Radiation doses that raise the risk of cancer have been recorded in dozens of workers--or about 1 percent of the work force--at the Fukushima No. 1 nuclear plant.
Plant operator Tokyo Electric Power Co. on Dec. 6 released data for radiation doses recorded between March 11, 2011, when the disaster started, and Jan. 31, 2012.
The figures show 165 workers, or about 1 percent of those monitored, received doses of at least 100 millisieverts, a level widely believed to raise the risk of cancer over a person's lifetime.
TEPCO released the data after submitting it in March, upon request, to the World Health Organization. It was the company's first direct release of such data, although it has shared other data with the WHO, which the agency plans to release shortly.
The data contained no personal details, nor did it identify the duties of the workers concerned. It presented figures grouped according to age category.
Twenty-five individuals in their 20s received more than 100 millisieverts, or 1.2 percent of the 2,057 workers in that category; so too did 40 of 4,179 individuals aged 30-39. The threshold was reached in 49 workers of 5,893 in their 40s; by 46 individuals in their 50s, out of 5,409; and five aged 60-69, of whom there were 1,858 workers.
None of the 64 teenage workers employed at the plant, and none of the 26 in their 70s and 80s, were exposed to more than 100 millisieverts of radiation.
But the data shows that three workers in their 20s received an elevated dose of more than 250 millisieverts, together with one person each in their 30s, 40s and 50s.
Younger adults are more susceptible to injurious effects of radiation. A forthcoming WHO report says the risk of developing radiation-induced cancer over a person's lifetime is 1.5 times greater for a 20-year-old than a 40-year-old. It is three times greater than for a 60-year-old. Furthermore, a 20-year-old's risk of thyroid cancer is four times that of a 40-year-old's.
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