Fluorine is a poisonous pale yellow gaseous element found in Group VIIb (i.e. the Halogen Group of elements) of the periodic table. Fluorine is the most reactive element known. It reacts violently with water liberating oxygen and forming hydrofluoric acid (HF). Fluorine even reacts with some of the normally inert noble gases such as Krypton and Xenon.
Elemental fluorine and the fluoride ion are highly toxic. The free element has a characteristic pungeant odor, detectable in concentrations as low as 20 ppb, which is below the safe working level. (reference)
Small amounts of sodium fluoride help reduce tooth cavities, but high levels can harm your health. In children whose teeth are forming, high fluoride exposure can cause dental fluorosis with visible changes in the teeth. In adults, high flouride exposure over a long time can lead to skeletal fluorosis with denser bones, joint pain, and a limited joint movement. This is extremely rare in the U.S.
Fluorine, hydrogen fluoride, and fluorides have not been classified for carcinogenic effects. Studies in people have not shown fluorides to be carcinogenic, and the studies in animals are mixed. More research is in progress.
Acute toxicity has occurred by ingestion of household products containing high levels of fluoride such as certain insecticides. The mechanism of fluoride toxicity is conversion in the stomach to hydrofluoric acid. Gastrointestinal symptoms predominate and include nausea, vomiting, diarrhea, and abdominal pain.
The U.S. Environmental Protection Agency (EPA) sets a maximum amount of 4 milligrams fluoride per liter of drinking water (4 mg/L). EPA recommends that states limit fluoride in drinking water to 2 mg/L.
The Occupational Safety and Health Administration (OSHA) limits an 8-hour work day, 40-hour work week to 0.2 milligrams of fluorides per cubic meter air (0.2 mg/m3). The level for hydrogen fluoride is 2.5 mg/m3). The highest level of fluoride allowed by OSHA for an 8-hour work day, 40-hour work week is 2.5 mg/m3.