Defluorinating Bioaccumulative PFOS

Perfluorooctane sulfonate (PFOS) has been used as an ingredient in many industrial and consumer products such as surfactants and fire-fighting foams. Some companies stopped manufacturing the persistent and bioaccumulative chemical nearly a decade ago, and little is known about its environmental degradation pathway. Reyes Sierra-Alvarez and colleagues at the University of Arizona, Tucson, have shown for the first time that vitamin B-12, a cobalt-based macrocycle, can catalyze the partial defluorination of PFOS (Environ. Sci. Technol., DOI: 10.1021/es702842q). Although vitamin B-12 might seem like a surprising reagent in this context, the researchers were aware that most known reductive dehalogenase enzymes depend on vitamin B-12 to help cleave halogens. They suggest that microbes that produce vitamin B-12 might be able to break down PFOS in the environment. In lab tests, the researchers monitored PFOS in the presence of vitamin B-12 and a reducing agent, observing fluoride release by monitoring the solutions with an ion-selective electrode and by ¹⁹F NMR spectroscopy. PFOS is a 75:25 mixture of linear and branched isomers, including the branched 6-CF₃-PFOS shown. The team's results indicate that branched PFOS isomers are more prone to degradation than linear isomers, but the scientists have yet to elucidate a mechanism.