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Posts Tagged ‘Above the Fold’

Above the Fold with William Tucker: Bulletin of Atomic Scientists Returns to Low-Level Radiation

Monday, June 4th, 2012

Bulletin of Atomic Scientists Returns to Low-Level Radiation

By William Tucker

Nothing energizes the anti-nuclear movement more than the concern that exposure to low-level radiation is harmful and that nuclear power plants are emitting death rays that quietly spread cancer throughout the population.  

Those who remember the 1970s will not have forgotten Dr, John Gofman fulminating on late night television that "for every reactor that is built, babies die," or the ubiquitous Dr. Ernest Sternglass informing the public that every blip in cancer incidence that occurred around the country was the result of a radioactive cloud passing overhead months before,  

With the current revival of nuclear power, then, it is not surprising to find that the Bulletin of Atomic Scientists has decided to return to the issue of low-level exposures.  

The May/June edition contains a special forum of eight essays ranging across fields from the biology of the hypothesized "bystander" effect to the communications theory of why people fear nuclear reactors more than routine medical diagnoses.  Guest editor is Jan Beyea, former director of energy programs at the Audubon Society, moderates the discussion.  

In his introductory essay, Beyea begins with a simple but indisputable observation:  No one knows the effects of exposure to low-level radiation:  

"Though the debate takes on many shapes, it always revolved around one magical number: 0.1 Sieverts (Sv), the dividing line between what is considered high and low exposure today.  It is equivalent to about 40 cumulative years of the average unavoidable background radiation and to about 40 years of average medical diagnostic radiation in the United States.  And from this magical number, more disputes spring, specifically on the radiation risks below 0.1 SV, as well as the risks from protracted radiation exposure above and below this number.  The debates can be brutal – so much so that, at times, they make the spats between William Jennings Bryan and Clarence Darrow look lame.  

Long-term data from Japanese victims at Hiroshima and Nagasaki have confirmed a very clear, linear dose-response curve for cancer incidence down to 0.1 SV – the equivalent of 10 rems.  Below that, however, cancer incidence disappears into the general background levels in the population.  You might think the invisibility of any statistics would allay minds, but with such an important question as whether to build more nuclear plants nothing can be overlooked.  And so critics extrapolate the numbers right down to the lowest levels.  When these hypothetical rates are then projected across huge populations – the size of Europe, for instance – numbers can emerge that make for newspaper headlines.  

Beyea outlines four ways in which cancer incidence can be projected below the 0.1 Sv level: 

  1. The ratio of dose-to-response proceeds in a straight line down to zero, so there is "no safe dose of radiation," even though the effects may be so small as to be undetectable.
  2. The dose-response curve may proceed in a straight line until it reaches some "threshold," below which there is no danger.
  3. The adverse response may actually increase at lower levels due to a hypothetical phenomenon called the "bystander effect."
  4. Exposures at the lowest level may be beneficial, in that they act like a vaccine and stimulate the body's defense mechanisms against further radiation damage. This is the “hormetic” effect – a word that still does not appear in most dictionaries.

Beyea gives attention to all four possibilities but in the end decides that it doesn’t much matter.  Existing levels of exposure to radiation are already so high that any increment from nuclear sources becomes unacceptable under any circumstances:  

Given the increase in radiation from medical diagnostics and the interest in protracted exposure, the possible existence of a threshold or hormetic effect for public policy appears to be a moot issue for developed countries when it comes to future exposure. Even if the level of medical diagnostic exposures does not increase in the future, over the course of 40 years most people in developed countries will receive an average of 0.1 Sv from medical procedures alone.  With this in mind as a dose starting point for millions of people, it is fair to say that any exposure to radioactive elements from a nuclear accident or a dirty bomb would definitely contribute to their delayed cancer risk (emphasis added).  

The assumption behind this diagnosis, of course, is that the dangers of radiation exposure are cumulative and that being exposed to 10 rems from 40 years of background and medical exposures is the same as being exposed to 10 rems in a single burst from a nuclear accident or nuclear weapon.

Whether this assumption can be justified and where it leads in terms of public policy implications is something we’ll discuss in future columns.