YOKOHAMA -- Radioactive strontium has been found in a street gutter in Yokohama, appearing to confirm that the radioactive isotope has spread far beyond districts close to the Fukushima No. 1 nuclear power plant.
YOKOHAMA -- Radioactive strontium has been found in a street gutter in Yokohama, appearing to confirm that the radioactive isotope has spread far beyond districts close to the Fukushima No. 1 nuclear power plant.
Sediment in the gutter in the Okurayama district of Kohoku Ward contained 129 becquerels of radioactive strontium-89 and strontium-90 combined per kilogram, city officials announced on Oct. 14. The results follow an earlier report that deposits of strontium had been found on a nearby apartment building's rooftop.
"We believe (the deposits) were caused by the disaster at the Fukushima No. 1 nuclear power plant," a city official said. "We cannot judge potential risks. We want to consult with the central government."
Radioactive cesium of 39,012 becquerels per/kg was also detected in the sample from the gutter but it is the presence of strontium that makes the Yokohama reports exceptional. There had previously been no reports of strontium contamination beyond 100 kilometers of the Fukushima plant.
Although Kohoku Ward is about 250 kilometers from the Fukushima plant, the concentration found in the gutter is higher than the 77 becquerels per kilogram detected in soil in Fukushima city between April and May.
Dirt at the bottom of a dry fountain in the Shin-Yokohama district in Kohoku Ward was also found to contain 59 becquerels/kg of strontium and 31,570 becquerels per/kg of cesium.
In mid-September, the city took dirt samples from the roof of an apartment building where a local resident had reported radioactive strontium, as well as from the gutter in Okurayama and the fountain in Shin-Yokohama. A private lab was commissioned to analyze the data.
Although the city did not reveal the measurements from the apartment roof, saying it did not have permission from the occupants, the resident who filed the initial report said the city found 236 becquerels of strontium per kilogram.
Dirt from the contaminated locations has since been removed and radiation levels in the atmosphere around the gutter in the Okurayama district have fallen to 0.13 microsievert per hour from 0.91 microsievert per hour, city officials said on Oct. 14. Atmospheric radiation at the fountain in Shin-Yokohama has fallen to 0.09 microsievert per hour from 0.13 microsievert per hour.
Explaining the concentration of radioactive materials in particular areas, a city official said: "Dirt and water are likely to gather and accumulate in those spots. We would like to decontaminate such areas."