In rural areas of Southwestern China, villagers' habits of picking up loose coal for use in their homes has lead to an epidemic that may have poisoned millions. The coal is exposed through erosion, and then picked up by locals and used for cooking and heating. Unfortunately the coal is unusually high in fluoride, which is then burned, and enters the system through inhalation of particles, and through food which absorbs the pollutant.
This leads to an incredibly high incidence of fluorosis, both of the skeleton and the teeth, which can lead to crippling joint problems, deformed bones and severely damaged teeth.
The Chinese government is attempting to combat the epidemic by pushing programs to install chimneys in rural and poor communities, which would effectively vent the particles.