The World Health Organisation (WHO) report on risks from the Fukushima accident was published on Feb 28 2013. It can be downloaded here.
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“This [assessment] is not intended to provide estimates of disease burden in the population or cases of excess disease resulting from radiation exposure. This report uses preliminary
dose estimates based on environmental and food monitoring data for the calculation of
lifetime attributable risks. This makes no assumption of how many persons were exposed
according to the different exposure scenarios, for which distributions of individual dose
estimates are needed. In addition to the environmental and food monitoring data, an
evaluation of the population dose distribution requires the knowledge of the behaviour
of persons, e.g. how much time they spent in the differently exposed areas. Moreover,
population figures by sex, age and area were not considered for this report, especially in
light of the expected substantial migration and movement in the months following the
accident. Reliable numbers would be needed for the estimation of population doses and
associated risks. Provided these become available, such assessment could be performed
in future studies, such as the upcoming 2-year UNSCEAR study and the on-going survey
conducted in Fukushima prefecture to determine the whereabouts of the residents.”
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 question therefore arises as to whether the risk estimates for the atomic bomb survivors are applicable to populations that have accumulated radiation doses on the order of 100 mGy or below over a long time. Thus far, radiobiological research has provided ambiguous answers to this question. Based on the findings of the two meta-analyses discussed above (74,92), which showed similar risks for protracted and acute exposures, the HRA Expert Group considered it prudent to base risk calculations on models derived from the atomic bomb survivors cohort without applying any modification factor for low dose or low dose rate. This decision, which represents a departure from standard practice in radiation risk assessment, was not unanimous as two members expressed a dissenting Opinion. (Dr O. Niwa and Dr M. Akashi supported the use of a DDREF of 2)”
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).
It is stressed again these are only initial quick comments.
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