Just how dangerous are low doses of radiation?
Mar 12, 2012, Vol. 17, No. 25 • By TOM BETHELL
After Japan’s tsunami a year ago, about 20,000 people either drowned or were lost along the country’s northeastern coast. The same tidal wave overwhelmed nuclear reactors at Fukushima Daiichi. But no ill-health effects from radiation have been reported to date.
Ahhhh: Radon springs in Misasa, Japan
Separately, a professor of toxicology at the University of Massachusetts analyzed decades-old data on the biological effects of radiation. He concluded that studies after World War II claiming that low-level radiation is hazardous were deceptive. Since the 1950s, the U.S. government has relied on these studies to argue that there is no safe level of ionizing radiation.
U.S. policy was established by the National Academy of Sciences in 1956. The risk of harm was deemed proportional to the dose. A low dose would still do some harm, in other words, and there is “no threshold” below which radiation can be considered harmless. In 1977 the National Academy of Sciences Committee on Safe Drinking Water applied the same standard to chemicals, imposing huge cleanup costs on society; for example, at “Superfund” sites.
The research on which the “no threshold” policy was based was recently challenged by Edward J.
Muller, who won the Nobel for Physiology or Medicine, had earlier shown that atomic radiation can induce mutations in fruit flies. There is no doubt that it can—if the dose is high enough. The contentious issue is whether low doses are also harmful. After months of research at the American Philosophical Society, Calabrese has concluded that U.S. radiation experiments conducted after 1945 failed to confirm that low doses are hazardous.
A test in 1946 by a well-known radiation geneticist at the University of Rochester, Curt Stern, helped by one colleague and showing no safe dose, was contradicted by a later and better-designed test, also by Stern but with a different colleague. The later test showed a “threshold” below which no effects are seen. The second test used effective dose levels that were far lower, but still well above normal background radiation levels.
Muller knew that the latter result had contradicted the earlier one: But as though nothing had happened, he said in his Nobel lecture that there was “no escape from the conclusion that there is no threshold.” No safe level, in short. Both studies were later published in the journal Genetics, then edited by Curt Stern. But a key sentence published earlier, noting “the possibility of a tolerance dose for radiation,” was omitted.
In the Proceedings of the National Academy of Sciences last December, Calabrese wrote that the U.S. government’s “no threshold model” for the assessment of risk became the regulatory standard “as a result of ideological motivations and manipulations of the scientific literature at the highest possible level.” He was referring to Muller’s Nobel speech.
As to his political views, Muller was employed as a geneticist in the Soviet Union from 1933 to 1937. The experience is said to have cured him of his earlier Communist sympathies, but he remained a socialist. Elof Carlson’s biography of Muller notes that from the mid 1950s, Muller “favored a cessation of nuclear tests as a step to disarmament.”
In an email to me, Calabrese wrote that he has received some criticism for his remarks on Muller, but his critics “have not been able to attack any factual basis.”
For years, Calabrese has argued that low-level radiation not only does no harm, but is actually beneficial. There is much to support that claim, and the evidence for it was favorably reviewed by Science in 2003 [v. 302,
Since the 1960s, the Atomic Bomb Disease Institute of Nagasaki University kept records of approximately 120,000 survivors of the Nagasaki bombing, comparing their health with that of matched cohorts of unexposed Japanese. Conclusion: Low doses of atomic-bomb radiation increased the lifespan of atom-bomb survivors.
The world is constantly exposed to natural radiation—from uranium in the rocks, from radon gas, and from cosmic rays from outer space. Areas of high background radiation in the United States (the Rocky Mountain plateau) have cancer rates markedly lower than areas with low background radiation (the Mississippi Valley).
With the passage of time, as the half-lives of various radiation sources dwindle away, background radiation is constantly declining. Calabrese told me that we live in a “radiation-deficit environment.”