Japanese tea & radiation -- research notes & links

Disclaimer: I’m a marketing specialist with Kyoto Obubu Tea Plantations as a client and not an expert on radiation contamination or related issues. The following are my notes to understand what is going on in Japan.

Doing the research yourself on whether tea from a specific region is susceptible to radiation contamination or not is difficult, especially with language barriers, but not impossible. http://atmc.jp lists background radiation, radiation levels in tap water and radiation levels in rain by the day in Japanese, but with a Google translate toolbar.

Of course, understanding what the figures mean takes a bit of work, and I’m still trying to figure it out. But here’s what I know.

This article has a good explanation to start (though still difficult to understand since all this about Sieverts and Becquerels is difficult to understand).
http://mdn.mainichi.jp/mdnnews/news/20110321p2a00m0na006000c.html

In Nara Prefecture (Obubu’s fields are just north of Nara in southern Kyoto), average background radiation is normal: 0.05 microsieverts per hour.

By contrast average radiation level in America is 0.34 microsieverts per hour
http://en.wikipedia.org/wiki/Sievert#Hourly_dose_examples
Of course there are other sources of radiation, such as
An x-ray exam at the dentist: 90 microsieverts (0.090 millisieverts or mSv)
Or radiation from consumer products: 100 microsieverts/year
http://en.wikipedia.org/wiki/Orders_of_magnitude_(radiation)

However, what is of most concern is how much radiation contamination is in the rain…which gets into the groundwater. This is measured in Becquerels and is affected by the half-life of the radiation particles.
http://en.wikipedia.org/wiki/Becquerel

From the Mainichi News article sited above:
“Q: What’s the difference between the units becquerel and sievert?
A: Becquerels represent the strength of radioactive sources, and must be converted to sieverts to indicate the effects of radioactive materials on the human body. The effect that eating spinach with 15,020 becquerels of radioactive iodine per kilogram has on the body is 0.33 millisieverts (330 micro sieverts). The average Japanese person consumes an average of around 15 grams of spinach per day, which means the actual effect is 0.0049 millisieverts (4.9 microsieverts).”

I believe contaminated rain getting onto plants that you eat can be dealt with by washing your food properly.

In Nara, Kyoto, and regions west, this level has been zero.

In one minor production region, Saitama, there have been more significant levels…to the point where you should wash your hands before eating if you were outside in the rain.

Finally, we feel the most important thing is to know where your food is coming from. Whether Chinese tea or Japanese tea, how far back into the supply chain can you trace your tea? (Can you guess Obubu’s selling point? ;) )

By the way, we’re working to get more farmers from various countries, including China, to be more available to their customers online via http://www.teafarms.org (still under development).