The science ministry, citing 60 sites around Japan, said it found no radioactive strontium contamination caused by the Fukushima nuclear crisis last year.
The ministry, which had been investigating radioactive strontium released by nuclear meltdowns triggered by the Great East Japan Earthquake, released a map of soil contamination in eastern Japan on Sept. 12.
It said all strontium deposits identified at the 60 locations were due to past atmospheric nuclear tests conducted decades ago by the United States and the Soviet Union.
The science ministry surveyed soil samples from 50 locations outside an 80-kilometer radius of the Fukushima No. 1 nuclear power plant with air radiation levels of 0.2 microsievert per hour or more. The 50 sites are in the 10 prefectures of Iwate, Miyagi, Fukushima, Ibaraki, Tochigi, Gunma, Saitama, Chiba, Tokyo and Yamanashi. The ministry also analyzed soil from 10 locations in Soma, Fukushima Prefecture, where a June 2011 survey had identified a high ratio of strontium to radioactive cesium.
The maximum concentration of strontium-90 deposits was 130 becquerels per square meter in Nishigo, Fukushima Prefecture. No strontium was detected at 19 of the sampling locations.
All readings were below the 950 becquerels per square meter detected in Ibaraki Prefecture in 2004, the maximum measurement in Japan during an 11-year period from 1999 to 2009.
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