Abstract
With the development of nuclear reactors and nuclear weapons during World War II the potential for both workers and members of the public to be exposed to ionizing radiation had increased significantly. At about the same time it was also becoming apparent that chronic exposures to low levels of ionizing radiations had the potential to cause carcinogenic and hereditary effects. In response to these developments the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was formed by the General Assembly in 1955 to report on the sources and effects of ionizing radiation.
The detonation of 60 megaton of hydrogen bombs in the atmosphere from 1952 to 1954 significantly increased global radioactive fallout. The challenge for UNSCEAR was to develop techniques for the assessment of exposures from radioactive contamination and to assess the effects of these exposures on people. The Committee oversaw world wide programs for the assessment of contamination from fallout which was largely based around 90Sr measurements which was thought at the time to be one of the most important pathways for exposure to humans. In its 2000 report the Committee estimates that by 1963 world wide doses had increased five percent above normal background levels due to atmospheric weapons testing. The work of the Committee was instrumental in the adoption of the Partial Test Ban Treaty in 1963.
Over the last fifty years UNSCEAR has continued its work and has reviewed the sources of radiation exposure as well as the effects of ionizing radiations on human and non-human species. The Committee has assessed the radiological impact of the nuclear fuel cycle and other man-made sources, as well as medical radiation exposures and exposures from natural sources of ionizing radiation. Today it is apparent the doses from medical and natural sources are far greater than those from man-made sources.
In 2006 UNSCEAR finalised five annexes on the biological effects of radiation.
• Sources-to-effects assessment for radon in homes and workplaces,
• Epidemiological studies of radiation and cancer,
• Epidemiological evaluation of cardiovascular disease and other non-cancer diseases following radiation exposure,
• Effects of ionizing radiation on the immune system and
• Non-targeted and delayed effects of exposure to ionizing radiation.
In summary the Committee expressed the view that the estimation of the health effects of radiation is based on epidemiological and experimental observations where there is a statistically significant dose-related increase in disease incidence. These direct observations of adverse health outcomes implicitly take account of mechanistic elements relating not only to the targeted (direct) effects of irradiation but also to the non-targeted and delayed effects. At low doses, an understanding of the range and nature of cellular and tissue responses is needed to provide insights into the mechanisms by which radiation exposure induces detrimental health effects. UNSCEAR continues to believe that the data on low dose effects in UNSCEAR 2000 provide a suitable foundation for judgements on mechanisms that affect risk estimation.
UNSCEAR is continuing its work and is currently preparing reviews on the consequences of the Chernobyl accident after 20 years, the effect on non-human biota of ionizing radiation and occupational public and medical exposures to ionizing radiation. At the 56th Session in 2008 the committee will approve a program of work for the next few years.
