INDOOR AIR POLLUTION FROM COAL COMBUSTION; HETEROGENEITY IN COAL COMPOSITION AND THE IMPLICATIONS FOR THE LUNG CANCER RISK IN XUANWEI AND FUYUAN COUNTY, CHINA

Background: Xuanwei and Fuyuan county in Yunnan province, China have among the highest lung cancer rates in the country. This has been associated with the domestic combustion of locally sourced “smoky” (bituminous) coal. Additionally, significant geographical variation in cancer rates among smoky coals users has been observed, suggesting heterogeneity in fuel source composition and/or combustion characteristics. Relatively little is known as yet about heterogeneity in coal composition in the region. Limited research thus far has indicated that smoky coal from the region contains high levels of organic compounds (in particular polycyclic aromatic hydrocarbons) and free crystalline silica.

Methods: Smoky and “smokeless” (anthracite) coal samples were collected as part of a large cross-sectional molecular epidemiology study throughout the Xuanwei and Fuyuan areas. Coal samples were analysed for a variety of characteristic parameters including: type and maturity of organic matter, pyrolysis yield, carbon and sulphur content, mineralogical content and elemental composition of the coal ash. Heterogeneity in coal characteristics between smoky and smokeless coal and within coal types was assessed by the Kruskal-Wallis test.

Results: 145 coal samples (116 smoky and 29 smokeless coal) were analysed. Analysis revealed significant differences between smoky and smokeless coal with regard to organic geochemical content, carbon-sulphur content, mineralogy and elemental composition. Of note, smoky coal contained higher levels of hydrocarbons, silica and quartz and lower levels of aluminium than smokeless coal. Further significant variation was observed among smoky coal in hydrocarbon yield and elemental composition (including aluminium and silica) on the basis of the coal’s geographic location.

Discussion: This paper has identified several differences between and within smoky and smokeless coals sourced from Xuanwei and Fuyuan counties. Decreased aluminium together with increased silica may indicate elevated free silica in smoky coal, a finding consistent with observed higher levels of quartz. Elevated hydrocarbon yields are consistent with previous observations of elevated polycyclic aromatic hydrocarbon (PAHs) content in coals from the area and high levels of PAHs in the indoor air.