select search filters
roundups & rapid reactions
before the headlines
Fiona fox's blog

expert reaction to study reporting that monkeys near Fukushima, Japan have lower blood cell counts

A study published in Scientific Reports reported that wild Japanese monkeys inhabiting the forest area of Fukushima City have lower blood cell counts than monkeys from North Japan, and suggested that these changes may be due to exposure to radioactive materials in the wake of the Fukushima Daiichi nuclear disaster.


Prof Jim Smith, Professor of Environmental Science at University of Portsmouth, said:

“I think this study is interesting, but I am highly sceptical of the claim that low blood cell counts in these monkeys is caused by radiation. The levels of radiocaesium in the Fukushima monkeys are about the same as those found in sheep in some parts of the UK following the Chernobyl accident – i.e. extremely low in terms of damage to the animals themselves. The authors do not estimate the radiation doses these monkeys received, but from the information given I have calculated them to be around 6 milliGray per year in the most exposed group. This is a relatively low radiation dose – for example, a medical whole body CT scan of a person gives them a radiation dose of about 10 milliGray at a much higher dose rate.

“It is known that extremely high radiation doses delivered in a very short time – such as doses greater than 1000 milliGray used in cancer treatment in humans – can significantly reduce blood cell counts, but such changes haven’t been seen below about 100 milliGray. So I don’t think it likely that a dose of 6 milliGray delivered over a period of one year would have a significant effect on blood cell count in these monkeys.

“Whilst I agree with the authors that further study would be valuable, particularly in more contaminated areas, I think it much more likely that the apparently low blood cell counts in the Fukushima monkeys are caused by something other than radiation.”


Prof Geraldine Thomas, Professor of Molecular Pathology in the Department of Surgery and Cancer, Imperial College London, said:

“There are a number of problems with this paper, not least that the authors quote references in support of their findings relating to health effects of Chernobyl that are not regarded as scientifically validated.

“I note that the graph (Figure 2) which leads them to suggest that muscle content of Caesium is related to white blood cell count in immature animals is heavily predicated on 5 animals with the highest readings of radioactivity. Take those away and it is difficult to see any correlation at all. In Figure 1 I can see very little real difference between the groups – there is a large standard deviation which makes me highly suspicious of the stats here, and I suspect a 95% confidence interval would show that this could easily be a sampling problem that is inherent with small studies. It is also interesting to note there was no correlation between white cell count and whether the monkeys lived in areas of higher or lower contamination.

“It is also arguable whether measurements in muscle would adequately represent dose to the bone marrow, which is what would really make a difference. A dose of radiation is not like a dose of medicine. The risk of damage to tissue depends partly on the type of radiation released by the radioactive substance. The mSv measurements take into account the type of radiation, and physical and biological half–lives of the isotope, and sensitivities of different tissue types, so are much easier to interpret when relating dose to effect (for more information see

“So overall it is an interesting finding but requires further study – as is suggested by the researchers themselves – to demonstrate that the changes in white cell count is due to radiation exposure rather than to other confounders that have also changed in the environment, such as access to specific foodstuffs or other changes in the environment brought about by the tsunami.

“If we compare with Chernobyl, there is no current scientific evidence to link long term environmental exposure to Cs-137 post-Chernobyl with effects on blood in humans. It is also not clear that the health of these monkeys has even been affected – one would expect not as there does not appear to have been a reduction in their numbers.

“It is important to remember, when trying to extrapolate these findings to humans living in this area, that the human population is recommended not to consume locally grown produce that does not meet Japan’s strict radiological protection limits of 100 kBq/kg. It has already been documented that following this advice leads to undetectable levels of of radiocesium in humans. The monkeys are not subject to these dietary interventions, and would therefore be expected to have low levels of Cs-137 present in their body tissues. However, the actual doses of radiation to tissue received by these animals would be in the order of a few hundredths of a mSv – very small when compared with natural background radiation exposure in this area, and less than one would receive on a flight from London to Tokyo. Much larger studies would be required to validate these findings and their relevance to human health”.

“Unfortunately this is yet another paper with insufficient power to distinguish real effects and relevance to human health. We know that one of the most damaging health effects comes from fear of radiation, not radiation itself; and it concerns me that it will lead to a lot of hype about doses that are, in reality, vanishingly small.”


‘Low blood cell counts in wild Japanese monkeys after the Fukushima Daiichi nuclear disaster’ by Kazuhiko Ochiai et al was published in Scientific Reports  on Thursday 24 July.


Declared interests

Prof Smith: “I currently have a Natural Environment Research Council grant (ca. £450k) studying the effects of radiation on fish at Chernobyl. I have done a small (about £10k, paid to the university) consultancy job for Horizon Nuclear Power (completed 2012) and another of £5k (again paid to the university) for the Japan Atomic Energy Agency (completed 2013). I have also carried out a variety of consultancy to independent regulatory bodies (including Environment Agency; Food Standards Agency) worth about £100k to my institution. I don’t do consultancy in a personal capacity.”

Prof Thomas: “My research projects in the molecular pathology of Chernobyl related thyroid cancer have been supported by grants from the EU, NCI and Sasakawa Foundation.”

in this section

filter RoundUps by year

search by tag