Hermann Muller, the 1946 Nobel Prize winner in Physiology and Medicine, insisted that there was no threshold of risk from ionizing radiation. His opinion has had a long lasting influence on standards for radiation dose. He was wrong.
History is complicated. Influential people often impose their will with long-lasting results. The stories can be difficult to unravel, especially when the sources of information are buried away in boxed archives.
Dr. Edward Calabrese and his colleagues have engaged in serious documentation excavation efforts to find out what Hermann Muller knew about the genetic effects of radiation and when he knew it. They undertook this effort to try to unearth why Muller worked hard to establish an assumption that they they could not validate through their research.
Muller was influential because he had been awarded the 1946 Nobel Prize in Physiology or Medicine “for the discovery of the production of mutations by means of X-ray irradiation.” Later, Muller used his reputation to influence the radiation standard setting body to accept the linear no threshold dose response assumption without any serious questions about its scientific validity.
During his acceptance speech, Muller made the following statement about the genetic effects of radiation,
In our more recent work with Raychaudhuri (1939, 1940) these principles have been extended to total doses as low as 400 r, and rates as low as 0.01 r per minute, with gamma rays. They leave, we believe, no escape from the conclusion that there is no threshold dose, and that the individual mutations result from individual “hits”, producing genetic effects in their immediate neighborhood.
Unfortunately, the phrases in the quote above with minor emphasis do not actually support the phrase with the strong emphasis. 400 R (roughly 4 Sv if the dose is from gamma radiation) is a big dose, not a low dose. The current International Atomic Energy Agency standard used to determine if people should be allowed to live in an area that has been contaminated by radiation is 1/200th of that dose – 20 mSv/year. A dose rate of 0.01 R/min is also not a low dose rate; radiation workers take serious action to avoid an extended stay in a radiation field that is 6 mSv/hr (600 mrem/hr or 0.01 R/min).
If those doses and dose rates were the lowest that Muller investigated, there is still plenty of room for a threshold somewhere below those levels. One of Muller’s research associates – a man named Ernst Caspari – undertook a painstaking series of experiments using significantly lower doses and dose rates than those that Muller used in his groundbreaking work.
Caspari’s experiments used a population of 50,000 fruit flies. His results showed that below a certain dose and dose rate, irradiated flies had no more mutations than the control population. Below an even lower level, the irradiated flies had fewer mutations than the control group. Caspari sent Muller a paper documenting his results and explaining how they supported a threshold dose model about five weeks before Muller delivered his Nobel Prize lecture.
Caspari’s results did not get lost in the mail. Muller acknowledge the results within a week. His response indicates that he recognized their implication. However, since those results contradicted his assumptions, he demanded additional testing and verification.
Though his response and challenge to verify was understandable, that does not explain his decision to use the stage provided by his Nobel Prize award to make a definitive statement about the absence of a threshold for radiation effects. He had in his possession a credible study from one of his own associates that contradicted his assertion that there is “no escape from the conclusion that there is no threshold.” Caspari’s results provided an escape and a path to a different conclusion, namely that there is a threshold below which there is no damage.
There is a logically defensible explanation for a December 1946 decision by a politically active scientist to make a statement indicating that there is no safe dose of radiation. The most politically important discussion of the day within the scientific community was finding a way to influence government leaders to eliminate the threat of atomic weapons. The devastation at Hiroshima and Nagasaki were fresh in people’s minds. There was talk about how the US would base its future influence on maintaining a monopoly of the technology.
Dr. Muller spent a significant part of the next ten years working to eliminate nuclear weapons, with a special focus on halting widespread atmospheric testing. He pushed the genetics community to establish the linear dose response model as being the unquestioned consensus view. By 1956, when the BEAR (Biological Effects of Atomic Radiation) first met, it was a foregone conclusion that it would accept the linear dose hypothesis and change the basis for radiation regulation from the tolerance dose of 0.2 R/day (roughly 20 mSv/day for gamma radiation) established in 1934 to a model that assumes there is a finite risk from any excess radiation exposure, all the way down to a dose of zero.
That effort played a major role in generating public interest in fighting fallout. The doses from the testing were minuscule; other than a very few highly publicized incidents, there was no evidence of any public exposures that were even close to the existing dose limits. Muller and his colleagues knew that unless they could convince large numbers of the public that they were personally at risk, they would not be able to gain the support they needed to influence political leaders to stop the testing programs.
They desperately needed people to believe their assertion that “there is no safe dose of radiation” because only those people would be interested enough to organize protests and other political action campaigns.
I’ve known about this fascinating, but complex history for several months, but I had no way to share the raw material that documents the story in excruciating detail.
There’s now a way to point to the whole collection, starting with an introductory letter from Dr. Jerry Cuttler. Go to Submissions Received during Public Consultation of Discussion Paper DIS-13-01, Proposals to Amend the Radiation Protection Regulations (Warning: the document is an 18.7 MB PDF). Scroll to page 2. Under the heading of Individuals, look for Dr. Jerry Cuttler. His name is a clickable link that will take you directly to his submission, which includes several attached papers.
Dr. Calabrese published a lengthy explanation of his research through the scientific history in Archives of Toxicology. That paper, published in August of 2013 is titled How the US National Academy of Sciences misled the world community on cancer risk assessment: new findings challenge historical foundations of the linear dose response. (Starts on page 89 of the PDF document linked above.)
Perhaps unsurprisingly, the chair of the National Research Council of the US National Academy of Sciences did not like the title or the content of Dr. Calabrese’s paper and responded with a sharply worded letter. His letter was titled Letter from Ralph J Cicerone regarding Edward Calabrese’s paper published online first on August 4th: “how the US national academy of sciences misled the world community on cancer risk assessment: new findings challenge historical foundations of the linear dose response.” [DOI 10.1007/s00204‑013‑1105‑6, Review Article] (Starts on page 108 of the PDF document linked above.)
Here is an illuminating quote from Dr. Cicerone’s letter.
It distresses us to see this article’s accusations, with no actual supporting evidence, in a serious scientific journal. Drs. Muller and Stern are deceased and cannot defend themselves against these accusations. Both scientists were elected to our academy by their peers (Muller in 1931 and Stern in 1948) in recognition of their considerable scientific achievements, and Muller was honored with the 1946 Nobel Prize in Physiology and Medicine for his lifesaving work on the physiological and genetic effects of X-rays. In the 1950s, he joined his fellow scientists in warning the American people about the dangers of atomic war and fallout. With Linus Pauling, he worked to bring about a worldwide nuclear test ban treaty.
(Page 109 of the PDF document linked above.)
This quote supports Dr. Calabrese’s interpretation of the history. It exposes Muller’s heroic status within a certain segment of the scientific establishment and demonstrated that part of the basis for that status was Muller’s moral, well-intentioned effort to halt nuclear weapons testing by spreading fear-inducing information about the effects of “fallout.” From a scientific accuracy point of view, it is ironically accurate that Cicerone chose to link Muller with Linus Pauling, who was also a Nobel Prize winner. Pauling is the man who famously told everyone who would listen that massive doses of vitamin C would cure the common cold.
Dr. Calabrese was offered the opportunity to respond to Dr. Cicerone’s letter. He did so with a letter titled Response to Letter of Ralph J Cicerone and Kevin Crowley regarding “How the US National Academy of Sciences misled the world community on cancer risk assessment: new finding challenge historical foundations of the linear dose response.: [DOI 10.1007/s00204-013-110506, Review Article]. Here is a quote from the final paragraphs of that letter response.
“My article revealed that something seriously wrong occurred with the actions of Stern and Muller, leaders of the radiation genetics community. The failure of BEAR I Committee Genetics Panel to achieve its scientific mission of an objective and detailed appraisal of the scientific foundations of the dose response for mutation was also seriously wrong particularly given its societal importance. Yet, national leaders such as President Cicerone would prefer to protect the image of the NAS and the reputations of Stern and Muller rather than assessing objectively the foundations of the risk assessment scheme they created.
While President Cicerone claims that I have unfairly judged Stern and Muller, he is incorrect. The critical judgement emerges from their actions and words, as documented in open publications, now declassified publications and in publicly available private correspondence. The BEAR I Committee Genetics Panel did not study in detail the key papers upon which the decision on LNT was based, but relied upon the judgements of Stern and Muller. The NAS administration failed to properly vet the actions of this committee. The title of my article is appropriate and its content properly substantiated. It is there to be read by all.”
(Page 113 of the PDF document linked above.)
This story, which was hidden from the view of most people who do not have access to university libraries and their collections of peer-reviewed journals, is now more openly available. The documents and their extensive references are available for anyone who cares enough about the topic. I’ve read the documents and a sufficient number of the references be convinced that Calabrese and Cuttler are correct.
Before jumping in with contradictory opinions, please take the time to read the documents you want to challenge.