Radiation doses from tap water and foods consumed by Tokyo residents following the accident at the Fukushima No. 1 nuclear power plant remain at safe levels, scientists at the University of Tokyo said March 12.
Radiation doses from tap water and foods consumed by Tokyo residents following the accident at the Fukushima No. 1 nuclear power plant remain at safe levels, scientists at the University of Tokyo said March 12.
A group of researchers led by Taikan Oki, professor of hydrology at the university's Institute of Industrial Science, and Michio Murakami, project lecturer at the university, recently estimated whole body doses of internal radiation at 48 microsieverts for newborns and 18 microsieverts for adults.
The estimate for newborns is one-20th the annual dose limit of 1 millisievert for members of the public, and was a fraction of the annual background doses of 130-217 microsieverts from radioactive substances that naturally exist in human bodies.
However, the study may not give the full picture.
"Doses from exposure to radioactive iodine between March 18-20 last year, immediately following the nuclear disaster, cannot be neglected," Murakami said. "But we have not been able to evaluate them reliably because of the scarcity of data."
The scientists estimated the doses of internal exposure to radioactive iodine and cesium from the intake of beverages and food during a one-year period from March 21, 2011, the day the central government started banning food shipments and taking other safety measures.
The calculations are based on the results of an analysis by the Bureau of Waterworks of the Tokyo metropolitan government, the health ministry and other agencies on the radioactive content of tap water, dairy products, vegetables, seafood, tea and other items. They also took into account the health ministry's data on the average intake of different food groups by age bracket.
As part of the safety measures, the Tokyo metropolitan government handed out bottled water for newborns, while the health ministry banned shipments of contaminated food.
When those measures were taken into account the topical thyroid gland doses of internal exposure to radioactive iodine were evaluated at 1,140 microsieverts for newborns, 970 microsieverts for infants and 280 microsieverts for adults.
The combined whole body doses of internal exposure to radioactive iodine and cesium were evaluated at 48 microsieverts for newborns, 42 microsieverts for infants and 18 microsieverts for adults.