Data from the Tokyo Metropolitan Institute of Public Health show atmospheric radiation levels in the capital are at the same level as before the Fukushima nuclear disaster started three years ago and are below those in Paris and London.
The average radiation level in central Tokyo was 0.0339 microsievert per hour in Shinjuku Ward on March 6, data showed. That’s about the same as the day before the March 11, 2011, earthquake and tsunami caused three reactor core meltdowns at the Fukushima No. 1 plant, 220 km to the northeast.
That reading compares with 0.085 microsievert in London and 0.108 microsievert in Seoul on March 3, and 0.057 microsievert in Paris on Feb. 27, according to a compilation of world monitoring sites on the website of the Japan National Tourism Organization. Radiation levels in central Tokyo were as high as 0.809 microsieverts per hour on March 15, 2011, before declining to 0.0489 microsievert by the morning of March 18.
Radiation occurs naturally in the environment. While a careful search could still reveal trace levels of Fukushima-linked radioactivity in Tokyo, it now barely registers over readings from background sources, such as solar particles, rocks and soil, said Kathryn Higley, who heads the nuclear engineering and radiation health physics department at Oregon State University in Corvallis.
“You have this widely ranging natural background,” Higley said in a telephone interview. “It varies because of the geology. It varies because of your elevation.”
Radiation levels in central Tokyo on March 15, 2011, peaked at about 24 times the level of the day before the accident, prompting thousands of expatriates to flee the country over the following few months.
Last year’s record number of foreign visitors and rising enrollment at international schools show how those concerns have abated, as Tokyo’s radiation readings fall below those in other major cities.
New York recorded 0.094 microsievert an hour on May 31, 2011, according to the last available Geiger counter reading from Background Radiation Survey, a project where owners of the equipment feed their readings into a central database.
By comparison, a commercial flight exposes passengers to about 10 microsieverts per hour, according to the Health Physics Society’s website.
Closer to the wrecked plant, levels remain high enough to prevent the return of many of the 160,000 residents evacuated after the disaster started.
In the town of Namie, about 10 km northwest of the plant, levels were as high as 17.59 microsieverts per hour at 8 a.m. on Friday, prefectural data show.
If sustained for a full year, that would be 154 times the maximum possible dose of 1 millisievert per year recommended for public exposure by the International Commission on Radiological Protection. The high radiation has made Namie part of an area of the northeast where it will be a “long time” before residents can return, according to a Feb. 18 presentation by Masako Ogawa, an Environment Ministry director.
Tests also still find levels higher than the government safety guidelines of 100 becquerels per kilogram of cesium in small amounts of fish caught in local waters.
The Fisheries Agency found fish with levels exceeding guidelines in 24 of the 2,777 samples tested in January and February, including a rockfish caught off the Fukushima coast with 500 becquerels per kilogram, according to Haruo Tominaga, associate director of the agency’s processing and marketing division.
Health officials in Fukushima Prefecture tested 254,000 residents aged 18 or under at the time the disaster struck and had detected 75 with definitive or suspected thyroid cancer as of Feb. 7, the Asahi Shimbun reported.
Hokuto Hoshi, a doctor involved in the prefectural survey, said the cases are not thought to be connected to the meltdowns.