Snakes monitor radioactive contamination

You might be familiar with the concept of canaries in a coal mine, but have you heard of snakes in a radioactive zone?

Ten years on from the 2011 Fukushima disaster in Japan – the most severe nuclear accident since Chernobyl – researchers are still investigating the ecological impacts on the landscape. Now, a study led by the University of Georgia in the US has measured radioactive contamination in the Fukushima Exclusion Zone – using snakes.

Over three months, the researchers used tiny GPS transmitters taped to the backs of Japanese rat snakes to monitor their movement across the rugged terrain of the Abukuma Highlands, about 25 kilometres northwest of the power plant. They also used manual VHF tracking to locate the snakes every few days and identify the habitat in which they were located – from grasslands to riversides to buildings.

“Our results indicate that animal behaviour has a large impact on radiation exposure and contaminant accumulation,” says Hannah Gerke, lead author on the study, from the University of Georgia.

A hand holding a snake, showing a gps tracker attached to the snake's tail.
A Japanese rat snake is fit with a GPS transmitter that will allow researchers to track its movements over the next several weeks. Credit: Hannah Gerke

“Studying how specific animals use contaminated landscapes helps increase our understanding of the environmental impacts of huge nuclear accidents such as Fukushima and Chernobyl.”

The study, published in the journal Ichthyology & Herpetology, found that snakes are even better bioindicators of residual radioactivity than more mobile species such as songbirds, East Asian raccoon dogs and wild boar.

“Snakes are good indicators of environmental contamination because they spend a lot of time in and on soil,” says co-author James Beasley, also from the University of Georgia. “They have small home ranges and are major predators in most ecosystems, and they’re often relatively long-lived species.”

The rat snakes were found to move an average of 65 metres per day.

More than half of the tracked snakes hung out in buildings such as abandoned barns and sheds, which may have helped shield them from contaminated soil, but in winter, when they shelter underground, their risk of exposure is increased.

This work builds on a 2020 study, also led by Gerke, that captured snakes and measured their levels of radiocesium, a common radionuclide that accumulates in the bodies of animals, especially predators. The study found that these levels correlated to the radiation levels in the soil where the snakes were captured, raising the possibility of using snakes as biomarkers to determine differing levels of contamination across uneven terrain. This new work adds in information about the snakes’ movement and habitat use, clarifying the link between these and contaminant exposure..

The new study was also part of a larger one tracking animal behaviour and radiation exposure within the Fukushima Exclusion Zone. Last year, a research team led by Beasley captured footage of more than 20 species within the zone, showing that it still contains abundant wildlife – although presence is not an indicator of an animal’s health.

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