Fluorine beyond PFAS: Tracking fluorine during photolysis of fluorinated pesticides and pharmaceuticals

Rachel Carson brought to light the dangers of persistent chlorinated chemicals in 1962, and we have spent decades dealing with these pollutants. Rather than learn from this lesson, we have incorporated another halogen, fluorine, into numerous industrial and consumer chemicals, including poly- and perfluorinated substances (PFAS). PFAS as a class of chemicals are under intense scrutiny by regulators and the public due to their persistence and toxicity. Fluorine incorporation into organic chemicals is, however, much more ubiquitous than is generally known by the public. There are many mass-produced chemicals, including pharmaceuticals, pesticides, and medical contrast agents, containing one or more fluorine atoms in a variety of chemical functional groups that are released into the environment and (waste)water treatment systems. Yet, we understand little about the fluorinated byproducts produced upon degradation of fluorinated pesticides and pharmaceuticals. Upon photolysis or oxidative treatment in aquatic systems, persistent fluorinated byproducts or fluoride from pesticides and pharmaceuticals are formed depending on the type and stability of the fluorine-containing functional group. Byproduct quantification was performed using ¹⁹F-NMR and high-resolution mass spectrometry. Some motifs are persistent, generating new PFAS, while others degrade to fluoride. Advanced oxidation often leads to a higher yield of fluoride as an end product, but also trifluoroacetic acid which is persistent. These results will assist in the future optimization of water treatment methods and development of pharmaceutical/pesticide structures to reduce persistent byproduct formation.