In regulating nuclear energy to provide protection against radiation, most countries, including Canada, accept the recommendations of the International Commission on Radiological Protection (ICRP) on dose response and other matters. The ICRP consists of thirteen individual scientists with international reputations who are selected for their relevant expertise. The main Commission is assisted by permanent committees in four specialities, and various working groups as required.
In 1977 the ICRP enunciated three basic principles of radiological protection that have been widely endorsed by national regulatory agencies:
The first principle merely states the very understandable attitude that nobody wants to accept a risk, however small, unless there is some accompanying benefit to outweigh the risk. The essence of the last two principles is that exposures should not be minimized but optimized for the public benefit, considering technical, economic and social factors; and that there be an absolute limit to the allowable exposure for any individual however great the benefit to society at large. Some of the controversy over radiation exposures results from a common misquotation of the ALARA Principle by omitting the qualification "economic and social factors being taken into account". Not minimizing the risk may seem strange until one realizes that making any one sector much safer than others results in limited resources being unavailable to reduce greater risks in other sectors. The ALARA Principle has been incorporated in the Canadian Environmental Protection Act which allows companies to take into account social and economic factors in determining whether the goal of not releasing dangerous toxins in any measurable form is reasonable.
The current exposure limit recommended by the ICRP for the general public, under its Limitation Principle, is 1 mSv per year for the critical group, i.e., those individuals at greatest risk from a combination of exposure and susceptibility to radiation. This recommendation has been reduced several times since the ICRP was established in 1928. Most recently, in 1990, it was reduced from 5 to 1 mSv per year partly due to better information becoming available from monitoring Japanese bomb survivors but also as a result of recognizing changing perceptions of risk. These reductions in only half a century have been extrapolated by some critics to suggest that a few centuries hence the acceptable limit will be a small fraction of the present 1 mSv. However, this ignores the fact that the current limit is already less than the variation in exposures from natural sources across Canada, so that further reductions would achieve little, if anything.
The ICRP, because of its nature, restricted its principles to the potential harm from radiation, strictly ionizing radiation but, logically, the principles should be extended to include all risks, of which that from radiation is only one. It would be illogical and unethical to reduce the radiation risk to society or individuals if this were at the expense of increasing the overall risk.
In addition to the ICRP, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the U.S. National Academy of Science's committees on the Biological Effects of Ionizing Radiation (BEIR) are important in assessing technical publications in this area but, unlike the ICRP, they do not make recommendations on radiological protection. Although these three bodies are independent, and often differ on details, they are in broad agreement on the dose response for radiation in regulating radiation doses. They deduce this by extrapolating back from the high doses at which effects have been observed to the very low doses to which people are exposed from natural and man-made radiation, assuming that there would be no effect at zero dose.
The consensus is summarized in the Linear NonThreshold Hypothesis (LNTH) in which it is proposed that the risk of harm (fatal and non-fatal cancers and genetic defects) is linearly proportional to the dose, e.g., halve the dose and the risk is halved, but with some adjustment for the period over which the exposure occurs; and that there is no threshold dose below which the harm is zero. Numerically, the ICRP recommends that the risk of a fatal cancer be assumed to be 1 in 20,000 per millisievert, for a general population of all ages. Worded the other way round, it would take 20,000 mSv distributed through a population to cause one fatality. A mathematical consequence of the LNTH is that this predicted cancer is independent of how the dose is distributed in the population, e.g., it would be the same for 1 mSv to each of 20,000 people or 10 mSv to each of 2,000 people, or any other such combination. The product of the average dose and the number of people receiving it, 20 person.Sv is termed the collective dose or population dose. Other numerical factors are recommended for non-fatal cancers and genetic defects.
The ICRP's recommendations are just that, recommendations, but most national bodies responsible for nuclear regulation, including the Canadian Nuclear Safety Commission (CNSC) in Canada, have endorsed most of them in their regulations. However, the CNSC does not endorse ICRP recommendations automatically. Its own qualified staff review any recommendations and its Advisory Committee on Radiological Protection (ACRP), composed of independent individuals selected for their scientific expertise, provides additional input to decisions. (In 2001 the CNSC dissolved the ACRP and a complementary committee, the Advisory Committee on Nuclear Safety.) For instance, the CNSC, following extensive canvassing of opinions among those affected, issued a requirement limiting radiation exposures to pregnant workers that differed in significant detail from the ICRP recommendation on the subject.
The various expert bodies are often misquoted as saying that any radiation, however little, causes cancer. This is simply untrue. All values quoted for the risk of incurring cancer from doses around 1 mSv are theoretical, calculated estimates: there are no reliable observations of adverse health effects in humans exposed to radiation doses in this range. Given the normal incidence of cancer, and the very small probability of doses around 1 mSv to which people are regularly exposed causing any increase, it is impossible to prove or disprove the LNTH at this level. The hypothesis is not recommended as a fact but as a prudent assumption on which to base regulations for radiological protection.
Although the ICRP internationally and the CNSC in Canada consider the LNTH a reasonable basis on which to assess the risk from radiation and to frame regulations, there are some scientists who argue that it significantly overestimates the risk at doses around 1 mSv, and others who argue that it underestimates the risk. However, the claim that "Low-level radiation is more dangerous than high-level", often quoted by nuclear critics, is a distortion in omitting the vital qualification "per unit dose". At this level the argument is an academic one over relatively large differences but in very small risks. The reason that the argument continues unresolved is that the differences in absolute risk are so small that they cannot be measured in practice.
The ICRP's considered opinion in a 1977 publication was:
"However, the more cautious such an assumption of linearity is, the more important it becomes to realize that it may lead to an overestimate of the radiation risks, which in turn could result in the choice of alternatives that are more hazardous than practices involving radiation exposures. Thus, in the choice of alternative practices, radiation risk estimates should be used only with great caution and with explicit recognition of the possibility that the actual risk at low doses may be lower than that implied by a deliberately cautious assumption of proportionality."
Among those arguing that the LNTH overestimates the risk, Bernard Cohen is pre-eminent. He has assembled and analyzed a growing volume of epidemiological results that appear to show an effective threshold for adverse effects around the dose we all receive from natural sources (the background level); and that there may even be beneficial effects at these low doses. Research on bacteria has shown that colonies deprived of radiation dwindle, while those exposed to three times the natural level thrive. Mice exposed to very low levels of additional radiation lived longer and had fewer cancers than controls that experienced the natural level. In humans, multiple low doses of radiation in the treatment of leukemia have been found to enhance immune defense mechanisms and improve the chance of survival.
All this may seem incredible until one remembers that mankind has developed in radiation from the start, so that we have presumably adapted to it through the evolutionary process, just as we have adapted to ambient levels of temperature, pressure and oxygen concentration in the atmosphere. In other areas of biology, hormesis has been observed, i.e., when a living organism is subjected to a small biological stress a reaction is stimulated that serves to protect the organism against subsequent exposures to the same stress. Since radiation is just such a stress, the possibility of small doses proving beneficial is not out of the question.
Many members of the public opposing nuclear energy, apparently out of fear of radiation, cite one of the more vociferous critics, Rosalie Bertell. For many years she has been rejecting the recommendations of the ICRP, UNSCEAR and BEIR on the grounds that they are "dominated by physicists and medical administrators, most of whom headed their countries' nuclear research or regulatory agencies"; that they are male-dominated; and lack representation by epidemiologists and physicians trained in pediatrics. These criticisms ignore the composition of the subcommittees of the three bodies. Ironically, Dr. Bertell, whose doctorate is in mathematics, fails to mention that during the 1990s the President of Canada's CNSC, the regulatory agency that decides whether to endorse the ICRP's recommendations, was Dr. Agnes J. Bishop, former Professor and Head, Department of Pediatrics and Child Health, University of Manitoba.
Bertell considers that "the ICRP risk estimates are out of touch with reality" and, at a more technical level, she argues that it underestimates the actual risk by a factor of four at low doses. While it is possible that her risk estimates are valid, her criticisms of the ICRP, etc., imply an incredible international conspiracy involving many independent scientists. Judging by the continuing support for the ICRP's recommendations by national and international regulatory bodies, Bertell's criticisms have not been found convincing by well qualified scientists. Even representatives of the antinuclear organization Energy Probe relied on ICRP risk estimates in their submission to the 1985 Interfaith Program for Public Awareness of Nuclear Issues, ignoring Bertell's dissenting opinions expressed in another submission.
Bertell argues that radiation is responsible for several other adverse health effects, in addition to cancer and genetic defects, but she has again failed to convince most members of the health-sciences community. The most relevant evidence on this point comes from an international study of populations affected by the 1986 Chernobyl accident (Chapter 8). This found that:
"Psychosocial effects, believed to be unrelated to radiation exposure, resulted from the lack of information immediately after the accident, the stress and trauma of compulsory relocation to less contaminated areas, the breaking of social ties, and the fear that radiation exposure could cause health damage in the future."
and
"(Results show) a surprisingly high incidence of these symptoms (headaches, depression, fatigue and appetite loss), ... (but) not clearly related to whether people are living in 'contaminated' or 'uncontaminated' areas. These effects could be attributed to the accident itself or to economic hardship and social disruption in the region."
It is debatable whether blame for any adverse health effects resulting from a fear of radiation, in the Chernobyl populations and worldwide, should be laid on nuclear technology or on critics, like Bertell, who generate the fear that is generally believed to be ill-founded. Other reasons for questioning Bertell's claims are to be found in Chapter 13
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