#10 BBC Horizon: radiation risk and Chernobyl

This was a note written by Paul Seaman (www.paulseaman.com) as a July 2006  account by the BBC’s leading science programme of the different ways of thinking about and accounting for the death-doll from cancer caused by radiation. It helps show why different experts come to very different predictions of the scale of, for instance, the Chernobyl disaster. Trouble is (for those who’d like a simple life) it debunks “LNT” which is the underpinning theory of the low estimates of people like the Chernobyl Forum, and does so by arguing that these are way too high.

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The BBC’s Horizon has done excellent work debunking the scare stories surrounding low level radiation risk – the sort most people are frightened of on account of the Chernobyl accident in 1986.

Horizon, the BBC’s science flagship has – rather belatedly – reported research which suggests that low-level radiation is not a risk to humans. This should reassure people worried about the “victims” of Chernobyl and the danger posed by the rest of the nuclear power industry.

A recent BBC Horizon (http://news.bbc.co.uk/2/hi/science/nature/5173310.stm) questioned whether the Linear No Threshold (LNT) model that has formed the basis for assessing radiation risks in the nuclear industry since 1958 reflects the evidence we have observed since then. The programme suggested not, and if it’s right, it’s time at last to radically alter how we assess radiation risks.

This ought to matter to every man-jack of us: the dangers of civil nuclear power largely consist of low-level radiation risk. Over-estimate them, and fear stalks the land.

LNT has been a two-edged sword for those who argue that most “manmade” sources of radiation for most people add very little to what was already a low “natural” risk from radiation. On the one hand, it helped people understand that risk was dose-related (and very small where there was a small dose). On the other, however, it assumed (with little or no evidence) that there was no dose so low that it posed no risk whatever. It was, in short, a precautionary hypothesis rather than a scientifically proven one.

“When people hear of radiation they think of the atomic bomb and they think of thousands of deaths, and they think the Chernobyl reactor accident was equivalent to the atomic bombing in Japan which is absolutely untrue,” says Dr Mike Repacholi, a radiation scientist working at the World Health Organization (WHO). http://news.bbc.co.uk/2/hi/science/nature/5173310.stm

Nevertheless, the experience of the survivors of the atomic explosions in Nagasaki and Hiroshima in Japan had a major impact on radiological protection policy making. And therein lies the paradox. The atomic survivors mostly received a one-off high dose of radiation. However, doses received by victims of the Chernobyl accident – like those received by almost every “exposed” person in the world – were relatively low, on average not much higher than normal background radiation, and the exposure was more long lasting. As The Chernobyl Forum’s – http://www-ns.iaea.org/meetings/rw-summaries/chernobyl_forum.htm – chairman, Dr Burton Bennett puts it:

“The risk factor (effects or deaths per unit dose) was derived from other studies of exposed populations, e.g. the atomic-bomb survivors in Japan. The exposure circumstances and the background level of cancers in the Japanese population are different from the Chernobyl-affected population. This makes the validity of the estimation [ed’s note: from the Chernobyl Forum] quite uncertain. The projections do, however, provide rough, order-of-magnitude estimates that refute the speculation that there could be tens or even hundreds of thousands of deaths caused by radiation exposures. The doses were simply not high enough to elicit such consequences. This is quite definite.” http://www.chernobyllegacy.com/index.php?cat=3&sub=8&storyid=75

There can be no doubt that the LNT has helped discredit the more extreme claims made about radiation in general and the health consequences of the Chernobyl accident in particular. However the LNT is premised on the notion that all radiation carries a health risk. This notion has trapped people in fear, especially in areas of Belorussia and Ukraine which were much more affected by Chernobyl’s radiation than the rest of Europe. Hence it is important that we get a good scientific handle on the issue. http://www.timesonline.co.uk/article/0,,8122-2263204.html

At one extreme, Horizon pokes fun at how the LNT methodology is used to justify keeping 200,000 British sheep – located on hilly land – labelled too radioactive for human consumption as a consequence of the Chernobyl accident 20 years ago. What consumers are not generally told is that if they were to eat chops from these sheep every day for a year their additional annual radiation exposure would be equivalent to half of one dental x-ray.

More seriously, it is estimated elsewhere that in the USA, US$85 billion will be spent cleaning up the Hanford nuclear site to avoid low-level radioactive waste that may well pose no public health risk. And the public may also have been needlessly worried about the consequences of diagnostic x-rays and nuclear medicine to the detriment of their treatment and health. http://www.world-nuclear.org/sym/1998/cohen.htm

The LNT methodology produces seemingly bizarre predictions about the consequences of serious nuclear accidents. On the basis of the LNT it is posited that 90% of all deaths will result from low-level radiation sources. Put it another way: LNT generates an assumption that large numbers of people have been adversely affected, and does so on the basis that since they received a small increased dose of radiation, they must have been. Yet there is no evidence that most of these theoretical deaths relate to real people who can be expected to die or to develop any tangible illnesses. http://www.world-nuclear.org/sym/1998/cohen.htm

Today, the world’s radiological protection regulations are largely based on the recommendations of the International Commission on Radiological Protection (ICRP) which accepts the LNT hypothesis. Yet the epidemiological data from Chernobyl seems to contradict what the model predicts. The model says – and thus so do the official assessments from, for instance, the Chernobyl Forum – that there will be up to 4000 deaths among the most exposed group and a further 5000 deaths among the less affected but more numerous population living in contaminated regions.

This number is very low when compared with predictions by Greenpeace and many other campaigners and scientists (the last especially in Ukraine and Belorussia). But it may well be far too high.

There is a very serious argument which suggests that there are unlikely to be many future deaths from cancers caused by Chernobyl because we have probably already seen the vast majority of whatever cancers the accident caused.

For example, Dr Repacholi tells Horizon that leukaemia cases normally occur up to 10 years after radiation exposure. Moreover solid cancers should make themselves most apparent 20-to-25 years on from an exposure, and – twenty years out from the Chernobyl accident – there are no signs of them at all (the implication being that if they haven’t occurred in the rest of that timeframe they won’t occur at all). He concludes:

“We’re not going to get an epidemic of leukaemia… and, based on the exposure levels we’ve seen within these affected populations, we don’t expect an epidemic of solid cancers either.”

Horizon puts it more vividly: “Deaths directly attributable to radiation from Chernobyl currently stand at 56 – less than the weekly death toll on Britain’s roads… Scientists involved in the Forum expect the death toll to rise but not far….and these figures are hundreds of times lower than that based on the LNT” http://news.bbc.co.uk/2/hi/science/nature/5173310.stm

Horizon asks, what if the evidence actually suggests that radiation is not harmful below 100 millisieverts (mSv)? What if low doses could be proved to beneficial rather than harmful? http://www.awe.co.uk/main_site/scientific_and_technical/Factsheets/URR/index.html

There is strong evidence to suggest that low-level radiation is much less harmful than the LNT presupposes. There is other evidence to suggest that low-level radiation may have a positive impact on human and animal health. The programme-makers explore some strong examples.

Horizon highlights studies in the United States that show how background radiation varies by a factor of ten. Moreover they showed that the regions with the highest background radiation – such as Utah, Idaho and Colorado where it tops twice the national average – had the lowest frequency of cancer mortality rates. Commenting on this, Professor Antone L Brooks of Washington State University says, “if radiation is playing a role at all, it is not a big player.”

Airline crew, for example, receive on average 11 mSv per year, or equivalent to 1100 chest x-rays every year of their working lives.  While an aeroplane passenger flying at 35,000 feet, a typical height of an international flight, receives an equivalent annual dose of nearly 36 mSv per year or 20 times normal background levels. But there is no record of any increased cancer risk or birth defects among airline staff despite numerous studies designed to check if any link exists.

Horizon reports how a team of scientists visited Ramsar in Iran where natural background radiation is well in excess of 200 mSv per year. The team took blood samples from residents there and from their neighbours living in towns nearby with normal background radiation levels (world average 2.5 mSv). They subjected all the samples to 1.5 sieverts of radiation exposure: a very large dose. They then studied the chromosomal abnormalities that resulted. What they found, reports scientist Dr Andrew Karam of Rochester Institute of Technology, “was that people living in Ramsar had significantly fewer chromosomal abnormalities than their neighbours living a few kilometres away in areas where background radiation was normal”. (For comparison, the population evacuated after the Chernobyl accident received an average dose of between 17 mSv and 31 mSv in 1986 in Ukraine and Belarus respectively.)

Professor Ron Chesser of Texas Tech University, US, tells Horizon how he compared voles living around the stricken Reactor Four to another set of voles living elsewhere. He examined 100,000 cells from each animal in the two sets to see how much genetic damage – proportion of broken chromosomes – a lifetime’s exposure equivalent to 8, 000 chest x-rays per day had done to the voles living near Chernobyl. Surprisingly, he found no difference between them (the radioactive and non radioactive voles). In fact, after double checking his results, the Chernobyl voles were shown to have boosted those genes that protected them against cancer; this was evidence he was able to quantify.

“One of the thoughts that comes out of this is that prior exposure to low levels of radiation actually may have a beneficial effect,” Professor Chesser tells Horizon.

Fear certainly has few benefits. Tatiana and her daughter Allyona (phonetic) go back to Pripyat with the Horizon crew. The mother shows us where she lived in the town. For her the accident and subsequent evacuation was very traumatic because she was pregnant at the time. She recalls how women were put under heavy pressure to have abortions because hospital doctors argued Chernobyl’s radiation threatened their unborn children. She says, “there wasn’t enough room in the ward, so many had them (abortions) in the corridors.” Some two hundred thousand pressurised abortions were carried out immediately after the accident, according to Horizon. Tatiana was one of the few to resist. As she says this, she looks at her healthy 19-year-old daughter who is standing beside her, pauses, and starts crying.

“It is the fear of radiation that has caused a huge number of health complaints (rather than radiation) which has overloaded the healthcare system”, says Dr Repacholi. And in a memorable phrase the Horizon narrator refers to Chernobyl sending “a radiation plume of fear across Europe”. But it was the concluding words of Dr Karam which summed up my worries best: “If we continue to set risk estimates based on LNT what we are doing basically as society is accepting a myth and letting the myth set our energy policy.”

Whatever the truth of that view, the evidence certainly seems to suggest that the risk of low levels of radiation has been overstated. “The model was based on high doses and we just didn’t know what was going on at lower doses of between one and 200 millisieverts,” says Dr Repacholi. http://news.bbc.co.uk/2/hi/science/nature/5173310.stm

But, as Horizon demonstrated, we are beginning to have the epidemiology and the cause-and-effect science of low level radiation exposure. Indeed, it may be time to base our assumption on the reassuring factual evidence from Chernobyl rather than continue with old gloomy assumptions for Chernobyl which were based on flawed extrapolation from Hiroshima and Nagasaki.

People suffered in all kinds of ways as a result of Chernobyl. We need a fitting testimony to the radiation sickness of a very few, the thyroid cancer endured by thousands, and the anxiety of millions. How about honouring them by taking the facts of Chernobyl and using them to dump LNT?


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Publication date

02 December 2010


Mind & body