Quantification and characterization of household air pollution exposure from the use of solid fuels; Clues to the lung cancer epidemic in Xuanwei and Fuyuan, China

Background: Xuanwei and Fuyuan are two neighbouring counties in Yunnan province China which are remarkable in that they have among the highest lung cancer rates in the nation regardless of gender or smoking status. Previous research has implicated the domestic combustion of locally sourced “smoky” (bituminous) coal as being responsible for the lung cancer epidemic (there are 2 main coal types available, smoky coal, which is common throughout both counties, and “smokeless” coal, which is an anthracite coal available to only limited areas). Previous exposure surveys have suggested that either crystalline quartz and/or polycyclic aromatic hydrocarbons may play a role in carcinogenesis however, this research has been limited in sample size and geographic scope meaning that overall, relatively little is currently understood regarding which component(s) of smoky coal directly contribute to lung cancer risk. The work presented in this thesis represents an extensive exposure assessment survey of residents and households from throughout the Xuanwei and Fuyuan counties.

Methods: We enrolled 163 households and their non-smoking female heads from throughout Xuanwei and Fuyuan for study. Samples of fuel, ash, and personal and indoor air measurements were collected. Samples were analysed for multiple pollutants including particulate matter, black carbon, polycyclic aromatic hydrocarbons, and crystalline silica and were compared across different fuel (e.g. smoky coal, smokeless coal, wood) and stove types (e.g. unvented firepits, ventilated stoves).

Results: Analysis of coal samples revealed that smoky coal contained higher amounts of volatile matter and quartz than smokeless coal. Analysis of air samples found that the use of smoky coal was associated with higher measurements of particulate matter, particle phase polycyclic aromatic hydrocarbons, and black carbon than smokeless coal but that wood was associated with even higher measurements of particulate matter and black carbon. Minimal quartz was observed in air measurements with ash analysis indicating that the elevated quartz observed in smoky coal largely went on to form part of the ash. Also of note was the finding that air measurements were typically reduced among households using ventilated stoves than households using unvented firepits with the exception of black carbon.

Conclusions: The findings presented in this thesis provide valuable insight into potential carcinogenic factors in an area with an exceptionally high lung cancer rate and will be used in an ongoing investigation of lung cancer among non-smoking females in the area. While our findings have generally found that exposure levels are lower among users of ventilated stoves and/or smokeless coal, these levels were still considerably high, indicating that none of the solid fuels in use by this population could truly be considered safe.