John Maddox explains an important, but scarcely noticed, EU-inspired change to radiation exposure rulesby John Maddox / March 20, 1997 / Leave a comment
A crucial change is on the way in the management of radiation hazards throughout the EU. Hitherto legislation on the subject has been based on the notion that there is some degree of exposure to radiation, or some “dose” of radiation below which no damage will be done. No longer. The essence of a European directive promulgated by the European commission on 13th May last year is that even small doses of radiation can increase the chance that a person exposed to it will at some stage develop cancer. European governments have four years in which to amend their legislation accordingly.
It is strange that this development has caused so little excitement. Forty years ago, when nuclear power stations were being built for the first time in several countries, the issue of whether there is a “threshold” quantity of radiation that can damage a person was one of the most contentious in the field. At the UN conference on nuclear energy in 1955, Admiral Lewis Strauss (pronounced “straws”), then chairman of the US Atomic Energy Commission, effectively created the concept of a “maximum permissible dose” of radiation, which has been the yardstick in most national legislation ever since. The “permissible” has now been dropped.
Plainly, the authorities have never been wholly wedded to the notion of a threshold. British legislation has always, for example, dealt separately with people registered as “radiation workers” and members of the “general public.” The permissible dose for the former has always been greater than that for the latter. That would be inconsistent with a belief that radiation doses less than some fixed amount are incapable of damaging a person’s health.
Accumulating evidence seems now to have thoroughly undermined the threshold notion, at least so far as the causation of cancer is concerned. Molecular biology has helped to make the case by confirming what had been suspected, that quite simple mutations of the DNA in body cells can become foci for the development of tumours. The clinching evidence seems to be the rate at which cancers have occurred among the survivors of the Hiroshima and Nagasaki bombs.
All this has been plain since 1991, when the body known as the International Commission on Radiological Protection (ICRP) issued its most recent recommendations. ICRP, which goes back 70 years, is a remarkable organisation. It is a self-perpetuating body of independent scientists, which is now registered as a charity under British law. Over the years, it has called the shots on radiological protection. Its influence stems from its acknowledged independence, and from never having put a foot wrong-yet.
There is no reason to believe it has done so on this occasion, but there will be lots of rows ahead. The practical difficulty is that the abolition of the doctrine of a threshold creates problems for the operators of nuclear plants, where some degree of exposure to radiation is unavoidable. (The technical term is “ionising radiation,” which excludes radiation from the Sun and domestic radiators, but includes X-rays and fast atomic particles such as those given off by radioactive substances.) What should they now use instead of “permissible” limits?
ICRP and the European commission have helped them out. The directive specifies numbers to replace the old limits, but also a new principle to determine how sources of ionising radiation should be managed. The objective is that exposure to radiation should be minimised, to which end there must be an “optimisation” procedure by which “all exposures shall be kept as low as reasonably achievable, economic and social factors being taken into account.” That is where the rows ahead will spring from.
The new numbers are not much of a surprise, although they have been tightened to allow for the data from the Japanese survivors. Technically, the dose to radiation workers cannot exceed 100 mSv in any consecutive period of five years, compared with the previous “permissible” limit of 50 mSv a year. (A “mSv” is a thousandth of the unit of radiation dose called a “Sievert”.) For the general public, the limit is 1 mSv a year, one fifth of the old limit.
At a conference the commission held in Luxembourg last year, these issues were spelled out clearly, but the response was rather muted. Perhaps the most plaintive question was that of a Spanish woman who asked how she could promise her constituents that this, the latest in a series of tightening regulations, would be the last.
In practice, some nuclear operators may have difficulties with the new numbers, but for the general public there should be little unease. A survey by the German Federal Radiation Protection Office (presented at the conference) shows that nuclear power is responsible for 3.7 per cent of the total radiation dose to which people have been exposed in 50 years. Natural radiation accounts for 80 per cent and medical diagnosis and treatment something like 20 per cent. But that will not still the argument that, if radiation in or from nuclear plants should be “as low as reasonably achievable,” why should it not be reduced to zero? The nuclear industry, not in the best of shape anywhere in Europe, is unlikely to welcome that further fight when governments get round to changing the law.