Tracking forever chemicals reveals that not all isomers behave the same
research news
A double-crested cormorant feeds near the shores of Lake Huron in Ontario. A UB study analyzed these birds’ egg yolks for per- and polyfluoroalkyl substances (PFAS).
Published December 15, 2025
When UB chemists tested samples of water, fish, and bird eggs, they weren’t surprised to find plentiful PFAS in the environment. Known as “forever chemicals,” PFAS appear almost everywhere in nature.
What surprised them was how PFOS, one of the most hazardous PFAS compounds once used in nonstick cookware and firefighting foam, showed up in slightly different structural forms called isomers depending on the sample.
More than half of the PFOS detected in wastewater and in supermarket fish consisted of branched isomers. These branched forms are spherical and compact and dissolve more readily in water. In contrast, PFOS in the egg yolks of fish-eating birds was almost 90% linear, a longer, more stretched form that tends to bind to proteins and stay in tissues longer.
“Taken together, these findings suggest that as PFOS moves through the food web—from water to fish to birds—its linear isomers become more dominant than the branched ones,” says the study’s corresponding author, Diana Aga, SUNY Distinguished Professor, director of the UB RENEW Institute and Henry M. Woodburn Chair in the Department of Chemistry.
Isomers share the same chemical formula, but the arrangement of atoms gives them distinct behaviors. For example, one isomer of methamphetamine is a controlled substance, while another is used in over-the-counter nasal inhalers.
Yet U.S. and European regulations still recommend treating PFAS as a single group, lumping all isomers together when measuring exposure.
“Our study adds to the evidence that PFAS isomers can bioaccumulate at different rates and should not be assumed to behave the same,” Aga notes.
The work spans two studies and was funded by the U.S. National Science Foundation and the Environmental Protection Agency.
Separating isomers with advanced techniques
Distinguishing PFAS isomers requires cyclic ion mobility spectrometry, a cutting-edge method that separates isomers based on subtle differences in their three-dimensional shapes as they move through a gas-filled tube.
Imagine dropping two sheets of paper—one flat and one crumpled—through the same air. They’re the same material and weigh the same, yet the crumpled one lands differently due to its shape.
In a similar way, cyclic ion mobility spectrometry differentiates PFOS isomers by their drift times—the time needed for each isomer to reach the detector. Branched isomers, with compact shapes, traverse the gas faster than elongated linear isomers.
The UB RENEW Institute’s cyclic ion mobility instrument, funded by the Office of the Senior Vice President for Research, Innovation and Economic Development, analyzed PFAS in seven unfrozen supermarket fish samples. These included benthic species like blue catfish, cod, and haddock, which dwell near the bottom, and pelagic species such as rainbow trout, salmon, and tilapia, which inhabit open water.
The findings were published in the American Chemical Society’s Journal of Agriculture and Food Chemistry. Aga’s team observed that benthic fish generally contained more branched PFOS isomers than pelagic fish and even identified two additional branched isomer types in benthic species that weren’t detected in pelagic ones.
Combining branched and linear isomers, benthic fish showed a notably higher overall PFOS concentration than pelagic fish. Benthos species also tended to accumulate more long-chain PFAS like PFOA and PFNA, which have eight and nine carbon atoms, respectively.
“These results imply that people who frequently eat bottom-dwelling fish may face higher PFAS exposure,” explains Mindula Wijayahena, a PhD student in Aga’s lab and the study’s first author.
Isomer patterns shift in birds
In a separate study published in the Journal of the American Society for Mass Spectrometry, Aga’s team tracked PFOS isomers in both wastewater and double-crested cormorant eggs. Wastewater samples came from a municipal facility in Erie County, while the eggs were collected from abandoned nests near the Buffalo Harbor.
In wastewater, more than half of PFOS was branched. Yet in the cormorant eggs, roughly 90% of PFOS was the linear form.
“Even though we know linear isomers tend to accumulate more in tissue than branched ones, the strong tilt toward linear is puzzling and warrants further study,” says PhD student Jenise Paddayuman, the study’s first author. “Nonetheless, these results provide valuable insight into how PFOS behaves in the environment and how its isomer composition evolves as it travels through ecosystems.”
With the capability to distinguish PFAS isomers now established, Aga suggests it may be time to investigate whether different isomers have distinct toxicological effects, a finding that could support regulating them separately.
“For instance, if evidence continues to show branched isomers don’t bioaccumulate as much as linear ones, we might start designing more PFAS molecules with branched structures in mind,” she notes. “That’s a direction worth exploring in the future.”
