The Effects of Fukushima Fallout on Butterflies



The Fukushima-Daiichi nuclear disaster in 2011 is widely considered to be the world’s second-worst nuclear disaster (after Chernobyl), leading to huge concerns about the potentially hazardous material that leaked out into the wider environment.

A team of Japanese researchers has been looking at how eating leaves contaminated by Fukushima fallout could affect the development and survival rates of pale grass blue butterflies.

So, what’s the point?

No-one was killed in the immediate radiation leak, and a recent report by the World Health Organisation stated that ‘no discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants’.

However, the mid-term and long-term effects on the local wildlife and wider environment are not yet clear. Potential danger can come from main two sources: chemical poisoning and ionising radiation.

Ionising radiation occurs when an atom with an ‘unstable’ nucleus releases energy in the form of either a particle or high-energy light. It is the bombardment of living tissue with this radiation that can cause direct damage to the cells or to the DNA, which can result in mutations.

Radioactive materials release the majority of their radiation over differing periods of time, ranging from fractions of a second to thousands of years. Shorter-lasting isotopes are more of an immediate cause for concern as these result in a more concentrated dose of radiation.

This study concentrated on two radioactive isotopes of Caesium (134 and 137), with half-lives of ~2 and 30 years respectively. This means the effects of the radiation can be expected to remain in the environment for decades, although they will become less dangerous over time.

Understanding how severely the radiation has affected the wildlife in regions across the country could help to direct future conservation efforts and limit any further damage to the ecosystem.


What did they do? 

The scientists collected over 500 butterfly larvae (Zizeeria maha) and divided them into 5 groups. Each group was raised on a diet of leaves collected from various locations thought to have been hit by different levels of radioactive fallout and one that was relatively far away (the control group).

The scientists tracked the progress of the larvae to see if there was a link between the radioactivity (specifically Caesium-134 and Caesium-137 activity) of the leaves and in the larvae and how likely they were to survive or develop abnormalities.

Did they prove anything?

Generally, the more radioactive the leaves were, the more abnormalities were seen and the lower the survival rate of the larvae.

Only 6.2% of the control group developed abnormalities compared to around 75% of the 3 most contaminated groups.

Similarly, the death-rate rose from 4.8% to 63% as radioactivity  of the leaves increased. Interestingly, the death-rate for the most contaminated leaves actually fell to 46.6%.

These larvae were also found to have an unusually low level of Caesium-134 in their bodies – only the control sample was lower.

So, what does it mean?

The results do seem to show a link between the amount of radioactive Caesium absorbed by the larvae and the likelihood of death and developing abnormalities.

The researchers reckon that the Caesium in the most-contaminated leaves may have been so concentrated that it damaged the digestive tract of the larvae, preventing them from absorbing more and actually improving their chances of survival.

They claim (perhaps optimistically) that the larvae are ‘generally resistant to internal radiation exposure’, citing that the ‘mortality and abnormality rates never reached 100%’.

While this is true, it can be argued that a mortality rate of almost two-thirds and an abnormality rate of around three-quarters are significant and can be expected to have an important impact on the ecosystem.

Bear in mind also that these leaves weren’t taken from right next to the nuclear plant – they were taken from towns and cities dozens of kilometers from the site, which are still inhabited by humans.


The fallout of Fukushima, both literal and figurative, will no doubt continue to make headlines for years to come. Three years on from the disaster and the effects on people and wildlife are only just beginning to be understood.

But the more information that can be gathered, the more likely we are to effectively curb any further damage and prevent the effects of Fukushima from getting worse.

Original article in Scientific Reports May 2014

All images are open-source/Creative Commons licence.
Credit: JM Garg (First); Nyerguds et al.(Second); KEI (Third)

Text © thisscienceiscrazy. If you want to use any of the writing or images featured in this article, please credit and link back to the original source as described HERE.

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