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We recently got a message from a reader of this blog, asking about the safety of living in Sendai. Since I had been looking into the radiation situation in Tohoku for a while, I wrote him a lengthy email. Here is what I wrote (slightly edited):

We will probably be living in or near Sendai from this summer, so I have been doing quite a bit of reading concerning the radiation situation. As you say, information and opinions are all over the place, some people saying this is the apocalypse, and others saying it’s no big deal. I think reality is somewhere in the middle. Life in Fukushima in many places will be severely impacted for many years to come. In terms of radiation in the air, it really depends on the individual location though. Sendai is about 100km away from Fukushima Daiichi and has had fairly little exposure. Here are daily background radiation levels for Sendai: http://atmc.jp/?n=4

The levels for different places around Japan are often shown in microsievert per hour. The average annual exposure in the US is about 300 millirem (without medical exposure), which is 3000 microsieverts.
http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm#rdttusp
Divided by 365 and then divided by 24 gives you the microsievert per hour number.
The figure is 0.34, which actually seems quite high. So 0.06 in Sendai is low, I don’t think it really changed much after March 11th. You can find those numbers for lots of places in Japan, simply google 放射能 plus the name of the town. This site has tons of readings and maps, Sendai numbers here are actually a bit higher, I guess since they are measured at a lower level off the ground: http://blog.safecast.org/

There is a lot of discussion about whether small increases in background radiation are harmful or not. The LNT model argues that they are harmful: http://en.wikipedia.org/wiki/Linear_no-threshold_model
The opposite of that would basically be hormesis: http://en.wikipedia.org/wiki/Radiation_hormesis
This guy is very much in the second camp: http://www.radiationandreason.com

I think the bigger issue in everyday life is actually the food situation. It is easy to simply stay away from food that says 福島県産 on it. What is trickier is verifying the contents of foods that have ingredients from all over the place. There is also wide disagreement over which levels (becquerels per kg) are ok. The government just set new standards which are quite stringent: http://www.yomiuri.co.jp/dy/national/T120217006336.htm
Stuff can always slip through the cracks and it will make headlines for quite a while I think. But so did Apple juice in the US recently, with arsenic levels. Monitoring and testing will get better, the Japanese are usually very paranoid about this. Funny how veggies from China became more attractive all of a sudden. If you want to be really careful with food, it should be possible to avoid foods from Tohoku altogether and try to buy imported foods almost exclusively. I think about 60% of food in Japan is imported anyways. You are not going to find enough scientific information to really make a black-and-white type of decision or statement. In the end, it is a very personal decision and people are going to come to very different conclusions based on the same evidence. The prediction of a potential next big earthquake is certainly worrisome. But we will have the ability to simply pack our bags and go back home if need be. Millions of Japanese would not be so lucky. You might want to check out this group and look at some of the posts that asked questions similar to yours and the answers they got. There are some really knowledgeable people answering questions:
http://www.facebook.com/Tokyo.Radiation.Levels

Here are some sites I check regularly for updates on the state of Tohoku:
http://www.hiroshimasyndrome.com/fukushima-accident-updates.html (3x/week) http://ex-skf.blogspot.com/ (translated from jp. sites)
http://ajw.asahi.com/category/0311disaster/
http://thefukushima.tumblr.com/

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