Inform yourself about caesium exposure before picking wild mushrooms

The degree of contamination varies depending on the site and the species of mushroom

With the start of the mushroom season, many venture into the forest to collect culinary delights. However, it is sometimes advisable to resist temptation and leave certain edible mushrooms be. According to the current mushroom report of the Federal Office for Radiation Protection (BfS), some mushroom species, especially those that grow in southern Germany, have highly elevated levels of radioactive caesium (caesium-137).

"The radioactive caesium in the mushrooms still comes from the reactor accident in Chernobyl 35 years ago", explains BfS President Inge Paulini. "Unlike in agricultural soils, in forest soils, caesium-137 is present in a form that can be taken up by plants and fungi – and some species of fungi are particularly good at this."

The BfS investigates the caesium-137 contamination of mushrooms

President of the Federal Office for Radiation Protection, Dr Inge Paulini

For the annual mushroom report, the BfS investigates the caesium-137 contamination of mushrooms at selected sites in southern Germany. "The contamination is slowly decreasing overall. However, in isolated cases, there are still values of over 4,000 becquerels of caesium-137 per kilogram of fresh mass", says Paulini.

"Mushrooms placed on the market are not allowed to have more than 600 becquerels per kilogram of fresh mass. However, the limit value does not protect those who collect mushrooms for their own use", says Paulini.

Especially areas in southern Germany are more heavily contaminated

Soil contamination with caesium-137 in Germany in 1986 (becquerels per square metre)

"It is not forbidden to occasionally eat mushrooms with higher levels of contamination. Nevertheless, people should be aware of the types of mushrooms that are usually more contaminated and leave them in the forest in order to avoid unnecessary exposure to radiation."

The degree to which a mushroom is contaminated depends on both the species and the location of a mushroom. More highly contaminated mushrooms grow mainly in regions in which above-average amounts of caesium were deposited after the Chernobyl reactor accident. These include parts of Bavaria such as the Bavarian Forest. An overview map of the caesium distribution in Germany is included in the mushroom report of the BfS.

Cultivated mushrooms contain only little caesium-137

In 2018 to 2020, the BfS found particularly high values (over 1,000 becquerels) of caesium-137 per kilogram of fresh mass in hedgehog mushroom (Hydnum repandum), terracotta hedgehog (Hydnum rufescens), various Hygrophorus species, yellowfoot (Craterellus tubaeformis), red cracking bolete (Xerocomellus chrysenteron), bay bolete (Imleria badia), sooty milkcap (Lactarius lignyotus), ochre brittlegill (Russula ochroleuca), light violet cortinarius (Cortinarius alboviolaceus), blue spot knight (Tricholoma columbetta), amethyst deceiver (Laccaria amethystina), and boring brown bolete (Boletus subtomentosus).

The forest mushroom (Agaricus silvaticus), the monk's head (Infundibulicybe geotropa), the giant polypore (Meripilus giganteus), the shaggy parasol (Chlorophyllum rhacodes), and the shaggy ink cap (Coprinus comatus) had only low levels of contamination (i.e. regularly below 5 becquerels of caesium-137 per kilogram of fresh mass) and are thus harmless to eat from a radiation protection point of view. Cultivated mushrooms such as button mushrooms also have only low levels of caesium-137.