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Attitudes towards Radiation Protection
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IV. | The dose limits are not based on current and comprehensive review of scientific findings. |
The currently legal yearly exposure limit of 50 milli-Sievert (mSv) for radiation workers in Germany is based on the 1977 ICRP recommendation, which for its part was based on the assumption of the risk amounting to 100 cancer deaths per ten thousand person Sievert (see attitude III). Provided only a mean ten percent of the exposure limits is used up, a damage of only 0.5 additional cancer deaths could be calculated. The ICRP considered this acceptable compared to the death rate in other "safe" industries, where the accident-induced death rate was about one to two per ten thousand full-time workers per year. Following this concept, the protection of individuals at high risk working places in the nuclear industry was ignored.
A re-evaluation in the Eighties of the health consequences of the atomic bombing of Hiroshima and Nagasaki resulted in considerably higher detriments per dose unit than formerly estimated. Compared to earlier statements, the new cancer mortality rates were 7 to 15 times higher. Furthermore the observed effects were due to sparsely ionising radiation (gamma radiation), which was thought to have a negligible biological effectiveness the low-dose range. The data from the life span study of the atomic bomb survivors have another principle deficiency which underestimates the cancer risk. This is because the study was confined to those who survived the first 10 years after the bombing. All those who died before 1955 of cancer, infections and other diseases have not been accounted for. Therefore the studied population represents a selected group of people with better health perspectives than the average Japanese population..
In 1990 the ICRP deduced from these data a risk factor of 600 additional cancer deaths per ten thousand person Sievert, merely a six times higher radiation risk for nuclear workers than before. This divergence from the original results is scientifically incomprehensible. What is even less comprehensible is the fact that the ICRP lowered the exposure limits for radiation workers by a factor of only 2.5.
The radiation limits have also been defended since then on the basis that the number of cancer deaths to be expected would be so low as to remain statistically undetectable. This statement appeared to be refuted after the publication of two major studies in the early Nineties. Wing et al. found increased cancer death rates among 8,300 nuclear workers employed at the Oak Ridge nuclear research national laboratories [4]. The derived risk factors exceeded those of the ICRP by a factor of 10. Kendall and coworkers from the British National Radiological Protection Board presented the results of their combined epidemiological study covering 95,000 nuclear workers at the British nuclear establishment [5]. They also found cancer rates about twice as high as predicted by the ICRP calculations but considered their results to be compatible with the ICRP assessment.
The mean follow-up time in the Wing investigation was 26 years, and thus twice as long as in the British study. Since most cancer cases appear more than 20 years after exposure, the total number of excess cancer cases has not yet been registered in the British investigation. The importance of these investigations is in the fact that the detriments to health appeared after exposure doses well below the existing dose limits and that the original predictions of the ICRP proved to be wrong. The results found in nuclear workers were corroborated by observations after diagnostic x-ray exposure [6,7] and after radioactive contamination of the environment [8,9].
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V. | The real quantitative dimensions of detriments to health after low-dose exposure are not yet known. |
In quantifying the radiation effects, the present ICRP risk factors pretend a safety margin which was severely shaken by the observations made in the populations exposed to the fallout of the Chernobyl accident at the very latest. The expected increase in various forms of cancer was accompanied by a number of diseases previously not associated with radiation exposure. These included diabetes, circulatory problems, malfunctions of the nervous system, and a series of syndromes apparently due to lesions of the immune system. Other than in the case of the A-bomb survivors, these are consequences of chronic low-dose exposure to incorporated radionuclides.
While radiation protection used to be concerned mainly with the genetic consequences for future generations, genetic damage was now of less interest in the discussion on health effects of radiation exposure, due to the cancer cases observed in the A-bomb survivors. The extensive ignorance of the quantitative dimensions of genetic damage must not, however, allow these effects to be neglected. The fundamental possibility of mutations being induced even at very low doses is well established in radiation biology and the fact that such mutations can be passed on to future generations is an incalculable burden. The newly discovered genomic instability has recently revealed that not even the basic developmental mechanisms are known. Genomic instability refers to the observation that genetic changes do not appear in the immediate daughter cells of exposed cells but only after ten to fifteen cell generations. What consequences this may have for organisms cannot yet be predicted.
A further very strongly neglected problem in the debate on dose limits is presented by teratogenic radiation effects (those induced in utero), which lead to dysfunctions, malformations or premature death of the foetus. In the Hiroshima and Nagasaki population, brain damage and negative effects on intelligence development have been reported after very low exposure. The Chernobyl contamination has in reality produced a diverse spectrum of malformations.
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VI. | All radiation is not equivalent: The concept of the equivalent dose has failed. |
With the normative introduction of the equivalent dose into law, all kinds of ionizing radiation were to be made comparable and the dose was to be a measure of the level of damage independently of the way of production. Sparsely ionizing radiation (beta, gamma, X-rays) are given a radiation weighting factor of one, this means these different forms of radiation are presumably equal with regard to their relative biological effectiveness (RBE). The same energy absorption in the tissue, measured in joules per kilogram, would accordingly have the same biological effect.
The recommendations of the ICRP concerning radiation weighting factors do not represent reality, however. It is certified that the RBE of sparsely ionizing radiation - depending on the observed effect, kind of radiation and energy - may differ by a factor of up to 5. The largest and most important reference collective for radiation damage, the Japanese atomic bomb survivors, was exposed to an extremely high-energetic - and thus comparably low efficient - gamma radiation. The risk factors of the ICRP deduced from this collective would have to be tripled for usual situations of radiation exposure to X -rays and low-energy gamma rays for employees in nuclear industry.
A further serious problem arises from the action of densely ionizing radiation (alpha rays and neutrons) as compared to sparsely ionizing radiation. Alpha rays constitute particle radiation with an extremely short range in tissue, so that this type of radiation can affect people only after incorporation or on the skin. It is produced by natural decay of uranium and its daughter elements in the earth's crust (uranium-radium decay series) and by the transuranium elements (plutonium, americium, and others) produced by nuclear reactors and atomic bomb explosions. Epidemiological analyses of bone cancer incidences following radiation exposure by radium and of lung cancer after exposure to the natural noble gas radon exhibit an inverse dose and dose rate effect, i.e. at low doses and dose rates (dose per time), as they usually prevail at workplaces and through environmental contamination, the radiation effect per dose unit increases. This effect, too, has been ignored by the ICRP.
Neutrons as highly effective indirectly ionizing radiation have a penetration capacity comparable to that of X-rays and gamma rays. In the context of transports of used nuclear fuel in so-called CASTOR containers and in the debate on the radiation risk to flight personnel, the work of Kuni has come to the fore, revealing a significant underestimation of the effects of neutrons by the ICRP and in the radiation protection regulations [10]. Confirmation of Kuni's results can be seen, for example, in the elevated cancer rates among flight personnel, which cannot be explained by the ICRP assumptions [11,12,13].
Similar facts are borne out by several epidemiological findings after incorporation of naturally and artificially produced radionuclides. The dose factors for inhalation and ingestion of different radionuclides set by the German Ministry of Environmental Affairs fail to take adequate account of the individual differences and age of those exposed. For instance embryos, which are known to be extremely radiosensitive are not mentioned at all. In addition the calculated equivalent dose of incorporated radionuclides is a mean over a macroscopic tissue volume which does not reflect the complexity of the radiation effect in the microvolume of the cell.
In the vicinity of nuclear plants, cancer cases especially in small children have occurred worldwide time and again. The stereotypical declaration by bureaucracies and national radiation commissions used to be that no causal correlation to radioactivity may be deduced, since the dose - based on the concept of equivalent dose - would never be sufficient to have such an effect. This argument was also used in the case of Krümmel nuclear power plant, adjacent to the largest and most striking cluster of leukemia cases, according to an analysis by the German Childhood Cancer Registry in Mainz . Even members of an expert commission insisting on an analysis of possible radiation causes were accused by the official radiation protection commission of being scientifically incompetent. The radio-isotopes emitted by Krümmel nuclear power plant into the environment and regarded by the expert commission as causes of the leukemia cases were ignored or denied by the radiation protection commission of the German government, by whom an alternative explanation has yet to be offered.
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6th August 1998
Prof. Dr. Wolfgang Köhnlein,
Münster, FRG
President of the German Society for Radiation Protection
(Gesellschaft für Strahlenschutz e.V.)
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| http://www.gfstrahlenschutz.de/en/detmen3.htm Last Update: 15.02.1999 Responsible: Prof. Kuni, horst@kuni.org | Homepage Prof. Kuni |