Bold truth: Not all PFAS are created equal, and their health impact may hinge on subtle molecular twists. Now, here’s why that matters and what the latest UB research reveals.
Researchers from the University at Buffalo examined samples of water, fish, and bird eggs to study per- and polyfluoroalkyl substances (PFAS), the infamous “forever chemicals” that appear everywhere in the environment. Their goal wasn’t just to detect PFAS, but to understand how different structural forms, called isomers, behave as PFOS moves through ecosystems—from water to fish to birds.
The findings are striking. In wastewater and supermarket fish, a majority of detectable PFOS consisted of branched isomers. These branched forms are compact and water-loving, dissolving readily in water. In contrast, PFOS in the egg yolks of fish-eating birds was overwhelmingly linear—about 90%—a form with a longer, chain-like structure that tends to bind to proteins and linger longer in tissues.
Lead author Diana Aga, PhD, notes that this pattern suggests PFOS isomers shift in prevalence as they travel up the food chain. Linear isomers become more dominant from water to fish to birds, hinting at different environmental fates and bioaccumulation dynamics for each isomer type.
Isomers share the same chemical formula, but the arrangement of atoms matters. That tiny difference can drastically change how a substance behaves—for example, one isomer of methamphetamine is a controlled drug, while another is used in over-the-counter nasal sprays. Yet current U.S. and European regulations often tally all PFOS isomers together, treating them as if they were identical.
The UB study adds a crucial wrinkle: PFAS isomers bioaccumulate at different rates, so they should not be treated as a single group. Aga emphasizes that recognizing these differences could inform future regulatory and public health strategies.
Two related studies underpin these conclusions, supported by the National Science Foundation and the Environmental Protection Agency. The team used advanced separation methods—cyclic ion mobility spectrometry—to distinguish PFAS isomers by how their shapes affect movement through a gas-filled tube. In this analogy, two sheets of paper—one flat, one crumpled—drop at different speeds; similarly, PFOS isomers travel at different paces due to their shapes.
Applying this technique to seven unfrozen supermarket fish samples (including benthic bottom-dwellers like blue catfish, cod, and haddock, and pelagic species such as rainbow trout, salmon, and tilapia), researchers found that benthic fish harbored more branched PFOS isomers than pelagic fish. Notably, benthic species contained two additional branched isomer types not detected in pelagic fish. The total PFOS concentration was higher in benthic fish, partly because these species also carried more long-chain PFAS like PFOA and PFNA.
Mindula Wijayahena, a PhD student and the study’s first author, points out that frequent consumers of bottom-dwelling fish may face greater PFAS exposure. This insight helps explain who is at higher risk and why diet matters when assessing PFAS burden.
A separate study examined PFOS isomers in wastewater from a municipal treatment facility in Erie County and in the egg yolks of abandoned double-crested cormorant nests near Buffalo Harbor. Here, wastewater samples contained mostly branched PFOS, while the bird eggs were about 90% linear PFOS. Jenise Paddayuman, also a PhD student, notes that linear isomers’ tendency to accumulate in tissue aligns with the eggs’ high linear PFOS levels, though the exact mechanisms behind this skew warrant further investigation.
With the ability to distinguish PFAS isomers now in hand, Aga suggests it’s time to investigate whether these isomers exert different toxic effects. If branched isomers prove to bioaccumulate less than linear forms, future regulatory and design efforts might favor molecules with branched structures—or, at minimum, treat isomers as distinct entities in risk assessments.
In short, recognizing and separating PFAS isomers reveals important differences in environmental fate and potential health impacts. This work encourages regulators and researchers to consider isomer-specific data when evaluating PFAS risks and crafting policy.
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