Researchers have sounded the alarm over river water containing cesium levels at tens of billions of becquerels a day flowing into the sea near Fukushima Prefecture, site of the crippled nuclear power plant.
A joint study by Kyoto University and the University of Tsukuba, among other entities, estimated that water at the mouth of the Abukumagawa river running through the prefecture was contaminated with cesium levels of about 50 billion becquerels a day.
They called for immediate and continued monitoring of the situation.
The daily radiation levels are equivalent to the total of amount of cesium in low-level contaminated water released into the sea in April by Tokyo Electric Power Co., operator of the stricken Fukushima No. 1 nuclear power plant.
The Abukumagawa river runs to the north in the prefecture, near Koriyama and Fukushima, the prefectural capital, and flows into the Pacific Ocean at Iwanuma in Miyagi Prefecture.
Its watershed area spans 5,400 square kilometers, including a vast stretch contaminated by the plant.
The researchers estimated the level for cesium-137 at 29.1 billion becquerels a day and that for cesium-134 at 23.4 billion becquerels a day--both at the mouth of the river.
More than 90 percent of the cesium was contained in small particles, including waterborne clay and other fine-grained soil, while the rest had dissolved in the water.
"The study shows a high level (of cesium) is being carried (into the ocean)," said Yosuke Yamashiki, associate professor of environmental engineering at Kyoto University. "The inflow will likely continue for some time. But the content can be reduced."
Yamashiki said that could be accomplished by taking advantage of the fact that cesium tends to accumulate in areas where there is a dam.
The estimated levels near Date, a city situated at the middle reaches of the river, were 92.5 billion becquerels a day for cesium-137 and 83.8 billion becquerels a day for cesium-134.
The researchers explained that cesium levels are lower at the mouth of the river because deposits may have built up around dams along the way.
The research team monitored the volume of flow and cesium levels in the middle reaches and mouth of the river, as well as its tributaries, in June through August.
The monitoring was commissioned by the science ministry.
The researchers said cesium is continuing to contaminate the river water after it fell to the the ground in the watershed area and was carried into the river by rainfall.
More cesium could contaminate the river during decontamination operations and tilling of rice paddies in preparation for transplanting young rice plants, they added.
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