Cancer Frequency in the Samtgemeinde Asse

A special analysis carried out by the Epidemiological Cancer Register Niedersachsen (EKN) in response to an enquiry from the district of Wolfenbüttel about the incidence of cancer in the municipal confederation (Samtgemeinde) Asse showed that between 2002 and 2009 there were significantly more new cases of leukaemia and thyroid cancer than would have been expected by comparison with the rest of the district of Wolfenbüttel (excluding the Samtgemeinde Asse).
The Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) asked the German Commission on Radiological Protection (SSK) to evaluate the results of the EKN’s analysis.
In preparation of its statement the SSK conducted a critical examination of the EKN’s epidemiological study and the available radiobiological information on the radiation-induced risks in relation to leukaemia and thyroid cancer. It also explored the question of whether the local increases in leukaemia incidence in men and thyroid cancer incidence in women identified by the EKN should be regarded as statistically random. In connection with the hypothesis that these increased incidences were caused by ionizing radiation, the SSK considered the radiation exposure of the population in the Samtgemeinde Asse arising from the release of radioactive substances from the Asse II mine and the radiation exposure of staff at the Asse II mine. By comparing this radiation exposure with the radiation doses that would be needed to explain the increased incidences that were observed, the SSK arrived at its final conclusion and evaluation.
The SSK explains in its report that the radiation exposure of the population in the vicinity of the Asse II mine can only be estimated on the basis of model calculations. The release of radioactive substances in the exhaust air from the Asse II mine does not result in any measurable concentrations in the environment.
The Commission concludes that even at the most unfavourable point of exposure, i. e. at the fence north-west of the diffuser, the radiation exposure of the population arising from the release of radioactive substances with the exhaust air is too small by several orders of magnitude to explain the observed incidence. The release of radioactive substances from the Asse II mine cannot therefore be considered the cause of the observed abnormalities in the Samtgemeinde Asse in the period 2002 to 2009.
The SSK also establishes that statistically there is no leukaemia clustering in the overall area surrounding the Asse II mine, although on account of the prevailing wind direction other municipalities ought to be affected to a greater extent than the Samtgemeinde Asse. There was merely an isolated cluster in the Samtgemeinde Asse; in the overall context it is entirely possible for this to occur by chance. There were no indications of a cluster of thyroid cancer cases.
The report notes that when a cluster – i. e. an elevated number of cases of disease in a particular place or over a particular period – is suspected or perceived, the general public becomes anxious and concerned. This is entirely understandable and needs to be taken seriously. Nevertheless, it is also necessary to follow national and international recommendations on the circumstances in which it is meaningful and appropriate to pursue epidemiological studies as a result of observed small-scale clusters of disease.
The literature shows that there is generally a very small probability that a detailed epidemiological study based on a small-scale cluster of disease will provide evidence of possible causes – if such causes exist.
In particular it should be borne in mind that individual clusters are generally too small for epidemiological analysis. In such situations the available information is insufficient for an analysis with low residual uncertainties. This is the case with the observed increase in cancer frequency in the Samtgemeinde Asse.

The German version of this statement was published as Issue 66 of the series "Berichte der Strahlenschutzkommission" (Reports of the Commission on Radiological Protection).