PFAS isomers in aquatic biota: revealing differences in occurrence, bioaccumulation, and biotransformation through isomer-specific analysis

Abstract

Historical production of per- and polyfluoroalkyl substances (PFAS) via electrochemical fluorination has resulted in complex mixtures of linear (L) and branched (Br) isomers, yet most environmental studies still treat them as single compounds. Emerging research highlights that isomer-specific differences critically shape PFAS environmental fate, bioaccumulation, and toxicity. These distinctions are particularly critical for aquatic organisms, which experience continuous exposure to PFAS and serve as sentinels of ecosystem health. A comprehensive review of literature from January 2000 to December 2025 reveals that most studies on PFAS in aquatic species overlook isomer resolution, constraining insights into mixture behavior. The relatively few studies that report isomer profiles across fish, sharks, marine mammals, aquatic insects, seabirds, alligators, and polar bears primarily focus on PFOS (perfluorooctane sulfonic acid), leaving substantial knowledge gaps for other PFAS classes. Evidence also indicates that precursor compositions strongly influence isomer-specific bioaccumulation; several studies show that L-isomers tend to bioaccumulate more than their Br counterparts, suggesting potential differences in environmental stability and metabolism. Advancing knowledge on PFAS isomer distribution requires broader use of orthogonal separation techniques. Ion mobility spectrometry can resolve L- and Br-isomers based on differences in their collision cross-sections. Other techniques that can separate L- and Br-isomers include gas chromatography/mass spectrometry with derivatization, and supercritical fluid chromatography/mass spectrometry, capable of efficient separation of isomers based on differences in partition coefficients between two phases. Integrating these techniques into current conventional PFAS analytical methods is essential for uncovering the PFAS structure-environmental behavior and for enhancing future ecological risk assessments.