Armillaria mellea
Nuclear fallout from the Chernobyl disaster is an important issue concerning mushroom picking in Europe. Due to the wide spread of their mycelium, mushrooms tend to accumulate more radioactive caesium-137 than surrounding soil and other organisms. State agencies (e.g. Bellesrad in Belarus) monitor and analyze the degree of radionuclide accumulation in various wild species of plants and animals. In particular, Bellesrad claims that Svinushka ("Paxillus" ssp.), Maslenok ("Suillus" ssp.), Mokhovik ("Xerocomus" ssp.), and Horkushka ("Lactarius rufus") are the worst ones in this respect. The safest one is Opyonok Osyenniy ("Armillaria mellea"). This is an issue not only in Poland, Belarus, Ukraine and Russia: the fallout also reached western Europe, and until recently the German government discouraged people gathering certain mushrooms.