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.