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Radiation and risk

By Jim Green - posted Friday, 8 April 2011


Wade Allison presents a benign picture of low-level radiation in his On Line Opinion piece yesterday. It's important to understand that his views are at odds with the overwhelming weight of scientific opinion.

The weight of scientific opinion holds that there is no threshold below which radiation poses no risk and that the risk is proportional to the dose − this is the 'linear no threshold' (LNT) model.

For example a US National Academy of Sciences panel, the Committee on the Biological Effects of Ionising Radiation (BEIR), comprehensively reviewed the evidence and concluded in its 2006 report: "The Committee judges that the balance of evidence from epidemiologic, animal and mechanistic studies tend to favor a simple proportionate relationship at low doses between radiation dose and cancer risk. ... [T]he risk of cancer proceeds in a linear fashion at lower doses without a threshold and ... the smallest dose has the potential to cause a small increase in risk to humans."

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The BEIR report noted that uncertainty remains: "It should be noted however, that even with the increased sensitivity the combined analyses are compatible with a range of possibilities, from a reduction of risk at low doses to risks twice those upon which current radiation protection recommendations are based."

That's an important point: there will always be uncertainty about the health effects of low-level radiation because it is an inherently complicated topic, but it's at least as likely that we're underestimating the risks as overestimating them.

A few scientists argue that low-level radiation is harmless or even beneficial. Their voice is greatly amplified by the nuclear industry. In Australia, for example, uranium mining and exploration companies such as Toro Energy, Uranium One and Heathgate Resources have funded speaking tours by overseas scientists who claim that low-level radiation exposure is harmless or beneficial. If the mining and exploration companies truly believe that claim, one wonders whether their OH&S procedures are up to scratch.

Now some applied science − the death toll from Chernobyl. Allison says that the latest UN report "confirms the known death toll − 28 fatalities among emergency workers, plus 15 fatal cases of child thyroid cancer", giving a total of 43 deaths.

In fact, Allison is misrepresenting the report of the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). This is what the report says: "The Committee has decided not to use models to project absolute numbers of effects in populations exposed to low radiation doses from the Chernobyl accident, because of unacceptable uncertainties in the predictions. It should be stressed that the approach outlined in no way contradicts the application of the LNT model for the purposes of radiation protection, where a cautious approach is conventionally and consciously applied."

So UNSCEAR cites "unacceptable uncertainties in the predictions" as its reason for shying away from an assessment of the impacts of widespread radiation exposure. The rest of us needn't be so shy. It's quite easy to do a ball-park estimate of the death toll from Chernobyl by using estimates of the total radiation exposure and multiplying by a standard risk estimate for fatal cancers from low-level radiation.

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The International Atomic Energy Agency estimates a total collective dose of 600,000 Sieverts over 50 years from Chernobyl fallout. A standard risk estimate from the International Commission on Radiological Protection is 0.05 fatal cancers per Sievert. Multiply those figures and we get an estimated 30,000 fatal cancers. Now let's recall that, according to the BEIR report, the LNT model may overstate risks or understate them by a factor of two. Thus the estimated death toll ranges from something less than 30,000, up to 60,000.

A number of studies apply that basic methodology − based on collective radiation doses and risk estimates − and come up with results varying from 9,000 to 93,000 deaths.

These debates will be rehashed in relation to Fukushima. We'll be told ad nauseum that few if any people died as a result of the nuclear disaster (though don't expect Ziggy Switkowski to repeat his claim that "the best place to be whenever there's an earthquake is at the perimeter of a nuclear plant because they are designed so well"). But to estimate the real impacts of Fukushima, we'll have to wait some months or years until we've got an estimate of the total radiation exposure, both direct and indirect via contaminated food and water.

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About the Author

Dr Jim Green is the national nuclear campaigner for Friends of the Earth and a member of the EnergyScience Coalition. His PhD thesis dealt with the history of the Lucas Heights nuclear plant and the debate over the replacement of its nuclear research reactor.

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