Coal combustion emissions and lung cancer in Xuan Wei, China

Xuan Wei County has the highest female lung cancer mortality rates in China, but the rates vary by two orders of magnitude among communes located in the same general area in the county. The different coals are linked to the different lung cancer mortality rates in commune residents who burn them for heating and cooking. Fifteen types of coal were collected from this county. I developed a controlled laboratory system to burn the coals in a manner similar to the way these fuels are used in the research area, and collected the particulate and gas phase emissions. The coals and their emissions were characterized by various techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), electron paramagnetic resonance (EPR), electron microscopy, and gas-chromatography coupled with mass spectrometry (GC-MS). Using the emission factor data obtained from the laboratory, I estimated the indoor air emissions of various pollutants and examined the relationship between these exposure variables and the lung cancer risks in an ecological study. The lung cancer risk associated with each specific coal type was estimated by the lung cancer mortality rate of the villages within a certain distance of the coal mine. I found no association between the lung cancer risks and the exposures to polycyclic aromatic hydrocarbons (PAHs), free radicals, or transition metals. The exposure variable associated with the lung cancer risk was the indoor air emission of crystalline silica, which was estimated by the elemental concentrations of Si and Al. Abundant crystalline silica was found in certain types of coals, soot emissions, and 2 lung cancer tissue samples. Silica in some coals occurs as quartzine, a microfibrous form of quartz. The hypothesis of crystalline silica as an risk factor of the lung cancer epidemic in Xuan Wei, China needs to be confirmed in the future by more detailed characterization of the silica crystals in soot particles and lung cancer tissue samples, both qualitatively and quantitatively.