Researcher Hideo Yamazaki from Osaka’s Kinki University found that contaminated sludge has accumulated due to runoff into the bay from rivers flowing from highly contaminated regions.
This has caused radioactive cesium levels to rise by 1.5 to 13 times since August, Yamazaki says.
The contamination is said not to pose any immediate health risks since no seafood from the bay has been found to exceed government-set standards.
In a related development, researchers from MIT say that low, but elevated levels of radiation are not responsible for any significant genetic damage to humans.
The same amount of exposure found in previous studies to produce DNA damage if given all at once now seems to have no effect if spread out over a long period of time.
The finding may allow authorities to shift policy and let people return home to contaminated areas, such as Chernobyl and Fukushima, much earlier than current guidelines allow.
“Now, it's believed that all radiation is bad for you, and any time you get a little bit of radiation, it adds up and your risk of cancer goes up,” says Doug Boreham, a professor of medical physics and applied radiation sciences at McMaster University, who was not involved in this study. “There's now evidence building that that is not the case.” DNA damage is known to occur spontaneously even at background radiation levels, conservatively at a rate of about 10,000 changes per cell per day.
Most of that damage is patched up by DNA repair systems within each cell.
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