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The major natural sources of airborne hydrogen fluoride (HF) are volcanic activity, ocean spray, and crustal weathering of fluoride-containing rocks. Anthropogenic sources include emissions from industrial operations such as aluminum and fluorocarbon production, and uranium processing. For children and adults who do not have any occupational exposure to or do not live in the immediate vicinity of industrial operations that emit HF, the average daily fluoride intake is on the order of 1.2-3.0 mg/day from food and water, respectively. Use of fluoridated dentifrices contributes an additional 0.25 mg/day; less than 0.1 mg/day comes from inhaled fluoride. This total exposure level (approximately 0.06 mg/kg/day) has been shown to have a cariostatic effect, especially in children, and is generally considered to be the No Observed Adverse Effect Level (NOAEL). This level of exposure has been established as the oral reference dose (RfD) by the Agency, although it should be noted that very mild dental fluorosis (mottling) has been observed in about 20 percent of the people who are chronically exposed at this level. The possible carcinogenic potential or chronic exposure to fluoride has been investigated, and the Agency has stated that there is not enough information to conclude that fluoride presents a cancer risk to humans.
Theissen, K. Summary Review of Health Effects Associated with Hydrogen Fluoride and Related Compounds: Health Issue Assessment. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/8-89/002F (NTIS PB89220495).