Residential radon and cancer mortality in Galicia, Spain

Highlights: • Chronic exposure to indoor radon could be associated with an increase in mortality from lung, stomach and brain cancer. • Ingestion of water containing dissolved radon would entail exposure of the stomach and other organs of the digestive system. • The mixed regression models applied allow misaligned data analysis involving a fusion of lattice and geostatistical data. Residential radon exposure is a serious public health concern, and as such appears in the recommendations of European Code Against Cancer. The objective of this study was to assess the association between residential radon levels and mortality due to different types of cancer, using misaligned data analysis techniques. Mortality data (observed cases) for each of the 313 Galician municipalities were drawn from the records of the National Statistics Institute for the study period (1999–2008). Expected cases were computed using Galician mortality rates for 14 types of malignant tumors as reference, with a total of 56,385 deaths due to the tumors analyzed. The effect estimates of indoor radon (3371 sampling points) were adjusted for sociodemographic variables, altitude, and arsenic topsoil levels (1069 sampling points), using spatial/geostatistical models fitted with stochastic partial differential equations and integrated nested Laplace approximations. These models are capable of processing misaligned data. The results showed a statistical association between indoor radon and lung, stomach and brain cancer in women in Galicia. Apart from lung cancer (relative risk (RR) = 1.09), in which a twofold increase in radon exposure led to a 9% rise in mortality, the association was particularly relevant in stomach (RR = 1.17) and brain cancer (RR = 1.28). Further analytical epidemiologic studies are needed to confirm these results, and an assessment should be made of the advisability of implementing interventions targeting such exposure in higher-risk areas.