Additional information to what I posted on Sunday, as information is very slowly filtering through to the Internet.
195 becquerels/kg of strontium-90 was detected from the sludge on top of the apartment building in Kohoku-ku, Yokohama City, where the very high level of radioactive cesium was also detected back in mid August, though the news did not break until mid September. (See my post here.)
So in the same sludge sample, there were:
Cesium-134: 29,775 becquerels/kg
Cesium-137: 33,659 becquerels/kg
Strontium-90: 195 becquerels/kg
Yokohama City is supposedly conducting its own testing of the different sample from the same rooftop using the same laboratory, and the result may be announced this week.
The ratio of strontium-90 to cesium-137 in the soil samples within 80-kilometer radius from Fukushima I Nuclear Power Plant varies widely from less than 0.1% to over 8% - in other words, as the Ministry of Education and Science said in its report on strontium and plutonium, there is no telling if strontium is there if there is cesium.
There is an unconfirmed piece of information on a blog by a Yokohama citizen that the city knew about radioactive strontium in the sludge as early as mid September and dismissed it because the city's radiation advisor said it was impossible to find radioactive strontium of Fukushima origin in Yokohama.
The reality seems more like this, though: Since strontium was not supposed to fly far from Fukushima, so the city bureaucrats didn't know what to do or how to respond. (from communication with the person who ordered the testing)
Yasumi Iwakami, independent journalist who broke the news yesterday, asked the Minister of Education and Science in the press conference on October 11 (in Japan) and asked about strontium in Yokohama. The minister said "Thank you for your information. We may do the testing in wider area if necessary." Other people who was watching the press conference live in USTREAM said the Minister answered "There is no report to me yet."