Low levels of radioactive strontium have been detected in soil at 11 locations in Fukushima Prefecture, the government announced June 8.
The radioactive strontium was found in samples taken at places around the region where radioactive cesium was previously detected.
The government says continued monitoring is necessary because some strontium have a long half-life and could affect human health for a prolonged period if absorbed by the body. However, at the levels found, the substance is not a health hazard, the ministry said.
The Ministry of Education, Culture Sports, Science and Technology said it took soil samples between April 10 and May 19.
The ministry detected small amounts of the substance--77 becquerels of strontium-90 per kilogram and 54 becquerels of strontium-89 per kilogram of soil--in Fukushima, 62 kilometers from the crippled Fukushima No. 1 nuclear power plant.
Strontium-90 has a half-life of about 29 years, and strontium-89 a half-life of about 50 days.
Of the 11 locations, Namie's Akogi district had the most accumulation, registering 250 becquerels of strontium-90 and 1,500 becquerels of strontium-89 per kilogram of soil.
At Iitate, 36 km northwest of the Fukushima plant, 120 becquerels of strontium-90 and 1,100 becquerels of strontium-89 were found.
These figures are higher than amounts detected within the 20-km no-go zone from the plant.
The substance was also detected in Tamura, Hirono, Kawauchi, Minami-Soma and Nihonmatsu, all in the prefecture.
The ministry says it will continue to monitor and analyze soil samples.
Radioactive strontium tends to accumulate in bones when absorbed.
Shigeharu Kato, a senior official of the Cabinet Office who is at the Nuclear Safety Commission Secretariat, said strontium always exists when a certain level of cesium is present. When considering strontium's presence in food grown in contaminated soil, as long as people adhere to the permissible limits for cesium, they won't have to worry about the influence of strontium, Kato said.
Although the amounts detected were small and much lower than levels harmful to human health, the government will continue monitoring by increasing soil sample locations.
Hideo Yamazaki, a professor of environmental analysis at Kinki University, says about the same amount of cesium and strontium are created after nuclear fission. Cesium, however, is likely to evaporate and scatter widely.
The education ministry found cesium scattered mainly to the northwest of the Fukushima plant after the accident.
"We can expect that where cesium is detected, a certain amount of strontium will be found," Yamazaki said. "But strontium is extremely difficult to measure, so the data has yet to be obtained."
According to the education ministry, in locations where cesium-137 was detected, radioactive strontium levels were equal to about 0.4 to 0.1 percent of the level of cesium found.
The education ministry said, "That amount is not a risky level even if the radiodensity is converted to radiation doses. Each figure is far below the level affecting human health."
In fact, as the acceptable standard of cesium in food has been set assuming a certain percentage of strontium is present, it is unlikely that there is influence on health.
The Nuclear Safety Commission cautions against absorbing the substance into the body through inhalation.
"It is necessary to study at each site whether the strontium is not stirred up from the soil," an NSC official said.
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