OBJECTIVETo measure the content of silica in C1 bituminous coal and its combustion products in the high-incidence area of lung cancer in Xuanwei, Yunnan Province, China and to investigate the relationship between high incidence of lung cancer among non-smoking women and silica produced naturally in C1 bituminous coal in Xuan Wei.

METHODSThe C1 bituminous coal widely used in the high-incidence area of lung cancer in Xuanwei was selected as experiment group, while the C2+1, K7, and M30 bituminous coal that was mined and used in the low-incidence area of lung cancer in Xuanwei for more than 10 years were selected as control group. Fourteen paraffin-embedded cancer tissue samples from the non-smoking women with non-small cell lung cancer who were born in Xuanwei and were at least the 3rd generation of the family living there were collected from the department of pathology, the third affiliated hospital of kunming medical university (tumor hospital of yunnan province). Titrimetric potassium silicofluoride method was used to measure the content of silica in raw coal and its bottom ashes in 20 samples from the experimental group and control group. Scanning electron microscopy (SEM) was used to observe the morphology of silica particles in C1 bituminous coal and its bottom ashes, and scanning electron microscopy coupled with energy dispersive X-ray analyzer (SEM-EDX) was used to analyze the microscopic composition. Transmission electron microscope (TEM) was used to observe the morphology of silica particles in the bottom ashes and coal soot of C1 bituminous coal as well as the lung cancer tissue from the non-smoking women in Xuanwei, and transmission electron microscope coupled with energy dispersive X-ray analyzer (TEM-EDX) was used to analyze the microscopic composition. The silica particles were separated from the coal soot and bottom ashes and characterized by physical method.

RESULTSThe silica content in C1 bituminous coal and its bottom ashes was significantly higher than that in C2+1, K7, and M30 bituminous coal (P < 0.05). The bottom ashes of C1 bituminous coal contained a large quantity of silica particles, mostly with microscale sizes. Silica particles were found in the soot of C1 bituminous coal and the lung cancer tissue from non-smoking women in Xuanwei. The silica particles in the bottom ashes were mostly 120 ∼ 500 nm in diameter, had various shapes, and contained such elements as iron, aluminium, calcium, and potassium; the silica particles in the coal soot were mostly nanoscale, ranging from 37 nm to 80 nm in diameter, had various shapes, with some in fibrous form, had non smooth surfaces, and contained such elements as iron, potassium, calcium, aluminium, and sulfur.

CONCLUSIONIn Xuanwei, the incidence of lung cancer among non-smoking women is high in the area where silica-rich C1 bituminous coal is produced. There are silica particles enriched in both the combustion products (coal soot and bottom ashes) of C1 bituminous coal and the cancer tissue from the non-smoking women with non-small cell lung cancer, with similar morphology and microscopic composition. We hypothesize that the silica particles from combusted C1 bituminous coal in Xuanwei are mixed with indoor air and inhaled along with other suspended particles.