Pre-eminent world experts on the effects of atomic radiation agree today to start an assessment of the radiological impact of the events at the TEPCO (Fukushima-Daiichi) nuclear power plant following the March 11, 2011 earthquake and tsunami.
The United Nations Scientific Committee on the effects of Atomic Radiation (UNSCEAR) expects to have preliminary findings by May of next year.
"They ought to provide scientific insight on the magnitude of the releases to atmosphere and to the ocean, and the range of radiation doses received by the public and workers -- the assessment will be in broad terms," Wolfgang Weiss, chair of the Committee said today.
"We will be deciding on the scope and organization of the work this week, clarifying what areas we will be looking at," Weiss said. The Committee which he chairs comprises scientists from 21 Member States of the United Nations. Today is the opening day of its regular annual session.
UNSCEAR's first full report with supporting scientific evidence about the radiation impact of the ongoing events at the Fukushima Daiichi nuclear power plant will take at least two years.
The Committee's assessments represent a scientific basis for standards and protection against ionizing radiation for United Nations agencies and governments. Since the Chernobyl accident in 1986 the Committee has published three extensive assessments about its impact. The last one was released in February 2011.
Of relevance to the new assessment will be the release today in all six UN official languages of an UNSCEAR summary report on the effects of low doses of radiation (see Summary Report below).
Scientific Committee Members: Wolfgang Weiss, Chair (Germany), Abel González (Argentina), Carl-Magnus Larsson (Australia), Hans Vanmarcke (Belgium), Marcos Nogueira-Martins (Brazil), Norman Gentner (Canada), Pan Ziqang (China), Mohamed Gomaa (Egypt), Laurence Lebaron-Jacobs (France), Krishna Sainis (India), Susilo Widodo (Indonesia), Yoshiharu Yonekura (Japan), Jaime Aguirre Gómez (Mexico), A. Lachos Dávila (Peru), Michael Waligórski (Poland), Mikhail Kiselev (Russian Federation), Emil Bédi (Slovakia), E. Eltayeb Ali (Sudan), Leif Moberg (Sweden), John Cooper (United Kingdom), and Fred Mettler (United States).
UNSCEAR secretariat: Malcolm Crick (UNEP)
UNSCEAR Summary Report on Effects of Low Doses of Radiation
• There is strong evidence of "statistically significant" elevations of risk of solid tumours and leukaemia above doses of 100 -- 200 milligray (mGy)
• Findings of elevated incidence of circulatory disease in populations irradiated at high doses are raising some concern
• There is "increasing evidence" of radiation exposure leading to increased incidence of cataracts
The Report uses the term 'low dose' to mean doses of radiation below 200 mGy -- a computed tomography scan delivers about 10 mGy. It consolidates and summarizes findings from its detailed reports on various aspects over the last several years.
The Committee evaluated information in two general classes:
(a) studies of populations irradiated at moderate or high doses (epidemiological studies), such as survivors of the Hiroshima and Nagasaki bombings; and
(b) experimental studies that examine the mechanism by which the biological effect or disease arises, from animal and cultured cell studies
There are many difficulties in attributing observed cases of disease to low dose exposure. (1) There are no specific markers for radiation-induced diseases. (2) A significant passage of time, "years or decades" may elapse between exposure and onset of disease. (3) And diseases associated with radiation also occur spontaneously in an ageing population. This means that epidemiological studies often fail to reveal clear links.
Nevertheless "there is strong epidemiological evidence that exposure of humans to radiation at moderate and high levels can lead to excess incidence of solid tumours in many body organs and of leukaemia." The report states that "statistically significant elevations in risk are observed at doses of 100 -- 200 mGy and above." (The increased risk of fatal cancer is about 1 per cent at these levels, which are equivalent to between 10 and 20 computed tomography scans). The report notes that younger people are more sensitive.
It also says that experimental studies have hypothesized several responses to radiation exposure that could serve to increase or decrease cancer risks at low doses:
• adaptive response -- low doses of radiation may cause cells and tissues to become more resistant to cancer development
• effects on immune systems -- which recognize and destroy abnormal cells, could influence the likelihood of cancer development
• genomic instability -- radiation can produce changes that have long lasting and transmissible effects on the stability of cellular DNA
• bystander effects -- radiation may trigger the transfer of signals from damaged cells to undamaged neighbours.
The Committee has reviewed these studies and judges that these processes do not contribute significantly to the interpretation of the epidemiological data.
Unlike the studies on cancer, epidemiological studies have not provided clear evidence of excess heritable effects of radiation exposure in humans, not even from the survivors of the atomic bombings in Japan. Nevertheless these studies provide an upper boundary for the estimate of any associated risk.
Radiation exposure of the developing embryo or foetus above about 100 mGy during specific periods of pregnancy can induce congenital malformations and affect the central nervous system.
There is clear evidence of an increased risk of cardiovascular disease associated with radiation exposure at doses above 1000 to 2000 mGy, Evidence is emerging indicating elevated incidence of non-cancer diseases below these levels. But the Committee's review could not draw any conclusions about a direct causal relationship between lower levels of irradiation and cardiovascular and other non-cancer diseases, though this is an area of active research.
The Committee also notes that recent studies have suggested that an increased incidence of cataracts may be associated with low-dose radiation exposure.
The Committee will continue to monitor and review new findings in these areas that might contribute to a more complete understanding of the health effects of low-dose radiation exposure and of the mechanisms that explain them.
The mandate of 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.
Note: The Summary Report on the effects of low-dose radiation is available at: http://www.unscear.org/unscear/en/publications.html
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