100 millisieverts or more, including six subjected to at least 250 millisieverts. The highest number was 679 millisieverts, for a worker who helped to prepare venting as rising pressure threatened an explosion. A Tokyo Electric spokesman said that none of those workers has developed health problems so far, adding that the company is closely monitoring their conditions.
Dr. Yamashita, of Fukushima Medical University, said that, though radiation exposure for the general population has likely been low, evacuations and fear of radiation could lead to problems such as increased consumption of alcohol and stress-related illnesses. Tens of thousands of residents remain uprooted.
“ 'From a radiological perspective, we expect the impact to be really, really minor,' said one specialist. ”
For days after the March 11 accident, tons of radioactive waste were dumped into the Pacific. But it has been well dispersed by ocean currents, according to marine chemist Ken Buesseler at the Woods Hole Oceanographic Institution in Massachusetts. By June, the levels of radioactive cesium-137 between 18 and 300 miles offshore were safe for human exposure, he said.
Since cesium binds to the sediment on the ocean floor, the radiation has likely had the biggest effect on bottom-dwelling fish and other animals—though the consequences still aren't clear, said Tatsuo Aono, a specialist at Japan's National Institute of Radiological Sciences. Scientists have found cesium levels in those fish up to 1,000 times higher than the previous norm.
Ecologists and biologists who toured Fukushima prefecture earlier this year found that the radiation release appeared to have had a dramatic impact on birds in the region. Biologists led by radio-ecologist Timothy Mousseau at the University of South Carolina studied 300 locations around Fukushima last July and found that local bird populations had dropped by about a third. "The response was about twice as much as after Chernobyl," said Dr. Mousseau. "We don't know why yet."
Their absence was noticeable. "It is an eerie quietness," he said. "The environment is just quieter."