Summary of the SSK assessment of the KiKK-study
25 Sept 2008
On 10 December 2007, the study "Epidemiological Study on Childhood Cancer in the
of Nuclear Power Plants" ("Epidemiologische Studie zu Kinderkrebs in
von Kernkraftwerken"; KiKK Study)
was presented to the public. The
the study's main finding as follows: "Our
study has confirmed that a
is observed in Germany between the proximity of a person's residence to the
nuclear power plant, at the time of a relevant diagnosis, and the person's risk
cancer (or leukaemia) prior to his or her fifth birthday. This study cannot
any information as to what biological risk factors might explain this
results of the deliberations of the Commission on Radiological Protection (SSK;
can be summarised as follows:
Comments by A. Korblein
The KiKK Study's new data
confirm the results of earlier exploratory studies that found
increased risk of leukaemia, for children younger than five, within a 5 km
German nuclear power plants, relative to the risk in the outer areas around the
study areas. Studies carried out in other countries produced conflicting
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.
An ecological study in GB
found increased leukemia rates in the 5-km zone (RR=1.30; p=0.169).
A similar study in France yields RR=1.19 in the 10-km zone (p=0.248). Due to small numbers, both studies lack statistical power.
By virtue of its design, the
KiKK Study exhibits numerous methodological weaknesses
regard to determination of exposure and surveying of influencing factors.
the study should not have been carried out in the manner in which it was
out. In spite of such weaknesses, the study's design is suitable for the task of
analysing dependence on distance.
|The main question to be investigated by the KiKK study was whether there was a negative distance trend. Inverse distance was taken as a proxy for exposure.|
The evidence for increased
cancer rates in children is limited to areas that are no more
5 km from the relevant nuclear power plant sites. There is thus no justification
attributable risks to calculate hypothetical additional cancer cases for greater
|A significant increase is only found in the 5-km zone. This does not mean, however, that there is no risk beyond 5 km.|
The study is thus not suited to
the task of establishing a correlation with exposure to
from nuclear power plants. All of the radioecological and risk-based
reviewed by the SSK indicate that exposure to ionising radiation caused
nuclear power plants cannot explain the result found by the KiKK Study. The
radiation exposure caused by nuclear power plants is lower, by a factor of
more than 1,000, than the radiation exposure that could cause the risks
reported by the KiKK Study.
|The official dose and risk estimates from NPP emissions are orders of magnitude too low to explain the observed effects. But is it unthinkable to question the validity of the multi-stage models that are used to calculate doses and risk?|
The natural radiation exposure
within the study area, and its fluctuations, are both
by several orders of magnitude, than the additional radiation exposure caused
the relevant nuclear power plants. If one assumes that the low radiation
by the nuclear power plants are responsible for the increased leukaemia risk for
then, in light of current knowledge, one must calculate that leukaemias due to
radiation exposure would be more common, by several orders of magnitude,
than they are actually observed to be in Germany and elsewhere.
|The natural background radiation is likely to be responsible for part of the spontaneous cancer rate. The distance dependency cannot be explained by its spatial and temporal fluctuations.|
KiKK Study was unable to survey risk factors to a sufficient degree. For this
the KiKK Study cannot be used to help explain the causal reasons for the
observed distance dependence of leukaemia rates.
|Part 2 of the KiKK (interview part) study did not have enough statistical power. A possible effect of confounders could therefore not be identified.|
reason for the increased leukaemia rate that the KiKK Study observed in children
unclear. Since leukaemia is caused by multiple factors, numerous influencing
have been responsible for the observed result. If the many relevant conflicting
in the literature, and the finding of the KiKK Study, are to be understood,
extensive, interdisciplinary research into the causes and mechanisms of the
development of leukaemias in children will have to be carried out.
|Given the pronounced distance dependency, causes other than radiation from NPPs are rather implausible. Radiation should therefore not be ruled out as a possible cause.|