A new study has shown that the volcanic eruptions thought responsible for Earth's largest mass extinction 250 million years ago has been linked to unusually high rates of lung cancer in a particular area of China.
The study shows for the first time that the high silica content of coal in one region of China, which may have been released by volcanic eruptions 250 million years ago, may be interacting with volatile substances in the coal to cause unusually high rates of lung cancer.
The study, by scientist David Large and colleagues, note that parts of China's Xuan Wei County in Yunnan Province have the world's highest incidence of lung cancer in nonsmoking women - 20 times higher than the rest of China.
Women in the region heat their homes and cook on open coal-burning stoves that are not vented to the outside.
Scientists believe that indoor emissions from burning coal cause cancer, but are unclear why the lung cancer rates in this region are so much higher than other areas.
Earlier studies show a strong link between certain volatile substances, called PAHs, in coal smoke and lung cancer in the region.
The scientists found that coal used in parts of Xuan Wei County had about 10 times more silica, a suspected carcinogen, than US coal.
Silica may work in conjunction with PAHs to make the coal more carcinogenic, they indicate.
The scientists also found that this high-silica coal was formed 250 million years ago, at a time when massive volcanic eruptions worked to deposit silica in the peat that formed Xuan Wei's coal.