Silica-volatile interaction and the geological cause of the Xuan Wei lung cancer epidemic

Parts of Xuan Wei County, Yunnan Province, China have the highest known lung cancer mortality in non-smoking women. This high mortality displays a clear spatial relationship to the mines producing coal from the uppermost Permian. Geochemical, petrographic and grainsize analysis were undertaken on a set of coal samples from Xuan Wei. Results demonstrate that the single geochemical property that makes this coal unusual is its high concentration of quartz (13.5 wt%) of which 35-55% occurs as <10m grains. We propose the potential for silica-volatile interaction (PSVI) as a new method for assessing the combined influence of silica and volatile organic matter and use this as a basis for re-evaluating existing ecological data. Published lung cancer mortality values are more strongly correlated with PSVI values for Xuan Wei coal than with volatiles or silica alone and the PSVI values measured are distinct from other coals. Finally we propose that the localisation of this epidemic to Xuan Wei results from enhanced weathering of the local Emeishan basalts as a consequence of geochemical perturbations at the Permo-Triassic Boundary.