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The natural background level of radiocarbon in the atmosphere and our food is very low. There is only about one radioactive carbon-14 for every 750 billion carbon atoms. Isn't that safe? After all, it is natural...
Nobel Prize-winner Linus Pauling didn’t think it would be safe to double the natural background level of radiocarbon, and offered convincing arguments in his Nobel Lecture. So if doubling the natural background level of radiocarbon would cause significant human health risks, why wasn’t the natural background baseline level itself considered hazardous?
Perhaps the baseline natural background radiocarbon level was simply accepted as an unavoidable natural hazard. There may also have been belief in an implicit (and unproven) assumption that the detrimental effects of any form of radiation at or below certain levels were non-linear, and in particular sub-linear (i.e., that below a certain lower threshold it was completely harmless, or at least much less harmful), and that the natural background level of radiocarbon fell within that safe region.
But a National Academy of Sciences panel recently completed a five year study which concluded that the evidence best supports a “linear, no threshold” (LNT) model for extremely low doses of radiation (Board on Radiation Effects Research, 2006).
The LNT model states there is no safe lower level or threshold for radiation, and that any amount, no matter how small, is potentially damaging to health. The panel also made particular note that radiation can alter the molecular structure of DNA, and that “some of these molecular changes are so complex that it may be difficult for the body’s repair mechanisms to mend them correctly.