ARE radioactive particles that get inside the body far more dangerous than current international models predict? The jury is still out. An expert committee set up by the British government to investigate this claim has made no progress towards resolving the issue, according to a preliminary report seen by 快猫短视频.
The committee, which includes environmentalists and nuclear industry representatives as well as academics, remains split along predictable lines. 鈥淪ome members are of the view that鈥urrent models underestimate internal radiation risks substantially,鈥� the report states. 鈥淪ome members are of the view that the current models tend to overestimate risks.鈥�
The 12 committee members will meet other experts to discuss the preliminary report next week. But there seems little hope of progress being made before the final report is due in 2004: 鈥淎ll members feel that further research is required but they wish to emphasise that this research is unlikely to resolve major areas of disagreement in the short term.鈥�
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If the risks posed by radioactive particles taken into the body are indeed being substantially underestimated, then the nuclear energy industry would struggle to reduce emissions to revised safe limits. The use of radioactive isotopes in medicine would have to be severely curtailed. But most researchers think that no major changes in regulations are needed.
However, there are reasons to believe that the radiation risks are far greater than current models predict. For example, around the Sellafield nuclear reprocessing plant in north-west England an unusually high number of children have leukaemia. The plant has discharged plutonium, caesium and strontium into the environment, which can be inhaled or swallowed. But there are far more cancers than the current risk models predict.
鈥淣obody has yet found enough radiation to explain the effect and that leaves you with a number of possibilities. One is that the risk assessment process is very severely flawed,鈥� says Dudley Goodhead, director of the MRC Radiation and Genome Stability Unit at Harwell, Oxfordshire, and chair of the Committee Examining Radiation Risks of Internal Emitters (CERRIE), set up in 2001.
The debate centres on the risk estimates set by the International Commission on Radiological Protection (ICRP), and used by governments around the world. It calculates what a safe dose is based on the impact that the radiation has on living tissue, so the dose depends both on the energy pumped into the tissue and on the type of radiation that the atoms emit.
Critics of the ICRP say the doses for internal emitters are not calculated correctly. Committee member Chris Busby, a scientist with environmental consultancy company Green Audit, has long argued that internal emitters give localised doses hundreds or thousands of times higher than ICRP models suggest. 鈥淵ou could sit by a fire and warm yourself, or you could swallow a hot coal and that would be the same dose [of heat],鈥� is the analogy he gives.
Few other members of the committee go as far as Busby, though several believe that the risks may well be underestimated. 鈥淚鈥檝e not seen any evidence that makes me think, gosh, we are getting these really wrong,鈥� says Sarah Darby, an epidemiology expert at the University of Oxford. She thinks that, at most, the doses are underestimated by a factor of ten. One theory about the Sellafield leukaemia cluster, for example, is that it is caused by viral infections brought in by workers.
But Busby thinks other members are ignoring evidence that certain radionuclides can be more damaging than others (see Table). For example, preliminary experiments suggest that strontium can bind to chromosomes, which would make DNA damage more likely, while tritium鈥檚 chemical influence causes mutations in the genome. Only further laboratory research can address these concerns.
鈥淚 insisted that both sides should be represented, and that they should thrash out their findings until they reached a consensus,鈥� says Michael Meacher, who set up the committee while he was the UK鈥檚 environment minister. 鈥淚f we haven鈥檛 got agreement then we have to go ahead with further research.鈥�