SENDAI—On a cool night in early February, Masatoshi Suzuki carried a black plastic bag containing four macaque carcasses to his laboratory at Tohoku University.
The monkeys were killed as agricultural pests, but for researchers like Suzuki, the animals are invaluable specimens for determining the effects of radiation from the Fukushima nuclear disaster.
Nearly 11 years after the triple meltdown at Fukushima No. 1 Nuclear Power Plant, questions remain about the extent of damage to animals and plants caused by radioactive substances released in the accident.
Suzuki, who specializes in radiobiology, hopes her studies will provide clues to the possible impact of radiation on humans.
He and his colleagues have studied 709 macaques in Fukushima prefecture since 2012. Of all the wildlife species available for study in contaminated areas, macaques are the most similar to humans.
The four dead macaques were given to Suzuki by farmers who had destroyed the animals hours earlier in Namie, a town about 4 kilometers from the crippled nuclear power plant. Parts of Namie are still off-limits due to high radiation levels.
Other primates used in the studies come from off-limits areas in Minami-Soma, a town north of the nuclear plant, and elsewhere in the prefecture.
Researchers are dissecting the carcasses to determine if the livers, lungs, thyroid gland and muscle tissue were affected by radiation from the nuclear accident.
Deformations of aphids and fir trees have been reported since the start of the nuclear disaster.
But Suzuki said he had seen no credible reports of such physical abnormalities in wild animals, including macaques, as well as domestic livestock.
However, damage can occur at the cellular level in animals.
Background radiation levels in most mountain forests in Fukushima and neighboring prefectures are higher than those in residential areas, which have undergone decontamination procedures.
In nature-filled areas that have not been decontaminated, macaques continue to be exposed to radioactive materials while feeding on polluted fruit and other food sources.
According to Suzuki’s studies, muscles had the highest concentration of radioactive cesium of all macaque organs.
The average level of radioactivity in the thigh muscles was around 40,000 becquerels per macaque captured at Namie in fiscal year 2013.
In fiscal year 2018, the figure had dropped to around 20,000 becquerels per macaque.
Researchers found that macaques exposed to higher radiation doses had slightly fewer blood-producing cells in their bone marrow than animals with lower exposure readings. The nuclear accident may have compromised the ability of some macaques to produce blood.
The researchers used the density of radioactive cesium in the muscles of the macaques and in the soil of the areas where they were captured to calculate the level of radiation doses to which the animals were exposed both internally and externally.
Suzuki also said he detected chromosomal abnormalities resulting from radiation damage to genes.
He said radiation exposure can increase stress levels in one organ, but the same dose could have the opposite effect in a different organ. One possible reason for this is that the animal’s defense system has been galvanized to reduce stress levels after exposure.
Suzuki stressed the need to continue monitoring macaques and other animals to determine the impact of prolonged exposure to radiation.
“So far, we have not found any significant health hazards in the macaques studied,” he said. “But they continue to show changes in their cells and organs, albeit minor. We don’t know what these changes will mean in the long term. »
CESIUM PASSING THROUGH THE FOOD CHAIN
A study by other scientists showed that radioactive cesium from the nuclear accident could move through food chains in the environment.
“If we can track the movement of radioactive cesium through the food chain, the results will show us its cycling mechanism in the ecosystem,” said Sota Tanaka, a radioecology researcher at Akita Prefectural University.
He believes that studying the cesium cycle mechanism will help predict its long-term movement and lead to better use of resources in mountain forests and the reconstruction of agriculture in contaminated areas.
Joint research by Tanaka and Taro Adachi, a professor of applied entomology at the Tokyo University of Agriculture, has found that radioactivity levels have been declining year by year in grasshoppers in the rice fields of Iitate, a village west of the stricken nuclear plant which still has outages. boundary areas.
In 2016, all grasshoppers monitored had radioactivity readings below 100 becquerels per kilogram.
But the garden spiders at Iitate showed a wide range of readings from year to year. Their levels of radioactivity were indeed higher in 2015 than in 2014.
In 2016, a spider had a reading of over 300 becquerels per kilogram.
The radioactive cesium remains on the ground even after the rains.
Plants rarely take up cesium through their roots, but can be contaminated by falling cesium particles. And the researchers believe cesium levels in the grasshoppers have steadily dropped because they feed on the leaves of living plants.
As for the spiders, they eat insects with a high cesium content because they feed on contaminated dead leaves mixed with contaminated soil, according to Tanaka.
This may be why eight-legged predators show higher radioactivity readings than grasshoppers, he said.
Their study also found that earthworms had higher levels of radioactivity than grasshoppers and spiders, likely because they eat contaminated soil and wilted leaves.