Friday 2 September 2011

Radiation (4)

Today I'm going to look at food. The 'provisonal' limit which was brought in after the accident (in the absence of any other) is for 500 bq/kg. So milk, fish, vegetables or meat with more than 500 bq/kg is not allowed on the market.  There's a complicated formula for measuring the accumulated dose but Professor Takeda says that if you divide the becquerels by 100, you will get the equivalent in mSv/year. So, if you ate one kilogram of food with 500 bq of caesium in it (divide by 100) you would be exposed to 5mSv/yr. (Once it gets in the body it keeps emitting radioactivity for years.)

From the beginning of the accident the local paper everyday has listed foods which have been tested. At first it was spinach showing very high levels of iodine but nowadays most vegetables are clean, blank columns on the chart. Some peaches are clear but some are showing levels of say, 18 bq/kg. So it you ate a kilogram of peaches you would get exposure of 0.18 mSv/yr. No big deal if you ate one peach and aren't living in Fukushima and getting all the other stuff.

Currently fish is showing between 20 and 200 bq/kg (0.2 to 2 mSv/year). These are below the limit of 500 bq/kg so are 'safe'. Seems quite high for me, when added to my tally. I haven't eaten fish since the quake.

Professor Takeda is leading a campaign to get the becquerels marked on food. Baby millk is now marked but not ordinary milk. His advice is to put up with the small amounts in fruit and vegetables - most of it can be washed away in water. But to go easy on meat, fish and milk which he wants labelled.

Most people in Fukushima with children have for a long time been buying different food for their children, with the grown ups eating Fukushima produce but buying foodstuffs  from the west of the country for the kids. The other day a friend gave me some small cartons of milk - from Kyushu! Very welcome. I put it in my tea.

I find myself in a dilemma. When people in the rest of the country are being really good about supporting our farmers, I'm afraid I'm not too keen on taking in extra radiation from local food myself. (A dilemma especially since the agricultural sector is important business for our company.) I get round it by buying  food when I go to Aizu and Ura Bandai (in the west of the prefecture) at the weekends since levels are negligible there.

I remember a link Takeshi sent me a while back to a BBC documentary on Chernobyl. The Soviet Union put milk from Chernobyl into the national supply so it was diluted. Everyone got a vey slight amount of radiation and the farmers stayed in business. But after the Soviet Union collapsed so did the distribution system and people had to depend on  local produce. That's how the problem with children's  thyroids came about. (Correction: Sorry, other medical problems. Thyroid cancer is caused by Iodine 131 which has an 8 day half life.)

So here's a suggestion. Would the rest of Japan eat our peaches, tomatoes and beef to keep the farmers in business whilst we who live here and have already been exposed to radiation don't take on any extra? A few cucumbers or peaches wouldn't be dangerous whereas for us, it's in everything: the air, the water, the rice, milk, fruit and veg.

Here's the link to Professor Takeda's blog. It's in Japanese only.

Next time I'll try and come to some conclusions about how the radiation's affecting me and see if I need to do anything.


  1. Hi Anne, I have been following your blog for several months now and just wanted to say thanks for putting some interesting information out there and putting forward a balanced point when living very close to both the disaster area and the Fukushima reactors. It must be challenging and cause a sense of underlying worry.I was up in Minami-Souma on Wednesday and I really felt I should bring some fruit and veg back to Aichi to support the local economy in that area of Fukushima. Like you say, a tiny amount of exposure really isn't going to do any harm (more radiation on the plane over here from the UK no doubt) and I want to do my bit to help. This is just one of many very small things everybody outside of Fukushima can do.

    Keep up the good blogging and good luck with the business - Alastair

  2. Thanks for your kind comments. I'm struggling with this 'radiation' series as I'm no scientist but I do think we all need to increase our 'literacy' in this area, especially those of us who live here. Pretty soon I'll get back to reporting the news and general goings on around here. Thanks for getting in touch.

  3. Hi Anne,
    I stumbled upon your blog and I need to point out a major error: when you divide by 100, you get the answer in micro-Sv, NOT milli-Sv.

    Secondly, cesium 137 has a biological half-life of 70 days, meaning that in 70 days, half of the Cs quantity are naturally excreted through urine, sweat, etc... The contamination does not stay for years.

    Hence the 500 Bq/kg limit which is pretty reasonable.

  4. That's a good point - that makes a difference with an order of magnitude of a thousand (in the better direction). Maybe you can eat more fish after all!

    In case you are wondering how to type a micro (µ) sign, press alt-m on most keyboards.

  5. Hi Matt,
    My source for the accumulated dose for internal exposure 'divide the becquerels/kg by 100 to get exposure in mSv/yr' is Professsor Takeda of Chubu Univesity. He constantly uses this measure. He has been known to make mistakes but in his blog on 28 August he specifically said that this was not a mistake and is the correct figure. I'll try and contact him and get some more details of his calculations.
    He says this is a ball park figure for a more complicated calculation which adds up the radioactivity remaining in the body and spreads it over a 50 year period for adults. The ICRP uses this method but he may be overstating their figures.
    I will check this some more but can anyone else help us on this?

  6. Anne,
    disclaimer: I am working for the nuclear industry, though not in radioprotection. I am living in Tokyo and I am specially careful about food for my child.
    As a scientist, the Takeda figure stroke me as difficult to believe so I did a quick Internet search and found this (page 2)
    FYI, Euradcom is anti-nuclear and uses ICRP and ECRR rates.

    Moreover, the 500 Bq/kg is one the strictest worldwide (EU is at 600 Bq/kg).

    I don't have the level of Japanese to understand in details Pr Takeda (any translation welcome) but my impression is that he is wrong. A quick look at his bibliography showed works on environmental subjects but nothing specific to nuclear before the Fukushima crisis. Furthermore, half of his posts are related to speeches or media appearances; this does not smell good.

    In everyday's life, I am not buying anything from Fukushima, Ibaraki, Miyagi. I still eat lunch everyday at restaurant, without any worries. If I eat something contaminated, I don't care because it will be one time only. If I would try to screen everything, I would loose sleep.
    This is comparable to post-9/11 when everybody was frantic about everything. I believe that when time goes by, people will be more relaxed about this.