Ionizing and non-ionizing radiation and the risk of childhood cancer-illustrated with domestic radon and radio frequency electromagnetic field exposure

摘要

BackgroundudChildren are exposed to many different environmental factors, including exposure to low-dose ionizing radiation and to non-ionizing radiation. udLow-dose ionizing radiation comprises anthropogenic modified radiation and natural ionizing radiation from cosmic rays from the atmosphere, terrestrial gamma radiation from radionuclides in rocks and soils and radiation from radon. udNon-ionizing radiation comprises optical radiation and radiation from electromagnetic fields. The latter comprises radiation from extremely low-frequency electromagnetic fields (ELF-EMF; high voltage power lines, electrical installations) and radiofrequency electromagnetic fields (RF-EMF; broadcast transmitters, mobile phone base stations, mobile and cordless phones). udBoth ionizing and non-ionizing radiation are assumed to be associated with childhood cancer. udAimsudWithin this dissertation, we primarily aimed to assess whether there is an association between domestic radon exposure and childhood cancers. We further investigated whether there is an association between low-dose ionizing gamma radiation and childhood cancers. We finally assessed whether there is an association between RF-EMF exposure from broadcast transmitters and childhood cancers.udMethodsudWe performed prospective census-based cohort designs, considering all children, aged less than 16 years and living in Switzerland at the date of census 2000 (December 5th 2000). Time at risk was set to begin at census and lasted until the date of diagnosis, death, emigration, a child’s 16th birthday or until the end of the year 2008. In terms of non-ionizing radiation from far-field RF-EMF sources from broadcast transmitters, we carried out a further prospective cohort analysis, considering all children, aged less than 16 years and living in Switzerland between 1985 and 2008. udWe assessed exposure at baseline (date of census 2000) for each child’s home address. For the analyses on RF-EMF exposure to broadcast transmitters and childhood cancers where a longer follow-up was considered, we considered exposure at the time of diagnosis. udFor the analyses on domestic radon exposure and childhood cancers, exposure assessment was based on a nationwide radon prediction model. For the analyses on low-dose ionizing gamma radiation and childhood cancers, exposure assessment was based on modelled and measured dose rates from outdoor gamma radiation. For the analyses on RF-EMF exposure to broadcast transmitters and childhood cancers, exposure assessment was based on modeled field strengths. udResultsudWe estimated arithmetic mean radon concentrations to be 85.7 Bq/m³ (range: 6.9-337.2 Bq/m³) for childhood cancer cases and 85.9 Bq/m³ (range: 0.7-490.1 Bq/m³) for the rest of the study population. Despite relative high radon levels in Switzerland, we found no evidence for an association between domestic radon exposure and childhood cancers.udWe found increased leukaemia risk (including acute lymphoblastic leukaemia) with respect to gamma radiation for children who lived at the same address between 1995 and 2000. udFinally, we found no increased leukaemia risk but increased central nervous system (CNS) tumour risks with respect to RF-EMF exposure from broadcast transmitters. udConclusions and OutlookudThe findings of our analyses, indicating no association between domestic radon exposure and childhood cancers were consistent with past studies that estimated doses of domestic radon concentrations for different body organs (lung, red bone marrow, brain). udThe results of the analyses on gamma radiation and childhood cancers indicate that low dose ionizing gamma radiation might be relevant in terms of childhood leukaemia. These results were also found to be consistent with dose estimations for different body organs (red bone marrow, brain). They indicated that the same gamma radiation dose to the red bone marrow over a longer time period is probably necessary for gamma radiation to lead to childhood leukaemia.udThe findings from the analyses on RF-EMF exposure from broadcasting and childhood leukaemia were found to be consistent with results from animal, in-vitro and laboratory studies. On the contrary, the findings indicating increased CNS tumours from RF-EMF exposure to broadcast transmitters contradict results from former studies. Our results are further in contradiction to a previous case-control study on wireless phones. This study could not find an increased risk for CNS tumours from the use of wireless phones that lead to substantially higher exposure to the head.udAlthough no evidence for an association with childhood cancers was found, domestic radon exposure is of public health relevance with regard to lung cancer in adults.udThe findings from the analyses on gamma radiation and childhood cancers indicate that gamma radiation is of public health relevance as well, especially when children are exposed to the same gamma radiation dose over a longer time period.udStatements on possible public health relevance concerning non-ionizing radiation of RF-EMF from broadcasting on the other hand are not yet possible, as the results for CNS tumours need further clarification. ud