More than 1,900 Japanese workers at the Fukushima nuclear plant that exploded last year and still leaking dangerous radioactive materials to the ocean, have been exposed to unsafe levels of radiation in their thyroid glands, media reports said.
Their radiation levels are more than 10 times the number previously announced by the plant operator Tokyo Electric Power Co (TEPCO), The Asahi Shimbun reported.
TEPCO had reported in December that radiation doses topped 100 millisieverts -- the widely accepted threshold for an increase in the risk of cancer -- in 178 people, with a maximum reading of 11,800 millisieverts.
But that number covered only a fraction of those who have been exposed. The workers themselves say TEPCO has provided little or no information about radiation doses in their thyroid glands. The new figure is based on a review of an expanded number of study subjects.
TEPCO and its partner companies not only re-evaluated the readings from thyroid gland dose tests, but they also estimated doses when the amount of radioactive iodine that entered the body was unavailable. These estimates were based on cesium intake amounts, the airborne iodine-to-cesium ratio on the days they worked, and other data.
The latest study showed that doses topped the 100-millisievert mark in 1,973 workers. In one worker, the estimated thyroid gland dose increased by more than 1,000 millisieverts during the review.
A thyroid gland dose reflects the amount of internal exposure to radioactive iodine that has entered the body through inhalation and other processes, the paper said.
It took TEPCO 28 months since the earthquake and tsunami on March 11, 2011, caused the nuclear disaster to learn that so many workers have been exposed to cancer-inducing levels of radiation doses in their thyroid glands.