Proximity to coal mining activity and cancer risk in Illinois: A geospatial approach

Background     Studies have indicated population-level associations between coal mining and cancer incidence and mortality (I/M), but few have specifically examined residential proximity to this exposure.  Of the small number of studies exploring coal mining and population cancer risk in the United States, few were performed outside Appalachia. Our work utilized spatial and statistical analyses to test two coal mining exposure variables and their associations with cancer I/M across Illinois. 

Methods           We calculated age-adjusted, county-level cancer I/M rates for five cancers groups: all malignant, lung, colorectal, breast (female) and prostate. Coal mining exposure was defined as coal production group (CoalPG) and distance-weighted exposure (D-WE).  CoalPD was categorized at the county-level as: 1) never mined; 2) mined prior to 1987; and 3) mined after 1987. Census tract level population and proximity to the nearest mine were used to calculate D-WE, which was then aggregated at the county level. Spatial analyses were performed to identify spatial autocorrelation and stepwise regression analyses were used to explore the relationship between cancer I/M and coal mining exposures. Covariates considered for inclusion in stepwise regression analyses were: socioeconomic deprivation, former/current smoking prevalence, race and rurality.

Results             Global spatial autocorrelation indicated significant spatial clustering of incidence, mortality and coal production with Moran’s I values of 0.23, 0.22, and 0.23 respectively. Regression analyses indicated an association between CoalPG and colorectal cancer incidence (p=0.009) and mortality (p=0.035), and an inverse association with prostate cancer mortality (i.e. protective; p=0.018). D-WM was significantly associated with lung cancer incidence and mortality (p=0.004 and P<0.001, respectively) and all cancer mortality (p<0.001). No other cancer I/M rates were significantly associated with either measure.

Conclusion      Coal production and cancer incidence and mortality are spatially clustered in Illinois. Exposures to coal mining were associated with elevated risk of colorectal and lung cancer. Our study corroborates other studies indicating a relationship between proximity to coal mines and cancer risk.  Future studies are needed to further elucidate the population exposure dynamics of coal mining and which methods may be most accurate. These studies should consider individual-level exposures and cancer outcomes to further substantiate population-level findings.