However, as shown in the table below, many governments, banks, utilities and energy companies across the world have been pulling out of nuclear projects. Over 30 pull-outs are listed. One wonders if they know anything that the UK Government does not.

Nuclear Pull-outs since 2009: as of March 2013

The Symposium was quite a success with over 20 speakers, and about 400 people attending and another 4,300 watching from 650 cities all over the world via live webcasting. A permanent archive is available online at http://www.totalwebcasting.com/view/?id=hcf .

My talk on the source terms and expected health effects from Fukushima is available as a pdf. A previous post on March 3 contains my estimates of long term collective doses and expected fatal cancers arising near Fukushima. Link.

The quadruple-explosion, triple-meltdown accident at Fukushima Dai-ichi nuclear plant in Japan after March 11 2011 is the world’s second-worst nuclear disaster, after the 1986 Chernobyl catastrophe.

Fukushima’s second anniversary in March 2013 is an opportune moment to assess its likely long-term consequences, although the accident is by no means over given the precarious state of the four wrecked reactor buildings – especially the spent fuel pond at Unit 4.

The figure below (reproduced from the French Government’s Institut de Radioprotection et de Sûreté Nucléaire (IRSN 2011)) indicates the extent of the radioactive fallout from Fukushima’s explosions and gaseous emissions in areas near Fukushima. In addition, lower concentrations fell over other areas of Japan, over neighbouring countries and eventually circulating the Northern Hemisphere.

Exposure to radioactive fallout will result in radiation doses to the people living in these areas and this post will attempt to estimate future cancer deaths arising from these doses. Population doses are usually termed collective doses.

Estimating collective doses crucially depends on adherence to the Linear No Threshold (LNT) theory which assumes that radiation risks decline linearly with dose until zero dose is reached, ie there are small risks at very low doses well below background levels. Much evidence supports this view and the LNT is used by virtually all of the world’s radiation authorities including the ICRP, UK-HPA, US EPA, US NRC, BEIR VII, etc.

However UNSCEAR has recently attempted to limit the assessment of collective doses by recommending that doses below global average background levels (ie about 3 mSv per year) should be ignored. This follows the UNSCEAR chairman’s early suggestion that radiation exposure from the Fukushima nuclear accident would have no health effects (Dahl, 2011). I have examined and discounted these statements in a separate post. As we shall see, several studies have also ignored UNSCEAR’s recommendation and made collective dose estimates arising from Fukushima.

Initially this assessment is restricted to the population in Fukushima Prefecture as not enough information is yet available to estimate collective doses to other areas in Japan, to neighbouring countries and to the Northern hemisphere. However these collective doses will be considerable and should be added to the total for Fukushima Prefecture.

Initial Considerations

First, it is important to realise that air emissions from Fukushima are much more important, in terms of health effects, than Fukushima’s sea discharges. Therefore what follows is an examination of health effects from aerial emissions, ie from the radioactive fallout arising from Fukushima’s several plumes.

To gauge Fukushima’s impacts, it’s a good idea to compare them with Chernobyl’s impacts. The radioactive air emissions from Fukushima were about 3 to 5 times lower than those from Chernobyl apart from the inert gas, Xe-133. (A future post will examine source terms in more detail.)

In addition, it is estimated (Masson et al, 2011) that ~80% of Fukushima’s radioactive fallout fell over the Pacific Ocean whereas most of the radioactivity from Chernobyl fell on land. Also, collective radiation to workers and local populations appear to be lower from Fukushima compared with Chernobyl due to the better safety precautions taken after the Fukushima accident. (This is not to say that official Japanese actions were perfect, but they were better than their virtual absence at Chernobyl.) On the other hand, population densities in Japan are much greater than near Chernobyl. Overall, I shall conclude that Fukushima’s doses are about 10% those from Chernobyl, but this is a very approximate estimate.

In areas near Fukushima, most of the long-term dose to the public originates from Cs-134 and Cs-137 isotopes which fell from Fukushima’s plumes to the ground. These have longish half-lives (2 years for Cs-134 and 30 years for Cs-137) and they irradiate people with gamma and beta rays. This is called groundshine. Smaller doses originate from being immersed in the plume, from eating contaminated food and drinking contaminated water. In areas further away, the situation is reversed with most of the dose coming from ingestion and lesser amounts from groundshine.

Collective Doses and Future Cancer Deaths

Many studies have examined the emission, environmental transport and deposition of the radionuclides in Fukushima’s fallout using either observed datasets or chemical transport models or both. Takemura et al (2011), Masson et al (2011), Kinoshita et al (2011), Yasunari et al (2011), Stohl et al (2011), Morino et al (2011), and Sugiyama et al (2012).

However relatively few studies have estimated the likely levels of collective doses and future cancer deaths from the Fukushima releases. The early estimate by von Hippel (2011) was essentially a scoping study which scaled up doses from land areas contaminated with Cs-137 levels greater than 37 GBq per square kilometre. Nevertheless his estimate of about 1,000 deaths near Fukushima is consistent with later estimates.

Ten Hoeve and Jacobson (2012) [TH&J] used a more detailed global model to simulate the emissions, advection, decay, dissolution, aerosol–aerosol coagulation, aerosol–cloud coagulation, aerosol-nucleation scavenging, rainout, washout, and dry deposition of radionuclides from Fukushima’s fallout.

As the largest single source of radiation exposures to the public near Fukushima is from ground contamination, ie groundshine, they used a Cs-134 and Cs-137 ground contamination model to calculate doses. Their model assumed that these isotopes disappeared from the ground with a half life of 14 days, based on historical US measurements. Using this ground contamination-to-dose model plus the US EPA’s  dose-risk coefficient of 5.8% per person Sv, their central estimate was for 130 future cancer deaths with uncertainty bounds stretching from 15 to 1100 deaths, mostly in Japan.

However the later Beyea et al study (2012) spotted that the parameter value used TH&J’s study for radiocaesium weathering in soils was out of date. Instead of relying on older US data that tracked radioactivity only while resident on vegetation, Beyea et al pointed to a more recent study (Drozdovitch et al, 2007) on radiation exposures to the European population following Chernobyl. This study tracked radioactivity beyond residence time on vegetation to include its migration into soil, using a weathering attenuation factor with two half-life time constants of 2.4 years and 38 years – both considerably longer than 14 days used by TH&J.

This vital European weathering factor was obtained from an analysis of over 300 soil samples taken during 1987–1999 in areas of Russia (Drozdovitch et al, 2007), complemented with soil measurements of radiocaesium from weapons fallout in north-eastern US and Bavaria, Germany. Measurements in other land areas had similar findings.

This use of more up-to-date data should not be taken as a criticism of the TH&J study, because this is how science works. One uses the data known to the researchers and then corrects it with later data: this is normal. Indeed Beyea et al compliment the TH&J study for the depth of its detail, and for having the temerity to make collective dose estimates which other researchers have notably shied away from: I agree with their views.

Beyea et al’s Assessment

Beyea et al then made their own assessment of collective doses from Fukushima using the longer weathering factor to adjust the modelling results of TH&J.

It’s important to realise that the use of 2.4 and 38 year soil weathering half lives means that groundshine doses from Fukushima (and Chernobyl) last more than 70 years – ie a lifetime. Many scientists remain unaware of this implication but it is based on good evidence – see above. The dose consequences are shown in graphical form in figure 1 below (reproduced from Beyea et al, 2012) which shows that, after 75 years, the total collective dose from groundshine is about 6.5 times greater than the groundshine dose received in the first year. Unfortunately the recent second WHO (2013) report on the health risks from Fukushima used a factor of 2 and not 6.5: one of a number of deficiencies in its report.

Figure 1. Reproduced from Beyea et al, 2012. Cumulative external ground dose from Cs-134 and Cs-137 relative to first-year external ground dose, derived using equations in Beyea et al, 2012.

Beyea et al first assessed likely external doses from groundshine near Fukushima (ie ground contaminated with Cs134 and Cs-137) using the following assumptions –

(a) soil weathering attenuation with two exponentials (half-lives of 2.4 years and 38 years) to model the effect of caesium’s soil penetration on dose rate

(b) Cs-134 to Cs-137 Bq ratio = 0.9

(c) Cs-134 dose per disintegration 2.7 times greater than that for Cs-137

(d) dividing their collective doses from groundshine by 2 (range 1 to 4) to account for the effects of restrictions on food and water, and relocation.

(e) a shielding reduction factor of 0.28 (range 0.14 to 0.56).

For internal doses, the authors divided their estimated collective external ground dose by 3.3. They also divided their collective doses from ingestion by 2 (range 1 to 4) to account for the effects of restrictions on food and water, and relocation. After adding external and internal collective doses, the authors used the US EPA’s absolute risk of fatal cancer of 5.8% per Sv (ie incorporating a DDREF of 1.5) to convert from collective dose to future cancer deaths.

The net result was a mid-range estimate of 1,000 added cancer deaths instead of the 135 estimated by TH&J, with large uncertainties also being acknowledged.

My Own Estimates

In table A below, I estimate the cumulative population dose over 70 years from groundshine in Fukushima Prefecture based on tables 1 and 2 of the IRSN report (2011) (assuming a shielding factor of 0.65) as summarized in Beyea et al (2012).

Table A. Cumulative collective doses over 70 years to Fukushima Prefecture

*derived (by me) from an assumed first year average dose of 1 mSv to the rest of the population of Fukushima Prefecture x 6.5 for 70 years

** derived (by me) from the 2010 population in Fukushima = 2,030,000 less 360,000 in the previous dose categories = 1,670,000

Notes to Table A

1. Table A relies on 70 year life-time exposures from radiocaesium groundshine (as used by IRSN, 2011) as these dominate all other routes and sources of radiation exposure.

2. It only applies to Fukushima Prefecture: more collective doses will need to be added for the rest of Japan, neighbouring countries and the rest of the Northern Hemisphere when this data is made available. These added collective doses will be significant.

3. Groundshine doses do not take into account exposures from other exposure pathways, such as immersion within the Fukushima fallout plume, and internal contamination from inhalation of particles in the plume, as well as internal doses already received from contaminated food ingestion. These exposures are important in assessing first year doses, but less so for 70 year doses. Similarly, doses from the deposition of I-131 and other isotopes including tellurium-132/iodine-132, rhenium-103/rhodium-103, barium-140/lanthanum-140, and niobium-95 are not included: again these are important for early exposures, but less so for 70 year exposures.

4. My collective dose estimate partly depends on my assumption of a first-year average dose of 1 mSv to the rest of the population of Fukushima Prefecture from the Fukushima fallout. The 1 mSv figure comes from data from official reports of glass badge dosimeter surveys in Fukushima Prefecture townships, compiled by the independent radiation monitoring group Safecast in Japan. This introduces added uncertainty (range 0.5 to 2 mSv) but it is in only one of six dose categories.

5. Like Beyea et al, I assume that no evacuated people moved back into the evacuation zones. This is probably incorrect (ie collective doses could be higher) but we have no information as to how many people may have returned and/or when they returned.

6. To convert from collective doses to fatal cancers, I use the ICRP’s absolute fatal cancer risk of 10% per Sv: in other words I have not applied the dose and dose rate reduction factor (DDREF) used in the other dose assessments cited here. The use of a DDREF reduces the number of estimated fatal cancers in Europe by 2, and in the US by 1.5. However, as pointed out by Beyea (2012) many epidemiology studies offer little support for the use of such a factor, certainly for solid cancers (Little et al, 2008). Also, the recent WHO (2013) report on risks from Fukushima recommends that a DDREF should not be used for longer term exposures.

7. Considerable uncertainties surround my estimates. They should only be used as rough guides. Given the uncertainties involved for fatal cancers, only a single significant figure should be used, ie 3,000. This figure lies within the uncertainty range for Beyea et al’s main calculation.

Table B sets out various collective dose and fatal cancer estimates from the studies mentioned above.

 Table B. Published estimates of collective doses and fatal cancers

* pers comm from Jan Beyea

** NB the average shielding factor (0.28) used by Beyea et al was twice the value used by me (0.65), and Beyea et al allowed another factor of 2 reduction for evacuation and decontamination

*** 23,000 reduced to 6,000 assuming above two factors

Reasons for differences between Beyea et al’s and my estimate

The 9.7-fold difference in estimated cancer deaths between the Beyea et al ‘s estimate based on IRSN and myself is due to the following four factors:

(a) I include a collective dose estimate for people receiving doses below 41 mSv,ie increasing the collective doses by a factor of 1.43. Beyea et al did recognize and discuss the limitation in their calculations on this score.

(b) my shielding factor (0.65) is ie twice the central value used by Beyea et al (0.28),

(c) Beyea et al allow another factor of 2 reduction for decontamination in their mid-range calculation, although they state decontamination would only apply above a threshold dose and they questioned the efficiency of decontamination.

(d) Beyea et al use a risk factor of 5.8% per Sv and I use 10%, ie increasing the risk by a factor of 1.72.

Multiplying these four factors together (1.43 x 2 x 2 x 1.72= 9.8) accounts for the increase.

8. Table C for comparison sets out collective dose and fatal cancer estimates from Chernobyl’s fallout.

Table C: Chernobyl effects

The overall interim conclusion, based on incomplete data, is that estimated collective doses and fatal cancers from Fukushima are about an order of magnitude lower than those from Chernobyl.

I wish to thank Jan Beyea, Ed Lyman and Frank Hippel for their informative and helpful article (2012) which has been used extensively in preparing this post.

REFERENCES

Anspaugh LR, Catlin RJ, and Goldman M (1988) The Global Impact of the Chernobyl Reactor Accident. Science 242. pp 1513-1519.

Beyea J, E Lyman and F von Hippel (2013) Accounting for long-term doses in “Worldwide health effects of the Fukushima Daiichi nuclear accident” Energy Environ. Sci., 2013, Accepted Manuscript. DOI: 10.1039/C2EE24183H

Beyea J (2012) The Scientific Jigsaw Puzzle: Fitting the Pieces of the low-level radiation debate. Bull. Atomic Sci., 2012, 68, 13-28.

Cardis et al (2006) Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident. Int. J. Cancer, 119, 1224–1235.

Dahl F, U.N. expert sees no serious Fukushima health impact. Reuters, 18 April 2011. ^{http://www.reuters.com/article/2011/04/06/us-japan-nuclear-health-idUSTRE7354H920110406}

Drozdovitch et al (2007) Radiation exposure to the population of Europe following the Chernobyl accident. Radiat Prot Dosimetry (March 2007) 123(4): 515-528.

Fairlie I and Sumner D (2006) The Other Report on Chernobyl (TORCH): An independent scientific evaluation of the health-related effects of the Chernobyl nuclear disaster with critical analyses of recent IAEA/WHO reports. Commissioned by Rebecca Harms, MEP, Published by Greens/EFA in the European Parliament. April 2006. www.chernobylreport.org

IRSN (2011) Assessment on the 66th day of projected external doses for populations living in the north-west fallout zone of the Fukushima nuclear accident – outcome of population evacuation measures, draft Report DRPH/2011-10. L’Institut de Radioprotection et de Sûreté Nucléaire. http://www.irsn.fr/EN/news/Documents/IRSN-Fukushima-Report-DRPH-23052011.pdf

Kinoshita et al (2011) Assessment of individual radionuclide distributions from the Fukushima nuclear accident covering central-east Japan. Proc. Natl. Acad. Sci. USA,108, 19526–19529.

Little MP, Hoel DG, Molitor J, Boice JD, Wakeford R, Muirhead CR (2008) New models for evaluation of radiation-induced lifetime cancer risk and its uncertainty employed in the UNSCEAR 2006 report. Radiat Res 2008 Jun;169(6):660-76. doi: 10.1667/RR1091.1.

Masson et al (2011) Tracking of Airborne Radionuclides from the Damaged Fukushima Dai-Ichi Nuclear Reactors by European Networks. Environ. Sci. Technol. 2011, 45, 7670–7677. http://pubs.acs.org/toc/esthag/45/18

Morino et al (2011) Atmospheric behaviour, deposition, and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011.Geophys. Res. Lett.,38, L00G11.

Stohl et al (2011) Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition Atmos. Chem. Phys. Discuss., 11, 28319–28394.

Sugiyama et al (2012) Atmospheric Dispersion Modeling: Challenges of the Fukushima Daiichi Response. Health Phys, 102, 493–508.

Takemura T, Nakamura H, and Nakajima T (2011) Tracing airborne particles after Japan’s nuclear plant explosion. EOS Transactions American Geophysical Union, 92, 397-398, doi:10.1029/2011EO450002.

Ten Hoeve JE and Jacobson MZ (2012) Worldwide health effects of the Fukushima Daiichi nuclear accident. Energy Environ. Sci., 2012, 5, 8743-8757.

UNSCEAR (2012) Supplement No. 46 (UN document A/67/46, 14 August 2012) http://daccess-dds-ny.un.org/doc/UNDOC/GEN/V12/553/85/PDF/V1255385.pdf?OpenElement

von Hippel F (2011) The radiological and psychological consequences of the Fukushima Daiichi accident. Bulletin of the Atomic Scientists. 67, 27–36.

WHO (2012) Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan earthquake and tsunami. (www.who.int)

WHO (2013) Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami. http://apps.who.int/iris/bitstream/10665/78218/1/9789241505130_eng.pdf

Yasunari et al (2011) Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident Proc. Natl. Acad. Sci. USA 108, 19530–19534.

This is an INITIAL quick assessment in response to several queries. A more detailed view will be posted later.

1. Main findings

The report assessed that leukaemia risks from Fukushima were increased by 5% over the background risk  in males exposed as infants in the highest exposure areas,  similar to the increased risk of breast cancer in girls exposed as infants. For all solid cancers, a maximum relative increase of about 4% was estimated.

The report stated that no increase in the incidence of spontaneous abortions, miscarriages, perinatal mortality, congenital malformations, developmental abnormalities or cognitive impairment was expected as a result of in utero radiation exposure at Fukushima.

Also in the most contaminated area, there was a 70% higher risk of females exposed as infants developing thyroid cancer over their lifetime, cf males.

2. Collective Doses

Despite the report containing some useful information (and some good members on its expert team) it fails in what should have been its most important task –  ie to calculate collective doses to the people of Fukushima, to the people of Japan and to the people of the Northern hemisphere from the Fukushima accident. Indeed the phrase “collective dose” does not appear in the report.

Instead the report states

In my initial view, these appear pretty thin excuses. It compares badly for example with the previous 2005 WHO report on the health effects from Chernobyl which did contain collective doses.

Not only does the report not contain population doses, it appears to have been designed to prevent independent readers and scientists from doing their own calculations. For example, it tries to blind people with science by giving lots of estimates on organ doses (tables 4 and 5) but none on whole body doses, and lots of worker data (tables 6,7,8,9) but relatively little on public doses.

3. Long Term vs Short Term Doses

In estimating doses to the public from Fukushima’s fallout, a crucial factor is the ratio of doses over the long term (ie 70 years) to the first year estimated dose. This in turn depends on the doses from groundshine emanating from Cs-134 and Cs-137 deposited on the ground from the several Fukushima plumes, and how long these isotopes will stay in the soil and irradiate people.

In an early report, the French Government’s IRSN (2011) on Fukushima’s health effects used a ratio of 8.2.  That is, one should multiply the first year dose by 8.2 to get the whole lifetime dose:  clearly,  an important factor in estimating doses from Fukushima. A more recent independent report (Beyea et al, 2012) estimated (from post-Chernobyl Russian soil data) that the ratio should be about 6.5.  However the WHO report chose to multiply first year doses by a factor of 2 rather than 6.5 or 8.2, citing the 2011 UNSCEAR report in support. See pages 41 ff of the WHO report.

In other words, large differences exist in dose assessment methodologies. So who is right?  My money would be on IRSN and Beyea et al, but more time is needed to obtain the original Russian reports and translate them. More later.

4. Dose and dose rate effectiveness factor

The report contains one very useful recognition. It recommends that long term radiation risks should NOT continue to be halved by applying a Dose and Dose Rate Effectiveness Factor (DDREF). This is a major step forward, and the WHO expert team should be congratulated on its recommendation. It stated

The result of this change is that in future when one estimates risks from assessed doses, these risks will be double what they used to be when a DDREF of 2 was applied. (For US readers, BEIR VII and the US EPA had recommended dividing radiation risks by a DDREF of 1.5 rather than 2. Therefore, in future, estimated US risks will be increased by 1.5).

More later.

It is stressed again these are only initial quick comments.

References:

Beyea J, E Lyman and F von Hippel (2013) Accounting for long-term doses in “Worldwide health effects of the Fukushima Daiichi nuclear accident” Energy Environ. Sci. Accepted Manuscript. http://pubs.rsc.org | DOI: 10.1039/C2EE24183H

IRSN (2011) Assessment on the 66th day of projected external doses for populations living in the north-west fallout zone of the Fukushima nuclear accident – outcome of population evacuation measures, draft Report DRPH/2011-10: http://www.irsn.fr/EN/news/Documents/IRSN-Fukushima-Report-DRPH-23052011.pdf, L’Institut de Radioprotection et de Sûreté Nucléaire

The second anniversary of the Fukushima accident in March 2013 is an opportune moment to assess its likely long-term consequences in terms of future cancer deaths arising from Fukushima’s fallout. The diagram below shows fallout patterns in areas near the Fukushima Dai-ichi nuclear plant.

However, a number of official bodies appear to have decided on a policy not to estimate most collective doses from the Fukushima nuclear accident.

For example, the first draft of the French Government’s Institut de Radioprotection et de Sûreté Nucléaire (IRSN 2011) on Fukushima’s effects contained various collective dose estimates, but these were all deleted from its final version. (Readers who wish to see a copy of IRSN’s draft version should contact me.)

Second, the recent official WHO report (2012) on Fukushima doses surprisingly contains no collective dose estimates, despite its research team containing several scientists who have previously published collective dose estimates.

These changed views appear at the same time as the publication of UNSCEAR’s recent Supplement No. 46 (UN document A/67/46) (2012) which sets out UNSCEAR’s rationale for this policy. Section (f) of paragraph 25 on page 10 of the report, states

“(f) In general, increases in the incidence of health effects in populations cannot be attributed reliably to chronic exposure to radiation at levels that are typical of the global average background levels of radiation. This is because of the uncertainties associated with the assessment of risks at low doses, the current absence of radiation-specific biomarkers for health effects and the insufficient statistical power of epidemiological studies. Therefore, the Scientific Committee does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels;”

Just to be sure that readers have grasped this, the main point is that UNSCEAR has changed its policy and now does not recommend estimating collective doses (including those from nuclear accidents) where the average dose to a population is the same as, or below, about 3 mSv per year.

This new policy has adverse implications for the assessment of radiological accidents, because the majority of the doses to populations will occur at doses lower than 3 mSv. UNSCEAR now says in effect you don’t have to count them.

This is a potentially retrograde step, therefore we examine the above UNSCEAR’s paragraph. As we shall see, it does not stand up to scrutiny, as it is either incorrect or misleading on just about every point.

UNSCEAR’S POOR RATIONALE

First, UNSCEAR alleges that increased adverse health effects cannot be attributed reliably to chronic exposures at background levels. But several very reliable studies at background levels show precisely that. For example, several studies have estimated that 15% to 20% of childhood leukemias are caused by background radiation. Others show effects from exposures to indoor radon.

Second, it tries to justify its recommendation by the presence of uncertainties in risk estimates at low doses. This is a weak excuse. Uncertainties exist here for sure, just as they do in practically every epidemiology report or radiation biology study, but these should not be used to justify sweeping exclusions in assessing the population effects of radiation exposures. For example, the Precautionary Principle states scientific uncertainty should not be used as an excuse for inaction (see Kriebel et al 2001). At the least, uncertainty bounds could and should be added to such estimates.

Third, it alleges that there are no radiation-specific biomarkers for health effects, but acute lymphoblastic leukemia in infants is arguably such a biomarker.

Fourth, it raises the perennial excuse – insufficient statistical power of epidemiological studies. Wrong again: many new studies are remarkable, precisely because of their large sizes and strong statistical power.

Fifth, UNSCEAR’s new policy, in effect, states that radiation exposures below background levels of about 3 mSv per year need not be considered. This is misleading as it plays upon the public’s misconception that “natural” background levels are safe. They may be natural  but they are not safe. Some scientists think it is unreasonable of UNSCEAR’s Scientific Committee to rely on this wrong perception by lay people.

In Defence of Collective Dose

Where a population has been exposed to radioactive fallout, population doses are derived by multiplying their average dose with the population number. These doses are often termed collective doses.

The concept of collective dose was developed in the 1970s and 1980s by a world famous radiation biologist, Professor Bo Lindell, former chairman and emeritus member of ICRP and former chairman of UNSCEAR’s scientific committee (Valentin, 1995). UNSCEAR’s recent statement amounts to an abrogation and partial denial of Lindell’s famous work. Several strong reasons, both practical and theoretical, exist for estimating collective doses. These are too detailed to be discussed here but they were set out by Fairlie and Sumner (2000) and more recently explored by Thompson (2012).

The Linear No Threshold (LNT) theory

The strongest argument for collective doses and against UNSCEAR’s new stance lies in the Linear No Threshold (LNT) theory of radiation. This states that there is no level of radiation without risk apart from zero: very small risks exist at tiny levels even below background levels.

As regular readers will be aware, the LNT model is opposed by advocates of nuclear power, but the latest available evidence for the LNT– both in practice (ie epidemiology studies) and in radiation biology theory – is very strong and has not been disproven.

Most important, UNSCEAR’s changed policy amounts to a partial repudiation of the LNT. But the LNT is vital for radiation protection, because most, if not all, of our concepts in radiation protection rely on the LNT theory. For example, LNT allows radiation doses to be (i) averaged within an organ or tissue, (ii) added from different organs, and (iii) added over time. It underpins the concepts of absorbed dose, effective dose, committed dose, and the use of dose coefficients.

LNT also permits the ICRP principle of limitation – ie annual dose limits/constraints; the ICRP principle of optimization -ie the comparison of practices; radiation risk assessment at low and very low doses; individual dosimetry with passive detectors; the use of collective dose, and the use of dose registers over long periods of time. In fact, the LNT underpins all legal regulations in radiation protection. Indeed if the LNT were not used, it’s hard to imagine our current radiation protection systems existing at all.

But UNSCEAR’s new policy amounts to a partial repudiation of the LNT. This is bad science, as it’s poor scientific practice to accept bits of a theory that you like and reject bits you don’t like.

In Contradiction to Official Policies in Some Countries

UNSCEAR’s apparent new policy is strange as it contradicts official policies in some countries. For example, the UK’s Environment Agency and other UK regulatory agencies have set out principles for assessing radiation doses to the public (Environment Agency et al, 2012). These include Principle 12 which states “For permitting or authorisation purposes, collective doses to the populations of UK, Europe and the World, truncated at 500 years, should be estimated.”  The important point here is that doses from nuclide discharges to European and World populations will be very small and well below background levels. Yet Principle 12 states these are to be assessed, contrary to UNSCEAR’s new statement.

Who benefits from UNSCEAR’s changed policy?

UNSCEAR’s main recommendation not to multiply low doses by large population numbers to estimate health effects is a reversal of its previous practice. In the 1970s, 1980s, 1990s, and up to 2005, UNSCEAR published many reports doing precisely that: see, for instance, Bennett (1995,1996) and UNSCEAR’s older quinquennial reports.

So why did UNSCEAR change its policy and who is the main beneficiary of the change? It appears to be the nuclear power industry which remains concerned at negative perceptions of large global collective doses – not just from nuclear accidents but from large routine radionuclide emissions, especially from nuclear reprocessing plants. See Thompson, 2012.

It is regretted that the formerly balanced and respected (ie pre 2005) UNSCEAR has adopted such an apparently partisan policy. It is understood this stems from recent past and current memberships of its Scientific Committee which include several  pro-nuclear protagonists, including recent past chairmen. For example, its current chairman unwisely predicted that there would be no health effects from Fukushima’s fallout. Several citizen scientists have also noticed UNSCEAR’s new policy and have written blogs opposing it: see, for example.

As shown in an accompanying new post, several academic studies in this area have ignored UNSCEAR’s recommendation and have made collective dose estimates arising from Fukushima. These are to be welcomed.

I thank Jan Beyea for obtaining information for parts of this post.

REFERENCES

Bennett B (1996) Assessment by UNSCEAR of Worldwide Doses from the Chernobyl AccidentIn Proceedings of an IAEA Conference One Decade After Chernobyl: Summing up the Consequences of the Accident, Vienna, 8-12 April 1996 Pp 117 – 126.

Bennett B (1995) Exposures from World-wide Releases of Radionuclides. In Proceedings of an International Atomic Energy Agency Symposium on the Environmental Impact of Radioactive Releases. Vienna, May 1995. IAEA-SM-339/185.

Environment Agency et al (2012) Principles for the Assessment of Prospective Public Doses arising from Authorised Discharges of Radioactive Waste to the Environment. Published by UK Environment Agency, August 2012.

Fairlie I and Sumner D (2000) In defence of collective dose. J. Radiol. Prot. Volume 20 Number 1. Page 9 doi:10.1088/0952-4746/20/1/302

IRSN (2011) Assessment on the 66th day of projected external doses for populations living in the north-west fallout zone of the fukushima nuclear accident – outcome of population evacuation measures, Report DRPH/2011-10: L’Institut de Radioprotection et de Sûreté Nucléaire.

Kriebel D, Tickner J, Epstein P, Lemons J, Levins R, Loechler EL, Quinn M, Rudel R, Schettler T, and Stoto M. The precautionary principle in environmental science. Environ Health Perspect. 2001;109(9):871-6.

Thompson G. Unmasking the truth: The science and policy of low-dose ionizing radiation. Bulletin of the Atomic Scientists 68.3 (2012): 44-50.

UNSCEAR (2012) Supplement No. 46 (UN document A/67/46, 14 August 2012) http://daccess-dds-ny.un.org/doc/UNDOC/GEN/V12/553/85/PDF/V1255385.pdf?OpenElement

Valentin J (1995) Truth or consequence–Bo Lindell’s contribution to radiation protection. Acta Oncol.1995;34(8):1051-4.

WHO (2012) Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan earthquake and tsunami. (www.who.int)

It is dispiriting to read many articles – on both sides of the Atlantic – by media pundits and poorly-informed scientists about low-level radiation risks. These articles commonly assert, with little or no evidence, that there is nothing to worry about radiation and that nuclear projects are encumbered by overly strict safety limits. In particular, they usually state that no risks are seen below 100 mSv; that the Linear No-Threshold (LNT) model is wrong; and that there were only about 50 deaths at Chernobyl with no more expected.

There often seems to be a close relationship between the level of ignorance evidenced in articles on this subject and the over-confidence with which they are written.

For example, two such comments have been recently published in the US. One by a media pundit (http://www.forbes.com/sites/jamesconca/2013/01/11/like-weve-been-saying-radiation-is-not-a-big-deal/) and the other by a scientist and a layman (http://www.nytimes.com/2013/01/08/opinion/nuclear-accidents.html?_r=0). Of course, these writers are entitled to their opinions, but newspaper and journal editors should check these opinions before publishing them.

This post aims at providing editors with some balance and help in their checking.

I’ve previously shown  that a great deal of evidence supports the LNT hypothesis and indicates radiation effects well below 100 mSv.

But in recent months, a flurry of epidemiological studies go further than merely refuting ill-informed articles. They indicate adverse effects to people exposed to very low doses from medical CT scans and other clinical procedures; to infants living near nuclear power stations; and to Chernobyl clean-up workers. They even reveal adverse effects from background radiation to which all of us are exposed.

Together they reveal a pattern of higher-than-expected risks from very low exposures to radiation.

1. Background Radiation

Perhaps the most eye-opening of the recent studies concern background radiation. Most people think that background radiation levels (typically 2 to 3 mSv per year) are very low and are of little concern. But recent authoritative studies clearly indicate that background radiation is not harmless.

For example, a team of British scientists based at the University of Manchester, Imperial College and the UK Health Protection Agency has been examining this matter. Using two leukaemia risk models and estimates of red-bone-marrow doses received by children from background radiation, the team initially estimated that 20% of the childhood leukaemia cases in Great Britain were attributable to background radiation (Wakeford et al, 2009) – see references at end.

This surprising result was first refined to 15% of GB childhood leukaemias (Little et al, 2009) (Kendall et al, 2011), then the team predicted the risk rate from background gamma radiation. After conducting a large record-based case–control study with 27,000 cases and 37,000 controls to test associations between childhood cancer and natural background radiation, the authors estimated that the excess risk of childhood leukaemia was 12% per millisievert of cumulative red bone marrow dose from background gamma radiation (Kendall et al, 2012). The most recent comprehensive review (Wakeford, 2013) confirms these estimates.

Just to make sure the point gets across, these studies mean that all children will receive about 1 mSv of gamma radiation from background radiation each year and this results in their leukemia risk being increased by 12%.

It’s well known that leukemia is closely associated with radiation exposures and that children are more sensitive to radiation than adults. But the new evidence is not just from childhood leukemias, it comes from radon studies as well.

In Canada, following a survey of 14,000 homes with a geometric mean radon concentration of 42 Bq/m³, Chen et al (2010) from the Radiation Protection Bureau of Health Canada estimated that 16% of lung cancer deaths in Canada were attributable to indoor radon. However this fits slightly awkwardly with another large (7,000 cases and 14,000 controls) risk assessment of radon exposures (Darby et al, 2006) which estimated an excess relative risk of lung cancer of 16% (95% CI 0.05-0.31) at an average radon concentration of 100 Bq/m³. Whichever of these scientific teams turn out to be correct, the cancer risks from background radon exposures are still higher than were expected even just a few years ago.

Another very large Canadian study by Turner et al (2012) of over 800,000 Americans found that indoor radon was significantly associated with deaths from chronic obstructive pulmonary disease, ie chronic bronchitis and/or emphysema. The hazard ratio was 1.13 per 100 Bq·m^?3 (95% CI = 1.05–1.21). There was a significant positive linear trend in deaths with increasing categories of radon concentrations (p<0.05). For comparison, the UK HPA’s recommended Action Level for radon is 200 Bq·m^?3: indoor concentrations above this level require remediation.

And in areas with high levels of natural background radiation (usually from monazite sands), Møller and Mousseau (2012) studied radiation effects in local peoples and found increased risks in immunology, physiology, mutation and disease. They stated “.. if we see effects at these low levels, then we have to be thinking differently about how we develop regulations for … intentional exposures to populations, like the emissions from nuclear power plants, medical procedures, and even some x-ray machines at airports”.

2. Medical Exposures

Most exposures from medical diagnostic procedures are relatively low, and although their collective doses are increasing in most developed countries, in almost all cases they are justified by their clinical benefits. Nevertheless there have been a score or so of articles in scientific journals in recent years expressing concern about the risks of increased doses from CT scans, especially to children. Even the WHO has issued a draft report expressing the need for more vigilance.

In order to investigate these concerns, Pearce et al (2012) conducted a massive UK retrospective cohort study of computed tomography (CT) scans among 178,000 patients. The team estimated absorbed brain and red bone marrow doses per CT scan and assessed the excess incidence of leukaemia and brain tumours cancer with Poisson relative risk models. They observed a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy = 0·036, 95% CI 0·005–0·120; p=0·0097); and a positive association with brain tumours (0·023, 0·010–0·049; p<0·0001). They found CT scans caused statistically significant increases in cancer risks in under three-year olds: three head scans tripled their risk of brain cancer and five to ten scans tripled their risk of leukemia. Although the authors did not comment on these risks, there is no doubt that these are large risk increases from relatively small doses.

I shall be writing more on this matter in due course.

In Canada, similar risk increases were observed by Eisenberg et al (2011) after low-dose exposures from cardiac imaging in adult patients with acute myocardial infarction. For every 10 mSv from cardiac imaging, a 3% increase in cancer risk (RR= 1.03 per 10 mSv, 95% CI = 1.02–1.04) was observed. The authors stated “These results call into question whether our current enthusiasm for imaging and therapeutic procedures after acute myocardial infarction should be tempered.”

3. Leukemias in Chernobyl Clean-up Workers

Since the Chernobyl disaster in 1986, several studies have attempted to find increased leukemia risks among the tens of thousands of clean-up workers most of whom received relatively low doses, to little avail. This was due to the smallness of the studies and their lack of statistical power. However the latest study, (Zablotska et al, 2013) is very large (over 110,000 workers) and succeeded in finding statistically significant leukemia increases, even at the relatively low doses experienced by most of these adult workers (average dose = 92 mSv). The authors found a significant linear dose response for all leukemias with an ERR/Gy of 2.38 (95% CI: 0.49, 5.87).

4. Leukemias near Nuclear Power Stations

The final area is exposures from nuclear power stations.

Readers will be aware of my lectures showing that about 40 studies worldwide indicate increased leukemia risks among children within 5 km of nuclear power plants (NPPs). In particular, the important 2008 KiKK case-control study (discussed in Fairlie, 2009), which was commissioned by the German Government, found large increases in the risks of child leukemias and embryonal cancers near all German NPPs. This authoritative report led to geographical studies sponsored by the governments of France, UK, Switzerland and Germany. These have now been published and all four had similar findings, ie  30% to 40% increases in child leukemias near NPPs – see table from Körblein and Fairlie (2012) which contains the references to these four government studies.

Table: Studies of observed (O) and expected (E) childhood leukemias (under 5 year olds) within 5 km of NPPs

The important point here is that most scientists think that radiation exposures to local residents from NPPs are extremely small. Indeed, many nuclear scientists remain in denial about the relationship between proximity to NPPs and child leukemias despite the bountiful clear evidence which exists. Yet the evidence of child leukemias near NPPs fits well with the evidence emerging from background radiation and medical radiation.

Conclusion

The new studies mentioned in this post provide much food for thought. Readers should note that they are all very large studies commonly with over 100,000 data points. This means that they all have good statistical power, and the usual caveat of lacking statistical significance does not apply to them. Note also that these studies are mostly from government or academic sources- indeed some are by scientists who used to work in the nuclear industry. That is, we need to take their results very seriously.

Taken together, the new studies indicate that our current understandings about radiation risks, especially in infants and children, may be incorrect and they may need to be revised upwards. In particular, the current adult (absolute) ICRP risk for fatal cancer of 5% per Sv and the ICRP’s use of a dose and dose-rate effectiveness factor (DDREF) look increasingly out of date.

The new studies also mean that our public radiation limits and constraints may need to be revised.

REFERENCES

Chen et al (2012) Canadian population risk of radon induced lung cancer: a re-assessment based on the recent cross-Canada radon survey. Radiat Prot Dosimetry 152 (1-3): 9-13. doi: 10.1093/rpd/ncs14. http://rpd.oxfordjournals.org/content/152/1-3/9.abstract.html?etoc

Darby S,  et al  (2006) Residential radon and lung cancer: detailed results of a collaborative analysis of individual data on 7148 persons with lung cancer and 14,208 persons without lung cancer from 13 epidemiologic studies in Europe. Scand J Work Environ Health; 32 Suppl 1:1-83. Erratum in: Scand J Work Environ Health. 2007 Feb;33(1):80.

Eisenberg et al (2011) Cancer risk related to low-dose ionizing radiation from cardiac imaging in patients after acute myocardial infarction. Canadian Medical Association Journal 183.4, 2011, 430-436. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3050947/pdf/1830430.pdf

Fairlie I (2009) Childhood Cancers Near German Nuclear Power Stations: hypothesis to explain the cancer increases. Medicine, Conflict and Survival Vol 25, No 3. 2009, pp 206–220.

Kendall GM, Little MP, Wakeford R (2011) Numbers and proportions of leukemias in young people and adults induced by radiation of natural origin. Leuk Res. Aug;35(8):1039-43. doi: 10.1016/j.leukres.2011.01.023. Epub 2011 Feb 21.

Kendall GM, Little MP, Wakeford R, Bunch KJ, Miles JCH, Vincent TJ, Meara JR and Murphy MFG (2012) A record-based case–control study of natural background radiation and the incidence of childhood leukaemia and other cancers in Great Britain during 1980–2006. Leukemia (5 June 2012) doi:10.1038/leu.2012.151).

Körblein A and Fairlie I (2012) French Geocap study confirms increased leukemia risks in young children near nuclear power plants. Letter to Editor. Int J of Cancer. September.

Little MP, Wakeford R, Kendall GM (2009) Updated estimates of the proportion of childhood leukaemia incidence in Great Britain that may be caused by natural background ionising radiation. J. Radiol. Prot. 29(4), 467–482.

Møller AP and Mousseau TA(2012) The effects of natural variation in background radioactivity on humans, animals and other organisms. Biological Reviews DOI: 10.1111/j.1469-185X.2012.00249.x

Pearce et al (2012) Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. The Lancet. June 7, 2012 DOI:10.1016/S0140-6736(12)60815-0, http://press.thelancet.com/ctscanrad.pdf

Turner MC et al (2012) Radon and COPD mortality in the American Cancer Society Cohort. Eur Respir J. 2012 May; 39(5): 1113–1119.

Wakeford R, Kendall GM and Little MP (2009) The proportion of childhood leukaemia incidence in Great Britain that may be caused by natural background ionizing radiation. Leukemia 23, 770–776.

Wakeford R (2013) The risk of childhood leukaemia following exposure to ionising radiation-a review. J Radiol Prot. 2013 Jan 7;33(1):1-25. [Epub ahead of print]

Zablotska et al (2013) Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers. Environmental Health Perspectives. Volume 121 | number 1.  Pp 59-65. January 2013.

In addition, several media pundits in the UK newspaper, the Guardian, and on the BBC have implied – without adducing evidence – that radiation effects are exaggerated and that there are no observed effects below 100 mSv.

However, in an accompanying post, I’ve shown that a growing number of studies show radiation effects well below that level. Indeed, they show effects down to very low levels – even at background levels of radiation. In other words, there does not appear to be a threshold, ie a dose below which no effects are seen, apart from zero dose.

But is the dose-response relationship linear?

This post addresses the “linear” part of the LNT theory. Graph 1 below shows the different kinds of relationships which could exist, ie (a) linear, (b) supra-linear, (c) sub-linear, (d) threshold, and (e) hormetic.

Graph 1

To assess whether a linear dose-response relationship is valid, we need to examine both the epidemiological evidence at low doses and dose rates, and the evidence from radiobiology theory derived from the evidence in cell and animal studies.

A. Epidemiological Studies

Does the available epidemiological evidence show risks declining linearly with dose at low doses? Yes, several recent epi studies do indeed show this, and the important new points are that these are (a) very large studies with statistically significant results, and (b) at very low doses, even down to background levels. In other words, the usual caveats about the validity of the linear shape of the dose response relationship down to low doses are becoming less and less justified.

The most recent evidence is from Zablotska et al (2012). (See references at end)

Graph 2 below, reproduced from Zablotska et al, shows statistically significant risks for all leukemias and for chronic lymphocytic leukemia (CLL) in over 110,000 Chernobyl cleanup workers. It can also be seen that there are 6 data points showing increased risks below 100 mSv. The Excess Relative Risk (ERR) can be estimated as 2.3 per Gy, all cases, at 1 Gy.

Graph 2

Second is the very recent cohort study of radiation exposures from medical CT scans in the UK by Pearce et al (2012). 74 out of 178,604 patients diagnosed with leukaemia and 135 out of 176,587 patients diagnosed with brain tumours were analyzed. As shown in graph 3 reproduced from their study, the authors noted a positive association between radiation doses from CT scans and leukaemia (ERR per Gy = 36, 95% CI 5–120 p=0·0097) and brain tumours (ERR per Gy = 23,10–49; p<0·0001). The large dashed line showed a linear fit to the data with a 95% confidence interval shown by small dashed lines.

Graph 3

Third are the risks from background radiation. Kendall et al (2012) recently conducted a large UK record-based case–control study testing associations between childhood cancer and natural background radiation with over 27,000 cases and 37,000 controls. Surprisingly, they observed an elevated risk of childhood leukaemia with cumulative red bone marrow dose from natural background gamma radiation. ERR/Gy = 120 (95% CI: 30, 220).

In graph 4 below reproduced from their study, the x-axis represents cumulative gamma ray doses in mGy. The red line shows not merely a linear but a slightly supralinear curve fitted to the data. The small dotted lines mark a 95% confidence interval.

Graph 4

Fourth is the third analysis of the UK National Registry for Radiation Workers (NRRW). This study of observed 11,000 cancer cases and 8,000 cancer deaths in 175,000 UK radiation workers with an average individual cumulative dose of 25 mSv and an average follow-up of 22 years. Graph 5 reproduced from the study shows the relative risks for all solid cancers with the continuous blue line representing the NRRW data, and the continuous red line the results from the US BEIR VII report for comparison – the two are very similar, as can be seen. An estimated ERR of 0.27 per Gy at 1 Gy can be derived from this graph.

Graph5 

Fifth is the Cardis et al (2005) meta-analysis of 196 leukaemias and 5,024 other cancers among 400,000 nuclear workers in fifteen countries with an average follow-up of 12.7 years and a mean individual cumulative dose of 19.4 mSv. The study found ERRs for leukaemia of 1.93 (95% CI: <0, 8.47) per Sv (2-year lag) and 0.97 (95% CI: 0.14, 1.97) per Sv for solid cancers (10-year lag).

Sixth is the meta-analysis of 13 european studies in 9 EU countries on indoor radon exposure risks by Darby et al (2005). This examined lung cancer risks at measured residential Rn concentrations with over 7,000 cases of lung cancer and 14,000 controls. The action level for indoor radon in most EU countries is 200 Bq per m³, corresponding to about 10  mSv per year. (This is derived from a UNSCEAR (2000)  reference value of 9 nSv per Bq·h/m³. This means that people living 2/3rds of their time indoors (5,780 h/year) at a Rn concentration of 200 Bq/m³ would receive an effective dose of ~10 mSv/year.)

Graph 6 reproduced from the study shows elevated risks at concentrations well below this level. (The solid line is the authors’ linear fit to the data.)

Graph 6

B. Radiobiological Evidence

In addition, much current radiobiological theory is consistent with a linear dose-response relationship down to low doses (ie below 10 mSv).

The radiobiological rationale for linearity comes from the stochastic energy deposition of ionising radiation. It was explained by 15 of the world’s most eminent radiation biologists and epidemiologists in a famous article. (Brenner et al, 2003)

It stated as follows:

“1. Direct epidemiological evidence demonstrates that an organ dose of 10 mGy of diagnostic x-rays is associated with an increase in cancer risk.

2. At an organ dose of 10 mGy of diagnostic x-rays, most irradiated cell nuclei will be traversed by one or, at most, a few physically distant electron tracks. Being so physically distant, it is very unlikely that these few electron tracks could produce DNA damage in some joint, cooperative way; rather, these electron tracks will act independently to produce stochastic damage and consequent cellular changes.

3. Decreasing the dose, say by a factor of 10, will simply result in proportionately fewer electron tracks and fewer hit cells. It follows that those fewer cells that are hit at the lower dose will be subject to (i) the same types of electron damage and (ii) the same radiobiological processes as would occur at 10 mGy.

4. Thus, decreasing the number of damaged cells by a factor of 10 would be expected to decrease the biological response by the same factor of 10; i.e., the response would decrease linearly with decreasing dose. One could not expect qualitatively different biological processes to be active at, say, 1 mGy that were not active at 10 mGy, or vice versa. The argument suggests that the risk of most radiation -induced endpoints will decrease linearly, without a threshold, from ~10 mGy down to arbitrarily low doses.”

C. Official Reports

Both kinds of evidence (epidemiology and radiobiology) have been examined in five relatively recent international official reviews.

• UNSCEAR (2008)
• US NCRP Report No 136 (2001)
• Académie Nationale de Médecine et Académie des Sciences Joint Report No 2 (2005)
• US BEIR VII (2005) and
• ICRP 99 (2006)

Four of these five reports emphatically confirmed the LNT as being the most prudent assumption for radiation protection purposes. The odd one out is the French Académie Nationale de Médecine et Académie des Sciences Joint Report No 2 (2005). However France relies on nuclear power for about 80% of its electricity, so this finding is perhaps not unexpected.

In 2009, Little et al  examined this matter in some detail and they concluded linearity was the best bet. They discussed: (i) the degree of curvature in the cancer dose response within the Japanese atomic bomb survivors and other groups, (ii) the consistency of risks between the Japanese and other low-dose cohorts, and (iii) biologic data on mechanisms.

D. The Importance of LNT in Radiation Protection

Regardless of dissenting views on LNT, the reality is that most if not all concepts used in radiation protection today are strongly based on the LNT theory. For example, LNT allows radiation doses (i) to be averaged within an organ or tissue, (ii) to be added from different organs, and (iii) to be added over time. The LNT also underpins the concepts of absorbed dose, effective dose, committed dose, and the use of dose coefficients (eg Sv per Bq of a radionuclide).

The use of the LNT also permits

• the ICRP principle of limitation – ie annual dose limits/constraints
• the ICRP principle of optimization -ie comparison of practices
• radiation risk assessment at low and very low doses
• individual dosimetry with passive detectors
• the use of collective dose, and
• the use of dose registers over long periods of time.

In fact, the LNT underpins all legal regulations in radiation protection. Indeed if the LNT were not used, it’s hard to imagine our current radiation protection systems existing at all.

References

Brenner David J, Richard Doll, Dudley T. Goodhead, Eric J. Hall, Charles E. Land, John B. Little, Jay H. Lubin, Dale L. Preston, R. Julian Preston, Jerome S. Puskin, Elaine Ron, Rainer K. Sachs, Jonathan M. Samet, Richard B. Setlow, and Marco Zaider (2003) Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know. PNAS. vol.100 no.24. pp 13761-13766. www.pnas.orgjcgijdoij10.1073jpnas.2235592100

Cardis et al (2005) Risk of cancer after low doses of ionizing radiation: retrospective cohort study in 15 countries. BMJ. 2005 Jul 9;331 (7508).

Darby et al (2005) Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ 2005;330:223.

Kendall G M, M P Little, R Wakeford, K J Bunch, J C H Miles, T J Vincent, J R Meara and M F G Murphy (2012) A record-based case–control study of natural background radiation and the incidence of childhood leukaemia and other cancers in Great Britain during 1980–2006. Leukemia (5 June 2012) | doi:10.1038/leu.2012.151.

Little MP, Wakeford R, Tawn EJ, Bouffler SD, Berrington de Gonzalez A. Risks associated with low doses and low dose rates of ionizing radiation: why linearity may be (almost) the best we can do. Radiology. 2009 Apr;251(1):6-12. doi: 10.1148/radiol.2511081686.

Muirhead et al (2009) Mortality and cancer incidence following occupational radiation exposure: third analysis of the National Registry for Radiation Workers. Br J Cancer 2009; 100: 206-212.

Pearce et al (2012) Radiation exposure from CT scans in childhood and subsequent risk of eukaemia and brain tumours: a retrospective cohort study. The Lancet. June 7, 2012. 380: 499-505. DOI:10.1016/S0140-6736(12)60815-0, http://press.thelancet.com/ctscanrad.pdf

United Nations Scientific Committee on the Effects of Atomic Radiation (2000). UNSCEAR Report to the General Assembly, with scientific annexes – Annex B, § 153.

Zablotska et al (2012) Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1204996 Online 8 November 2012.

However, many studies show radiation effects well below 100 mSv. It is true that these effects are often numerically small, so that large studies are needed to yield findings which are statistically significant, but they do exist. These studies are conveniently set out in the table below: those with statistically significant findings are highlighted in green. The other studies are included because non-significant findings should also be shown, as they can indicate or support a trend. This is because the lack of statistical significance is often due simply to small numbers and not the absence of effect.

Perhaps the most important of these studies (at least for risks from external exposures) is the Life Span Study of over 120,000 Japanese A-bomb survivors. The graph below reproduced from Preston et al (2003) shows the risks of solid cancers among the Japanese survivors. The data points are the mean of each dose category; the solid line is the weighted moving average of data points; the dotted line = ± 1 SE, and the dashed line is a linear fit to all data 0 – 2 Sv. This reveals 5 data points below 100 mSv.

Interestingly this graph appears to suggest that radiation rusks are supralinear between 250 and 350 mSv, ie even more hazardous than a linear model would suggest.

Conclusion

It can reasonably be concluded that very good evidence exists showing radiation effects well below 100 mSv.

References

Cardis E et al (2005) Risk of cancer after low doses of ionising radiation: retrospective cohort study in 15 countries. BMJ 2005;331:77.

Dale L. Preston, Yukiko Shimizu, Donald A. Pierce, Akihiko Suyama, and Kiyohiko Mabuchi (2003) Studies of Mortality of Atomic Bomb Survivors. Report 13: Solid Cancer and Noncancer Disease Mortality: 1950–1997. Radiation Research: October 2003, Vol. 160, No. 4, pp. 381-407.

Darby et al. Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ 2005;330:223.

Doody MM et al Land CE for the US Scoliosis Cohort Study Collaborators. Breast cancer mortality following diagnostic x rays: Findings from the US Scoliosis Cohort Study. Spine 25 (2000): 2052-2063.

Jacob P et al. Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia. British Journal of Cancer 80.9 (1999): 1461.

Noschenko et al. 2001. Patterns of Acute Leukemia Occurrence Among Children in the Chernnobyl Region.  Intl J of Epidemiology 30, 125-129.

Ron E and Schneider AB. Thyroid cancer. Cancer epidemiology and prevention 3 (1996): 975-994.

Sont WN, Zielinski JM, Ashmore JP, Jiang H, Krewski D, Fair ME, et al. 2001. First analysis of cancer incidence and occupational radiation exposure based on the National Dose Registry of Canada. Am J Epidemiol 153:309-318.

Stevens et al Leukemia in Utah and Radioactive Fallout From the Nevada Test Site: A Case-Control Study. JAMA. 1990;264(5):585-591. doi:10.1001/jama.1990.03450050043025.

Stewart A, Webb J, Giles D, and Hewitt D (1956) Malignant disease in childhood and diagnostic irradiation in utero. Lancet 271, 447.

Zablotska et al (2012) Radiation and the Risk of Chronic Lymphocytic and Other Leukemias among Chornobyl Cleanup Workers. Environmental Health Perspectives. http://dx.doi.org/10.1289/ehp.1204996  Online 8 November 2012.

Information and new insights about Fukushima are appearing almost on a daily basis. This briefing was updated on March 12, 2012.

The nuclear accident

Following the earthquake, the three operating reactors at the Fukushima Dai-ichi nuclear plant automatically shut down because of huge lateral vibrations caused by the quake. But the quake also disconnected the reactors from the national grid, therefore their cooling pumps could not operate. Emergency diesel-powered pumps kicked in but these were unwisely located in reactor basements which were flooded by the tsunami arriving 40 minutes later. The result was inexorable rises in nuclear fuel temperatures until the fuels melted then started to boil.

Because of the paramount need to remove the large amounts of decay heat from nuclear fuels both in the reactors and in the spent fuel ponds, cooling failures resulted in a compound, cascading series of explosions and other events which are still being unravelled. The major events were as follows:

• core meltdowns occurred in the reactors of Units 1, 2, and 3;
• explosions destroyed the reactor buildings of Units 1, 3, and 4
• an ‘explosive event’ damaged the containment structure inside reactor 2;
• several fires broke out at Unit 4;
• spent fuel stored in the pools of Units 1–4 overheated as their water levels dropped;
• many workers suffered high radiation exposures and often had to be evacuated
• machinery for reactors 1–4 damaged by floods, fires and explosions remained inoperable

On March 12, a probable hydrogen explosion at Unit 1 wrecked the plant, exposed its spent-fuel pool to the open air, released radioactive matter into the environment and caused delays in cooling Unit 3. This probably resulted in its explosion the following day.

On March 13, a much larger explosion occurred at Unit 3 which wrecked the plant, damaged seawater injection lines and vent lines for Unit 2, producing delays in its cooling. It is likely this then caused  “damage” on March 15 to the fuel area inside Unit 2 at about 6 am. Seconds later, an “explosive event” of some kind damaged the spent fuel pond at Unit 4 resulting in a fire in its pond area at about 9 am.

On March 16, at 05.45 am, a third major explosion occurred – this time in the fuel pond at unit 4 – wrecking the unit in its entirety.  No TV video footage of these latter explosions exists as they occurred early in the mornings.

In other words, explosions at one unit hampered responses to the damage at others, leading to a chain reaction of explosions and radiation releases. No wonder the staffs at the plant were often terrified and TEPCO (the electricity utility) wanted to withdraw all personnel from the plant at one stage.

­­­­­­­­­­­­­­­­­­­­Within about six hours of the Japanese earthquake and tsunami, it appears that full or partial nuclear fuel meltdowns had occurred within Units 1, 2 and 3 at Fukushima due to the inexorable heat from radioactive decay in nuclear fuel. This was quickly followed by the molten fuel (at ~2,000 °C) melting its way through the steel pressure vessels into secondary concrete containment vessels. It is now thought these containment vessels have cracked and much fuel is now in the basement areas of the reactors. At the same time, the water in the spent fuel ponds above the reactors also began to boil causing their water levels to drop thus exposing spent fuel to the elements.

So within a few days of the earthquake/tsunami, three major explosions and two “explosive events”had occurred at the Fukushima Dai-ichi Units. The explosions wreaked massive damage with the result that the reactor buildings at Units 1 and 4 in particular may collapse.

It is important to note that the reactor malfunctions, resulting fuel meltdowns and explosions were due to the earthquake as well as the tsunami, contrary to the explanations given by TEPCO and the Japanese regulators which only mentioned the tsunami. See http://www.theatlanticwire.com/global/2011/07/meltdown-what-really-happened-fukushima/39541/ The point is that the many Japanese nuclear reactors near fault lines are considerably more vulnerable to earthquakes than to tsunami.

Ever since the accident occurred, the main preoccupation has been to keep the nuclear fuels cool. This applies not only to the melted nuclear fuels in the reactor cores but also the large volumes in the storage ponds at Units 1, 2, 3 and 4. Fuel in unit 4 was at one stage exposed to air and caught fire, causing one of the three major explosions.

The continuing disaster

A year after the accident, it is still continuing in slow motion and will do so for years. Major efforts are still being made to keep the reactor fuel cool to stop it from melting through the bottoms of the reactor buildings into the soil below, although the concrete bases are ~10 m thick. If this were to occur, Japan would be deep in uncharted waters: further explosions would likely occur. Water is also still being pumped into the storage pools to keep their spent fuels covered.

In addition, it is hypothesised that criticality excursions are recurring in nuclear fuels[1]. It is also becoming known that many nuclear fuel fragments are spread throughout the plant and even as far as the large town of Iitate over 30 km away. A major headache is the structural instability of the wrecked reactor buildings which may collapse at any time due to the massive weight of the storage ponds situated, again unwisely, on top of the reactors. This would spill thousands of tonnes of dangerous spent fuel and radioactively-contaminated water over the site.

In December 2011, nine months after the crisis first erupted, Japanese Prime Minister Noda declared that reactors 1, 2 and 3 were now in a state of cold shutdown and the crisis at the plant had been contained. According to the government and Tepco, the melted nuclear fuel in the wrecked reactor cores was being kept below 100^o C and the leakage of radioactive materials had been reduced. According to the government and Tepco, these were criteria that met the definition of a cold shutdown.However this announcement was met with disdain and many questions in Japanese and international media. Newspaper reports stated that widespread public concern remained on two matters. The first was just how stable the facilities really were – could they withstand other powerful earthquakes? The second was that no one had yet determined the locations of the melted fuels inside the containment vessels or ascertained how badly damaged the fuel rods were. On the other hand, some nuclear experts believe the government’s assessment is  more or less accurate, in that the melted fuel in the reactor cores had stopped generating dangerously high levels of decay heat. See http://www.japantimes.co.jp/text/nn20120308x1.html

When we look further afield the situation is no better, as very large amounts of radioactivity were dumped into the sea and emitted to atmosphere. The latter resulted in about a thousand square km of land being contaminated with fallout and large amounts of crops and produce being contaminated. An estimated 100,000 people have had to be evacuated from their homes, possibly for decades. These effects are on top of the estimated 20,000 people killed by the earthquake and tsunami themselves. The situation is truly numbing and our hearts go out to the Japanese people struggling with the horrible consequences of the earthquake/tsunami and of the Fukushima disaster.

How long will this dire situation continue? It’s hard to say, but IAEA officials privately talk of years: other scientists say decades. Up until recently, contaminated water from the cooling operations was being dumped on land and into the sea. Nowadays this water is mainly being pumped into large temporary holding tanks.

Health Effects

Few deaths have been recorded at Fukushima so far, certainly in comparison to the thousands caused by the earthquake/tsunami. About 7 deaths to military personnel and plant operators were apparently caused by the site explosions. According to an NHK (TV) survey, 68 patients from evacuated hospitals died during the long hours of evacuation. None of these deaths were due to radiation exposures. But fears remain about longer-term effects, as radiation has decades-long latency periods before most solid cancers appear. Increased incidences of thyroid cancers – a prominent effect after Chernobyl – are unlikely to appear for another three years.

It is too early to make firm predictions, but judging from the exposures and effects seen at Chernobyl, it’s likely that at least a few thousand fatal cancers will occur among those exposed to Fukushima’s radioactive fallout. In addition, it’s likely that Fukushima plant workers will suffer as the Japanese Health and Labor Ministry reported that nearly 100 workers had exceeded legal radiation limits by June 2011.

Main Conclusions

Fukushima is clearly a serious disaster but it is not as serious as Chernobyl. Radioactive air emissions are much more important than radioactive sea discharges in terms of their  radiation doses to people, and the dispersed radioactivity to air from Fukushima has been estimated to be about 10% to 40% of the amount dispersed from Chernobyl. About a thousand square km near the Fukushima were contaminated, but at Chernobyl the area affected was much larger: over 200,000 square km throughout Europe were seriously contaminated by fallout, according to the European Commission.

A very recent report[2] by the Japanese chairman of the independent Rebuild Japan Initiative Foundation is recommended. It reveals many institutional failures at Fukushima and shows that TEPCO and the Japanese government and its nuclear agencies were completely unprepared for the disaster at almost every level. This lack of preparation was caused by the myth of absolute safety that nuclear power proponents had nurtured over decades. It was aggravated by poor communications and lack of trust within and between government agencies and TEPCO. Interestingly, the report also shows that the disaster, bad as it was and is, could have been worse. Apparently, luck and serendipity were on the side of the Japanese at several junctures during the disaster.

Perhaps the simplest of the lessons to be learned from Fukushima is that nuclear power is a supremely unforgiving technology. When things go wrong, they can go very, very wrong with consequences which are difficult or almost impossible to remedy. But nuclear power is merely a complicated way of boiling water and, after Fukushima, many countries are beginning to examine safer energy policies.

The Political Fallout in Europe

Interestingly, different countries have responded in diametrically opposite ways to the Fukushima disaster. In the UK, the coalition government, most political parties and many parts of the media appear to be ignorant of, or perhaps in denial about, the continuing events at Fukushima. Certainly most of the UK press and the BBC are heavily pro-nuclear in their outlooks. The result is that the UK is the most strongly pro-nuclear country in Europe. This was starkly illustrated on July 18, 2011 when only 14 out of 650 UK MPs voted against the government’s Nuclear Policy Statements. In contrast, two weeks earlier, on June 30, the German Parliament voted by 513 to 79 to phase out all nuclear power by 2022.

The UK government’s nuclear bias was also shown when FOI requests in July 2011 revealed deep collusion between the government and the nuclear industry. Apparently civil servants in energy and business departments attempted to minimise the impact of the Fukushima disaster on public support for nuclear power by leading and co-ordinating a misleading PR response to the Fukushima disaster with the nuclear industry. In 2011, the UK government did request the Chief Inspector of Nuclear Installations to report on the implications for British reactors from Fukushima. But with a few caveats, his final report was a whitewash for nuclear power: the Government’s plans for up to eight new nuclear power stations were little affected.

In France, which nowadays obtains ~73% of its electricity from nuclear reactors, the nuclear worm appears to be turning. An opinion poll in June 2011 showed 75% wishing to withdraw from nuclear energy vs 22% backing nuclear expansion. The French Presidential and Legislative elections in May and June 2012 respectively are currently expected to result in a Socialist President and a PS-Green coalition government formally opposed to nuclear power.Francois Hollande the PS leader has promised to phase out one-third of France’s nuclear fleet by 2025 andthe Socialist Party has called for a moratorium on new reactors and pledged a national debate on energy transition if elected.

In Germany, several  250,000-strong demonstrations took place after Fukushima with the result that major reversals occurred in regional (Lände) elections and opinion polls on the nuclear issue showed large increases in opposition to nuclear power. Weeks after the tsunami, the Merkel government decided to permanently close the eight oldest reactors it had already taken off-line and to close  the remaining nine over the next 11 years. Stiff anti-nuclear windfall taxes have also been imposed on nuclear power companies. These policies are very popular with 75% of Germans in agreement in various opinion polls.

In Germany, politicians have started taking energy efficiency seriously: the German government now plans to reduce electricity demand by 25% by 2050 through energy efficiency. In contrast, the coalition government in Britain is planning for electricity demand to increase by 25% over the same period.

In Italy, an astonishing 94% of those voting in a national referendum in 2011 opposed new nuclear which forced the (then Berlusconi) government to abandon its nuclear plans. In Switzerland, 25,000 attended an anti-nuclear demonstration, and the Swiss cabinet decided against new build: in effect supporting a phase-out programme as its old plants retire.

With Austria, Denmark, Portugal, Norway, Ireland and Greece all non-nuclear and phase-out programmes in Spain and Belgium, only four major EU countries – UK, France, Finland and Sweden – remain supportive[3]. But with nuclear problems in Finland[4] and the situation in France shifting, it is little surprise that French and Germany nuclear companies look to the UK as a safe haven for new nuclear projects – with the Con-Dem coalition offering enthusiastic, not to say slavish, support.

It is a sobering thought that on the nuclear power issue after Fukushima, the UK appears to be increasingly out-of step with the majority of its European Union neighbours.

Among the better websites, Wikipedia has a number of pages on Fukushima including http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster which is a large entry whose table of contents runs to 50 lines and whose references number over 350. Its website on health effects http://en.wikipedia.org/wiki/Radiation_effects_from_Fukushima_Daiichi_nuclear_disaster is almost as large. These two sites are kept up-to-date, are well-informed, and with good sources. Most important, they are pretty even-handed. Even counting the overlap, these two sites represent a vast amount of work: it seems they are maintained by a team or teams of Japanese academics.

For about two years after Chernobyl, because of the lack of information, the health effects agenda was driven by the USSR’s KGB with secrecy, equivocation, misleading information and outright deception being the norm.  This also happened at Fukushima: official information from TEPCO and official Japanese nuclear agencies is routinely misleading: seasoned observers examine official press releases for what they hide not what they say.

At Chernobyl, the Soviet Union’s stranglehold on health information was maintained until independent scientists in the East started to object to the distortions and secrecy. Later in Western Europe, scientists started to realise the real situation: information about the resulting thyroid cancer epidemics in Russia, Belarus and Ukraine was verified by two British professors, Dillwyn Williams and Keith Baverstock. Our thanks should be given to them for their laudable efforts.

Later in 2005, IAEA and WHO tried to hijack the health effects agenda again by being ‘economical with the actualité’ in the famous words of a former British government minister. But again they were rumbled – mainly by a Green Party politician, Rebecca Harms MEP and her scientific advisors who relied on Professor Cardis et al’s research and the TORCH report – see www.chernobylreport.org.

With the vast reservoir of information and comment on the web on Fukushima, TEPCO, the Japanese Government, its nuclear agencies and IAEA/WHO can’t fully control the health agenda as happened at Chernobyl. Of course, that doesn’t stop them from trying: their main ace being that they know much more than they publicly admit. It will probably take several years perhaps a decade for all the necessary information to be winkled out piecemeal to explain what really happened after March 11, 2011. This is exactly what happened after Chernobyl.

The equivocations, distorted data and misleading information issued by TEPCO and various Japanese nuclear agencies are still a problem. For example, from recent optimistic TEPCO press releases, readers could be forgiven for thinking the emergency at Fukushima is over. It is not, as I show in the accompanying post.

Compounding this official disinformation is the dire situation in the UK where most newspapers (apart from the Guardian and The Independent) and media ignore Fukushima or reprint reassuring TEPCO press releases without comment. Almost all of the information in my post was gleaned from independent websites and from Der Spiegel in Germany and the New York Times in the US.

Most shameful has been the BBC’s policy of biased information and censorship with regard to Fukushima. In 2011, the BBC produced and broadcast several radio and TV documentaries including a Horizon TV programme and an edition of its science programme Bang Goes the Theory. The latter were ostensibly focused on nuclear safety with the main messages of few deaths at Chernobyl and none expected at Fukushima. No views from the scientific mainstream, far less opposing views, were presented.

Hundreds of objections were made to the BBC Complaints section alleging bias. (www.sgr.org.uk/resources/sgr-supports-joint-complaint-bbc-over-fukushima-documentary and  www.nuclearconsult.com/information.php) These complaints were partly upheld by the BBC’s most senior adjudicating body, the BBC Trust, in an unpublicised decision. On the other hand, on October 9, 2011 BBC Scotland broadcast (only in Scotland) a balanced 30 minute programme “Fallout” in Chernobyl.

But the BBC’s control over nuclear matters apparently continues. On February 10, 2012, the BBC’s senior management pulled its Radio 4 scheduled Food Programme on the worrying high levels of food contamination at Fukushima. To be fair, on February 23, the BBC programme This World broadcast a balanced documentary “Inside the Meltdown” on Fukushima, though it was produced outside the BBC itself. So it seems there may be some differing views on nuclear issues within the BBC, which is encouraging.