Abstract

The scientific grounds of the above SSK-Statement is intended to provide detailed background information and go into the details of the arguments delivered in the statement.

The scientific grounds comprises the following chapters:

1. Childhood Cancer focussing leukaemia

Cases of cancer during childhood are very rare events. Cancer affects about 15 out of 100,000 children of up to 15 years of age, of which about one third is leukaemia. The spectrum of tumours in children is clearly different from that in adults. Causes and mechanisms involving cancer induction in children are largely not understood. However, cancer induction in children, similar to that in adults, is with a degree of certainty a multifactorial event. At least for leukaemia induction there is reason to believe that the initial changes leading to clinically manifest leukaemia occur already in fetal life. Epidemiological evidence of an increased cancer rate due to ionising radiation can be established only if certain levels of radiation dose are exceeded. For lower radiation doses (falling below levels of about 10 mSv), the risk may be calculated subject to a number of assumptions (e.g. linear extrapolation without threshold) but not established epidemiologically.

2. Epidemiological studies on childhood cancer focussing on leukaemia (up to 15 years of age)

The Oxford Survey of Childhood Cancers (OSCC) is by far the largest case-control study on childhood cancer following radiation exposure in utero. Analyses of the OSCC data reveal a relative risk of about 1,4 following X-ray examinations in utero with a fetal dose of 10 mGy for both leukaemia and the whole of all cancers occurring at less than five years of age. Cohort studies tend to suggest lower risk levels. Little is known on childhood leukaemia or cancer risks following postnatal exposure compared to exposure in utero. However, on the whole there is evidence suggesting that the risk following postnatal exposure is lower than that following exposure in utero.

A great number of factors has been supposed to cause childhood leukaemia: besides ionising radiation these are various chemicals (especially pesticides, a number of drugs, oil products), factors influencing the immunological system (infections, allergies, immunisations), magnetic fields, diet, social environment, genetic predispositions, to name only some of them. There are many reasons to believe that leukaemia induction is not due to one single “leukaemia-inducing factor”, but rather presupposes several interacting factors and thus is a multifactorial process.

3. Leukaemia incidence in the vicinity of nuclear power plants (NPPs)

Up to 1999 several ecological studies established slightly increased leukaemia incidence among children of less than 5 years of age (i.e. 0 - 4 years) in the vicinity of NPPs. A comprehensive analysis of these data revealed that the increase was restricted to individual sites. In contrast to the German KiKK-Study, no increased leukaemia risk was observed in children under 5 years of age according to more recent nationwide epidemiological studies conducted in Great Britain and France. The inconsistent results have not been able to be explained conclusively up to now. Radiation exposure caused by NPPs during normal operation is very low, and a causal connection with the radioactive effluents of the plants, therefore, appears to be incompatible with the state of scientific knowledge.

4. Radiation exposures of the public and of the children of the KiKK-Study

This chapter gives detailed information on all sources of human radiation exposure in Germany with special reference to the children of the KiKK-Study. All sources of natural and man-made radioactivity and radiation are identified with their importance for external and internal radiation exposure.

Natural radioactivity, atmospheric nuclear weapons test, the Chernobyl accident and a number of further events and circumstances have delivered abundant experience on human radiation exposure due to environmental radioactivity, thus permitting reliable statements on the environmental contamination required for relevant radiation exposures.

All radionuclides relevant in connection with discharges of radioactive substances from nuclear power plants (H-3, C-14, fission and activation products, radioactive inert gases, actinides) are known from radio-ecological experience as to both their environmental behaviour and the radiation exposures caused by them. All radiation types and energies also occur naturally.

Experiences of atmospheric nuclear weapons tests and the Chernobyl accident permit the following conclusion: radiation exposures from environmental radioactivity at annual doses exceeding 10 µSv leave marks in the environment which will be metrologically detected.

In Germany environmental radioactivity has been monitored since the 1960ies. This includes monitoring of discharges from nuclear installations as well as environmental monitoring and is based on the legal framework aiming at the proof of compliance with the dose limits according to § 47 StrlSchV.

Monitoring of German nuclear power plants consists of a combined system of discharge and environmental monitoring providing for assessment of human radiation exposure from radioactive substances discharged with air and water, and control of compliance with both permissible maximum activity releases and dose limits. The required detection limits of the monitoring programmes according to the Guideline on Discharge and Environmental Monitoring of Nuclear Installations (Richtlinie zur Emissions- und Immissionsüberwachung kerntech¬nischer Anlagen, REI) and the Integrated Measurement and Information System (Integriertes Mess- und Informations¬system, IMIS) provide the possibility to detect radiations exposures of 1 µSv per year .

Detailed information on discharges of radioactive substances from nuclear power plants are available for the total of all periods of operation. These data, combined with statistical weather data, permit a conservative estimate of the additional radiation exposure of the population due to NPPs.

Since the 1960ies the Federal Government has issued annual reports on radiation exposure of the general public in the Federal Republic of Germany. Since the beginning of the peaceful use of nuclear energy these reports have also included the levels of radiation exposures expected from discharges of radioactive substances with airborne and liquid effluents at the most unfavourable exposure sites for reference persons.

Each component of the highly variable natural radiation exposure is higher by some orders of magnitude than the reference person’s exposures from both direct radiation or discharges of radioactive substances through airborne and liquid effluents at the most unfavourable exposure sites in the vicinity of NPPs in Germany.

The radiation exposures of the children under the KiKK-Study are discussed with respect to the usefulness of the KiKK-Study design, its relevance for childhood leukaemia induction, and also viewing the lines of reasoning brought forward by third parties.

5. Report from an Independent Check on the Recently Published Paper on Leukaemia in Young Children Living in the Vicinity of German Nuclear Power Plants (by Sarah Darby und Simon Read)

The results of the independent check carried out by Sarah Darby and Simon Read are summarized in the present report. The analyses confirmed the main statements of the KiKK-Study and yielded some additional results.

The authors of the report on the comparative analysis conclude that there is an increased risk of acute childhood leukaemia within a 5 km radius around NPPs. The reasons are unknown. The analysis suggests that leukaemia induction might be associated with the living conditions in the rural environment in the vicinity of the NPPs.

The scientific grounds comprises four supplements (the data documentation of data referring to chapter 4 “Radiation Exposure of the general public and the children included in the KiKK-Study”).

The detailed scientific foundation on the statement “Assessment of the Epidemiological Study on Childhood Cancer in the Vicinity of Nuclear Power Plants (KiKK-Study)” was passed in the 232. SSK-meeting on 16 December 2008. It is published as Issue 58 of the Series „Reports of the Commission on Radiological Protection“.