text: "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