Radioactive cesium measured in samples of silt taken from Tokyo Bay has increased to 1.5-13 times the amount detected in similar samples last August, according to a survey conducted by Kinki University.
The cesium is believed to have entered the bay via rivers after its release from the Fukushima No. 1 nuclear power plant following last year's accidents there.
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The Japan Times reports:
Cesium Spikes in Tokyo Bay
Contamination linked to Fukushima plant
Sludge samples taken at the mouths of two major rivers emptying into Tokyo Bay showed radioactive cesium contamination linked to the Fukushima No. 1 nuclear plant crisis grew by 1.5 to 13 times since August, a researcher at Kinki University said Monday.
"If the contamination were to spread to fish, it is possible that radioactive isotopes could accumulate when bigger fish feed on smaller ones"The contamination poses no immediate health risk since no seafood from Tokyo Bay has seen contamination levels exceed the government-set threshold. But close, long-term monitoring of the seabed mud is needed, said Hideo Yamazaki, professor at Kinki University's Research Institute for Science and Technology.
"Contamination is flowing into the bay from rivers, including the Edogawa River, where cities with high radiation levels like Kashiwa (in Chiba Prefecture) are located upstream," Yamazaki told The Japan Times.
"Contaminated sludge appears to be . . . accumulating on the bottom at the mouth of the rivers," he added.
Yamazaki, an expert on how radiation and chemical substances impact the environment, and his team took the samples at three locations at the mouths of the Arakawa and Edogawa rivers on April 2 following studies carried out in August.
Samples of mud pulled from 1 meter below the seabed at the sites turned up cesium contamination ranging from 7,305 to 27,213 becquerels per square meter. The August readings were between 578 and 18,242 becquerels per square meter.
Yamazaki noted a thirteenfold rise was detected in a spot where the August readings were relatively low. He said, however, the contamination does not pose a health threat, even if a child were to play in the water.
Although radioactive mud will continue to flow into the bay, the peak contamination concentrations should be within the next couple of years, considering that the half-life of cesium-134 is about two years, Yamazaki said.
"If the contamination were to spread to fish, it is possible that radioactive isotopes could accumulate when bigger fish feed on smaller ones," he said. "We're scheduled to continue our monitoring in the following years" to study such cases.
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Last month, Japan's NHK-TV reported:
The health ministry has detected radioactivity above the legal limit in fish caught off Fukushima Prefecture and 11 kinds of vegetables grown in the prefecture.
The ministry says it found 12,500 becquerels per kilogram, or 25 times the limit, of radioactive cesium in small fish called sand lances caught off Iwaki City, south of the Fukushima Daiichi nuclear plant on Wednesday. It also discovered 12,000 becquerels, or 6 times the limit, of radioactive iodine in the fish.
On April 7th, sand lances caught off the city were already found to be contaminated with radioactive cesium in excess of the limit. Sand lances caught off Ibaraki Prefecture, south of Fukushima, were also found to be polluted with the radioactive substance.
The central government says sand lances are currently not being sold as fishing cooperatives in the 2 prefectures are not in operation.
Radioactivity was also detected on 11 kinds of vegetables sampled in Fukushima on Monday.
Authorities detected 1,960 becquerels per kilogram, or 4 times the legal limit, of cesium on Japanese parsley, known as Seri, grown in Soma City.
On Wednesday, the government banned the shipment of some shiitake mushrooms grown outdoors in eastern Fukushima after detecting radioactivity above the legal limit.
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