Radiation Exposure and Human Health
Exposure to radiation is a natural feature of life. Cosmic rays have permanently bathed the atmosphere and exposed the human race to radiation. Radioactive elements or radionuclides are found everywhere on Earth: in the air, on land, in the sea, in foodstuffs and in the human body itself. People receive natural background radiation from these sources and from radon gas emanating from the Earths surface. They may also receive radiation doses from various beneficial practices such as radiological medicine (ie. for X-ray imaging or cancer radiotherapy) and from man-made radiation legacies such as residual radioactive materials remaining from nuclear weapons tests conducted in the atmosphere and underground during the cold war.
Human exposure to radiation is usually measured as a dose of radiation, which is expressed in a unit termed millisieverts (mSv). The typical average dose to people from the natural sources of background radiation around the world is 2 to 3 mSv per year. In many parts of the world, the annual background radiation dose can be up to around 10 mSv and in a few places can be as high as 100 mSv. A routine diagnostic chest X-ray is equivalent to about 0.05 mSv, while a comprehensive X-ray examination may lead to a dose as high as 10 mSv.
Radiation exposure can harm peoples health, notably it can increase long term risks of incurring cancer. One person in five today dies from some form of cancer from various causes. Radiation exposure, however, is only one very minor contributor to cancer incidence. Nevertheless, for the purposes of establishing international radiation protection standards, it is assumed that any increase in radiation dose, however small, results in a proportionate increase in risk of incurring cancer.
The Legacy of Nuclear Testing
Since the first nuclear weapons were exploded at the end of the Second World War, more than 2,000 nuclear tests have been carried out predominantly by the five declared Nuclear Weapons States, China, France, the United Kingdom, the United States and the former USSR. More than 500 of these were atmospheric tests conducted above ground mostly in the 50s and 60s, after which more than 1,500 were carried out underground.
The explosion of a nuclear device leaves behind residual radioactive material containing a complex mixture of radionuclides including long-lived caesium-137, strontium-90, plutonium-239/240 and tritium./1 The potential radiation doses to humans, plants and animals in areas near test sites are determined by the amounts of residual radionuclides which are available to them in the soil and water, and those that, although currently beneath the Earth, could migrate from the underground into the biosphere. /2
Testing at Mururoa and Fangataufa Atolls
Mururoa and Fangataufa atolls are located in French Polynesia, in the middle of the South Pacific Ocean about halfway between Australia and South America. They are just north of the Tropic of Capricorn at the south-eastern edge of the Tuamotu archipelago. Geologically, the atolls were created around 10 million years ago and were originally the peaks of volcanic mountains that subsequently sank under their own weight and were overlaid with coral. Today, they consist of a narrow rim enclosing a lagoon and jutting a few metres at most above the surrounding ocean. Mururoa is 63 km in perimeter; Fangataufa, 40 km to the south, is only about one quarter the size. The atolls volcanic rock base is capped by about 400 metres of carbonate rock derived largely from the coral.
There is no record of prolonged habitation on either atoll. The nearest inhabited place - the atoll of Tureia, with about 120 residents - is 130 km away. Papeete, the capital of French Polynesia (which has a total population of 220,000), is over 1000 km from Mururoa, and New Zealand is some 5,000 km away.
Between 1966 and 1974, France conducted nuclear weapons tests in the atmosphere at the atolls, including 41 nuclear tests and five safety trials. In a safety trial, a nuclear weapon is destroyed with conventional explosives with no, or very little, release of nuclear energy. With the exception of four tests (three at Mururoa and one at Fangataufa) carried out on barges floating in the lagoons, most atmospheric tests were carried out, suspended from balloons, hundreds of metres above the lagoons so that there was very little local fallout of radioactive material. Indeed, most of the radioactive material was transported into the upper atmosphere and dispersed. Thereafter, testing was conducted underground in sealed vertical shafts some 500-1100 metres beneath atoll rims or under the lagoons. Between 1975 and 1996, a total of 137 deep underground tests took place, and 10 underground safety trials were also conducted. /3
A Request for Independent Evaluation
The Director General of the International Atomic Energy Agency (IAEA), the main specialized body in the UN family dealing with nuclear matters, received a request from France in 1995 to perform an independent, comprehensive and objective evaluation of both the present and expected future radiological conditions at the atolls resulting from the weapons testing there. The evaluation was not to assess any radiation effects in the past resulting from the previous 30 year testing period as these have been evaluated by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and periodically reported by UNSCEAR to the UN General Assembly. However, realizing the interest that people of the South Pacific region might have on the past history of radiation levels and effects, it was decided to request the UNSCEAR Secretariat to summarise its findings. UNSCEAR's summary is annexed to the Study report.
The evaluation was also not to assess the radiation exposure of workers involved at the time in the execution of the nuclear weapon testing activities. It is not feasible to verify independently individual workers' exposures after the exposure has taken place. The IAEA can monitor individual occupational exposures but only if it is requested to do so prior to exposure. It should be noted, however, that the international practice is to assign the responsibility of monitoring occupational exposures to the employers.
The French Government agreed that all relevant scientific data it had collected over many years would be made available to independent scientists. An International Advisory Committee (IAC) was assembled by the IAEA to oversee the Study, which commenced upon completion of the final series of nuclear weapons tests in January 1996. The IAC was composed of high-level experts from ten Member States and two intergovernmental organizations and two specialized UN bodies, and was chaired by Dr. E. Gail de Planque (US), formerly Director of the US Department of Energys Environmental Measurement Laboratory and Commissioner of the US Nuclear Regulatory Commission. These distinguished scientists (see list below) provided scientific guidance and direction in the Study, which reported to the IAEA its findings, conclusions and recommendations. In addition to the IAEA Secretariat staff, some 55 scientists from 18 countries and four international organizations took part in the study.
Conduct of the Study
Most of the information submitted by the French Government was newly available and had not been subject to scrutiny by the wider scientific community. The IAC therefore decided to assess and independently evaluate the available information. In particular, the IAC decided to independently measure the levels of radioactive material on Mururoa and Fangataufa in order to properly evaluate the extensive French environmental monitoring data. Samples of soil, vegetation, coral, sea water, fish, lagoon sediment and plankton were collected in the summer of 1996 and analysed for radioactivity. Eighteen laboratories in 12 countries, together with the IAEA Laboratory at Seibersdorf, Austria and the IAEA Marine Environment Laboratory in Monaco, participated in analysing the collected samples. The Study also carried out its own sampling and analysis of water in the cavities made by two underground nuclear tests, and of water in carbonate rock beneath both atolls. Limited samples for comparative purposes were collected from the island of Tureia, 130 km away.
Extensive assessments were carried out of the underground situation. This involved independent estimation of the yield of each test and the total inventory of radionuclides, and modelling of the migration of radionuclides through cracks in the rocks. The dispersion of radionuclides in the lagoons and the ocean was also modelled. Finally, estimates were made of the radiation dose that could be received by atoll dwellers and nearby inhabitants both now and in the future.
- Residual Radioactive Materials Presently in the Accessible Environment of the Atolls
The Studys evaluation of residual radioactive materials with which people could come into contact found that radionuclide concentrations on the atolls surfaces and in the surrounding seas -- with four exceptions -- are similar to or below those found elsewhere in the region where no nuclear weapons testing took place. The four exceptions are listed below:
- Predicted Future Migration of Residual Radioactive Materials from Underground
The Studys independent assessment confirmed the information on the underground inventories of various radionuclides obtained from the French sources. The total amount of radioactive materials remaining underground at the two atolls was equivalent to less than 2 percent of the amount that was released globally in all atmospheric nuclear weapon tests. /4
Following a nuclear explosion, these radionuclides become fixed in the solidified lava or distributed between rubble, water and gases remaining in the test cavity. A certain amount of this radioactive material will be dissolved in the water in the underground cavities. /5
Two kinds of release of radionuclides were considered in the Study: first, releases following normal migration of residual radioactive material through the volcanic and carbonate rocks from the underground cavities; and second, hypothetical releases that might occur as the consequence of some imagined disruptive event. Once the radionuclides escape from underground, either to the lagoons or directly through the sides of the atolls, they become available for dispersion in the ocean.
The Study found that migration of tritium into the lagoons from underground cavities will continue, but within about 100 years the radionuclide concentrations will be below current levels in the open ocean. Other radionuclides, including caesium-137 and strontium-90 would be effectively retained underground within the volcanic rocks, most of their activity decaying and only small amounts of radioactivity being released. The possible maximum increases in concentrations expected at the nearest inhabited atoll, Tureia, due to the predicted, continuous releases from the lagoons of strontium-90, caesium-137 and tritium would be very much less than current levels in the sea, which have been caused by the fallout from all global nuclear testing.
Concentrations of plutonium-239 and -240 in lagoon water, due to the plutonium in the lagoon sediments, have been decreasing and this trend is expected to continue in the short term. However, they are predicted to rise slightly in a few thousand years, as plutonium is released from the test cavities and migrates to the lagoons, although they are expected to remain below the present levels.
The consequences of several major hypothetical disruptive events on the atolls were also assessed. The most significant event considered was a major rock slide, on the north side of Mururoa, exposing the cavities of a safety trial and a nuclear test and causing a sudden release of radioactive materials into the ocean. Regional and large scale modelling was subsequently used to assess the potential dispersion and dilution throughout the South Pacific Ocean, as far afield as Australia and South America, of all radioactive material expected to be released from the atolls.
Of all the radionuclides, only plutonium released with the hypothetical rock slide gives a concentration at Tureia higher than current levels, although it would be small in absolute terms. This elevation would last only a few years. Concentrations in the ocean at places further distant from Mururoa and Fangataufa would generally be lower.
Potential Radiation Doses
- To People Now Living in the Region
The International Basic Safety Standards (BSS) of radiation protection, published by the IAEA and co-sponsored by a range of organizations, including the World Health Organization, provided the basis for assessing the potential risk to people living in the region, or settling at the atolls in the future.
The Study examined ways in which people visiting or living on the two atolls could be exposed to radionuclides: direct inhalation; eating food grown on Mururoa and Fangataufa or local fish and seafood; possible entry into the body (via a wound) of a particle containing plutonium; or consumption of contaminated soil (by children). It was concluded that members of a resident population on the atolls with a diet of local produce and seafood from the lagoons would not generally receive a radiation dose attributable to residual radioactive material exceeding 0.01 mSv per year. This is a very small fraction of the dose that they would receive from natural background radiation, including natural radionuclides present in fish which emit the same type of radiation as plutonium.
On the islets of Colette, Ariel and Vesta at Mururoa atoll, it would be possible for a residual particle containing plutonium from the safety trials to be incorporated, through an open wound, into the body of someone visiting the area. The chance of this happening is very low and the overall probability of ultimately incurring serious health consequences as a result for such an individual was estimated to be negligible, less than one in one million per year. This takes into account the remoteness of the islets, even for hypothetical inhabitants of Mururoa, the low probability of incorporation and subsequent retention in the body of a significantly radioactive particle, and the potential harm resulting from the radiation dose of such a particle.
The Study also examined the hypothetical situation in which a very small group of people might settle permanently in the Kilo-Empereur region of Fangataufa and live entirely on produce from the small areas which contain higher levels of caesium-137. The projected maximum radiation dose to such inhabitants would be 0.25 mSv per year, or one tenth of the dose due to natural background radiation. This hypothetical situation, however, is very unlikely to arise in practice as the Kilo-Empereur region is barren and virtually uninhabitable.
The Study found that while the amount of plutonium in the lagoon sediments is relatively large, it is of little radiological significance for several reasons including: the gradual burial of sediments by fresh sediments; the removal of sediment over time into the ocean, particularly by storms resulting in dilution; and the low uptake by marine organisms and hence low rate of incorporation in people. Similarly, although tritium concentrations in the lagoons are higher than those in the open ocean, they are still extremely low and they were not of radiological significance.
The Study concluded that people living on the nearest inhabited atoll, Tureia, are receiving essentially no dose as a result of the current radiological conditions at Mururoa and Fangataufa.
- To Future Human Populations
The Study estimated possible doses that people who may be living on the atolls or elsewhere in the South Pacific might receive as the result of gradual migration of residual radioactive material from the underground cavities both into the lagoons of the two atolls and directly into the ocean. It was concluded that no population group is likely to receive a future dose, attributable to the residual materials at the two atolls, exceeding about one percent of the background dose received from natural background radiation.
The radiological consequences of plausible potential disruptive events, such as potential climate change and the underwater rock slide, were also examined. Even on the basis of very pessimistic assumptions, the highest hypothetical annual dose to residents of the nearest inhabited atolls in the years immediately following a rock slide would be no more than a few thousandths of a millisievert, an extremely small increment of around 0.1 percent of the natural background radiation in the area.
Implications for Human Health
The radiation doses currently received by populations in the South Pacific region as a result of the residual radioactive materials remaining in Mururoa and Fangataufa are negligible fractions of natural background levels, and will continue to be so in the long term. The Study thus concluded that there would not be any health effects, either medically detectable in an individual or epidemiologically discernible in a population group, that could be attributable to radiation exposure due to the residual radioactive materials remaining at the atolls.
The Study recognized that reported cancer incidence may change, both in this region and throughout the world, as a result of many factors: improved diagnosis and registration of cancer cases; changes in environmental exposure to other cancer-causing agents; changes in personal habits (such as eating and smoking); population migrations that alter baseline cancer incidence rates; and changes in the incidence of other diseases. However, the doses estimated in the Study are so low that any future changes in cancer incidence in this region would not be attributable to radiation from residual radioactive materials from nuclear tests at the atolls.
The Study also reviewed the claim that other medical problems, such as food poisoning due to ciguatera in fish, are due to radiation doses from the nuclear testing. Ciguatera poisoning in fish has been recorded for over 100 years, however, and scientific investigation has demonstrated that a range of human and natural disturbances contribute to ciguatera outbreaks. The Study concluded that there is no relationship between radioactivity in fish and ciguatera toxicity and no evidence for radiation influencing the occurrence of the disease.
Impacts on Native Plants and Animals
The Study concluded that it is unlikely that the residual radioactive material will have any effects on healthy populations of living organisms on or near the Atolls. Overall, the additional doses, due to the tests, to the vast majority of native marine organisms are less than, or about the same level as, the doses due to natural background radiation. Aside from the Colette sandbank, in which plutonium containing particles from atmospheric safety trials were found, the highest doses in the vicinity of Mururoa and Fangataufa atolls to marine organisms are at least 200 times lower than those that could have detrimental effects on populations. For the Colette sandbank, it is possible that some individual creatures living in the sediment could receive absorbed doses from particles containing plutonium that would be sufficient to produce effects in microscopic volumes of tissue. However, there would be no harmful impact on the wider eco-systems.
IAC Conclusions and Recommendations
In light of the measured and predicted levels of radionuclides - and the assessed doses both in the present and in the future - the Study concluded that no remedial action is justified on radiological protection grounds, either now or in the future. There is also no need for further monitoring at the atolls for the purposes of radiological protection. However, the Study recommended that a programme of measurement of radioactivity in the environment could be useful, not only scientifically but also in assuring the public about the continuing radiological safety of the atolls.
|COMPARISON OF RADIATION DOSES
(mSv per year)
|Global natural background doses|
|Mururoa and Fangataufa natural background dose||1.4 - 3|
|Current additional doses from remaining residual radioactive material at Mururoa and Fangataufa|
|Maximum at Tureia||< 0.0001|
|Average at Mururoa and Fangataufa||< 0.01|
|Maximum at Kilo-Empereur region in Fangataufa||~ 0.25|
|Maximum additional dose at Tureia following a rock slide at Mururoa||0.007
|IAEA recommended guidelines for remediation||10|
The membership of the IAC is as follows: Chairman - Ms. E. Gail de Planque, former Commissioner of the United States Nuclear Regulatory Commission; Mr. D. Beninson, former Chairman of the International Commission on Radiological Protection (ICRP), Chairman of Argentina's Regulatory National Authority; Mr. R. Clarke, present Chairman of ICRP, Director of the United Kingdom's National Radiological Protection Board; Ms. Helen Garnett, Executive Director of the Australian Nuclear Science and Technology Organisation; Mr. G.E.G. Holm, Associate Professor, Lund University Hospital, Sweden; Mr. H.S. Karyono, Director, Nuclear Minerals Development Center, Indonesian National Atomic Energy Agency; Mr. A. Kaul, President of Germany's Bundesamt für Strahlenschutz (Federal Office for Radiation Protection); Mr. A. Matuchenko, member of the Russian Federation's Commission on Radiation Protection; Mr. T. Numakunai, Director General of Japan's Institute of Radiation Measurements; Mr. A. Poletti, Department of Physics, University of Auckland, New Zealand; and the following ex officio experts selected by relevant intergovernmental bodies - Mr. G. Fraser, Head of the Sector of Radiation Protection in the European Commission's Directorate General for the Environment, Nuclear Safety and Civil Protection (selected by the European Commission); Mr. V.A. Fuavao, Director of the South Pacific Environment Programme (selected by the South Pacific Forum); Mr. B. Bennett, Director of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR); Mr. W. Kreisel, Executive Director for Health and Environment of the World Health Organization (WHO), selected by WHO.
Radiological Situations Caused by Nuclear Weapon Testing: IAEA Response
Over 2000 nuclear weapon explosions have been carried out around the world since the bombing of Hiroshima and Nagasaki in 1945. About 20% of the nuclear weapons were tested in the atmosphere and - since the adoption of the Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water (Moscow, 5 August 1963) - the remainder have been carried out underground. Nuclear weapon testing has left a legacy of residual radioactive materials which have a variable degree of significance for human health and the environment.
Three IAEA Member States have requested the IAEA to assess the radiological situation created by nuclear weapon testing in territories under their control. In 1993, the government of Kazakhstan requested the IAEA to perform a preliminary study of the radiological situation at the test site in Semipalatinsk. In 1994, the government of the Republic of the Marshall Islands requested an assessment of the radiological conditions at Bikini Atoll and the prospects for resettlement of the Bikinian population in Bikini Island. In 1995, the government of France requested that the radiological situation at the atolls of Mururoa and Fangataufa in French Polynesia be studied. The IAEA statutory functions include the establishment of international standards of safety for the protection of health against radiation exposure and provide for the application of those standards of safety for the protection of health against radiation exposure and provide for the application of those standards at the request of a State. In discharging these functions, the IAEA met the aforementioned requests; the results are currently being published in the IAEA Radiological Assessment Report Series.
The following table provides a simplified summary of the madimym annual radiation dose that hypothetical individuals would expect to receive at the studied test sites, should they be inhabited. It should be noted, however, that unqualified comparisons of the results of these studies can be misleading due to different characteristics of the tests and of the sites where they took place and due to variations in the hypothesis used. For reference purposes, levels of exposure to natural background radiation around the world are also shown.
In September 1995, the IAEA General Conference adopted a Resolution calling all States concerned to fulfil their responsibilities to ensure that sites where nuclear tests have been conducted are monitored scrupulously and to take appropriate asteps to avoid adverse impacts on health, safety and the environment of such nuclear testing.
A total of 36 radionuclides produced by nuclear explosions were investigated by the Study. Most of these, however, are short-lived and/or do not carry a potential of risk for the environment or human health. Nuclear explosions conducted underground generate intense heat and high pressures. The immediate surrounding rock is melted and vaporised and then cools and condenses to form a lava in the explosion cavity. Within some hours, the cavity roof collapses, forming a cylindrical cavity about 5 times as high as its radius, filled with broken rock. At the atolls, where the surrounding rock is saturated with sea water, the cavity eventually fills with water. The radioactive products are initially contained within this cavern and some of them will dissolve in the water. The underground nuclear tests were conducted in the volcanic rock at a depth of 500 to 1100 metres. The 10 underground safety trials were all conducted at Mururoa, 7 of which were in the carbonate rock at depths below 280 metres. The levels of the two major long-lived radionuclides, caesium-137 and strontium-90, deposited on the earths surface attributable to the French atmospheric tests in the period 1966 to 1974 represent 13 percent of the total deposition of these radionuclides in the latitude of the two atolls. The remainder comes from fallout of these radionuclides from atmospheric tests performed, mostly in the northern hemisphere, by other nuclear weapon states. An independent survey of radionuclide concentrations in water taken from two underground cavities found that the concentrations of plutonium-239 are extremely low, confirming the high level of retention of this radionuclide in the glassy lava formed by the explosion.
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