Officials in Yokohama City confirmed that radiocative strontium-90 has been found at three locations in Yokohama, including sediment on the roof of an apartment in the city, which was reported on Oct. 12.
The level of radioactive strontium-90 at the two new locations were 59 becquerels and 129 becquerels per kilogram (2.2 pounds). The apartment rooftop in Yokohama, where tests were conducted by a private research institute found more than 60,000 becquerels of radioactive cesium per kilogram of sediments.
Strontium-90 is a radioactive isotope of strontium, with a half-life of about 30 years. Its presence in bones can cause bone cancer, cancer of nearby tissues and leukemia.
This is the first time that radioactive strontium has been found so far from the crippled Fukushima Daiichi nuclear power plant. Yokohama is about 250 kilometers (155 miles) from the Fukushima plant.
In Yokohama, the local government has asked the Japanese central government to investigate areas beyond 100 kilometers (60 miles) from the Fukushima plant for radioactive material.
The operator of the Fukushima Daiichi nuclear power plant says it has detected high levels of a radioactive substance that tends to accumulate in human bones.
Tokyo Electric Power Company says it took soil samples on May 9th at 3 locations about 500 meters from the No.1 and No.2 reactors and analyzed them.
The utility detected up to 480 becquerels of radioactive strontium 90 per kilogram of soil. That’s about 100 times higher than the maximum reading recorded in Fukushima Prefecture following atmospheric nuclear tests carried out by foreign countries during the Cold War era.
TEPCO reported detecting 2,800 becquerels of strontium 89 per kilogram of soil at the same location.
This is the second time since April that radioactive strontium has been found inside the plant compound.
The substance was also detected in soil and plants more than 30 kilometers from the Fukushima nuclear power station in March.
When people inhale radioactive strontium, it accumulates in bones. Scientists say that strontium could cause cancer.
Tokyo Electric Power says it believes that radioactive strontium was released from the damaged plant and it will continue to monitor radiation levels.
An expert on radioactive substances says he thinks radioactive strontium may continue to be detected around the Fukushima Daiichi nuclear plant. But he says the strontium levels that might be detected in soil will be far lower than those of the radioactive cesium released in the accident by a factor of several thousand.
Yoshihiro Ikeuchi of the Japan Chemical Analysis Center says strontium tends to accumulate in bones, like calcium. But he also says its levels in the air are thought to be lower than those for soil and even if people inhale the substance, no health problems will be caused by such internal exposure to radiation.
Wednesday, June 01, 2011 02:59 +0900 (JST)
Copyright NHK (Japan Broadcasting Corporation)