Colorectal cancer mortality and industrial pollution in Spain

Background: Records kept as a result of the implementation of Integrated Pollution Prevention and Control (IPPC) and the European Pollutant Release and Transfer Register (E-PRTR) constitute a public inventory of industries, created by the European Commission, which is a valuable resource for monitoring industrial pollution. Our objective is to ascertain whether there might be excess colorectal cancer mortality among populations residing in the vicinity of Spanish industrial installations that are governed by the IPPC Directive and E-PRTR Regulation and report their emissions to air. Methods: An ecological study was designed to examine colorectal cancer mortality at a municipal level (8098 Spanish towns), over the period 1997-2006. We conducted an exploratory near vs. far analysis to estimate the relative risks (RR) of towns situated at a distance of less than 2 km from industrial installations. The analysis was repeated for each of the 24 industrial groups. RR and their 95% credible/confidence intervals (95% CI) were estimated on the basis of Poisson regression models, using two types of modelling: a) the conditional autoregressive Bayesian model proposed by Besag, York and Mollie, with explanatory variables; and b) a mixed regression model. Integrated nested Laplace approximations were used as a Bayesian inference tool. Results: Statistically significant RRs were detected in the vicinity of mining industry (RR 1.258; 95% CI 1.082 - 1.463), paper and wood production (RR 1.071; 95% CI 1.007 - 1.140), food and beverage sector (RR 1.069; 95% CI 1.029 - 1.111), metal production and processing installations (RR 1.065; 95% CI 1.011 - 1.123) and ceramics (RR 1.050; 95% CI 1.004 - 1.099). Conclusions: Given the exploratory nature of this study, it would seem advisable to check in other countries or with other designs, if the proximity of industries that emit pollutants into the air could be an added risk factor for colorectal cancer mortality. Nevertheless, some of the differences between men and women observed in the analyses of the industrial groups suggest that there may be a component of occupational exposure, little-studied in the case of cancers of the digestive system.