alt=A rotating, transparent image of a human figure with targeted organs highlighted<unk>  may interact with<unk>  systems in the form of<unk> -containing compounds. Though elemental<unk>  (F2) is very rare in everyday life,<unk> -containing compounds such as<unk>  occur naturally as minerals. Naturally occurring organofluorine compounds are extremely rare. Man-made<unk>  compounds are common and are used in medicines, pesticides, and materials. Twenty percent of all commercialized pharmaceuticals contain<unk> , including Lipitor and Prozac. In many contexts,<unk> -containing compounds are harmless or even beneficial to living organisms; in others, they are toxic. Aside from their use in medicine, man-made<unk> ted compounds have also played a role in several noteworthy environmental concerns. Chlorofluorocarbons (CFCs), once major components of numerous commercial aerosol products, have proven damaging to Earth's ozone layer and resulted in the wide-reaching Montreal Protocol; though in truth the chlorine in CFCs is the destructive actor,<unk>  is an important part of these molecules because it makes them very stable and long-lived. Similarly, the stability of many organofluorine compounds has raised the issue of biopersistence. Long-lived molecules from waterproofing sprays, for example PFOA and PFOS, are found worldwide in the tissues of wildlife and humans, including newborn children.<unk>  biology is also relevant to a number of cutting-edge technologies. PFCs (perfluorocarbons) are capable of holding enough oxygen to support human liquid breathing. Organofluorine in the form of its radioisotope 18F is also at the heart of a modern medical imaging technique known as positron emission tomography (PET). A PET scan produces three-dimensional colored images of parts of the body that use a lot of sugar, particularly the brain or tumors.
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