Heterogeneity in coal composition and implications for lung cancer risk in Xuanwei and Fuyuan counties, China

article i nfo Background: Xuanwei and Fuyuan counties in Yunnan Province, China have among the highest lung cancer rates inthecountry.Thishasbeenassociatedwiththedomesticcombustionofbituminouscoal(referredtoas "smoky" coal). Additionally, significant geographical variation in cancer rates among smoky coal users has been observed, suggesting heterogeneity in fuel source composition and/or combustion characteristics. Research thus far has in- dicated that smoky coal emits high levels of polycyclic aromatic hydrocarbons (PAHs) and contains high concen- trations of fine grained crystalline quartz, however, much of this research is limited in terms of sample size and geographic scope. In order to more fully characterise geochemical and elemental compositions of smoky and smokeless coal use in Xuanwei and Fuyuan, we carried out a large exposure assessment study in households in this region. Methods: Fuel samples representing smoky and "smokeless" (anthracite, the major alternative coal type in the region) coals were collected from 137 homes in Xuanwei and Fuyuan. Rock-Eval, Leco-CS, XRF analysis and elec- tron microscopy were used to establish hydrocarbon content (to represent volatile organic compounds), major and trace element composition and mineral composition respectively. Heterogeneity in coal characteristics be- tween and within coal types was assessed by the Kruskal-Wallis test. Results: 145 coal samples (116 smoky and 29 smokeless coals) were analysed. Statistically significant differences between smoky and smokeless coals with regard to hydrocarbon content, sulfur, trace elements and mineral compositionwere observed.Of note,smokycoalcontainedbetween5and15 timestheamountof volatileorgan- icmatterandtwicetheamountofquartz (includingrespirablequartz)thansmokelesscoal.Smokycoalgenerally had lower levelsof traceelements (plus aluminium)than smokelesscoal. Significantvariation wasalsoobserved betweensmokycoal samples fromdifferent geographicalareas with regard tohydrocarbon content and elemen- tal composition (including aluminium and silicon). Discussion: This paper has identified compositional differences between and within smoky and smokeless coals sourced from Xuanwei and Fuyuan counties. A decreased ratio of aluminium to silicon in smoky coal suggests el- evatedfreesilica,a finding consistentwith observed higher levels of quartz.Elevatedvolatile organic matter con- tent in smoky coal (when compared to smokeless coal) is consistent with the geochemical expectations for smoky and smokeless coals. These findings also reflect previous observations of elevated volatile compound emissions (notably PAHs) from smoky coal in the area. The observed heterogeneity in coal composition between and within coal types may provide leads to the observed heterogeneity in cancer risk observed in this area.