A startling revelation has emerged from a recent study, shedding light on the presence of "forever chemicals" in our food chain. The research, conducted by chemists at the University at Buffalo, has uncovered a critical distinction in the distribution of these chemicals across different species.
The core issue: Not all "forever chemicals" are created equal, and their unique molecular structures can have a significant impact on how they move through the food web.
The study analyzed samples of water, fish, and bird eggs, and what they found was eye-opening. While per- and polyfluoroalkyl substances (PFAS) were expected, the variation in their structural forms, known as isomers, was a surprising discovery.
But here's where it gets controversial...
PFOS, a particularly hazardous PFAS, showed up in different isomeric forms depending on the sample. In wastewater and supermarket fish, branched isomers dominated, while in the egg yolks of fish-eating birds, linear isomers were prevalent.
"This suggests that as PFOS moves through the food chain, its linear isomers become more common than the branched ones," explains Diana Aga, the study's lead author and a distinguished professor at UB.
And this is the part most people miss: Isomers of the same compound may have the same chemical formula, but their unique atomic arrangements can lead to vastly different behaviors.
Take methamphetamine, for example. One isomer is a controlled substance, while another is used in over-the-counter nasal inhalers. Yet, current regulations in the U.S. and Europe advise treating all isomers of PFAS as equal.
"Our study adds to the growing body of evidence that PFAS isomers can bioaccumulate at different rates and should be treated individually," Aga emphasizes.
The study, supported by the U.S. National Science Foundation and Environmental Protection Agency, utilized advanced separation techniques to sort out these isomers. Cyclic ion mobility spectrometry, an analytical technique, distinguishes isomers based on their shape differences and how they move through a gas-filled tube.
To illustrate this, imagine two sheets of paper, one flat and the other crumpled. Drop them, and the crumpled one will hit the ground first, despite being made of the same material and weighing the same.
Similarly, cyclic ion mobility spectrometry measures the "drift time" of isomers, revealing that branched isomers, with their compact, spherical shapes, move faster through the gas-filled tube than the elongated linear isomers.
The study's results showed that benthic fish (bottom-dwellers like blue catfish and cod) generally had more branched PFOS isomers than pelagic fish (those living in open waters, like rainbow trout and salmon). This led to significantly higher total PFOS concentrations in benthic fish, which also had higher proportions of longer-chain PFAS.
"This suggests that frequent consumers of bottom-dwelling fish species may face higher exposure to PFAS," says Mindula Wijayahena, a PhD student and first author of the study.
In a separate study, Aga's team analyzed PFOS isomers in wastewater and bird eggs. The wastewater sample came from Erie County, while the egg yolks were collected from abandoned nests near Buffalo Harbor, belonging to double-crested cormorants, a fish-eating bird.
Interestingly, while over 50% of PFOS in wastewater was branched, nearly 90% of PFOS in cormorant egg yolks was linear.
"The reason for this heavy skew towards linear isomers in the eggs warrants further investigation," says Jenise Paddayuman, another PhD student and first author of this study. "But the results do provide insight into the environmental fate of PFOS, suggesting that linear isomers persist more as PFOS moves through the environment."
Now that chemists have the tools to distinguish PFAS isomers, Aga believes it's time to explore the differences in their toxicological effects, which could lead to the need for separate regulations.
"If evidence continues to show that branched isomers don't bioaccumulate as much as linear ones, we might start designing molecules with branched structures," she suggests.
So, what are your thoughts? Do you think it's time to reevaluate the regulation of PFAS isomers? We'd love to hear your opinions in the comments below!
