The thing is that there are long living isotopes in the upper soil of the forests. As they are long living, they have not decayed yet enough and are not going to in the next decades. Something does not need to kill 80% of the population to be a significant health risk. With the isotopes relevant in Bavaria, they are only dangerous when eaten. So there is nothing dangerous about living in those regions. However mushrooms tend to aggregate the radioactive particles and so do the wild boar eating from the mushrooms. Not every animal is contaminated, but every single one has to be scanned for radiation, before they can be eaten, and quite a few have to be destroyed every year.
200 grams of mushrooms with 3,000 becquerel cesium-137 per kilogram corresponds to a load of 0.008 millisievert .
This corresponds to the radiation load on a flight from Frankfurt to Gran Canaria.
And:
If wild game or wild growing fungi are consumed in conventional quantities, the additional radiation load is comparatively low, but it is avoidable.
In other words, there is no danger to one's health - no more that one is exposed to by living regular life and being subject to various low-level radiation sources present in the environment. The regulations have very low acceptable level, just to be safe, but there is very little actual danger from the levels present right now.
From Wikipedia[1]:
For comparison, natural radiation levels inside the US capitol building are such that a human body would receive an additional dose rate of 0.85 mSv/a.
So, working in a granite building for about 4 days is as dangerous as eating a meal of "contaminated" mushrooms. Thousand of people do the former every day. Or about the same as one dental xray. I think my conclusion that it is done out of overabundance of caution still seems to be correct.
First of all, it makes a lot of difference, whether you are exposed to external radiation, or eating contaminated food. Especially if, as for Iodine, the elements are accumulated in certain organs. Not sure how much this is the case here.
Anyway, I have not claimed, that occasional eating of mushrooms is going to kill you. Still, the doses are high enough to warrant an official warning not too often to eat these mushrooms (you have a dental X-ray not every day either), and enough animals are contaminated high enough to be destroyed.
Overall, the life in Bavaria is not impacted by the radiation. But I find it startling, that over a thousand kilometers away from Chernobyl, the Bavarian landscape is contaminated and will be for decades. It shows me, that we do not want to risk a reoccurrence of such events.
This article: http://www.umweltinstitut.org/themen/radioaktivitaet/tschern...
claims, that the Bavarian soil used for agriculture tends to not transfer radioactive particles quickly into plants. It seems the soil was also deeply plowed to distribute the particles amongst a large volume of soil. The situation in forests is different, as the trees captured more particles than the open farmland, and the soil is not plowed, leading to still high particle concentrations in the top layer.
Bavaria had been contaminated the most, other parts of Germany have less residual radiation - the weather situation (wind, rain) created very inhomogeneous distribution back then. I found this map about the distribution: http://files.abovetopsecret.com/files/img/gz54e7a9f2.png
The thing is that there are long living isotopes in the upper soil of the forests. As they are long living, they have not decayed yet enough and are not going to in the next decades. Something does not need to kill 80% of the population to be a significant health risk. With the isotopes relevant in Bavaria, they are only dangerous when eaten. So there is nothing dangerous about living in those regions. However mushrooms tend to aggregate the radioactive particles and so do the wild boar eating from the mushrooms. Not every animal is contaminated, but every single one has to be scanned for radiation, before they can be eaten, and quite a few have to be destroyed every year.