Application of perfluorinated acid isomer profiles for manufacturing and exposure source determination

Perfluorinated acids (PFAs) constitute a diverse class of compounds which have been manufactured for over 50 years and are now globally disseminated in the environment, including remote arctic food webs. The two most commonly detected PFAs in the environment, perfluorooctane sulfonate (PFOS, C8F17SO3- ) and perfluorooctanoate (PFOA, C7F15COO-) display significant adverse health effects in lab animals, and continue to garner concern from international regulatory agencies. Historical PFOS and PFOA manufacturing was predominantly by electrochemical fluorination (ECF), a process which results in 20-30% branched / 70-80% linear isomers. While ECF was for the most part phased-out in 2002, production of strictly linear PFOA continues today by a telomerization process. Among the questions pertaining to future regulation of these chemicals is to what extent PFOA in the environment can be attributed to ECF (mostly historical production) versus telomerization (ongoing production), and to what extent precursors (i.e. indirect exposure) contribute to environmental PFOS concentrations. It was hypothesised that PFA isomer profiles in humans and environmental samples may be useful as a tool for manufacturing and/or exposure source determination. To explore this, an LC-MS/MS method was developed to characterize the major PFA and PFA-precursor isomers in human and environmental samples. Whilst PFOA isomer profiles are predominantly linear in humans and wildlife, PFOS isomer profiles can be enriched or deficient in branched content, relative to historically manufactured formulations. These profiles were partially explained by isomer-specific pharmacokinetic and biotransformation experiments, whereby branching of the perfluoroalkyl chain typically resulted in faster elimination of PFAs in rodents, while branching of a PFOS-precursor typically resulted in faster biotransformation in human liver microsomes. Based on these results, quantitative assessment of manufacturing source in biological samples is expected to be difficult; therefore, we examined water samples in which isomer profiles were expected to be largely conserved. PFOA in sub-Arctic and Atlantic regions was found to be predominantly of ECF-origin, which confirms model predictions on the global release and transport of PFAs. Nonetheless, linear-telomer contributions were significant in most locations, suggesting that current production may represent a significant source of PFAs to remote arctic food-webs in the future.