YOKOHAMA (Kyodo) -- Radioactive strontium exceeding normal quantities has been detected in sediment from atop an apartment building in Yokohama, some 250 kilometers from the damaged Fukushima Daiichi nuclear power plant, city officials said Wednesday.

While the discovery of 195 becquerels of strontium 90 in the rooftop sediment has fueled concerns that leaked radiation may have spread further than the government had expected, the officials said the city office is carefully examining where the material came from.
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If inhaled or ingested, strontium tends to accumulate in bones just like calcium. It is believed to cause bone cancer and leukemia.

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[link to mdn.mainichi.jp]