More on the Linear No Threshold model

  1. People have lived with far more radiation than Fukushima
  2. An inappropriate mathematical guess
  3. Even the World Health Organisation admits the debate.
  4. Japan’s government have just raised their safety limits to 20 mSv per year!
  5. But let’s assume the LNT was right
  6. Stop worrying about trititum
  7. Is radiation necessary for life?

1. People have lived with far more radiation than Fukushima

As we saw under “Chernobyl, Fukushima, Radiation – Oh my!”, the Fukushima exclusion zone has various measures of radiation, with the highest stating it gets 20 mSv / year. But some places are naturally bathed in 50 mSv a year, and Ramsar’s residents built homes out of the wrong limestone and lived with 131 mSv / year, and even 72 mSv / year “committed dose”with no measurable health problems.

2. An inappropriate mathematical guess

This graph shows the mere assumption that there is no safe level of radiation. We see people get sick or even die with high doses, but don’t really know what happens with tiny increases of radiation. So we make it up and run a mathematical model based not on medical observations, but mathematical games. I can play games like that as well. Say I found out Iwas going to get a million dollars tomorrow: I would plan to pay off my mortgage this week! But what if I became curious about how long it would take if I just got an extra dollar per day? How long would it take to pay off my mortgage? No matter how clever the model, it says nothing about whether or not in reality I’m going to get an extra dollar per day!

Radiations_at_low_dosesWe know that Sieverts of radiation is deadly. But what about an increase of just 20 ten-thousandths per year? (20 mSv / year). Well, here’s the graph that tells us. But does it really? This is an assumption that has not been scientifically proven, and field work seems to indicate contradictory results. Some effects, such as neurological damage in unborn babies, seems more serious than indicated by LNT. Some seems far, far less!

3. Even the World Health Organisation admits the debate!

Even the World Health Organisation admits the raging controversy over the LNT model, and says:


According to UNSCEAR (2000), 134 liquidators received radiation doses high enough to be diagnosed with acute radiation sickness (ARS). Among them, 28 persons died in 1986 due to ARS. Other liquidators have since died but their deaths could not necessarily be attributed to radiation exposure…. Although there is controversy about the magnitude of the cancer risk from exposure to low doses of radiation, the US National Academy of Sciences BEIR VII Committee, published in 2006, a comprehensive review of the scientific evidence, and concluded that the risk seems to continue in a linear fashion at lower doses without a threshold (this is called the “linear no-threshold” or LNT model). However, there are uncertainties concerning the magnitude of the effect, particularly at doses much lower than about 100 mSv.

The Expert Group concluded that there may be up to 4 000 additional cancer deaths among the three highest exposed groups over their lifetime (240 000 liquidators; 116 000 evacuees and the 270 000 residents of the SCZs). Since more than 120 000 people in these three groups may eventually die of cancer, the additional cancer deaths from radiation exposure correspond to 3-4% above the normal incidence of cancers from all causes.
World Health Organisation, April 2006

For even more organisations that utterly disagree with the model, please check the Linear No Threshold wiki.


4. Japan’s government have just raised their safety limits to 20 mSv per year!

But do the anti-nuclear activists admit this could be due to the latest scientific evidence? No, that might take away from their tinfoil-hat parade. Dr Helen Caldicott is a world famous anti-nuclear activist who has been screeching “There’s no safe level of radiation!” for decades. She established the Physicians for Social Responsibility, who no doubt mean well. But they cannot help themselves, and push paranoid conspiracy memes  like this:

In November 2011, the Japanese Science Ministry reported that long-lived radioactive cesium had contaminated 11,580 square miles (30,000 sq km) of the land surface of Japan.[i]  Some 4,500 square miles – an area almost the size of Connecticut – was found to have radiation levels that exceeded Japan’s allowable exposure rate of 1 mSV (millisievert) per year.

About a month after the disaster, on April 19, 2011, Japan chose to drastically increase its official “safe” radiation exposure levels[ii] from 1 mSv to 20 mSv per year – 20 times higher than the US exposure limit.  This allowed the Japanese government to downplay the dangers of the fallout and avoid evacuation of many badly contaminated areas.

20 times higher than the US exposure limit! Government downplaying dangers! Oh the conspiracy! Oh the humanity! Run for the hills! But as we have seen, there’s no evidence of increased cancer at many times the Japanese limit. Nature doesn’t care for these artificial limits at all, and hits us with many times the exposure with no discernible effect.

Once again, we see smart people writing stupid things. I have no doubt that the author at Physicians for Social Responsibility wants to help. But he’s influenced by FUD, Fear, Uncertainty, and Doubt. We just don’t have enough conclusive evidence on slightly increased levels of radiation. Indeed, there may even be evidence that small doses of radiation are good for us. Why ban abudant, cheap, safe, reliable nuclear power that runs reliably all through the night and winter, whatever the season, simply because of an emotional paranoia hard-wired into us from the Cold War?

5. But let’s assume the LNT is right

But not so fast! Let’s assume that Dr Helen Caldicott is right, and that one day science will catch up with her ‘methods’. Let’s assume that there is no safe level of radiation, and that even tiny doses give us tiny increases in cancer rates. (Even though George Monbiot has shown that Helen’s books are largely self-referencing and fraudulent). What if she’s right?

Pro-nuclear author Mark Lynas assumes the LNT model and goes on to explore what that might mean for the Japanese people.  It seems to be a choice between massive mental health issues for the evacuees, with all the associated depression and increased suicide risks, and a slight increase in possible cancer rates. Let’s remember that climate change is accelerating and could end up killing hundreds of millions or billions in worst case scenarios. Let’s also remember that medicine is galloping along towards a cure for cancer that could arrive in the next few decades. And let’s think mathematically, statistically, about large population groups and what is best for the nation. I’ll finish by handing you over to Mark.

For the purposes of argument, therefore, if everyone living in the exclusion zone (and other severely-contaminated areas) could be persuaded to give up driving (and to eschew smoking, which presents a massive lifetime risk of 100 in 1000 of causing lung cancer) then everyone could in theory be allowed to return with no additional loss of life to the impacts of radiation. The risks could simply be traded off each other. One could also make a strong case that people living in the Fukushima exclusion zone would still be better off statistically than those in heavily-polluted city centres, near coal-fired power stations and in industrial zones, which likely present higher carcinogenic risks.

Indeed, these risks were quantified and compared in a fascinating 2007 paper published in BMC Public Health journal (open access, h/t ColinG, [x]). In it the author looks at the comparative risks of obesity, smoking and exposure to radiation – in terms of ‘years of life lost’, a male smoker can expect to lose 10 years of life, an obese white male 1-4 years of life, as compared to an average 2.6 years of life lost for Japanese atomic bomb survivors who had experienced the highest doses (2.25 Gy – for gamma radiation such as released by an atomic bomb, sieverts and grays are roughly equivalent, so the dose can be thought of as 2,250 millisieverts; about ten times higher than current doses anywhere in the Fukushima exclusion zone).

An equally useful comparison made by the author considers whether air pollution in city centres, passive smoking or radiation contamination from the Chernobyl accident are more dangerous. He finds that living in a polluted city (e.g. London, as compared to lightly-polluted Inverness) yields 2.8% mortality (28 per 1000), passive smoking 1.7% mortality, whilst radiation exposure of 100 mSv in the Chernobyl zone yields a mortality risk of 0.4% (4 per 1000). This latter risk is clearly on the same scale as the US scientific committee which calculates a 3-7 per 1000 risk of mortality for 100 mSv, and obviously compares rather favourably with the 28 per 1000 mortality risk for living in a polluted area. This raises the intriguing possibility that – if these calculations are correct – lives would be saved by moving people out of central Tokyo and into the more contaminated areas of the Fukushima exclusion zone.

This is in fact exactly the conclusion reached by the paper’s author:

The increased mortality rate of the populations most affected by the Chernobyl accident may be comparable to (and possibly lower than) risks from elevated exposure to air pollution or environmental tobacco smoke. It is probably surprising to many (not least the affected populations themselves) that people still living unofficially in the abandoned lands around Chernobyl may actually have a lower health risk from radiation than they would have if they were exposed to the air pollution health risk in a large city such as nearby Kiev.

Of course, real people do not base their risk assessments on scientific numerical quantifications such as this. There are also ethical issues in that obesity or living in a polluted city can be considered a personal choice, whilst having a nearby nuclear power station suffer a triple meltdown is something imposed on a population not used to such a danger. But the trading-off of risk is unavoidable, and the experience of Chernobyl shows that permanent exclusion from their homes and communities is also extremely damaging to people’s health, and increases mortality rates from ‘lifestyle’ causes such as suicide, alcoholism and so on. In addition, when people are labelled ‘victims’ and told they are doomed to die of cancer, an increased number may indeed suffer a psychologically-induced ill-health.

Naturally it will be extremely difficult for the Japanese authorities to make a decision about how far to relax the exclusion zone that has been set up (though the process of reaching this decision has already been cautiously begun[xi]). People are terrified of radiation – far more terrified than they are of traditional sources and activities which present a much greater statistical risk of causing cancer – and the activities of anti-nuclear campaigners in the area has doubtless increased this sense of terror. It has also added to the distrust of experts in general and the government in particular, despite the need for decision-making to be based on a scientific approach to real risk rather than the terrors imagined by an already-traumatised population.

In the final assessment we also need to remember the wider catastrophe of March 11 of which the nuclear disaster is only a small part. More than 20,000 people died as a result of the tsunami, and none have so far died or been injured because of the events at Fukushima Daiichi. I hope also that the continuing media and official attention being given to the nuclear crisis does not distract from the needs of those displaced (also perhaps permanently), bereaved and traumatised by the tsunami. And, as I have argued elsewhere, it is equally important that the accident at Fukushima does not lead to a hasty abandonment of nuclear power both in Japan and other countries, resulting in a return to the vastly more dangerous energy source of coal. For the sake of all those affected by this desperately unfortunate sequence of events, the Japanese government must continue to take a rational approach to risk, build up the trust of its people and resist the demands of both media hysteria and ideological campaign groups.
Mark Lynas, August 2011

6. Stop worrying about trititum

There are many over-blown news stories screeching about tritium water leaking into the ocean, as if the whole world was getting poisoned. As the Environmental Protection Agency says:

“How does tritium affect people’s health? As with all ionizing radiation, exposure to tritium increases the risk of developing cancer. However, because it emits very low energy radiation and leaves the body relatively quickly, for a given amount of activity ingested, tritium is one of the least dangerous radionuclides. Since tritium is almost always found as water, it goes directly into soft tissues and organs. The associated dose to these tissues are generally uniform and dependent on the tissues’ water content.”

In other words, you can drink it and not die.

7. Is Radiation Necessary for Life?

It seems so. Recent studies on the biological effects of radiation carried out under radiation levels from natural background to essentially zero radiation, demonstrate that the absence of radiation is not good for organisms (Castillo et al., 2015).

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