When radioactive foods are eaten, they emit radiation inside our body, it is called internal exposure.
Interim guideline about radioactive materials on food was announced 17th March.
Each limit value varies depending on radioactive material type and food type. For example, limit of radioactive iodine on vegetable is 2000Bq/kg, limit of "Alpha-emitting nuclides of plutonium and transuranic elements" on infant foods is 1Bq/kg. (lol plutonium guideline on infant foods.)
To say the truth I was at loss because I did not understand how dangerous or how safe these numbers were.
As I knew too little, I ate much banana, because all banana in Japan is imported form clean countries. And I read banana abounds radioactive thing just now. haha.
Banana is one of the potassium rich produce, like milk, and 0.0117% of all potassium in natural is potassium-40 which is radioactive. Banana is said to have several hundreds Bq/kg. As human body includes a lot of potassium also, human itself has 6000-7000Bq.
Unit "becquerel(Bq)" is kind of amount of radiation, unit "sievert (Sv)" shows how much human being is effected. Above WHO document shows how to calculate unit becquerel to sievert. When someone eat 300g vegetable which contain 2000Bq/kg iodine-131 and 500Bq/kg cesium every day, total amount of internal exposure after one year is (these are maximum value of interim guideline):
0.3(kg) * 2000(Bq/kg) * 0.00018(mSv/Bq) * 356 = 38.448 (mSv)
0.3(kg) * 500(Bq/kg) * 0.000013(mSv/Bq) * 356 = 0.6942 (mSv)
I agree that as the interim guideline is a interim thing, one year might be unexpected term.
But I eat not only vegetable but also grain, fruit, egg etc. I drink water too.
I will struggle to find lower radioactive foods for a while. I hope it will be a "for a while" problem.
Please confer above number to following dose limits: