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GENEVA – Infants exposed to radiation near Tokyo Electric Power Co.’s damaged nuclear power plant have a higher risk of developing cancer, though the threat outside the immediate area is low, the World Health Organization said Thursday in the first global assessment of risks from the 2011 disaster.
Girls in the most-affected area of Japan’s northeastern Fukushima prefecture have as much as a 70 percent greater probability of thyroid cancer in their lifetimes, while boys’ risk of leukemia is as much as 7 percent higher, the United Nations health agency said in a report.
TEPCO’s Fukushima Dai-ichi plant was hit by a magnitude 9 earthquake and a 15-meter tsunami on March 11, 2011, that forced about 160,000 people to evacuate. The disaster also left about 132 square kilometers as a no-go zone, some of it uninhabitable for decades. Doses of radiation were too low to affect fetal development or cause birth defects, and there’s no increased health risk outside the prefecture, according to the WHO report.
“Outside the geographical areas most-affected by radiation, even in locations within Fukushima prefecture, the predicted risks remain low, and no observable increases in cancer above natural variation in baseline rates are anticipated,” the Geneva-based WHO said in the 165-page report.
Thursday’s findings confirm a preliminary report published in May that found people outside the most-affected area were exposed to relatively low doses of radiation. The continuing monitoring of children’s health, and of food and the environment, remains important, the WHO said.
Japanese girls and women normally have a lifetime risk of 0.75 percent, and the additional risk for infant girls exposed to radiation in the most-affected area is 0.5 percent, the WHO said. The added risks in the second-most affected area are half those in the highest-dose location, the WHO said. More than twice as many thyroid cancers are diagnosed in women than in men, according to Cancer Research UK.
The U.N. agency said it deliberately used conservative assumptions that may have led it to overestimate the risks.
“It’s clear that more will be detected,” Angelika Tritscher, acting director for WHO’s food safety and zoonosis department, said at a briefing with reporters in Geneva Thursday, referring to thyroid cancer. A zoonosis is an infectious disease transmitted between species.
Infant girls exposed in the worst-affected area also have a 6 percent higher risk of breast cancer, and a 4 percent increase in the risk of developing any solid cancer, according to the report.
A study by Stanford University scientists last year found that radiation from the Fukushima nuclear plant may cause as many as 1,300 cancer deaths globally and as many as 2,500 cases of cancer, mostly in Japan. The WHO said it didn’t have estimates on the number of people affected by radiation.
Emergency workers at the Fukushima Dai-ichi plant have an increased lifetime risk of leukemia, thyroid cancer and all solid cancers, though the accident hasn’t resulted in acute radiation effects among workers and none of the seven reported deaths among workers is attributable to radiation exposure, the report said.
Radiation is measured in becquerels, and its effect on the body is measured in sieverts. Cumulative exposure to 100 millisieverts raises the risk of death from cancer by 0.5 percent, according to Japan’s National Institute of Radiological Sciences.
People in the most-affected locations of Fukushima were exposed to radiation doses between 10 and 50 millisieverts during the first year after the accident, though some infants had exposure to their thyroids of as much as 200 millisieverts, according to the report. Outside of Fukushima and its neighboring prefectures, the doses were between 0.1 and 1 millisievert, according to the report. In the rest of the world, doses were less than 0.01 millisievert.
The nuclear plant may have emitted about 900,000 terabecquerels of radiation into the air at the height of the disaster, Tepco said in May. The total radiation release at the 1986 Chernobyl accident in Ukraine was estimated to be about 5.2 million terabecquerels.
The Fukushima accident didn’t last as long as that in Chernobyl, the geographic spread of radiation was less, and people were evacuated more quickly from 20 kilometers around the Dai-Ichi plant, Tritscher said. The evacuation was “probably the best public health mitigation measure,” Maria Neira, the WHO’s director for public health and environment, said at the briefing.
Less radiation was delivered after the first year in Fukushima than in Chernobyl because of the nature of the radioactive material released, the report said.
— With assistance from Peter Langan in Tokyo.
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