Chernobyl and Fukushima nuclear accidents will affect small mammals for a long time to come

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The two accidents resulted in widespread radioactive fallout in nature. Such fallouts cause a relatively low exposure to ionising radiation, but in the worst case scenario such exposure can last for several centuries. Tapio Mappes’ study examines the evolutionary impacts of low ionising radiation on the animals in the area, including their populations, reproduction, mortality and physiology. Although the study is in its early stages, some questions have already been answered.

Size of the population, brain and inner organs affected

Both external and internal factors influence the dose of radiation that affects animals. Such factors include soil, air, nutrition, water and other sources of background radiation. In the wild, animals absorb radiation in a different way to humans because they are unable to take precautions or select their food.

Radiation is measured through absorbed dose rate. Normal background radiation is up to 0.3 microsieverts per hour. Mappes has found that a rise in radiation level to a few microsieverts per hour is already enough to affect brain size in voles.

“The higher the intensity of radiation, the lower the population density of small mammals. Reproductive success and individual development suffer. If radiation intensity rises to ten microsieverts per hour, this is approximately one hundred times higher than natural radiation. Once this happens, population densities are so low that it’s difficult to find any specimens to study.”

Radiation reduces the size of litters and the numbers of reproducing individuals, while affecting the size of the most important internal organ, the brain. Deterioration occurs in the quality of sperm produced. The voles develop cataracts and go blind, affecting females in particular. These factors may result in voles dying more easily and at a younger age, which would explain lower population densities in areas affected by higher radiation.

Cells degenerate and age faster

Mappes finds that the shortening of telomeres as a consequence of radiation is another significant observation. Telomeres are DNA chains at the end of chromosomes, with a number of functions including impacts on the regeneration, ageing and degeneration of cells.  The in-built repair mechanisms of cells weaken as telomeres become shorter.

“Because the Fukushima accident occurred relatively recently, it’s possible that some long-term consequences have yet to emerge,” says Mappes. In Fukushima, the radiation is slightly less intense than in Chernobyl, but more evenly distributed over a fairly large area. Radiation influence on animal populations in Fukushima is nonetheless strikingly similar.

More information:

Tapio Mappes, University Lecturer
University of Jyväskylä, Department of Biological and Environmental Science
tel. +358 40 586 0978

Academy of Finland Communications
Risto Alatarvas, Communications Specialist
tel. +358 295 335 007

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