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Seven years after the Fukushima, Japan nuclear disaster began, forcing evacuations of at least 160,000 people, research has uncovered significant health impacts affecting monkeys living in the area and exposed to the radiological contamination of their habitat.

Shin-ichi Hayama, a wild animal veterinarian, has been studying the Japanese macaque (Macaca fuscata), or snow monkey, since before the Fukushima nuclear disaster. Now, his research has shown that monkeys in Fukushima have significantly low white and red blood cell counts as well as a reduced growth rate for body weight and smaller head sizes.

Hayama, who began his macaque research in 2008, had access to monkeys culled by Fukushima City as a crop protection measure. He continued his work after the Fukushima nuclear explosions. As a result, he is uniquely positioned to discover how low, chronic radiation exposure can affect generations of monkeys.

The macaque is an old world monkey native to Japan, living in the coldest climates of all of the non-human primates. Like humans, macaques enjoy a good soak in the mountain hot springs in the region. It is even said that they have developed a “hot tub culture” and enjoy time at the pools to get warm during winter.

However, snow monkeys and humans share more than a love of hot springs. Human DNA differs from rhesus monkeys, a relative of the snow monkey, by just 7%. While that 7% can mean the difference between building vast cities to living unsheltered and outdoors, for basic processes like reproduction, these differences begin to fade. Consequently, what is happening to the macaques in Fukushima should send a warning about the implications for human health as well, and especially for evacuees now returning to a region that has been far from “cleaned up” to any satisfactory level.

Hayama’s research group has published two studies, each comparing data before and after the nuclear catastrophe began, and also between exposed and unexposed monkey populations. In a 2014 study, researchers compared monkeys from two regions of Japan, one group of monkeys from the Shimokita region, 400 Km north of Fukushima, and a second group of monkeys from contaminated land in Fukushima.

The monkeys in Fukushima had significantly low white and red blood cell counts. Other blood components were also reduced. The more a radioactive isotope called cesium was present in their muscles, the lower the white blood cell count, suggesting that the exposure to radioactive material contributed to the damaging blood changes. These blood levels have not recovered, even through 2017, meaning that this has become a chronic health issue.

Changes in blood are also found in people inhabiting contaminated areas around Chernobyl. Having a diminished number of white blood cells, which fight disease, can lead to a compromised immune system in monkeys as well as people, making both species unable to fight off all manner of disease.

Hayama followed up his 2014 study with another in 2017 examining the differences in monkey fetus growth before and after the disaster. The researchers measured fetuses collected between 2008 and 2016 from Fukushima City, approximately 70 km from the ruined reactors. Comparing the relative growth of 31 fetuses conceived prior to the disaster and 31 fetuses conceived after the disaster revealed that body weight growth rate and head size were significantly lower in fetuses conceived after the disaster. Yet, there was no significant difference in maternal nutrition, meaning that radiation could be responsible.

Smaller head size indicates that the fetal brain was developmentally retarded although researchers could not identify which part was affected. The mothers’ muscles still contained radioactive cesium as in the 2014 study, although the levels had decreased. These mothers had conceived after the initial disaster began, meaning that their fetuses’ health reflects a continuing exposure from environmental contamination. This study mirrors human studies around Chernobyl that show similar impacts as well as research from atomic bomb survivors. Studies of birds in Chernobyl contaminated areas show that they have smaller brains.

Although Hayama has approached radiation experts to aid with his research, he claims they have rejected it, saying they don’t have resources or time, preferring to focus on humans. But humans can remove themselves from contaminated areas, and many have chosen to stay away despite government policies encouraging return. Tragically, monkeys don’t know to leave, and relocating them is not under discussion, making study of radiation’s impact on their health vital to inform radiation research on humans, the environment, and any resettlement plans the government of Japan may have.

Hayama presented his work most recently as part of the University of Chicago’scommemoration of the 75th Anniversary of the first man-made controlled nuclear chain reaction. His work follows a long, important, and growing line of research demonstrating that radiation can not only damage in the obvious ways we have been told, but in subtle, yet destructive ways that were unexpected before. The implications for humans, other animals, and the environment, are stark.  Cindy Folkers is the radiation and health specialist at Beyond Nuclear.