Fluoride is an ionic form of the element fluorine. Traces of the fluoride are found in soil, water, tea leaves, shellfish and grapes. Most of the fluoride people consume comes from fluoridated water, foods and beverages. Approximately 80% of orally ingested fluoride is absorbed in the gastrointestinal tract in adults. About 50% of this is retained, and bones and teeth store up to 99% of this in adults. The other 50% is excreted in urine. In young children, more fluoride is taken up by bones and teeth than in adults.