Low-Dose Radiation Risk: An On-Going Debate

“I believe that the nations of the world that are carrying out the tests of nuclear weapons are sacrificing the lives of hundreds of thousands of people now living and of hundreds of thousands of unborn children, and that this sacrifice is unnecessary.”

– Linus Pauling, No More War!, 1958.

The recent disaster in Japan has lent renewed relevance to the various risks associated with human exposure to nuclear radiation, a subject to which Linus Pauling dedicated a substantial amount of time and energy during his lifetime. It is in this context that we revisit the general estimates made by Linus Pauling in the 1950s concerning the long-term effects of radiation on human populations, and compare them to some modern estimates today.

In the years following the detonation of two atomic weapons during World War II, Pauling became increasingly active in the realm of nuclear policy, politics, and regulation. He attended conferences and addressed atomic issues in many of his speeches, but tackled the subject most thoroughly in his sixth published book, No More War! Released in 1958, No More War! covers a wide range of topics ranging from the physical aspects of atomic explosions to the need for international nuclear non-proliferation and test-ban agreements. Along with its expressions of concern about the certain devastation that would be wrought by wars fought with atomic weapons, the book addresses many of the health risks that result from human exposure to lower doses of radiation, particularly in relation to the test detonation of nuclear weapons in the atmosphere.

For the most part, there was and is little disagreement among professionals when discussing the effects of large doses of radiation on the human body. It is well established that, at certain levels, exposure to radiation in a single dose or over a specific period of time will lead to radiation sickness or death. However, the nuclear age has seen a much livelier debate over the effects that increased exposure to low doses of radiation might have on human populations over an extended period of time. Pauling was generally of the opinion that the fissionable materials released by the testing of atomic weapons was slowly contributing to a build up of human genetic defects – maladies that were attributable in large part to increases in average atmospheric radiation levels around the world.

The mainstream opinion of the time held that there was a particular radiation exposure threshold below which there was no likelihood of significant increases in the risk levels for particular illnesses such as leukemia and other forms of cancer. Pauling, however, believed that with every nuclear detonation, humans everywhere were being subjected to an unnecessary increase in risk of such illnesses, and that increases in incidences of illnesses worldwide could be measured in accordance with increases in environmental radiation. The disagreements that resulted from these interpretations led to conflict among several prominent scientists and scientific institutions; and Pauling, for one, was subsequently portrayed by critics as stubborn or simply unwilling to accept a largely agreed-upon establishment consensus.

Upon close examination, however, there generally appear to be more similarities between Pauling’s message and that of his opponents than there are differences, and the major differences that do exist often result from alternative interpretations of widely accepted data. Furthermore, Pauling, in his book, was ultimately willing to admit that though he considered it very unlikely that a threshold for dangerous levels of radiation exposure could exist, “There is also the possibility, which I consider to be a small one, that there is a threshold for radiation, below which no damage occurs.”

Aside from clashes concerning acceptable levels of radiation exposure, one of the greatest conflicts between Pauling and those employing a conflicting perspective (Edward Teller and the Atomic Energy Commission for example) was that of extrapolating the increased level of genetic abnormality that might result from heightened exposure to increased atmospheric radiation, and the prevalence of increased disease and disability among future generations attributable to damage in the human gene pool.

When discussing the link between radiation and heredity, a very important component of Pauling’s general argument was rooted in an excerpt from a report released by the Committee on Genetic Effects of Atomic Radiation.  As quoted in No More War!, it reads

Any radiation is genetically undesirable, since any radiation induces harmful mutations. Further, all presently available scientific information leads to the conclusion that the total harm is proportional to the total dose (that is, the total accumulated dose to the reproductive cells from the conception of the parents to the conception of the child).

The committee was, in effect, suggesting that any increase in radiation dosage, no matter how small, has the potential to detrimentally affect humans that come into contact with it, a point Pauling that emphasized. According to Pauling, every detonation of a nuclear weapon could be counted on to lead to a proportional increase in detrimental birth defects and a rise in radiation-related illnesses. Indeed, according to Pauling’s interpretation of estimates made by Dr. J. Laurence Kulp and other contemporaries, if nuclear testing was to be continued over a ten-year period at a rate similar to that maintained in the mid-1950s, 8,000 additional deaths would result every year from leukemia alone.

Generally, Pauling was of the opinion that increased risk of illnesses such as leukemia and bone cancer was proportional to exposure to increased levels of radiation above and beyond naturally occurring forms of background radiation. Pauling was also concerned with the potential for damage to the reproductive organs when subjected to increased levels of radiation, and the impact that this damage might portend for future generations of children. Likewise, Pauling expressed alarm for children exposed to heightened levels of radiation in utero.

One of the chief vulnerabilities of Pauling’s estimates was, of course, that for such large global effects, no pure control group could be monitored, since the counterfactual scenario to a nuclear detonation in the atmosphere would be that of no detonation. This particular aspect of Pauling’s argument made it much more difficult for some of his colleagues, associates and rivals to tolerate or accept his analysis.

---

As was the case at the time of No More War!‘s original publication in 1958, there exists today considerable debate over estimates of risks to humans from exposure to low doses of radiation. The most obvious difficulty in establishing a concrete estimate is that humans are constantly subjected to low doses of radiation on a daily basis, and calculating additional risk to human health in terms of increased exposure to comparatively low doses of additional radiation is very difficult.

One practical difficulty is the fact that there exist few groups that can be studied in a long-term setting who could reliably establish the presence or absence of health risks that result from increased exposure to radiation. This noted, during the previous century, various groups who had been exposed to heightened levels of radiation have been the subjects of long-term, multi-generational analysis.  Several additional studies have illuminated the issue more fully in recent years, allowing for the formation of conclusions that are a few steps beyond mere hypotheses.

One similarity between modern estimates of radiation risk and those issued during Pauling’s time is the notion that any increase in radiation exposure leads to increased risk. However, estimates of the level of increased risk are still debated, or rather not debated, since there exists a broad consensus that any such estimate will likely suffer from a general lack of statistical significance. While several studies have been conducted on populations exposed to heightened levels of radiation over time (among them the first generation of x-ray technicians, miners of radioactive minerals and workers at nuclear facilities), one of the most extensive and long-term studies conducted on an affected population with a significant control group was based in Japan following the Second World War.

In what has become a very long-term epidemiological study, survivors of the atomic bombings in Japan were monitored to assess the long-term health effects of exposure to wide ranges of radiation. The Radiation Effects Research Foundation (RERF), an offspring of the Atomic Bomb Casualty Commission, is still monitoring atom bomb survivors and their offspring, and the results of their research are frequently reported to government officials and the public, most recently in the journal Disaster Medicine and Public Health Preparedness. In their most recent report, RERF identifies a few trends that bear relevant connections to Pauling’s general argument, and that address some of his more potent fears.

In terms of genetic abnormalities being passed down genetically as a result of exposure to increased radiation, the recent report (Douple, et. al., 2011 5: S122-133S) concludes that this type of theorized trans-generational build-up of genetic defect has been largely unobserved. According to the Japanese data, children who are exposed to certain levels of radiation are themselves much likelier to develop harmful syndromes than are either children exposed in utero or the offspring of those who have been exposed but conceived at a date following exposure. In this respect, a portion of Pauling’s argument has been proven to be less grave than projected. On the same token, some of the RERF research suggests that survivors who have lived several years past their initial exposure were in fact more likely to contract an illness that can be attributed to radiation exposure, but the researchers admit that the variations between bomb survivors and their control group were much less extreme than had been expected.

While the conclusions reached by the RERF studies help to illuminate portions of the debate, they do not necessarily validate or contradict important aspects of Pauling’s argument, since they focus on the effects of a singular event as opposed to prolonged exposure to increased levels of low-dose radiation. More germane this component of the question is work conducted by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which has carried out studies similar to those of the RERF.

While having conducted work similar to the RERF group, UNSCEAR has also reported findings from an analysis of other populations that have been exposed to extended and chronic low-dose levels of radiation. In so doing, UNSCEAR admits to explicit difficulty in identifying a lifetime risk calculation for exposure to radiation. This is generally a result of “the lack of specificity in the type of characteristics of disease induced by radiation exposure, the long delay (years or decades) between exposure and disease presentation, and the high spontaneous incidence of diseases associated with radiation in the aging general population.”  In other words, just as was the case in the 1950s, the issue is simply a difficult one to confidently test and measure.

While the most recent report (2010 – PDF link, see p. 6) released by UNSCEAR suggests that increased exposure to low doses of radiation can increase the risk of developing cancer and other human illnesses, they are generally of the opinion that the excess risk, particularly with regard to cancer, is significantly smaller than are the risks posed by other factors.  They write

There is strong epidemiological evidence that exposure of humans to radiation at moderate and high levels can lead to excess incidence of solid tumours in many body organs and of leukaemia.  There is also growing information on the cellular/molecular mechanisms through which these cancers can arise.

Cancers are due to many causes, are frequently severe in humans, and are common, accounting for about one quarter of deaths in developed countries and a growing burden of deaths in developing countries…any increase in cancer incidence thought to be caused by low-dose radiation exposures is modest by comparison.

---

Despite several attempts to reach a meaningful conclusion, high margins of error and low levels of statistical significance have rendered modern professionals reluctant to develop strong opinions about the effects of low-dose radiation on human health.  Reports like those published by the UNSCEAR tend to be less alarmist than was Pauling’s stance, while still supporting his contention that even small increases in exposure to radiation can lead to detrimental health effects. As UNSCEAR puts it in its 2010 report, “even at low doses of radiation it is likely that there is a very small but non-zero chance of the production of DNA mutations that increase the risk of cancer developing.”

On the same token, some of the most common conclusions made by extended radiation health risk studies suggest that the carcinogenic effects of low-dose radiation exposure are less significant than is exposure to other health-deteriorating substances and practices. Smoking tobacco, for instance, is seen to increase incidences of lung cancer more than is common lung exposure to radon. In final analysis, while many professionals still regard any extrapolation that low-dose radiation deleteriously impacts human health as misleading or irresponsible, it is clear that the debate which surrounded Pauling and his risk estimates more than forty years ago is still strong and lively in the current scientific community.