Forever chemicals, also known as per- and polyfluoroalkyl substances (PFAS), are pervasive in the environment, but a recent study reveals a surprising twist: not all isomers of these chemicals are distributed equally across the food web. This discovery is particularly intriguing when considering the hazardous nature of one of the most common PFAS, perfluorooctanesulfonic acid (PFOS).
The study, conducted by chemists at the University at Buffalo, analyzed samples of water, fish, and bird eggs. They found that the distribution of PFOS isomers varies significantly depending on the sample source. In wastewater and supermarket fish, more than half of the detected PFOS was in the branched isomer form, which is spherical and compact, dissolving more easily in water. However, in the egg yolks of fish-eating birds, PFOS was predominantly in the linear isomer form, which is elongated and tends to bind to proteins, remaining in tissues for longer periods.
This finding has significant implications for understanding the behavior of PFOS in the environment. As PFOS moves through the food web, from water to fish to birds, the study suggests that its linear isomers become more prevalent. This is a critical point because isomers of a compound, despite having the same chemical formula, can exhibit vastly different behaviors due to their unique atomic arrangements.
The U.S. and European regulations currently advise treating all isomers of PFAS as if they were identical, which may not accurately reflect their environmental and health impacts. The study's corresponding author, Diana Aga, emphasizes the need to recognize that PFAS isomers can bioaccumulate at different rates and should not be treated as a uniform group.
To distinguish between different isomers of PFAS, the researchers employed advanced separation techniques, including cyclic ion mobility spectrometry. This method separates isomers based on their shape differences, which influence how they move through a tube filled with gas. The study's results, published in the American Chemical Society's Journal of Agriculture and Food Chemistry, revealed that benthic fish generally contained more types of branched PFOS isomers compared to pelagic fish, leading to higher total PFOS concentrations in benthic fish.
In a separate study, the team identified PFOS isomers in wastewater and bird eggs. The wastewater samples showed a majority of branched PFOS, while the bird egg yolks contained a high proportion of linear PFOS. These findings provide insights into the environmental fate of PFOS and suggest that linear isomers may persist more as PFOS moves through the environment.
The implications of these findings are far-reaching. Chemists now have the tools to distinguish between PFAS isomers, and the next step, according to Aga, is to examine their differences in toxicological effects. This could support the argument for regulating isomers differently, potentially leading to the design of molecules with branched structures to mitigate the accumulation of linear isomers in the environment.
