Lung cancer rates in Xuanwei County have been among the highest in China for both males and females and have been causally associated with exposure to indoor smoky (
bituminous) coal emissions that contain very high levels of
polycyclic aromatic hydrocarbons. There are numerous
coal mines across the County. Although
lung cancer risk is strongly associated with the use of smoky
coal as a whole, variation in risk by smoky
coal subtype has not been characterized as yet. We conducted a population-based case-control study of 498
lung cancer cases and 498 controls, individually matched to case subjects on age (+/-2 years) and sex to examine risk by
coal subtype. Odds ratios (
ORs) and 95% confidence intervals (CIs) for
coal subtype were calculated by conditional logistic regression, adjusting for potential confounders. Overall, smoky
coal use was positively and statistically significantly associated with
lung cancer risk, when compared with the use of
smokeless coal or wood (OR = 7.7, 95% CI = 4.5-13.3). Furthermore, there was a marked heterogeneity in risk estimates for specific subtypes of smoky
coal (test for heterogeneity: p = 5.17 x 10(-10)). Estimates were highest for
coal of the Laibin (OR = 24.8, 95% CI = 12.4-49.6) and Longtan (OR = 11.6, 95% CI = 5.0-27.2)
coal types and lower for
coal from other subtypes. These findings strongly suggest that in Xuanwei and elsewhere, the carcinogenic potential of
coal combustion products can exhibit substantial local variation by specific
coal source.