Strahlenschutzkommission Geschäftsstelle der Strahlenschutzkommission Postfach 12 06 29 D-53048 Bonn http://www.ssk.de
Cancer Frequency in the Samtgemeinde Asse Statement by the German Commission on Radiological Protection
Adopted at the 260th meeting of the German Commission on Radiological Protection on 28 February/1 March 2013 The German original of this English translation was published in 2013 by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety under the title:
Krebshäufigkeit in der Samtgemeinde Asse
Stellungnahme der Strahlenschutzkommission
This translation is for informational purposes only, and is not a substitute for the official statement. The original version of the statement, published on www.ssk.de, is the only definitive and official version. Cancer frequency in the Samtgemeinde Asse 3
Contents
1 Background ...... 4
2 Epidemiological findings ...... 4
3 Statistical analysis of regional differences ...... 7
4 Risk factors for leukaemia and thyroid cancer ...... 8
4.1 Leukaemia ...... 8 4.2 Thyroid cancer ...... 9 5 Exposure of the population to radiation as a result of release of radioactive substances from the Asse II mine ...... 9
6 The radiation exposure needed to explain the observed increases ...... 12
7 Summing up and position statement ...... 13
References ...... 14
Cancer frequency in the Samtgemeinde Asse 4
1 Background
A special analysis carried out by the Epidemiological Cancer Register of Niedersachsen (Epidemiologisches Krebsregister Niedersachsen, EKN) in response to an enquiry from the district (Landkreis) 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) (EKN 2010a). The reason for the EKN’s analysis of Samtgemeinde Asse and the district of Wolfenbüttel was: “The background to this special analysis is an enquiry by the district of Wolfenbüttel to the Epidemiological Cancer Register of Niedersachsen (EKN) in 2008 regarding the frequency of leukaemias in the Samtgemeinde Asse. At that time there was insufficient data available and leukaemias and lymphomas were significantly under-recorded; small-scale analysis was not therefore possible. There is now sufficient data for the analysis to be carried out. The results of the analysis are presented in this report.” (EKN 2010a). The query thus related solely to leukaemias and the Samtgemeinde Asse. The EKN’s analysis of the incidence of leukaemia was therefore hypothesis-led; for other cancers and other municipalities in the former administrative district of Braunschweig, exploratory analysis was undertaken in (EKN 2010a) and later in (EKN 2010b). All distinctions between men and women were likewise exploratory. In view of the large number of tests carried out, it was necessary for a correction for multiple testing to be applied to significant results. Following the publication of (EKN 2010a), members of the state parliament and representatives of the district of Wolfenbüttel asked whether other municipalities in the district also had elevated cancer rates. In response the EKN conducted a supplementary analysis of all 41 reported diagnoses of cancer (EKN 2010b). The EKN established in (EKN 2010b) that after correction for multiple testing the results for all the municipalities of the district of Wolfenbüttel other than the Samtgemeinde Asse were not significant. The only significant findings were the results for leukaemia and thyroid cancer in the Samtgemeinde Asse. The Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) wrote to the Commission on Radiological Protection (SSK) on 20 December 2010 requesting a statement on the results of the EKN’s analysis of the incidence of cancer in the Samtgemeinde Asse. In particular, the statement needed to examine the statistical methods used and answer the following questions: Is there radiobiological information that could plausibly explain the findings? How can the findings be explained?
2 Epidemiological findings
The SSK has examined whether the EKN’s analysis conforms with good epidemiological practice and whether the findings are transparent and reliable. The SSK is of the view that the EKN’s analysis of the issue of a regional cancer cluster in the district of Wolfenbüttel was correctly carried out. The conclusions are likewise correct. The SSK asked the EKN to go beyond the published analyses (EKN 2010a, 2010b) and conduct a similar analysis of the data from the SG Asse using the former administrative district of Braunschweig as a comparison region. The larger population in the former administrative district of Braunschweig permits a more robust analysis. The SSK has also taken this analysis into account in its statement. Cancer frequency in the Samtgemeinde Asse 5
In (EKN 2010a) the EKN’s hypothesis-led analysis of cancer frequency in the Samtgemeinde Asse by comparison with the district of Wolfenbüttel excluding the Samtgemeinde Asse revealed a significant increase in the standard incidence ratio (SIR) for cases of leukaemia (ICD10 C91C95) (Table 1). Gender-differentiated analysis yielded different SIR values for men and women. This is based on 18 new cases recorded in the period 2002 until 2009 (males: 12; females: 6) by comparison with the expected number of 8.5 cases (males: 5.2, females: 3.3). In (EKN 2010a) the EKN’s exploratory analysis of cancer frequency in the Samtgemeinde Asse by comparison with the district of Wolfenbüttel excluding the Samtgemeinde Asse revealed a significant increase in the standard incidence ratio for thyroid cancer (ICD10 C73) in women (Table 2). Gender-differentiated analysis yielded different SIR values for men and women. This is based on 12 new cases recorded in the period 2002 until 2009 (males: 2, female: 10) by comparison with the expected number of 3.9 cases (males. 0.6, females: 3.3). Using the former administrative district of Braunschweig as a comparison region, the EKN again found a significantly elevated SIR for leukaemia in the Samtgemeinde Asse (Table 1). Here, too, gender-differentiated analysis yielded different SIR values for men and women. This is based on 18 new cases recorded in the period 2002 until 2009 (males: 12, females: 6) by comparison with the expected number of 8.3 cases (males: 4.8, females: 3.5). Using the former administrative district of Braunschweig as a comparison region, the EKN also found a significantly elevated SIR for thyroid cancer in the Samtgemeinde Asse (Table 2), although this was not significant at the 5 % level for 41 tests corrected for multiple testing. Gender-differentiated analysis again yielded different SIR values for men and women. This is based on 12 new cases recorded in the period 2002 until 2009 (males: 2, females: 10) by comparison with the expected number of 4.7 cases (males: 1.3, females: 3.4). Table 1: SIR of leukaemia in the Samtgmeinde Asse (compared to the district of Wolfenbüttel excluding the Samtgemeinde Asse (EKN 2010a) and the district of Braunschweig(EKN 2011)). The row shaded grey was the result of an external enquiry; the confidence interval (CI) can therefore be regarded as hypothesis-led. All the other findings should be regarded as exploratory.
SIR 95% CI
Total 2.12 1.253.35 Comparison region: district of Wolfenbüttel Men 2.33 1.204.06 excl. the Samtgemeinde Asse Women 1.80 0.663.91
Total 2.17 1.283.43 Comparison region: former administrative Men 2.49 1.294.35 district of Braunschweig Women 1.72 0.633.74 Cancer frequency in the Samtgemeinde Asse 6
Table 2: SIR of thyroid cancer in the SG Samtgmeinde Asse (compared to the district of Wolfenbüttel excluding the Samtgemeinde Asse (EKN 2010a) and the district of Braunschweig(EKN 2011)). All the findings should be regarded as exploratory.
SIR 95% CI
Total 3.05 1.585.33 Comparison region: district of Men 3.36 0.3812.13 Wolfenbüttel excl. the Samtgemeinde Asse Women 3.00 1.435.51
Total 2.55 1.324.46 Comparison region: former administrative Men 1.56 0.185.56 district of Braunschweig Women 2.94 1.415.40
The SSK is of the view that of the two available analyses of the Samtgemeinde Asse – one by comparison with the district of Wolfenbüttel (excluding the Samtgemeinde Asse) and the other by comparison with the former administrative district of Braunschweig – the calculations by comparison with the former administrative district of Braunschweig should be used for analysis, since they are based on a larger data set. It is possible that the district of Wolfenbüttel’s enquiry to the EKN was made not without cause but as the result of a concrete suspicion. This is supported by the fact that, of the two municipal confederations (Samtgemeinde Asse and Samtgemeinde Schöppenstedt) that border directly on the Asse II mine, a question was formulated only in respect of the Samtgemeinde Asse. In this case the analysis would be not hypothesis-led but data-led, which would reduce its significance. The analysis would not then meet the criteria for a confirmatory analysis in the narrow sense. A significantly abnormal leukaemia frequency was observed only in the Samtgemeinde Asse; no such abnormality was found in the other municipalities of the district of Wolfenbüttel or in the Samtgemeinde Schöppenstedt, which lies directly to the east of the Asse II mine. The age structure and subentities of the leukaemia cases in the Samtgemeinde Asse were not abnormal in any way; the absolute numbers for each age group are small. The relatively low incidence of thyroid cancer makes the incidence comparisons with the district of Wolfenbüttel without the Samtgemeinde Asse very unreliable. The comparison with the former administrative district of Braunschweig permits a more robust statement to be made. On this basis the exploratory analysis found a (non-significant) increase in the incidence of thyroid cancer only in the Samtgemeinde Asse and not in the other municipalities including the Samtgemeinde Schöppenstedt, which lies directly to the east of the Asse II mine. The distribution of age, gender and disease severity in the thyroid cancer patients (an unusually large number of women under 50, an unusually large number of low stages) in the Samtgemeinde Asse may possibly reflect a relatively large number of investigations without specific suspicion of disease. All the reports from pathologists complied with the requirements of the law governing Lower Saxony’s cancer registry and were therefore anonymous; this means that they cannot be followed up in an attempt to obtain further information. According to the EKN, the distribution of subtypes does not differ significantly from the distribution at state level in Lower Saxony. To answer the question of whether the increase in the number of new cases of leukaemia, lymphoma and thyroid cancer observed in the Samtgemeinde Asse in the period 2002 until Cancer frequency in the Samtgemeinde Asse 7
2009 could be linked to employment in the Asse II mine, the Federal Office for Radiation Protection (BfS) decided to check the 47 cases (35 cases of haematological disorders (leukaemias and lymphomas) and 12 cases of thyroid cancer) on an anonymized basis against the employees at Asse. Because the data involved is personal and could lead to individuals being identified, a cross- check of this sort is highly sensitive and governed by strict data protection rules. To enable the EKN’s data to be checked against the details of Asse employees, a data protection strategy was drawn up and consent was obtained from the management and works council of Asse GmbH, the data protection officer at the BfS (as trustee of Asse’s personal data) and the Federal Commissioner for Data Protection and Freedom of Information (BfDI). Under the data protection strategy the personal data from the two sources (EKN and BfS) was double-encrypted and the resulting data was passed to a third, independent body that conducted the check. The only finding of the check that was communicated was the number of matches or “hits” found. The cross-check between the 47 new cases of cancer (haematological disorder or thyroid cancer) in the Samtgemeinde Asse in the period 2002 until 2009 and the 800 people who worked at the Asse II mine between 1967 and 2008 yielded only one hit. This means that one of the 47 people in the Samtgemeinde Asse who developed one of the aforementioned types of cancer between 2002 and 2009 worked at the Asse II mine. The elevated incidence of thyroid cancer and haematological disorders observed in the Samtgemeinde Asse between 2002 and 2009 cannot therefore be attributed to working at the Asse II mine.
3 Statistical analysis of regional differences
The SSK has investigated whether the epidemiological differences between the Samtgemeinde Asse and the district of Wolfenbüttel or the former administrative district of Braunschweig could have occurred by chance. This was done by using disease mapping techniques to describe structural differences in the area covered by the study. Disease mapping techniques cannot be used to identify a causal relationship between exposure and disease: they are purely descriptive in nature. To provide a broader basis for the analysis, the SSK carried out a study of all the 71 municipalities and municipal confederations of the former administrative district of Braunschweig. For each municipality and the particular disorder under consideration, the “raw” SIR in relation to the former administrative district of Braunschweig was first calculated. In general a small number of cases is usually associated with relatively large fluctuations in the SIR (i. e. values a long way from 1); when the number of cases is large the fluctuations are smaller. It follows that municipalities with a small population and low incidence of disease are particularly susceptible to overrating of this sort. Empirical and full Bayes methods were therefore used to identify structural differences in disease risk over and above random fluctuations. Both methods (empirical and full Bayes) free the resulting SIR estimates for the region in question from chance fluctuations or “noise”. Any heterogeneity that remains means that there are differences that cannot be explained solely by random fluctuations. This reveals nothing about the causes of these fluctuations; the content of any differences in extent between the regions that remain after application of this procedure must still be evaluated. In addition to the empirical and full Bayes methods – of which the full Bayes method was preferred for reasons arising from the literature – non-parametric mixed Cancer frequency in the Samtgemeinde Asse 8 distribution models involving the formation of classes were also used and resulted in similar conclusions. In relation to both the diagnoses under consideration, the former administrative district of Braunschweig has a clear structural heterogeneity above and beyond random fluctuation, to which the Samtgemeinde Asse with its elevated SIR contributes. Among men there is a heterogeneity going beyond purely random fluctuation for leukaemia. After adjustment for random fluctuation there remains an estimated increase of 30 % in the Samtgemeinde Asse. However, by comparison with the administrative district of Braunschweig there is a similarly high risk of leukaemia in men in at least one other municipality, indicating that this is not a unique feature of the Samtgemeinde Asse. In relation to thyroid cancer in men there is no abnormal finding in the Samtgemeinde Asse. In relation to leukaemia in women there is no abnormal finding in the Samtgemeinde Asse. With regard to thyroid cancer in women, the Samtgemeinde Asse is among the regions with elevated risk. The statistical analysis reveals some residual heterogeneity for leukaemia disorders in men and thyroid cancers in women, although the credible intervals of the adjusted SIRs always involve the number 1.
4 Risk factors for leukaemia and thyroid cancer
For both leukaemia and thyroid cancer the SSK has conducted a critical review of the current state of knowledge with regard to the issue of possible causatory noxae, especially ionizing radiation. In the SSK’s view it is established that leukaemia and thyroid cancer can be caused by ionizing radiation. The state of knowledge in this regard makes it possible to quantify the dose-dependent risk.
4.1 Leukaemia
The causes of leukaemia and related disorders are largely unclear. Only a minority of cases can be linked to individual risk factors. These risk factors include genetic factors, certain viral diseases, certain drugs, smoking and exposure to various pollutants such as benzene or butadiene in the environment or workplace. Many studies demonstrate that ionizing radiation is a risk factor for leukaemia. In the late 1940s a Japanese doctor who was among the survivors of the atomic bomb explosions in Hiroshima and Nagasaki noted a clustering of leukaemias; this led to the establishment of a register and in the early 1950s the first scientific studies of leukaemia were published. The latest survey, published in 2004, covers all deaths from leukaemia between 1950 and 2000: it shows that among 49,204 participants in the Life Span Study (LSS) with a bone marrow dose of at least 5 mSv there were 204 leukaemia deaths; this contrasts with the 110 deaths that would be expected on the basis of the spontaneous risk. Analysis according to leukaemia type revealed dose-dependent increases in leukaemia mortality rates for acute myeloid leukaemia (AML), acute lymphatic leukaemia (ALL) and chronic myeloid leukaemia (CML) but not for other types of leukaemia including chronic lymphatic leukaemia (CLL). The previous analysis of leukaemia incidence rates in the period 1950 until 1987 yielded a similar conclusion. However, because of the low frequency of CLL in the Japanese population this data is unreliable and the issue of the extent to which CLL can be induced by radiation has recently triggered some controversy. A number of studies have investigated the correlation between radiation exposure and the incidence of leukaemia in people subjected to elevated radiation exposure in the workplace or as a result of environmental influences. Such people include workers in nuclear plants, individuals involved in clean-up operations after the reactor accident at Chernobyl, people living near the contaminated Techa River and inhabitants of regions with elevated levels of Cancer frequency in the Samtgemeinde Asse 9 natural radiation. Most of these studies have found increased leukaemia incidence or leukaemia mortality after exposure to radiation, although because of the low numbers of cases the increases are often not statistically significant. In a metaanalysis of 23 of these studies of leukaemia risk (excluding CLL) after prolonged radiation exposure to mainly weakly ionizing radiation in the workplace or the environment, the excess relative risk at 100 mGy was estimated to be ERR = 0.19 (95% CI: 0.07 – 0.32). This is in keeping with the leukaemia risk for men exposed as adults to the atomic bomb fallout in Japan (ERR = 0.15 at 100 mGy, 95% CI: 0.11 – 0.53).
4.2 Thyroid cancer
A number of factors are thought to trigger thyroid cancer or at least play a part in triggering it. Some relatively rare medullary cancers are attributable to genetic defects, which explains the clustering in families that is frequently observed in this type of cancer. Other forms of thyroid cancer are also assumed to have a genetic component. The goitres that occur in iodine-deficient areas increase the risk of developing thyroid cancer. People with thyroid adenomas (benign tumours) and chronic inflammation of the thyroid are also more susceptible to thyroid cancer. It has long been suspected that TSH (thyroid stimulating hormone) is a key factor in the development of thyroid cancer when it occurs in excess. The findings on iodine supplementation are contradictory. It appears that at the very least supplementation alters the spectrum of thyroid cancer forms. Whether supplementation increases the frequency of thyroid cancer is disputed, since the increases observed in some ecological studies could be the result of more thorough assessment and improved diagnostic methods. There is an as yet unexplained correlation between volcanoes and the frequency of thyroid cancer. It is noticeable that thyroid cancer is particularly frequent in areas with a large number of volcanoes (Hawaii, the Philippines, Iceland). Minerals containing arsenic and zinc are suspected of triggering the disease. Ionizing radiation can trigger thyroid cancer, especially when exposure to radiation occurs in childhood; the risk following exposure in adulthood (after the age of about 20) is much lower. In particular, there is as yet no evidence that I-131 causes thyroid cancer in adults. When attempting to calculate the risk that radiation poses for the thyroid, it is essential to take account of the screening effect. Many different microcarcinomas (less than 1 cm in diameter) can occur in the thyroid; normally they are never discovered because they have no adverse impact on health. If a population is systematically screened for changes to the thyroid, these microcarcinomas will also be discovered and may then be interpreted – at least to some extent erroneously – as an effect of radiation. The discovery of many early-stage tumours should strike a warning note and indicates a possible screening effect. It is entirely possible for rigorous screening to result in a three- or four-fold increase in the absolute number of thyroid tumours found.
5 Exposure of the population to radiation as a result of release of radioactive substances from the Asse II mine
Potash salt and rock salt were produced in the Asse II mine between 1909 and 1964. Between 1967 and 1978, 124,494 containers of low-activity waste (LAW) and 1,239 containers of medium-activity waste (MAW) with a declared inventory of 7.8 PBq (5.0 PBq in the LAW, Cancer frequency in the Samtgemeinde Asse 10
2.8 PBq in the MAW) were placed in 13 chambers at depths of 511 m (1 chamber), 725 m (1 chamber) and 750 m (11 chambers). H-3, C-14 and Rn-222 (the Rn-222 as a decay product of the stored Ra-226 waste) are released from the stored radioactive waste into the air of the mine. The progenies of Rn-222, including the long-lived Pb-210, enter the mine air with the Rn-222. The mine air is discharged into the environmental air by means of a diffuser on the mine building. There is no evidence of short-lived fission products, in particular I-131, in the mine air. Assessment by the SSK of the formation of I-131 from the spontaneous fission of actinide isotopes indicates that the risk of I-131 being present in air potentially extracted from the Asse II mine is negligible. Sample measurements have not revealed any trace of long-lived I-129 or plutonium isotopes originating from the waste. Workers are exposed to radiation from external sources, from the radioactivity in the mine air and when handling open radioactive substances when contamination occurs. The population in the vicinity of the Asse II mine is potentially exposed to radiation as a result of the discharge of radioactive substances with the exhaust air from the mine. According to the operator of the mine, no radioactive substances are discharged with liquid effluents. On the basis of reports from the operators’ and independent monitoring stations, the dispersion calculations and dose models produced by various institutions, the Asse health monitoring carried out by the BfS and the documents cited in the health monitoring report, the SSK comes to the following conclusion about the additional potential radiation exposure of the population of the Samtgemeinde Asse arising from the Asse II mine. The radiation protection monitoring of the Asse II mine, including the ambient and emissions monitoring, was in accordance with state-of-the art science and technology. The ambient monitoring data and the surveillance of environmental radioactivity (IMIS) in the vicinity of Asse show no measurable level of radioactive substances from the Asse II mine. The only measurable effects found resulted from the Chernobyl reactor accident. The ambient measurements yielded no evidence of any influence of the Asse II mine on environmental radioactivity in the vicinity of the mine or enhanced exposure of the population of the Samtgemeinde Asse to radiation. The reports of contamination incidents during the emplacement phase contained no evidence of enhanced exposure of the general population in the vicinity of the Asse II mine to radiation. The contamination events both above and below ground were in total too minor to leave traces in the emissions and ambient measurements. Their contribution to the potential radiation exposure of the population is negligible. The operators’ reports on emissions and ambient monitoring demonstrate that the limits on the exposure of the general population to radiation were observed. However, the information on radiation exposure that they contain is based on extremely conservative assumptions – i. e. they overestimate the actual exposure. They do not provide a realistic description of the exposure of people in the vicinity of the Asse II mine to radiation. They do however enable upper limits of radiation exposure to be given. Using a standardized method, the SSK has calculated the radiation exposure of the reference persons1 at the most unfavourable point of exposure at the fence at a distance of approximately
1 The reference persons under the General Administrative Provision (AVV) are assumed to engage in extreme and sometimes impossible behaviour; in view of this and other conservative principles of the AVV (cf. Section 5.6 of the scientific justification) it can be assumed that the radiation exposures thus calculated are greatly overestimated upper limits of the actual radiation exposures. Cancer frequency in the Samtgemeinde Asse 11
50 m from the diffuser for the whole period for which release data are available – i. e. from 1978 (the final year of the emplacement phase) onwards. The work was based on the calculations performed by Brenk (2001) under the General Administrative Provision (AVV) relating to Paragraph 47 of the Radiation Protection Ordinance (StrlSchV). These calculations were also performed for the period prior to 1978. Releases originating from the stored radioactive substances were assumed to be proportional to the emplaced activity up to that point. Since the radionuclides relevant in the context of release – H-3, C-14, Ra-226 and Rn-222 – occur mainly in the emplaced low-activity waste distributed between the storage chambers, this assumption is conservative. The emplaced activities as a source of the released radionuclides rose sharply between 1972 and 1978; in the initial years there was a relatively small radioactive inventory in the Asse II mine as the source of the releases. The calculated organ doses for the reference persons’ bone marrow at the most unfavourable point of exposure were below 110 µSv in the calendar year at all times; the calculated thyroid doses were below 29 µSv in the calendar year. The highest organ doses for red bone marrow (110 µSv for infants below the age of 12 months) were calculated for 1981. For the thyroid doses the maximum (29 µSv for infants between the ages of 12 and 24 months) occurred in 1982. In other years the calculated doses were significantly lower. The calculated doses are also strongly dependent on age. Pb-210 is responsible for by far the largest share of the calculated radiation doses. The dose figures for the reference persons at the most unfavourable point of exposure at the Asse II mine greatly overestimate the exposure of the residents of the Samtgemeinde Asse. This is a result not only of the unrealistic characteristics and habits attributed to the reference persons but also of the geographical location of the Samtgemeinde Asse relative to the unfavourable point of exposure. From calculating the dilution of the activity concentrations of the mine air released from the Asse II mine in the vicinity of the mine with a Lagrange dispersion model, it can be concluded that the potential radiation exposure, determined in accordance with the AVV relating to Paragraph 47 StrlSchV, of reference persons living in the immediate vicinity of the mine (for the Samtgemeinde Asse in Remlingen and Wittmar, for other municipalities in Gross Vahlberg and Klein Vahlberg) is lower than that of reference persons at the most unfavourable point of exposure at the mine fence by a factor of at least 10. In the more distant places long-term dispersion factors need to be taken into account; exposure here is lower than at the most unfavourable point of exposure by a factor of between 10 and 100. For the purpose of this report – i. e. in connection with the estimation of the radiological risks of stochastic effects in the population of the Samtgemeinde Asse – the SSK can thus state that the additional radiation exposure of reference persons in accordance with the AVV relating to Paragraph 47 StrlSchV in the places closest to the Asse II mine has always been less than 10 µSv per calendar year. This applies both to effective doses and to organ doses to the red bone marrow and the thyroid gland. For places in the Samtgemeinde Asse further from the mine these exposures are lower by several orders of magnitude. The SSK nevertheless points out that because of the extreme assumptions about the characteristics of the reference persons in accordance with the AVV relating to Paragraph 47 StrlSchV, the actual radiation exposure for real people with normal lifestyles and movement habits in the places closest to the mine are lower than 10 µSv per calendar year by several orders of magnitude. By 2009 a reference person born in 1978 would at the most unfavourable point of exposure at the fence of the Asse II mine have accumulated radiation doses calculated in accordance with the AVV relating to Paragraph 47 StrlSchV of 700 µSv for the red bone marrow and 200 µSv for the thyroid. In the nearest places – Remlingen and Wittmar – the potentially accumulated Cancer frequency in the Samtgemeinde Asse 12 radiation exposure was calculated as being 70 µSv for the red bone marrow and 20 µSv for the thyroid. In more distant places in the Samtgemeinde Asse the potentially accumulated radiation exposure in this period was in each case calculated as being less than 10 µSv. In the course of consultation on this report, the SSK established that for Pb-210 the calculated potential radiation exposure of reference persons at the most unfavourable point of exposure in the vicinity of the Asse II mine is unrealistically high. This is the result of an overestimate of the air pathway of Pb-210 in the AVV relating to Paragraph 47 StrlSchV. The SSK furthermore established that the radiation exposures cited in the German government’s parliamentary reports relating to the Asse II mine – and also to other nuclear facilities – are unrealistically high and do not meet the realism requirement of the EU basic standards. The SSK urges realistic reporting for existing facilities.
6 The radiation exposure needed to explain the observed increases
The SSK has calculated the radiation exposure that would be needed to explain the observed increase in cases of leukaemia in men and thyroid cancer in women in the Samtgemeinde Asse. For the purposes of the calculation it was assumed that all the exposure occurred in 1978 (see Section 5 of this report). The calculations were based on the radiation risk in the cohort of survivors of the atomic bombs in Hiroshima and Nagasaki. The risk functions were transferred to the period 2002 until 2009 and to the Samtgemeinde Asse in accordance with the method used by BEIR VII (2006). One of the parameters used in this method is the spontaneous risk in the Samtgemeinde Asse. This cannot be deduced directly from the observed incidence rate, because the incidence is being significantly elevated by an unknown factor or a statistical fluctuation. The observed incidence in the former administrative district of Braunschweig excluding Samtgemeinde Asse was therefore used for the spontaneous incidence in the Samtgemeinde Asse. Using population statistics for the Samtgemeinde Asse, then the bone marrow and thyroid doses that – under the given assumptions – would lead to the observed number of cancer cases were calculated. This yielded a best estimate of 0.73 Sv for the bone marrow dose that would explain the ten leukaemia cases among the men in the Samtgemeinde Asse involved in the assumed exposition scenario during the period 2002 until 2009. At the 95% confidence level at least one bone marrow dose of 0.50 Sv would be needed. The calculations yielded a best estimate of 1.3 Sv for the thyroid dose that would explain the ten cases of thyroid cancer among the women in the Samtgemeinde Asse. At the 95 % confidence level at least one thyroid dose of 0.32 Sv would be needed. It was assumed in the calculations that all the male residents of the Samtgemeinde Asse were exposed to the same extent, as were all the females. In the event of inhomogeneous exposure, the necessary dose in the critical group would of course have to be higher. Analysis of other exposure scenarios – some of them highly unrealistic – yielded hypothetical minimum values for the bone marrow or thyroid dose that amounted to at least 80% of the minimum values in the scenario involving exposure solely in 1978. The chosen exposure scenario is therefore suitable for estimating the minimum dose needed to explain the observed cancer incidence in the Samtgemeinde Asse. The values arrived at for the minimum doses needed to explain the observed cancer incidence – namely a minimum bone marrow dose for men of 0.5 Sv and a minimum thyroid dose for women of 0.32 Sv – are three orders of magnitude higher than the possible dose levels arising Cancer frequency in the Samtgemeinde Asse 13 from the release of substances from the Asse II mine that were estimated in Section 4. According to the present state of knowledge, therefore, the high incidence of cancer observed in the Samtgemeinde Asse cannot be explained by ionizing radiation from the release of substances from the Asse II mine.
7 Summing up and position statement
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. Extremely conservative models of the potential radiation exposure of the population in the vicinity of the Asse II mine yield only negligible annual doses (Table 3).
The SSK concludes that even at the most unfavourable point of exposure, i. e. at the site 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 municipality in the period 2002 until 2009.
Table 3: Comparison of the accumulated radiation exposure to 2009 of a reference person born in 1978 calculated in accordance with the AVV relating to Paragraph 47 StrlSchV using the Gaussian plume model with the dose needed to explain the observed incidence
Accumulated radiation exposure to 2009 Dose needed to explain the of a reference person born in 1978 observed incidence, in µSv calculated in accordance with the AVV relating to Paragraph 47 StrlSchV Most Closest More Best 95th unfavourable places – distant estimate percentile point of Remlingen places in exposure at und the Samt- the fence of Wittmar gemeinde the Asse II Asse mine Organ dose to red bone marrow 700 70 7 730,000 500,000 in µSv Thyroid dose in µSv 200 20 2 1,300,000 320,000
The statistical analysis reveals some residual heterogeneity for leukaemia disorders in men and thyroid cancers in women, although the credible intervals of the adjusted SIRs always involve the number 1. However, the relatively high uncertainties of the statistical analysis of the SIRs are not a consequence of the methods used but arise instead from the small scale of the problem and hence the low numbers of cases. This highlights a general problem with the evaluation of clusters. Cancer frequency in the Samtgemeinde Asse 14
If 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 municipality.
8 References
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