The United Nations is to adopt advice on radiation that clarifies what can be said about its health effects on individuals and large populations. A preliminary report has also found no observable health effects from last year's nuclear accident in Fukushima.
The studies come from the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) after five years of work. An independent body of international experts, UNSCEAR has met regularly since 1955 and helped establish radiation as the best understood carcinogen in the world through its studies of atomic bomb survivors and the effects of the Chernobyl accident.
Having been officially approved by the UN General Assembly, the reports - as well as a resolution welcoming them - will be endorsed in coming weeks. They will then serve to inform all countries of the world when setting their own national radiation safety policies.
Presenting to the UN General Assembly, UNSCEAR's chair Wolfgang Weiss said that preliminary findings were that no radiation health effects had been observed in Japan among the public, workers or children in the area of the Fukushima Daiichi nuclear power plant. This is in line with studies already published by the World Health Organisation and Tokyo University that showed people near the damaged power plant received such low doses of radiation that no discernible health effect could be expected.
Uncertainties at low doses are such that UNSCEAR 'does not recommend multiplying low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or below natural background levels.'
Six workers received total doses of over 250 mSv during their time tackling the emergency, while 170 received doses over 100 mSv. None of these have shown ill effects, said UNSCEAR, stating that radiation played no role in the coincidental deaths of six Fukushima workers in the time since the accident.Defining radiation risk
UNSCEAR said that it was not possible to attribute increases in health effects across populations to long term exposure at radiation levels typical of the global average background levels (1-13 mSv per year). 'This is because of the uncertainties associated with the assessment of risks at low doses, the current absence of radiation specific biomarkers for health effects and the insufficient statistial power of epidemiological studies.'
For exposures below 100 mSv UNSCEAR said that a health issue across a population could be put down to radiation exposue on two conditions: that spontaneous occurrence of that issue was low while the radiosensitivity of that issue were very high; and that the number of cases was high enough to overcome 'the inherent statistical uncertainties'.
An example that could fit the definition is the well-known risk of thyroid cancer from accidental releases of iodine-131. The substance is a short-lived isotope produced in operating nuclear reactors and, if released in sufficient quantities during an accident, could be absorbed in the thyroid glands of children and young people and lead to thyroid cancer. This was only major radiation-related health effect of the Chernobyl accident on the public.
UNSCEAR's work plan
• Complete the assessment of levels of exposure and radiation risks attributable to the Fukushima accident
• A report on the effects of radiation exposure on children
Topics for 2014:
• Radiation exposure from electricity generation
• Biological effects of selected internal emitters
• Revsed methodology for assessing discharges
• Epidemiology of low-dose radiation risks
Last year, Japanese authorities protected children in Fukushima prefecture from iodine-131 by evacuating them before radiation was released, issuing stable iodine pills to block iodine-131, and preventing food and water containing the radioactive isotope from being consumed. As a result, the largest dose thought to have been received by a Japanese child is 35 mSv - this figure also coming from UNSCEAR's preliminary report. This is 'reassuring' in comparison to the doses received by children after the Chernobyl accident, said UNSCEAR while, "That good news must be underlined," said Argentinian delegate to UNSCEAR, Gerardo Diaz Bertolome.
The statistical chance of health effects increases through the range of 100-1000 mSv exposures, 'but there are statistical limits in calculating that risk and the population in question had to be big enough to do so.' The only radiation events on this scale, where populations of thousands have received on the order of 100 mSv, have been the atomic bomb blasts in Japan from World War II.
In general, the effects of radiation only start to become clear at 'high acute absorbed doses... such as might occur following exposures in accidents or radiotherapy', for example a dose of over 1000 mSv. Even then it is necessary to eliminate other potential causes before radiation can be unequivocably said to be the cause, said UNSCEAR.
Researched and written
by World Nuclear News