Fukushima: Radiation Exposure
(updated June 2013)
No harmful health effects were found in 195,345 residents living
in the vicinity of the plant who were screened by the end of May
2011. All the 1,080 children tested for thyroid gland exposure
showed results within safe limits, according to the report
submitted to IAEA in June. By December, government
health checks of some 1700 residents who were evacuated from three
municipalities showed that two-thirds received an external
radiation dose within the normal international limit of 1 mSv/yr,
98% were below 5 mSv/yr, and ten people were exposed to more than
10 mSv. So while the was no major public exposure, let alone
deaths from radiation, there were reportedly 761 victims of
"disaster-related death", especially old people uprooted from homes
and hospital because of forced evacuation and other nuclear-related
measures. The psychological trauma of evacuation was a bigger
health risk for most than any likely exposure from early return to
homes, according to some local authorities.*
In July 2012 a Hirosaki University study reported on I-131
activity in the thyroid of 46 out of the 62 residents and evacuees
subject to detailed investigation in April 2011. The median thyroid
equivalent dose was estimated to be 4.2 mSv and 3.5 mSv for
children and adults respectively, much smaller than the mean
thyroid dose in the Chernobyl accident (490 mSv in evacuees).
Maximum thyroid equivalent doses for children and adults were 23
mSv and 33 mSv, respectively. This is consistent with health
authorities' screening tests on 1149 children under 15 in March
2011. Working from these data to estimated maximum doses in
the worst-exposed areas in the first week after the accident it was
estimated that some children could have received more than 50 mSv
dose, still only about one tenth of Chernobyl evacuees.
http://www.nature.com/srep/2012/120712/srep00507/pdf/srep00507.pdf
The residents of Minamisoma town, on the coast 23 km north of
Fukushima Daiichi, were found to have very low levels of radiation contamination. In a
study of internal radiation dose, measurements were taken of the
full-body contamination from caesium exposure of 9498 residents who
had returned to the town and stayed there between September 2011
and March 2012. The study found that two-thirds of the residents
had no detectable levels of caesium. Of the rest, only one appeared
to have received an equivalent dose more than 1 mSv, and that was
1.07 mSv. The current ambient dose rate in the town is about 3
mSv/yr from external sources, well within the government's 20
mSv/yr limit for returnees. Some 1500 of the town's 70,000
residents lost their lives in the tsunami. The internal dose
results were published in the Journal of the American Medical
Association.
In October 2012 the new Nuclear Regulatory Authority (NRA)
released new emergency preparedness guidelines. Its new
emergency planning zones, in line with International Atomic Energy
Agency standards, call for 'precautionary action zones' 5
kilometers around nuclear energy facilities and 'urgent protective
action planning zones' 30 km around the plants. NRA then drew
up specific evacuation criteria, which local municipalities will
use to formulate emergency response plans.
Japan's health ministry set up a special office to monitor the
health of workers at the plant. The new office compiles data on
radiation exposure for workers for long-term monitoring purposes,
and inspects daily work schedules in advance. To March 2013 Tepco
has employed some 25,837 workers at the site since the accident,
keeping records of their radiation exposure as clean-up and
remediation proceeded. Of these, over 95% received less than 50 mSv
during the 25 month period; 4% received 50-100 mSv and fewer than
1% received over 100 mSv.