept, followed by an AI-generated visual. Advanced separation techniques, particularly cyclic ion mobility spectrometry, are key to distinguishing PFAS isomers. This state-of-the-art method separates isomers by exploiting subtle shape differences that affect their movement through a gas-filled tube, such as nitrogen.
Imagine two sheets of paper—one flat, the other crumpled into a ball—dropped from the same height: the crumpled sheet hits the ground first despite identical material and weight. In a similar fashion, cyclic ion mobility spectrometry differentiates isomers of the same molecule by their drift time—the duration it takes PFOS isomers to traverse the tube to the detector. Branched isomers, with their compact, spherical shapes, glide faster through the inert gas than the elongated linear forms.
The RENEW Institute’s cyclic ion mobility instrument, supported by the UB Office of the Senior Vice President for Research, Innovation and Economic Development, analyzed PFAS in seven unfrozen supermarket fish samples. The study included both bottom-dwelling species such as blue catfish, cod, and haddock, and pelagic fish like rainbow trout, salmon, and tilapia.
Published in the American Chemical Society’s Journal of Agriculture and Food Chemistry, Aga and colleagues found that benthic fish generally harbored a greater variety of branched PFOS isomers than pelagic fish. In fact, benthic samples revealed two extra branched PFOS isomer types not detected in pelagic fish.
The mixture of branched and linear isomers contributed to a higher total PFOS concentration in benthic fish compared with pelagic fish. Additionally, benthic species tended to contain higher proportions of longer-chain PFAS such as PFOA and PFNA, which have eight and nine carbon atoms respectively.
“These results suggest that consumers who frequently eat bottom-dwelling species may have higher PFAS exposure,” notes Mindula Wijayahena, a PhD student in Aga’s lab and the study’s first author.
Isomer patterns shift in birds
In a separate investigation, Aga’s team identified PFOS isomers in wastewater and in the eggs of birds from North America. The study, published in the Journal of the American Society for Mass Spectrometry, analyzed samples from a municipal wastewater treatment facility in Erie County and eggs collected near Buffalo Harbor from double-crested cormorants, a fish-eating aquatic bird.
In wastewater, more than half of PFOS existed as branched isomers. By contrast, in the cormorant egg yolks, about 90% of PFOS was linear.
“Although linear isomers are known to accumulate more in tissues than branched forms, the reason for the eggs’ strong tilt toward linear is not yet clear and deserves further study,” explains Jenise Paddayuman, a PhD student and the study’s first author. “Still, these findings shed light on how PFOS travels through the environment and suggests that linear isomers persist more as PFOS disseminates through ecosystems.”
A new era for understanding PFAS toxicity
With scientists now able to distinguish PFAS isomers, Aga suggests it may be time to examine whether different isomers exhibit distinct toxicological effects, potentially supporting differentiated regulation.
“For instance, if ongoing evidence shows branched isomers bioaccumulate less than linear ones, it could prompt considerations for designing more branched-structure PFAS in the future,” she notes. “That’s a possibility worth exploring as research advances.”
Original publication
Mindula K. Wijayahena, Rawikan Kachangoon, Cheyanne Witmer, Joshua S. Wallace, Jitlada Vichapong, Diana S. Aga; “PFAS Isomers Matter: Distribution Patterns of Linear and Branched PFOS and PFOA in Consumed Fish Revealed by Cyclic Ion Mobility Separation”; Journal of Agricultural and Food Chemistry, Volume 73, 2025-10-6
If you’d like more background on PFAS, its environmental journey, and what regulatory shifts could mean for everyday consumers, this study offers a compelling glimpse into the future of chemical safety and environmental science.
