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