Low-dose study finds no effects [View all]

[FBaggins]

Living cells are constantly bombarded by ionizing radiation in various forms and from various sources. All this has the potential to damage DNA and unless this damage is corrected by self-repair mechanisms it can result in cell malfunction or the malignancy known as cancer. For most people the additional exposure from nuclear weapons detonation, nuclear power operations or nuclear accidents is a tiny fraction of the total, but this is not the case for everyone. The MIT team said their study contributed to asking the question, "How much additional radiation is too much?"

The effects of radiation on DNA have been clearly shown to be significant for high radiation doses, such as those received by Japanese survivors of atomic bombs. What is less well understood and far harder to study are the effects of lower doses over longer times. The prevailing method to deal with this area of uncertainty is to extrapolate the observable effects of high doses and assume the same relationship applies to low doses with no observable effect i.e. assume that all levels of exposure come with a commensurate health risk, no matter how small. This approach is used in practice as a basis for the management of occupational and public exposure worldwide.

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MIT said that the DNA strand in each living cell is subject to at least about 10,000 changes per day, but that self-repair mechanisms are able to correct these. Exposure to radiation at 400 times background levels resulted in only around 12 extra changes. "These studies suggest that exposure to continuous radiation at a dose rate that is orders of magnitude higher than background does not significantly impact several key DNA damage and DNA damage responses," said the paper.

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The paper concluded: "Taken together, studies of animals that live under conditions of prolonged continuous exposure to radiation at ~400x background do not show any evidence of increased levels of base damage... nor double strand breaks... nor induction of a DNA damage response... Importantly, when delivered acutely, the same total dose induced micronuclei and induced key genes involved in the DNA damage response." MIT said the absense of the genes in the low-dose group indicated a threshold for cell morphology and DNA damage responses, something that is absent from current extrapolation-based guidelines.

http://www.world-nuclear-news.org/RS_Low_dose_study_finds_no_effects_1605121.html