VIENNA -- 'Radiation exposure following the nuclear accident at Fukushima-Daiichi did not cause any immediate health effects. It is unlikely to be able to attribute any health effects in the future among the general public and the vast majority of workers,' concluded the 60 th session of the Vienna-based United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR).
The effects of radiation exposure on humans and the environment following the accident at the Fukushima-Daiichi nuclear power plant in March 2011 is one of the major issues being discussed at the Committee's annual session which started on Monday, 27 May. The second important issue is related to the short and long term effects of exposure to radiation on children. This covers medical as well as other kinds of exposure (not specifically related to the accident at Fukushima-Daiichi).
The report that is finally adopted by the Committee will be presented to the United Nations General Assembly when it meets later this year, and the scientific data and evaluation underpinning that report will be published separately.
1. Radiological impact of the Fukushima-Daiichi accident:
More than 80 leading international scientists have worked on analysing the information available on the levels and effects of exposure following the events of 11 March 2011 in Japan. Material they prepared was scrutinized by the 27 countries on the Scientific Committee at their annual session. When the Committee's report is published, it will be the most comprehensive international scientific analysis of the information available to date.
'The experience from the 1986 Chernobyl accident has shown us that apart from any direct impact on physical health, the social and societal effects, and their associated health consequences in the affected population will need special attention in the coming years,' said Carl-Magnus Larsson, Chair, UNSCEAR. 'Families are suffering, and people have been uprooted and are concerned about their livelihoods and futures, the health of their children-it is these issues that will be the long-lasting fallout of the accident. At the same time, it is important to maintain a long-term medical follow-up for the exposed population, and in relation to certain diseases to provide a clear picture of their health status development.'
The draft report was deliberated at length by the Committee, including more recent data received from Japan. Methodologies, assessments and doses were scrutinized in detail, and the Committee has made some recommendations that will be incorporated into the draft, which is now in the process of being finalized for presentation to the General Assembly. 'The Report has the full confidence of the Committee,' said Larsson.
On the whole, the exposure of the Japanese population was low, or very low, leading to correspondingly low risks of health effects later in life. The actions taken to protect the public (evacuation and sheltering) significantly reduced the radiation exposures that would have otherwise been received, concluded the Committee 'These measures reduced the potential exposure by up to a factor of 10. If that had not been the case, we might have seen the cancer rates rising and other health problems emerging over the next several decades,' said Wolfgang Weiss, Chair, UNSCEAR report on radiological Impact of the Fukushima-Daiichi accident.
For information only - not an official document
The doses delivered for the two most significant radionuclides were quite different: doses to the thyroid mainly from iodine-131 ranged up to several tens of milligray and were received within a few weeks after the accident; the whole-body (or effective) doses mainly from caesium-134 and caesium- 137 ranged up to ten or so millisieverts (mSv) and will be received over the lifetime of those exposed. The additional exposures received by most Japanese people in the first year and subsequent years due to the radioactive releases from the accident are less than the doses received from natural background radiation (which is about 2.1 mSv per year). This is particularly the case for Japanese people living away from Fukushima, where annual doses of around 0.2 mSv from the accident are estimated, arising primarily through ingestion of radionuclides in food.
No radiation-related deaths or acute effects have been observed among nearly 25,000 workers (including TEPCO employees and contractors) involved at the accident site.
Given the small number of highly exposed workers, it is unlikely that excess cases of thyroid cancer due to radiation exposure would be detectable. Special health examinations will be given to workers with exposures above 100 mSv including annual monitoring of the thyroid, stomach, large intestine and lung for cancer as a means to monitor for potential late radiation-related health effects at the individual level.
The assessment also concluded that although the rate of exposures may have exceeded the levels for the onset of effects on plants and animals several times in the first few months following the accident, any effects are expected to be transient in nature, given their short duration. In general, the exposures on both marine and terrestrial non-human biota were too low for observable acute effects. Potential exceptions are water plants, especially located in the area where radioactive water was discharged into the ocean. 'At this point, we can say that there is a potential risk to some organisms in the areas of highest exposure, but it is difficult to quantify it in detail with the available information,' said Malcolm Crick, Secretary, UNSCEAR (The UNSCEAR secretariat is administered by the United Nations Environment Programme, UNEP). 'The exposures of organisms in the environment are unlikely to cause anything more than transient harm to their populations,' he added.
2. UNSCEAR Report on Effects of Radiation Exposure of Children
Because of anatomical and physiological differences, radiation exposure has a different impact on children compared with adults. The Committee had started a general review of these differences before the Fukushima-Daiichi accident; its conclusions on this subject are considered in this year's report to the General Assembly.
There are differences in the doses received by children and adults from exposure to the same distribution of radioactive material in the environment, for example, when there are elevated levels of radionuclides on the ground. Children can also receive significantly higher doses than adults in situations such as medical exposure if the technical settings are not adapted appropriately.
If radionuclides are ingested or inhaled, the presence of radionuclides in one organ can give higher radiation doses to others because the organs of children are in closer proximity to one another than those of adults. In addition, both the metabolism and physiology depend on age, which also affects the concentrations of radionuclides in different organs and thus the dose to those organs for a given intake.
After radiation exposure, children are clearly more radiosensitive for about 30 per cent of tumour types when compared with adults. These types include leukaemia and thyroid, skin and brain cancer. They have the same sensitivity as adults when it comes to 25 per cent of tumour types such as kidney and bladder, and are less sensitive than adults when it comes to 10 per cent of tumour types including lung cancer.
For effects that are bound to occur after high doses, the Committee concluded that as seen with carcinogenesis, there are some instances in which childhood exposure poses more risk than adult exposure (e.g. for effects in the brain, cataracts, and thyroid nodules). There are other instances where the risk appears to be about the same (e.g. neuroendocrine system and effects in the kidneys) and there are a few instances where children's tissues are more resistant (lung, immune system, marrow and ovaries).
'More research is needed to fully understand the risks and effects following childhood exposure to radiation. This is necessary (and possible) because there are many individuals who were exposed as
children (such as the survivors of the atomic bombings) who are still alive. Their experiences must not be lost,' said Fred Mettler, Chair, UNSCEAR Report on Effects of Radiation Exposure on Children.
He added that the report was a valuable resource, as it is the first document that presents a comprehensive overview of the effect of radiation on children in totality.
Watch the webcast of the press briefing on 31 May at 13.30 pm at http://www.unis.unvienna.org/unis/en/webcast.html
The mandate of the United Nations Scientific Committee on the effects of Atomic Radiation (UNSCEAR), established in 1955, is to undertake broad reviews of the sources of ionizing radiation and the effects on human health and the environment. Its assessments provide a scientific foundation for United Nations agencies and governments to formulate standards and programmes for protection against ionizing radiation. UNSCEAR has conducted a scientific evaluation of the levels and effects due to radiation exposure resulting from the Fukushima accident. It does not deal with or assess nuclear safety or emergency planning issues.