The terms 'fluorine" and 'fluoride' are used interchangeably in the literature as generic terms. In this document, the terminology suggested by US NAS (1971) is followed: "This document, rather than following common usage, uses the term "fluoride" as a general term everywhere, where exact differentiation between ionic and molecular forms or between gaseous and particulate forms is uncertain or unnecessary. The term covers all combined forms of the element, regardless of chemical form, unless there is a specific reason to stress the gaseous elemental form F2, in which case the term "fluorine" is used." Fluorine and fluorides occur ubiquitously in the environment, and because of their wide and growing use in industrial processes, their environmental importance is increasing. The use of fluorides in dental health care products is also growing. Compounds dealt with in this document, besides fluorine, include hydrogen fluoride, alkali fluorides, fluorspar, cryolite, fluoroapatite, other inorganic fluoride compounds, and certain organic fluorides that release fluoride when metabolized.