A DISPUTE between French and British researchers erupted last week over whether there is any scientific justification for lowering the maximum doses of radiation that nuclear workers should be exposed to.
In a report to the government unveiled at a parliamentary hearing in Paris, the French Academy of Sciences argues that neither the molecular nor epidemiological evidence justifies lowering the limits. The academy is now in conflict with recommendations made by the International Commission on Radiological Protection (lCRP) that the maximum dose should be reduced from 50 to 20 millisieverts a year for nuclear workers, and from 5 to 1 millisieverts a year for the public.
Maurice Tubiana, a member of the academy and one of the report鈥檚 authors, said that in the face of uncertainty about the health risks of low levels of ionising radiation, the ICRP has opted for extreme prudence. 鈥淏efore creating panic among the population we must take the precautions to validate these recommendations,鈥� he said. 鈥淚f this were to take a century I would say we shouldn鈥檛 wait but studies can be carried out in a few years. There is no urgency to change the limits.鈥�
Advertisement
Roger Clarke, president of the ICRP and director of Britain鈥檚 National Radiological Protection Board, told the hearing that the lower levels bring the occupational risks to nuclear workers into line with those accepted for other types of job. The lower limit for the public, he said, still represents a 鈥渇airly robust risk鈥� when added to natural background radiation.
According to the French report, there is no epidemiological evidence to suggest that cancer is caused by any dose of less than 200 millisieverts. It also rejects the ICRP鈥檚 method of estimating the risks of low doses by simply extrapolating from the high doses received by victims of the atom bombs dropped on Hiroshima and Nagasaki. This method leads to 鈥渁 notable overestimation of the risk鈥�, it says.
The academy鈥檚 scientists acknowledge that high doses of radiation do so much damage to DNA that cells cannot repair it, and cancer may follow. But, they say, enzymes in cells can easily mend the damage from low doses at low dose rates.
Roger Cox, head of biomedical effects at the NRPB, said that the damage done to DNA by radiation is qualitatively different from that induced by other hazards, such as chemical carcinogens and free radicals, and that the 鈥渃apacity of the cell to repair it is lower鈥�. The NRPB argues that even the tiniest exposure to radiation can trigger a DNA mutation capable of causing cancer.
Clarke said the uncertainty that exists over the level of risk from low radiation doses could be cleared up by new data from the Japanese study of survivors of Hiroshima and Nagasaki, due to be published soon. But he predicted that future risk estimates are unlikely to be 鈥渢oo different鈥� from today鈥檚.
Any lowering of the maximum dose limits could have big implications for Europe鈥檚 nuclear industry. The state-owned nuclear company, Electricit茅 de France, told the hearings that 580 of its workers will be exposed to more than 20 millisieverts this year. This is an improvement on 1992, when 1200 workers were over the limit. Laurent Stricker, a vice-president at EDF, said that the company will have to invest in robotics to further reduce radiation doses to employees.
In Britain, the ICRP鈥檚 recommendations have been widely anticipated and the Nuclear Installation Inspectorate already applies the lower dose limits when inspecting reactors. In 1993, only about a dozen nuclear workers received more than 20 millisieverts.