Cancer incidence and residency in geothermal area: A census based cohort study

Purpose: To assess whether exposure to geothermal gases such as hydrogen sulphide and radon among residents of a geothermal area are associated with risk of cancer. Methods: The source of data was the census in 1981. Using personal identifier those 5 to 65 years of age were record linked with nation-wide death and cancer registries. Thus, vital and emigration status was ascertained for all and cancers cases found. The total population was 183 047, total number of person years was 4 533 812, and total number of first cancers was 23 360. Population in high temperature geothermal area, defined by community code, was compared with population in non-geothermal area in Cox-model, adjusted for age, gender, education, and lodgings. Results: The hazard ratio (HR) in the high temperature geothermal area for all cancer was 1.22 (95% confidence interval (CI) 1.05-1.42) as compared with non-geothermal area. The HR for pancreas cancer was 2.85 (95%CI 1.39-5.87), bone cancer 5.80 (95%CI 1.11-30.32) breast cancer 1.59 (95%CI 1.10-2.31), lymph-hematopoietic cancer 1.64 (95%CI 1.00-2.66), and non-Hodgkin lymphoma 3.25 (95%CI 1.73-6.07). The HR for selected cancer sites were in no case significantly lower than unity. Conclusion: There is an excess risk of cancer sites sensitive to radiation; indicating that radon exposure may contribute to the risk of cancer among the population in the geothermal area. Adjustment are made for social variables and data on reproductive factors and smoking habits shows that these do not seem to explain the increased risk of cancers. Limitations of the study are inadequate information on exposure.