Radiation effects on Fukushima monkeys

Radiation Effects on Fukushima Monkeys

The radioactive material injected into the environment by the 2011 Fukushima accident, the world’s second largest nuclear disaster after Chernobyl, has led to widespread consequences on human health. Studies tell us that this radioactivity is going to persist in the environment for a long time and highlight that there is no safe dose below which there are no side effects.

Low dose chronic radiation present in the environment can increase your risk of cardiovascular damage, as shown by very recent studies. [1] [2] And perhaps the most damaging health effects are coming from the fear of radiation itself, leading to long-term social, mental and emotion consequences among the survivors.

But the consequences of the meltdown of Fukushima Daiichi Nuclear Power Plant has also seriously damaged the wildlife – leading to genetic damage, increased mutation rates and population decline in non-human organisms such as butterflies, monkeys and birds.

Effects of Radiation on Japanese Monkeys

In a new study, the researchers compared changes in the foetal growth of Japanese monkeys in Fukushima City before and after the nuclear power plant disaster. Prior to this research, several studies have investigated the biological effects of Fukushima disaster on insects and animals; for example, morphological abnormalities in pale grass blue butterfly (in the form of reduced forewing size and retarded growth). At the same time, there is a lack of research that could throw some light on the effects on long-term exposure of radiation on mammals with longer life span. This is the first study to investigate such effects on a non-human primate population.

The study found that the monkeys conceived after the disaster (therefore, continuously exposed to radiation in the foetus) had lower body weight, and smaller head size and smaller brains compared with ones born before the disaster. [3] 

Previously in 2012, the same team studied the effects of radiation exposure on the blood components of wild Japanese monkeys from the Fukushima City, located approximately 70km from the Fukushima power plant. To compare the results, the team also examined the monkeys dwelling the Shimokita Peninsula in Aomori Prefecture, located approximately 400 km from the disaster site responsible for releasing massive amounts of radioactivity in the environment.

It was found that total muscle caesium concentration was higher in Fukushima monkeys. This population also had significantly lower white and red blood cell counts, hemoglobin, and haematocrit, compared with monkeys from Shimokita. The study concluded that “the exposure to some form of radioactive material contributed to hematological changes in Fukushima monkeys.” [4]

In addition, white blood cell levels in immature monkeys was found to be inversely related to the radio-caesium concentrations in their muscles, a pattern not observed in mature monkeys suggesting that immature monkeys were more vulnerable to radioactive exposure.

Hamaya, one of the study authors, explained that this appears to be chronic, “We have taken these tests from 2012 through 2017, and the levels have not recovered. So we have to say this is not an acute phenomenon. It has become chronic, and we would have to consider radiation exposure as a possible cause.” [5]

Such hematological abnormalities have been previously observed as a long-term effect of low-dose, chronic exposure to radiation. A team of researchers conducted hematological studies of Ukrainian children exposed to the Chernobyl accident and concluded:

More than 10 years after the Chernobyl accident, children in the Narodichesky region, Ukraine, approximately 80 km from Chernobyl, showed decreased counts for red and white blood cells and platelets, and a reduced concentration of hemoglobin associated with persistent residential 137Cs exposure.” [6]

New insights into the effects of chronic exposure to low-dose ionizing radiation

A series of articles detailing the consequences of radiation exposure on wildlife (in Chernobyl and Fukushima) has been published in the Journal of Heredity. These studies looked into various aspects such as decline in population size, genetic damage and morphological abnormalities in birds, monkeys, butterflies and even plants. [7] [8] [9]

There was a common premise to all the published studies that low-dose, persistent exposure to ionizing radiation causes genetic damage and increased mutation rates in reproductive and non-reproductive cells.

One of the most notable findings was that different species show variation in their sensitivity to radiation exposure. For example, for birds in Chernobyl, brightly colored and long-distance migrants were found to be strongly resistant to radiation damage. Studies show that some birds may have adapted to continuous radiation exposure by altering the way they use anti-oxidants to counter the radiation induced oxidative stress. Studies of both birds and humans exposed during Chernobyl accident show that chronic exposure to low-dose robs the body of antioxidants and contributes to oxidative damage.

These studies also delved into varied repair mechanisms that help some organisms deal with and survive the exposure better than the others.

As a direct repercussion of exposure to radiation in the environment (through contaminated air, water and food), birds and mammals at Chernobyl were found to have cataracts and smaller brains.

Studies also show that low-dose radiation may have significant impact on the reproductive traits of birds, insects and animals. A 2013 analysis for Chernobyl birds found that birds living in radioactive areas had higher rates of malformed sperm than those living in control areas across Europe. [10] Overall, declining population sizes of several species could be partly explained by low-dose, chronic radiation. [11]

Barn swallows from Fukushima have been found to have white spots on their plumage, an effect well-documented in birds from Chernobyl. A study found that cumulative effects of radioactivity resulted in decrease in population and bio-diversity of birds in Fukushima, a trend similar to the one observed in the birds of Chernobyl.

The study reported that “even though levels of background radiation decreased over time, the relationship between abundance and radiation became more negative over time. The relationship between abundance and radiation became less negative with increasing trophic levels. These findings are consistent with the hypothesis that the negative effects of radiation on abundance and species richness accumulate over time.” [12]

The effects of radiation in Fukushima region has also been documented in Pale grass blue butterfly, the most common species of butterfly found in Japan. It was found that radiation exposure has led to forewing size reduction, retarded growth, high mortality rates and high abnormality rates among both the contaminated butterflies collected at the site and in the laboratory reared butterflies with parents collected from the contaminated site. [13]

However, when the offspring of the contaminated butterflies (second generation) were fed an uncontaminated diet, the survival rates improved again. On the other hand, the rate of death and abnormalities were higher in the group of offspring that were fed contaminated sorrel. This implies that eating uncontaminated food may help improve survival and normality rates in second generation, and this possibility may even apply to humans. 

These studies also contribute to understanding the effects of radiation exposure during medical scans. As Timothy Mousseau, Professor of Biological Sciences, University of South Carolina, who has also co-led many of the above-mentioned studies, explains: We are increasingly relying on nuclear radiation for medicine and medical imaging and the average doses received by the general population in more developed countries is increasing dramatically. Studies of Chernobyl and Fukushima provides another tool for investigating the potential consequences of such increasing exposures.” [14]


  1. Azimzadeh et al. Proteome analysis of irradiated endothelial cells reveals persistent alteration in protein degradation and the RhoGDI and NO signalling pathways. Internation Journal of Radiation Biology. 2017
  2. Tapio S. Pathology and biology of radiation-induced cardiac disease. J Radiat Res. 2016
  3. Hamaya et al. Small head size and delayed body weight growth in wild Japanese monkey fetuses after the Fukushima Daiichi nuclear disaster. Scientific Reports. 2017.
  4. Ochiai et al. Low blood cell counts in wild Japanese monkeys after the Fukushima Daiichi nuclear disaster. Scientific Reports. 2014.
  5. Jeff McMahon. Three Ways Radiation Has Changed The Monkeys Of Fukushima. Forbes. 2016.
  6. Stepanova et al. Exposure from the Chernobyl accident had adverse effects on erythrocytes, leukocytes, and, platelets in children in the Narodichesky region, Ukraine: A 6-year follow-up study. Environmental Health 2008
  7. Timothy A. Mousseau Anders P. Møller. Genetic and Ecological Studies of Animals in Chernobyl and Fukushima. Journal of Heredity. 2014.
  8. Tomoko Y. Steen Timothy Mousseau. Outcomes of Fukushima: Biological Effects of Radiation on Nonhuman Species. Journal of Heredity. 2014.
  9. Taira et al. Fukushima’s Biological Impacts: The Case of the Pale Grass Blue Butterfly. Journal of Heredity. 2014.
  10. Hermosell et al. Patterns of sperm damage in Chernobyl passerine birds suggest a trade-off between sperm length and integrity. Biol Lett. 2013.
  11. Møller AP, Mousseau TA. Species richness and abundance of forest birds in relation to radiation at Chernobyl. Biol Lett. 2007
  12. A. P. Møller, I. Nishiumi & T. A. Mousseau. Cumulative effects of radioactivity from Fukushima on the abundance and biodiversity of birds. J Ornithol. 2015.
  13. Nohara et al. Ingestion of radioactively contaminated diets for two generations in the pale grass blue butterfly. BMC Evolutionary Biology. 2014
  14. Hannah Osborne. Chernobyl and Fukushima exclusion zones: Nuclear disaster sites are not wildlife havens. International Business Times. 2016.