The epidemiological study undertaken in the surroundings of Spanish nuclear and radioactive fuel cycle facilities analysed the cancer mortality and its possible relationship to the estimated effective doses to the population arising from the functioning of the facilities. The possible influence of the doses due to natural radiation was also studied.
The most important results were the following:
1) The accumulated estimated doses received by the public in the study areas as a result of the functioning of the facilities were very small and were much below those that current scientific knowledge could relate with effects on public health.
2) No consistent results were found that showed an increase in mortality for various types of cancer associated with the exposure of people to ionising radiations due to the functioning of the facilities. Some occasional dose/response associations were found that could not be attributed to exposure arising from the functioning of the facilities.
3) Neither was a statistically significant excess cancer mortality due to natural radiations found.
Introduction and background
Echoing a social demand regarding the impact of nuclear facilities on public health, the Plenary of the Congress of Deputies approved a Non-Legal Proposal (NLP) at its session on 9th December 2005 that urged the government to carry out a study considering, among others, the following aspects:
- The scope of the study must include all the nuclear facilities and their immediate surroundings, analysing any effects on public health
- The CSN must collaborate by providing the necessary information to assess the public’s exposure to radiation, both from artificial sources (facilities) and of natural origin.
- The independence of the investigation and the maximum transparency in the development of its activities must be guaranteed. For this purpose, the creation of an “Advisory Committee” was proposed to monitor the implementation of the study and the analysis of the results, with the participation of the affected institutions, independent experts, environmental groups and other stakeholders.
To carry out the study, the Institute of Health Carlos III and the Spanish Nuclear Safety Council signed a collaboration agreement in April 2006. The study started from this date and lasted until the end of 2009. The Advisory Committee was formed in September 2006 encompassing a wide range of organisations: health authorities from all the regions affected by the territorial scope of the study, trade unions, municipal authorities, companies owning the facilities, environmental organisations and six independent experts (on epidemiology, radiobiology and radiological protection), together with representatives of the Institute of Health Carlos III and the CSN. The committee met on six occasions to discuss methods, the results of dose estimates and the data and results of the mortality analyses as well as aspects relating to the communication and dissemination of the study.
Basic characteristics of the study
The study included all the nuclear power stations and the rest of the nuclear and radioactive facilities and nuclear fuel cycle facilities in the country regardless of whether they were in operation, in a definitive shutdown situation or in the decommissioning and dismantling phases. The study area included all the municipalities within a 30 km radius around the facilities, the situations of which were compared with municipalities in a control area with similar social and demographical characteristics but not affected by the operation of the facilities.
Additionally, the cancer mortality was studied in municipalities in two geographical areas with different natural radiation exposure indices and unaffected by the influence of any nuclear, radioactive or nuclear fuel cycle facility. Specifically, the municipalities in two circular areas within a radius of 30 km were chosen, one in the Region of Galicia with high indices of exposure to natural radiation and the other in the Region of Valencia, subjected to low exposure to natural radiation.
A total of more than 1,000 municipalities were studied, of which almost 500 are located in the facilities’ areas of influence. The rest are municipalities in the control areas and the two geographical areas with high and low indices of exposure to natural radiation.
The study methodology was that defined by the ISC-III according to current practices considered "state of the art" in the matter. This was an ecological study of retrospective cohorts that compared the mortality for different types of cancer and leukaemia of the residents in all the municipalities located around the Spanish facilities (30 km) with that found in the municipalities used as a reference (50 to 100 km). The study period included the years 1975-2003.
The study was of the ecological type because the central variable in the analysis, the radiation exposure, was assessed through an indicator, the effective dose, which is estimated for each population group consisting of the residents in each municipality and assigned to the individuals in that group (no individualised dose study was made of each person). The exposure indicator used was the "effective dose" because this parameter provides clear benefits, especially important in a study with a wide scope and spectrum such as this one. The study has taken into account the limitations of the use of the effective dose as an exposure indicator in epidemiological studies. This approach has been explicitly supported by the International Commission on Radiological Protection (ICRP) when consulted by the CSN.
The historical reconstruction of the exposure of the population in each municipality was carried out using an internationally recognised method based on estimating the population’s dose due to liquid and gaseous effluents from the facilities. Theoretical estimation models were used, with parameters adjusted to the specific properties of each geographical area in which each facility was located and representative of an "average individual."
With regard to the exposure to natural radiation, the annual dose received by a typical inhabitant was estimated for each municipality, those subjected to study, those in the control areas and those in the two geographical areas of Galicia and Valencia outside the areas of influence of the facilities.
Other important characteristics of the study
- For all the types of cancer studied, with the exception of leukaemia, a period (induction) of 10 years was considered as the necessary minimum time that had to elapse from an individual being exposed to radiation until the illness develops. One year was considered as the period for leukaemia.
- The variables that could act as confounding factors, that is, that could alter the results of the study, were considered. These included the exposure to natural ionising radiations and various social and demographic factors.
- Other exposures to artificial ionising radiations such as those from occupational exposures or medical treatment and diagnosis were not taken into account.
The cancer mortality for all the nuclear power stations and for all the rest of the nuclear and radioactive cycle facilities as a whole and for each individual facility was analysed. Cancer mortality due to exposure to natural radiation was analysed both in the areas of influence of the facilities and in the two chosen areas outside them.
Considering the population of the municipalities and the study period, in the area around nuclear power stations more than 7.5 million persons/year were counted for leukaemia and more than 5 million persons/year were counted for the rest of the tumours. Around the fuel cycle facilities, the study counted 8.5 million persons/year and 6.4 million persons/year for leukaemia and the rest of cancers, respectively.
Facilities / artificial radiation
The estimated accumulated doses received by the population due to the functioning of the facilities are very low; with a maximum value of 350 microSv (the dosage limit set in Spanish regulations for members of the public is 1,000 microSv in one year).
In both the joint analysis of areas of influence and nuclear power stations and in those of fuel cycle facilities, no consistent results were found that showed a pattern of increased cancer mortality associated with the dose. Neither were results found in the individual studies of each installation that indicated increases in this mortality. There were some specific observations that could not be attributed to the effect of the dose generated by their functioning because:
Generally, these were isolated findings that were not repeated in the rest of the facilities, so they were not consistent.
The estimated doses in the surroundings due to the functioning of each installation are very low and similar to those of other facilities in which the same effects were not found.
Some fuel cycle facilities showed exposure situations that share common properties with those produced in certain locations due to natural radiation (isotopes, transfer routes, incorporation into the organism), the magnitude of exposure to natural radiation being various orders of magnitude greater, with no effect associated with it found in the analyses made.
These specific results can be attributed to other forms of environmental exposure due to differences in living habits, the presence of other industries and activities or to randomness itself which, taking into account the large number of comparisons made, could in itself explain a certain number of positive associations (which could also explain some negative statistical associations, such as the occasional finding of a reduction in mortality accompanying an increase in radiation dosage).
The cancer mortality studies in both the areas around the facilities and in the two areas not affected by them in two geographical areas with different levels of exposure to natural radiation did not detect statistically significant increases in mortality as the doses received increased.