8 October 2012

Information Notice
IRSN analysis of the Japanese study on the biological impact of theFukushima nuclear accident, published by the scientific journal
Nature on 9 August 2012
IRSN's laboratories are involved in several scientific collaborations with Japanese universities andscientific organizations focusing on the environmental impact of the Fukushima accident. The
Institute's science watch team also focuses on the main scientific publications on this subject.
Within this context, it has produced an analysis of the recently published article on mutations
observed in a butterfly species.
On 9. August 2012, the scientific journal Nature published on its website an article entitled “Thebiological impacts of the Fukushima nuclear accident on the pale grass blue butterfly”1. The
publication reveals cases of physiological and genetic damage in several generations of a butterfly
population in the vicinity of the Fukushima Daiichi nuclear power plant. In the weeks following its
publication, the article was given considerable coverage in the French and international press.
Few scientific publications to date have reported on the results of studies relating to the ecologicalimpact of the Fukushima accident. To the best of IRSN's knowledge, only two reports, by Anders
Møller's CNRS team on observations of ecological effects within a 100 km radius of the Fukushima
Daiichi site, predate the Japanese study. The interpretation given to the results of A. Møller's team,
however, has been disputed in some scientific circles and needs to be confirmed. This is largely
because:i)dose rates to organisms have not been estimated in a reliable manner or properly
characterized;ii)

and no details are given as to the statistical method applied for processing the dataused.

In this new study led by Professor Otaki's team, the authors chiefly base the relevance of their workon the main results of A. Møller's team following the Chernobyl disaster. These include a change in
specific diversity, as well as reduced abundance particularly affecting a number of bird and insectspecies. This is connected with the level of ambient gamma radiation, essentially in the exclusionzone around the Chernobyl nuclear power plant. The authors also shed more light on the subject byreproducing some of their field observations in laboratory experiments.
One of the aims of this Japanese study was to examine the causal relationship between the level ofradiation exposure and the physiological condition (morphology, developmental characteristics fromegg to adult) of the population of Zizeeria maha, a species of blue butterfly that is very widespreadin Japan. This species is a “bioindicator”, which means that its state of health and/or abundance
can provide precious early warning of various changes in environmental conditions including, inparticular, the presence of different types of stressor. This characteristic has led the species to beused, for example, to explore the possible impact of transgenic maize pollen on insect populations.
Based on various studies carried out in situ and in the laboratory, the authors conclude that thepopulation of Z. maha in the vicinity of Fukushima has experienced physiological and genetic

1

Hiyama et al. “The biological impacts of the Fukushima nuclear accident on the pale grass blue butterfly” SCIENTIFICREPORTS | 2 : 570 | DOI: 10.1038/srep00570 11damage. Abnormalities found in the first generation following the accident were not necessarilyobserved in parents exposed at the larval stage. In the authors' opinion, the existence of thesevaried and unexpected abnormal phenotypes cannot be explained simply by the phenotypic
plasticity2 that normal populations may exhibit in response to changes in their environment.
Furthermore, the hypothesis that genes with an important role in morphological development might
inherit the observed mutations is borne out by the increase in the abnormality rate from one in situ
generation to the next, despite the fact that absorbed dose probably decreases over generations
owing to the decay of short-lived radioisotopes. Epigenetic3 processes cannot be completely ruledout either.
IRSN's analysis of this publication shows that the Japanese study is both original and serious. Its
main strength lies in the interrelatedness of the in situ and laboratory studies and in the adoption ofexperimental methods, normally used in evolutionary ecology, to identify which observable changes
in traits (and their accumulation over generations) are due to mutations, and which are due todirect physiological and radiotoxic effects, in other words, changes in traits observed within theexposed generation.
Its weak point, however, is that the estimation of in situ radiological exposure is based entirely on
the measured external dose rate and ignores the contribution of internal contamination through theingestion of contaminated plants. This has led to doses to these organisms being underestimated –perhaps significantly so. For this reason – and given the clear evidence of impact – this work should
be backed up by a dosimetric study that takes into account both external and internal exposure, inorder to assess the exposure of the population studied with greater accuracy. Scientific evidence
should also be provided to demonstrate that other stressors, such as metals and other pollutants(multiple pollution context) that might be found in the area, have no significant impact.

2

Phenotypic plasticity is the ability of an organism to exhibit different phenotypes (i.e. observable traits such as colour andshape) from a given genotype (i.e. all of an individual's genes) as a function of the biotic and/or abiotic environment.

3

Epigenetics: the study of heritable changes in gene function that cannot be attributed to a change in nuclear DNA
sequence.

2