Assessment of the epidemiological study on childhood cancer in the vicinity of nuclear power plants (KiKK Study)

The „Epidemiological Study on Childhood Cancer in the Vicinity of Nuclear Power Plants” (KiKK-Study) published on 10 December 2007 by the German Childhood Cancer Registry (Deutsches Kinderkrebsregister, DKKR), Mainz, confirms that there is a statistical correlation between the vicinity of the home from the nearest nuclear power plant (NPP) at the time of diagnosis and the risk of developing cancer (or rather leukaemia) before the 5th birthday. This result gave serious cause for concern in the general public. The Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, therefore, directed the Commission on Radiological Protection (SSK) to review these studies with an emphasis on the question of whether radiation emanating from NPPs might be accountable for the result observed in the KiKK-Study.

The results of discussions in the SSK may be summarised as follows:

• The KiKK-Study’s new data confirm the results of earlier exploratory studies that found an increased risk of leukaemia, for children younger than five, within a 5 km radius around German nuclear power plants, relative to the risk in the outer areas around the relevant study areas. Studies carried out in other countries produced conflicting findings, however. It thus cannot be concluded with finality that there is any evidence for increased rates of leukaemia, in general, in the vicinity of nuclear power plants.
• By virtue of its design, the KiKK-Study exhibits numerous methodological weaknesses with regard to determination of exposure and surveying of influencing factors. Consequently, the study should not have been carried out in the manner in which it was carried out. In spite of such weaknesses, the study’s design is suitable for the task of analysing dependence on distance.
• The evidence for increased cancer rates in children is limited to areas that are no more than 5 km from the relevant nuclear power plant sites. There is thus no justification for using attributable risks to calculate hypothetical additional cancer cases for greater distances.
• The study is thus not suited to the task of establishing a correlation with exposure to radiation from nuclear power plants. All of the radioecological and risk-based circumstances reviewed by the SSK indicate that exposure to ionising radiation caused by nuclear power plants cannot explain the results found by the KiKK-Study. The additional radiation exposure caused by nuclear power plants is lower, by a factor of considerably more than 1,000, than the radiation exposure that could cause the risks reported by the KiKK-Study.
• The natural radiation exposure within the study area, and its fluctuations, are both greater, by several orders of magnitude, than the additional radiation exposure caused by the relevant nuclear power plants. If one assumes that the low radiation exposures caused by the nuclear power plants are responsible for the increased leukaemia risk for children, then, in light of current knowledge, one must calculate that leukaemias due to natural radiation exposure would be more common, by several orders of magnitude, than they are actually observed to be in Germany and elsewhere.
• The KiKK-Study was unable to survey risk factors to a sufficient degree. For this reason, the KiKK-Study cannot be used to help explain the causal reasons for the observed distance dependence of leukaemia rates.
• The reason for the increased leukaemia rate that the KiKK-Study observed in children is unclear. Since leukaemia is caused by multiple factors, numerous influencing factors could have been responsible for the observed result. If the many relevant conflicting findings in the literature, and the finding of the KiKK-Study, are to be understood, more extensive, interdisciplinary research into the causes and mechanisms of the development of leukaemias in children will have to be carried out.

The Commission on Radiological Protection passed the statement “Assessment of the Epidemiological Study on Childhood Cancer in the Vicinity of Nuclear Power Plants (KiKK-Study)” in the 227th Meeting on 25/26 September 2008. The German version of this statement is published as issue 57 in the Series „Reports of the German Commission on Radiological Protection“.