ABSTRACT
Fluorine (F) is present in the fluoride form in all major rock types, typically at concentrations of 50–1000 mg kg-1. Fluorine is almost never present in its pure, gaseous form. Most Fluorine present naturally in the atmosphere is likely to be associated with suspended mineral particles but several Mt of fluoride are emitted by volcanoes each year. Fluorine is essential in many animals for formation of dental enamel and mineralisation in bones; a small amount is present in soft tissues. Highly toxic organofluorine compounds, such as fluoracetic acid, fluoropalmitic acid and fluoroleic acid, are formed naturally in the leaves and seeds of several plant species. Fluorine compounds such as sodium fluoroacetate are used as pesticides against mammalian pests and other Fluorine-containing compounds are used as household insecticides. Plants suffer from chronic exposure to gaseous fluorides at concentrations of up to three orders of magnitude lower than observed for other phytotoxic gases such as O3 and SO2.
