Controversial change in radiation standards rejected

Nuclear Monitor Issue: 

(June 9, 2000) Proposals for a drastic change in the international regime of radiation standards were rejected at the May 2000 congress of the International Radiation Protection Association (IRPA) in Hiroshima, Japan. Members of the international rad protection community said the proposals would not resolve problems that exist in the current regime, and this could cause trouble among regulators and the public.

(531.5181) WISE Amsterdam - The proposals came from Roger Clarke, chairman of the International Commission on Radiological Protection (ICRP) (see also WISE News Communique 527.5151: Safety standards under threat in US & UK, and elsewhere?). In his proposals, among others, the principle of "Collective dose", the means by which a total dose to a population is measured, would be scrapped and replaced by a system of controlling the exposure of the most at risk. If those are protected, then so is everyone else. He also proposed to give up the present dose limits for individuals (in a lot of countries, this being 1 milliSievert a year) and replace it with "investigation levels" of a few milliSieverts and "action levels" at 20-30 milliSievert. According to Clarke, working with collective dose could lead to inequities in protection among individuals, i.e., a small group of individuals receiving a high dose of radiation does not necessarily result in a high collective dose. He would rather prefer a more individual approach. He came to his proposals as a consequence of the controversial discussion that low doses of radiation would be less harmful than presently assumed.

UNSCEAR rejects threshold believers. In a draft report by the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which contents were presented at the IRPA Conference, it is concluded that there is no scientific basis to discard the linear non-threshold model of radiation effects. According to UNSCEAR chairman Lars-Erik Holm, ongoing and future studies will not solve the uncertainties surrounding the effects of low-dose radiation. He thinks that "The statistical power is insufficient, and it is not scientifically valid to equate the absence of a statistically observable effect at low doses with the absence of risk". With this, UNSCEAR considers radiation guilty until proven innocent. UNSCEAR maintains its position that as long as single radiation racks can cause (double-stranded) DNA breaks, the cause of cell damage and cancer, the assumption of anything but a linear dose-effect relationship down to zero is unwarranted. The final conclusions of UNSCEAR are to be reported to the U.N. General Assembly this fall. Nucleonics Week, 1 June 2000

At the 10th International Congress of the IRPA, a lot of attention was drawn to the discussion about the effects of low-dose radiation. Dale Preston, chief statistician of the Radiation Effects Research Foundation, a Japan-US venture that has been studying the radiological consequences of the Hiroshima and Nagasaki bombings, said he had no reasons to doubt the existing Linear Non-Treshold (LNT) hypothesis, which assumes that any additional exposure to radiation leads to an equivalent additional risk. Other speakers claimed the contrary, i.e., that low doses would not be harmful or might even be beneficial (known as the "hormosis" phenomenon or "adaptive response").

The group of adaptive-response believers is opposed to the group of scientists that believe in the theory of genomic instability, a phenomenon in which a cell remains initially normal after being irradiated but later leads to chromosomal aberrations after several cell divisions. This phenomenon is the reason that a group of scientists plead for more stringent radiation standards. Both factions of scientists lay claim to scientific truth.

The proposal of Roger Clarke was discussed in the IRPA conference to seek the formal advice of the rad protection community before the ICRP itself adopts new recommendations. The IRPA conference actually showed that there was no basis to abandon the present system of separate public and worker dose limits, collective dose justification, and optimization. Representatives of major countries warned that the ICRP might lose its credibility if it dropped the dose limits that it had recommended in 1991.

Clarke's idea to introduce a "trivial risk" dose also faced criticism. IRPA members said that the public would not accept the idea of a trivial risk, and that regulators need numerical limits on which to base decisions.

Clarke said he would take IRPA members' suggestions back to ICRP's Main Commission for use in formulating new draft recommendations that would be put out for comment. A task group is expected to release a draft position paper by 2002. After a consultation period, new recommendations could be adopted in 2005.

Source: Nucleonics Week, 18 and 25 May 2000
Contact: Plutonium Action Hiroshima, P.O. Box 1, Konan Post Office, Hiroshima 739-1491, Japan Tel/fax: +81-82-828 2603