Fukushima Human Exposure Badge Data; Glass Half Full?

Bits of data about human exposures in Japan have been trickling in. While it is impossible to make any sweeping claims on the actual outcome of the disaster, this information gives glimpses at what is going on.

Results of people wearing glass badge dosimeters gives some idea of external exposures in certain cities.
While some were below the “magic” 1mSv/year exposure level goal of the government, some were not. The ICRP suggested level of maximum exposure includes internal and external exposure. The glass badges only record external exposure. In Minamisoma badges were used from Oct – Dec 2011 and it is assumed badges in the other cities were used about the same time frame, then an annual dose is extrapolated from there.

These badges would not be able to detect any external exposure people received before October 2011 (or whenever the badge was handed out). Most dosimeter badges were passed out after September 1, 2011 when the plans were implemented. So exposures people had during those early months of March 2011 to August 2011 are not included in these calculations. This means plume exposures from the blasts at the plant and any iodine 131 exposure would not be included in these badge readings. They do however tell what people are being externally exposed to on a day to day basis. That is useful data for understanding how the environment in that area is exposing people to radiation.

These readings would not include internal contamination people receive though breathing in contaminated dirt and dust or eating contaminated food. Contaminated food is assumed to be a major source of internal exposure.

Fukushima City
35,000 people monitored,
19,000 1mSv/yr or under (54.28%)
16,000 over 1mSv/yr  (45.71%)
Minamisoma
5,327 people monitored,
3,374 1mSv/yr or under (63.33%)
1950 over 1mSv/yr (36.6%)
Soma City
about 5,000 people monitored
about 2,700 1mSv/yr or under (54%)
2300 over 1mSv/yr  (46%)

More details and graphs available here.

What can be assumed out of this data?
The US nuclear industry has been very busy trying to proclaim Fukushima is a non-disaster. They have also claimed repeatedly that people are not receiving exposures over 1mSv/year. This is very obviously not true if you look at this glass badge data or most of the other testing being done. It is also common for industry affiliated experts to look at only one type of exposure to come up with a 1 mSv/year exposure level and fail to mention people’s other exposure routes while telling the public exposures in Fukushima are below 1mSv/year. Some people’s combined exposure levels appear to be under 1mSv/year but some are not. More data is needed as is the need to look at all the exposure routes for an individual to know someone’s actual total exposure.

Some examples of potential exposure:
Iodine 131 both internal (thyroid) and external exposure early in the disaster.
Internal exposure early in the disaster and also ongoing through the air (breathing) and food.
External exposure early in the disaster and also ongoing through being in a contaminated place & ongoing releases from the plant.

The glass badge data itself shows that Fukushima City, 50 miles from the Daiichi nuclear plant had the highest percentage of people over 1 mSv/year. Minamisoma, much closer to the plant had only 36% over the 1 mSv/year level. Fukushima City did receive some concerning levels of fallout during the early days of the disaster and groups like Greenpeace have documented hot spots in the city. More data would be needed to make definitive conclusions about the Fukushima City readings.

Taking an air dose reading today, one of the higher radiation station readings in Fukushima City (image below) is around 1.6 uSv/hr, this equals an annual external exposure rate of 14 mSv/year. Luckily people are not living outside in that one spot 100% of the time for an entire year, but it shows how these elevated areas around the city can create an exposure problem in some situations. As a contrast, the monitor outside Fukushima City offices had a calculated yearly exposure of 8mSv/year. Employees in the building had average calculated readings of about 1.3mSv/year.

 

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