"The combustion of high fluoride-content coal as an energy resource for heating, cooking, and food drying is a major exhaust emission source of suspended particulate matter and fluoride. High concentrations of these pollutants have been observed in indoor air of coal-burning families in some rural areas in China."

---Health effects of indoor fluoride pollution from coal burning in China.
Ando M., et al.
Environ Health Perspect. 1998 May;106(5):239-44.

Steven D. Slott, DDS