YOKOTA AIR BASE, Japan — U.S. personnel experienced elevated levels of radiation from the Fukushima Dai-ichi nuclear power plant, but doses were not high enough to make them sick, according to the Department of Defense.
Radiation dose estimates have been compiled by scientists and doctors building a database — the Operation Tomodachi Registry — which eventually will list 70,000 U.S. servicemembers, civilians and family members on or near the mainland Japan during the 60 days following the massive March 11, 2011 earthquake and tsunami. Location-based dose estimates were made available Wednesday at http://registry.csd.disa.mil/otr.
Subsequent damage to the Fukushima plant caused the release of a radioactive plume that contaminated air and water as far south as Tokyo and prompted evacuation of thousands of concerned military family members to the U.S.
The highest estimates were for personnel stationed on bases in Sendai, about 50 miles from the nuclear plant. Adults there may have received doses of up to .12 rem of radiation to their entire bodies and 1.2 rem in their thyroids, according to the registry website.
The doses at most bases were far lower than at Sendai. Full-body doses for adults and children age 1 to 2 at Yokosuka Naval Base, for example, were .033 rem and .077 rem, respectively.
To put the data in perspective, a medical CT scan results in a full-body dose of 5.0 rem, a normal annual dose from environmental radiation in the U.S. is about .31 rem. Accepted safe limits for radiation doses to the thyroid are 50 rem for adults and 5.0 rem for children, based on U.S. Exposure Guidelines.
The dose estimates, which have been reviewed by the Veterans Advisory Board on Dose Reconstruction and the National Council on Radiation Protection and Measurements, include separate data for radiation absorbed by people’s thyroid glands. The thyroid is known to accumulate radioactive iodine, which made up 60 percent of the radioactive particles detected from Fukushima, according to Craig Postlewaite, a public health practitioner in the Office of the Secretary of Defense Health Affairs.
When finished in December, the registry will contain location-based dose estimates for individuals at 13 locations in Japan during the disaster.
Officials decided to make the information available through a website because the DOD wants to “… make sure this data is in a registry available within the lifetime of the individuals in case there are any questions related to … diseases,” Postlewaite said.
The registry is the first time the DOD has added dependents to its occupation health system, he said.
The website contains no information that can be used to identify individuals, but it allows people to click on their location and obtain dose estimates for a typical person there during the disaster. It also allows people to make inquiries of the registry support team to confirm whether they are included, and where they were supposed to have been located from March 12 through May 11, 2011, the period for which exposures were calculated.
Defense Threat Reduction Agency health physicist Paul Blake said the registry will be useful for people or doctors with questions about how much radiation a person might have received in Japan.
“If people develop health conditions in the future that their providers feel might be related to radiation they can go to the registry,” he said. “If mothers give birth to [sick] children and they are concerned that the radiation levels might have caused it. … If we didn’t have this information available there would be questions in people’s minds.”
David Brenner, a Columbia University professor who is studying the potential impact of low doses of radiation on cancer risk, said the registry is a good idea but added that there is a lot of uncertainty in how the data in it could be used.
Statistically it is likely that at least 40 percent of any group of people will ultimately get cancer, regardless of any extra radiation exposure, he said.
“If any individual who was in Japan last year does ultimately get cancer, they will be able to use the radiation registry to get a very rough estimate of the likelihood that the extra radiation exposure caused that cancer,” he said, adding that the data released by DOD suggests the likelihood would be extremely small.
Stars and Stripes reporter Chris Carroll contributed to this report.