|Year : 2011 | Volume
| Issue : 2 | Page : 87-88
Can the LNT controversy ever be solved?
Ex. RSSD, BARC
|Date of Web Publication||12-Jul-2012|
Ex. RSSD, BARC
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pushparaja. Can the LNT controversy ever be solved?. Radiat Prot Environ 2011;34:87-8
It is unfortunate that an accident of significant magnitude occurred at Fukushima-Daiichi nuclear power plant in Japan on 11 March 2011. It was not the earthquake that has caused the reactor damage. The damage was caused by the post-earthquake tsunami water entering the reactor site, crippling the emergency power supply system, which resulted in non-availability of cooling water for the reactor fuel. Any additional radiation levels due to the accident will contribute only a very small amount to natural background radiation exposure of about 2.4 mSv received by all of us in a year. It is clinically not possible to detect any adverse health effects even up to the dose of 100 mSv.
In cases of accidents involving radiation or radioactivity, evacuation of the nearby population groups is a precautionary measure followed so that the members of the public will not accumulate radiation dose over a period of time.
The public outcry has resulted in Japan declaring closure of all nuclear plants for a while. For nuclear industry to survive, the fears and reservations against "nuclear" should be addressed by the stakeholders so that risks are presented in proper perspective for the public to understand. The communication should be simple without the use of words like "probability" or "Linear Non-Threshold" (LNT) hypothesis. The LNT model assumes a linear radiation dose-response relationship between the exposure to ionizing radiation and the risk of development of cancers in humans, without any threshold.
Thousands of cancer fatalities projected using the LNT assumption, post-Chernobyl, has not taken place so far indicating that the LNT theory projections have over-estimated the fatalities. Similarly, not a single death could be attributed to radiation dose due to the nuclear reactor accidents at Fukushima. The deaths that occurred in Fukushima were due to the tsunami, and hence should not be linked to radiation exposures. Although the low-level contaminations were wide-spread, the radiation doses to the public were of minor nature and are very small fractions of the dose required to cause any clinically detectable health effects.
The LNT model has been the assumption of the International Commission on Radiological Protection (ICRP), which provides the basic recommendations for radiation protection. The conservative assumption is made without much decisive scientific support. The possible cancer risk, at low doses (up to 100 mSv), was estimated by extrapolation from carcinogenic risks observed at high doses, i.e., in the range 200 to 3000 mSv - received by Japanese atomic bomb survivors. With the available animal and human data, it is very difficult to estimate or "see" relatively a very low increase in the incidence of cancer following the exposure to relatively low levels of radiation doses, in the presence of the larger numbers of natural incidences of cancer. Scientifically, how to justify such extrapolated values from the high exposure data generated from the Japanese atom bomb survivors?
The concern has been the health effect of low dose levels. This dose range (up to 100 mSv) covers the unavoidable natural background radiation (around 2 mSv/y), high radiation background areas (5 to 10 mSv/y), the occupational exposures received by the workers during normal operations of nuclear facilities (up to max. 20 mSv/y), action level for radon at home (10 mSv/y) and exposures received by patients during diagnostic procedures using radiation sources such as X-rays (0.1 mSv) and CT scans of different organs (1.5 to 20 mSv per scan).
The stakeholders (the concerned parties) like operators of nuclear facilities, the regulators, researchers in radiobiology and the scientific community related with radiation protection are divided on the issue of assumption of the LNT relationship for radiation protection. There is a feeling that the assumption is not justified fully by the available data in biological systems or in epidemiology. Although the assumption provides convenience of designing radiation protection programs (RPP) at operational levels, it provides undue importance for trivial, mathematically calculated risks in the above-said low-level exposure situations.
As everyone knows, cancer is an old-age disease, connected with the lifestyle, the diet, genetic factors, use of tobacco and alcohol, exposure to the environmental pollutants and many more, which include radiation. It is reported that over 40 people out of 100 are likely to be diagnosed with cancer from causes unrelated to radiation. As per the calculations, 1 more cancer is likely to result from the exposure to 100 mSv dose. Incidentally, this 100 mSv is also the maximum ICRP recommended radiation dose for 5 years' period for the occupational radiation workers.
Another concern from radiation in the public mind is from the genetic effects. There is no direct evidence that exposure of parents to radiation leads to excess heritable disease in offspring. It has been found to be not present in the macro level either in the progenies of Hiroshima and Nagasaki bomb victims or in the data from high background areas. Another set of data, which is not much stressed but which is available in literature, is the lack of such effects in the survivors of radiation therapy treatments.
Zero-risk situation, although ideal, is not attainable anywhere in any industry; hence, it cannot be an option. Using the actual exposure data, the calculated radiation risk of cancer fatality in the nuclear industry is much smaller compared with the risk of fatality in other industries such as chemical, metallurgical, construction, engineering and mining.
To bring the fatality risks in India in proper perspective: over 1.5 lakh deaths a year are reported due to accidents on Indian roads. Often, we miss near-deaths on the roads while walking, traveling by autos and crossing roads. Bhopal gas-leak tragedy, in the year 1984, killed over 3000 people, within days. Tobacco use kills about 6 million and alcohol 2.5 million a year, Over 9000 people died of recent tsunami floods in Japan.
The author is of the opinion that under such uncertainty about the calculated risk values at low dose levels, one should follow the actual experimental and scientific findings for determining dose-response relationship rather than assuming mathematically derived risk numbers for radiation protection and regulation. Emphasis should be on "optimization" as a tool for dose reduction in all exposure situations, including patient dose reduction in medical exposures. Keep exposures to radiation as low as reasonably achievable or practicable. All the protective measures should be justified and optimized.
What is so scary about radiation, which people find it difficult to accept, while all other risks at much larger levels are accepted easily by the public? The answer is improper and ineffective communication about "nuclear." The LNT controversy will go on!
| For Further Reading|| |
Pushparaja, Can the LNT Controversy Ever be Solved? Express Healthcare, July Issue, 2011.
Gopinath D.V., Radiation Effects, Linear No-Threshold Hypothesis and Nuclear power, BARC Newsletter, Issue No. 322 (Sept. - Oct.), 2011.
Iyer, M.R., Generic Effects of Radiation - Facts and Myths, Industrial Economist, November issue, p. 11, 2011.