For the past several decades, cancerous skin lesions and deformed limbs have been all too common among the people of Guizhou Province in southwestern China. Today thousands of the region's residents suffer from arsenic poisoning, with symptoms ranging from freckled skin to squamous cell carcinoma. And more than 10 million are afflicted by fluorosis, which can soften and disfigure teeth and bones.

Only in the past few years have geologists figured out the source of the arsenic and fluorine: coal. Damp, cool autumn weather makes it impossible to dry corn, chili peppers and other crops outside, so families bring them indoors to dry over coal-burning stoves. But it turns out that the coal contains abnormally high concentrations of arsenic and fluorine. Fluorosis is more common than arsenic poisoning because high-fluorine coal is combined with high-fluorine clay to make briquettes. Now that scientists understand the source of the health problems, they have launched multiple projects to help to alleviate the dangers of "dirty" coal.

   
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