Forever chemicals are everywhere—but not all behave the same way. A new study tracking these toxic substances through the food web reveals a surprising twist that could change how environmental scientists and regulators approach pollution. And here’s the part that many overlook: the chemical structure of these pollutants actually determines how deeply they embed themselves in living tissues.
A team of chemists from the University at Buffalo (UB) studied water, fish, and bird eggs from Lake Huron, Ontario, uncovering how certain variants of per- and polyfluoroalkyl substances (PFAS) move through ecosystems. PFAS, often called “forever chemicals,” resist breaking down and have contaminated everything from drinking water to seafood. But when researchers examined perfluorooctanesulfonic acid (PFOS)—a well-known and highly toxic PFAS once used in firefighting foam and nonstick cookware—they made a striking discovery. The molecules weren’t identical: they existed in different structural forms, known as isomers, which behaved entirely differently depending on where they were found.
More than half of the PFOS in wastewater and grocery-store fish samples consisted of branched isomers—spherical, compact forms that dissolve more easily in water. In contrast, nearly 90% of the PFOS in bird egg yolks from fish-eating species like the double-crested cormorant was linear, a stretched-out form that clings to proteins and builds up in tissues over time. Why does this matter? Because the type of isomer determines how easily a chemical moves through the food chain and how long it stays there.
“Our findings suggest that as PFOS transfers from water to fish and finally to birds, the linear forms dominate,” explains Diana Aga, PhD, director of UB’s RENEW Institute and a distinguished professor of chemistry. Isomers, she notes, share the same chemical formula but differ in how their atoms are arranged—a subtle change that can dramatically alter their behavior. For instance, one isomer of methamphetamine is an illegal drug, while another is a safe ingredient in nasal inhalers.
Despite these differences, both U.S. and European testing guidelines still lump all PFAS isomers together rather than distinguishing between them. That’s a problem, researchers argue. “PFAS isomers accumulate in organisms at different rates and shouldn’t be treated as though they’re all chemically identical,” Aga says. The research, funded by the National Science Foundation and the U.S. Environmental Protection Agency, adds to mounting evidence that policies must evolve to reflect these molecular distinctions.
Decoding the invisible differences
To tell these molecular twins apart, scientists relied on an advanced technique called cyclic ion mobility spectrometry. This method separates PFAS molecules based on how their shapes affect their movement through a tube filled with an inert gas like nitrogen. Think of dropping a flat sheet of paper and a crumpled ball at the same time: both have the same mass, but the ball hits the ground first. Similarly, branched PFOS isomers, being rounder and more condensed, move faster through the analyzer than linear ones.
Using this technology, UB researchers analyzed seven supermarket fish species—some bottom dwellers (benthic fish like blue catfish, cod, and haddock) and others from open waters (pelagic fish such as trout, salmon, and tilapia). The findings, published in the Journal of Agricultural and Food Chemistry, showed that benthic fish contained a greater variety of branched PFOS isomers, including two additional forms not detected in pelagic samples. As a result, bottom-dwelling species carried higher total PFOS levels and showed greater contamination by long-chain PFAS compounds like perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA).
Mindula Wijayahena, a PhD student and the study’s lead author, warns that people who frequently consume benthic fish could face greater PFAS exposure. Such findings highlight how diet and species type influence the chemicals humans ingest, even unknowingly.
A different pattern in birds
The story takes an even more intriguing turn in a related UB study published in the Journal of the American Society for Mass Spectrometry. When researchers examined wastewater from an Erie County treatment plant and egg yolks from abandoned cormorant nests near Buffalo Harbor, they noticed an unexpected reversal. While wastewater samples were dominated by branched PFOS isomers, the bird eggs were almost entirely linear. Why the dramatic shift? Scientists know that linear PFOS tends to accumulate more in tissues, but the extent of the difference in bird eggs hints at complex biological or environmental filtering processes that deserve more investigation.
“These findings shed light on the environmental journey of PFOS,” says Jenise Paddayuman, another UB PhD student and first author of the bird study. “They show that linear isomers persist longer as the chemical travels up the food chain.”
Now that scientists can separate and study individual PFAS isomers, Aga says it’s time to consider whether they should also be regulated differently. If linear forms are indeed more toxic or bioaccumulative, should chemical manufacturers focus on designing branched alternatives that pose less long-term risk? “If future evidence supports that idea,” Aga adds, “then perhaps we can start engineering PFAS with safer molecular architectures.”
But here’s where it gets controversial: Should industry really be designing new PFAS at all, given the lasting legacy of contamination already caused by these compounds? Or is it time to rethink their use altogether? What do you think—should we innovate safer versions, or phase them out entirely? Share your perspective in the comments below.
