How dangerous is the Fukushima exclusion zone?

With the situation at the stricken reactors of Fukushima Daiichi nuclear power plant now relatively stable, the longest-term and most concerning aspect of the disaster in Japan is the exclusion zone, which has displaced thousands of people from their homes, villages and schools due to the danger of radiation. Needless to say, this is adding enormously to the misery and trauma of the earthquake and tsunami. In this article I examine what science can tell us about whether the exclusion zone is really needed, and how risky the radioactive fallout around Fukushima likely is in comparison to other dangers.

In recent days some anti-nuclear groups have been insisting that the evacuation zone should be expanded, that the situation is more dangerous than conventionally believed, and that official sources should not be trusted. This I believe flies in the face of the main lesson from the world’s worst civil nuclear disaster – Chernobyl in 1986 – which demonstrated convincingly that the fear of radiation, and the social and pyschological trauma suffered by irradiated ‘victims’ is at least as, and probably more, dangerous than the physical and biological impact of the radiation itself.

The expert report released by the Chernobyl Forum (comprising eight UN agencies, including the World Health Organisation, as well as the governments of Belarus, Ukraine and Russia) came to the following important conclusions:

Poverty, “lifestyle” diseases now rampant in the former Soviet Union and mental health problems pose a far greater threat to local communities than does radiation exposure. Relocation proved a “deeply traumatic experience” for some 350,000 people moved out of the affected areas. Although 116 000 were moved from the most heavily impacted area immediately after the accident, later relocations did little to reduce radiation exposure. Persistent myths and misperceptions about the threat of radiation have resulted in “paralyzing fatalism” among residents of affected areas.”[i]

In other words, as the Chernobyl Forum states, the mental health impact of Chernobyl was “the largest public health problem created by the accident” – a conclusion of great significance for Fukushima[ii]. In particular, this suggests that ideologically-motivated anti-nuclear campaign groups – some of which continue to stir up scientifically unwarranted fear of radiation in the affected Japanese population[iii] – may increase the trauma of the displaced people, and worsen their mental and physical health as a result. So far as I can tell, none of the campaign groups currently operating in the area, or those issuing wildly-inflated estimates of the likely eventual death toll, realise that their activities are likely to worsen the overall suffering of the Japanese people.

This is not to suggest that the levels of radiation now being measured in the exclusion zone, and some heavily-contaminated areas beyond, are inconsequential. In fact, the latest (August 7) radiation readings released by the Japanese ministry of science[iv] reveal that substantial radioactivity persists even outside the exclusion zone. At Iitate village, for example, which has some of the highest readings on the survey, a measurement of 133 millisieverts per year (mSv/yr) was taken. In general, most of the several dozen readings come in at the 1 to 10 mSv/yr range, though with the highest of all (at Namie town, 24km north-west of the stricken reactors) at 289 mSv/yr. (The Japanese authorities provide readings in microsieverts per hour, so to convert to millisieverts per year I have multiplied by 8760 and then divided by 1000.)

Here we need some context. What do these figures mean? On a global average we are all exposed to 2.4 mSv/yr of background radiation in the environment (though this varies geographically by an order of magnitude or more mainly depending on local geology), so for most of the exclusion zone around Fukushima, levels of radioactivity are only a few times higher than would naturally be expected. Even the Namie town readings are not unprecedented – in Ramsar, Iran, naturally-occurring radon in the surrounding areas leads to exposures as high as 250 mSv/yr for the local population, without any reported health effects[v].

Does this mean that everyone can forget about the radiation and return home? Not necessarily. The precautionary limits set internationally and by the Japanese government exist for a reason. The scientific consensus is that, as stated by the ‘linear no threshold’ hypothesis, there is no safe dose for radiation – so even a small increase in radioactive dose will lead to an equivalent small increase in cancer risk, and this risk needs to be properly considered in safety assessments. However, it also needs to be set against the risk of health impacts and other trauma suffered by people who are not allowed to return to their homes and suffer permanent displacement. Which risk is worse?

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, which can be considered a sort of IPCC for radiation risk science and reports to the UN General Assembly) concluded in 2010 in a report on ‘low-dose radiation effects on health’[vi] that a dose of 100 mSv (stated as 0.1 grays – we can consider grays and sieverts as roughly equivalent here) would lead to between 3 and 7 additional deaths from cancer per thousand people over their lifetimes. For leukaemia the additional lifetime risk is 0.3-0.5 additional deaths per thousand. So if the UN experts are correct, people moving back into heavily-irradiated zones like Iitate and Namie town can expect additional cancer mortality risks in this sort of range.

Another authoritative source, which also considers the ‘linear no threshold’ precautionary model to be the most scientifically-justified, is the 2006 US National Research Council report entitled ‘Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2’[vii]. The expert committee of authors calculates – based on their modelling work – that 10 people in 1000 would be expected to develop cancer (but not necessarily die from it) resulting from a dose 100 mSv above background. At a lower dose, of 10 mSv, the committee predicts an additional cancer incidence of 1 case per thousand. For context, about 420 people in a thousand (in this US case) will develop cancer anyway. This means that identifying additional radiation-induced cancers is statistically extremely challenging, and explains why multiple epidemiological studies have so far failed to find unambiguous evidence of increased cancer incidence at low doses even around Chernobyl (with the important exception of iodine-131-induced thyroid cancers).

So the scientific consensus currently is that the radioactivity released by the accident at Fukushima will very likely present a small additional lifetime risk of cancer for people whose homes are in the relatively high 10-100 mSv contamination range. Given that the contamination comes largely from caesium-137 (which has a half-life of about 30 years) this will persist for long enough to make permanent evacuation a worrying prospect. Think about it seriously: would you return to your home if doing so presented you with a one-in-a-thousand to one-in-a-hundred additional risk of cancer? This is the choice faced by the Japanese population and authorities.

The issue of relative risk is central to addressing this choice rationally. Many people around Chernobyl have decided that they would rather face an undefined (but potentially larger) additional risk and have unofficially returned to their homes already – rather than live miserable lives in permanent exile. We all face risk in everything we do, of course, and the additional risk presented by radiation is small in comparison both to the background statistical risk of getting cancer anyway. It should also be considered alongside the carcinogenic risks presented by other activities like smoking, consuming alcohol, eating a lot of meat and so on.

There are also risks presented by the voluntary exposure to radiation we subject ourselves to, where the small additional risk is considered lower than the potential medical benefit. A single CT whole-body scan gives an effective dose of 12 mSv, which – like any other radiation – adds a small amount to one’s lifetime risk of getting cancer. One scientific study on the subject estimates an additional cancer mortality risk of 0.8 in 1000 for a 45-year-old patient undergoing a CT scan [viii]. (An estimated 62 million CT scans are performed each year in the US, including 4 million on children[ix].) The study estimates that were the same adult to undergo annual CT scans until age 75 – giving them similar exposure to living in Fukushima-contaminated areas with radiation doses of 10mSv/yr – the additional risk of cancer mortality would be about 1.9%, or 19 in 1000. By comparison, an individual’s lifetime chance of dying in a traffic accident in the US is estimated at 1 in 77 (or 13 in 1000).

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.

[ii] http://www.iaea.org/Publications/Booklets/Chernobyl/chernobyl.pdf

[iii] http://planetark.org/wen/63102

[iv] http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/08/07/1309508_080718.pdf

[v] http://www.angelfire.com/mo/radioadaptive/ramsar.html

[vi] http://www.unscear.org/docs/reports/2010/UNSCEAR_2010_Report_M.pdf

[vii] http://www.nap.edu/catalog.php?record_id=11340

[viii] http://www.columbia.edu/~djb3/papers/radiol3.pdf

[ix] http://www.nejm.org/doi/full/10.1056/NEJMra072149

[x] http://www.biomedcentral.com/1471-2458/7/49

[xi] http://www.nisa.meti.go.jp/english/press/2011/08/en20110831-4-2.pdf