Wild mushrooms First find out about caesium exposure – then enjoy

Wild mushrooms may contain radioactive caesium Source: Markus Mainka/Stock.adobe.com

Even 37 years after the Chernobyl nuclear disaster, wild mushrooms in Germany can still contain trace amounts of radioactive caesium-137, which was released in the accident. On a larger scale, however, exceedances of the limit value of 600 Bq/kg fresh mass are to be expected only in some regions of Bavaria and parts of Upper Swabia. This can be deduced from the current mushroom report of the Federal Office for Radiation Protection (BfS). When compiling the annual report, the BfS examines wild mushrooms from selected sites.

Especially in the Bavarian Forest and the neighbouring areas, in the "Donaumoos" south-west of Ingolstadt, and in the Alps and at the edge of the Mittenwald region and in the Berchtesgadener Land, mushroom pickers should expect that some mushroom species still have high levels of caesium-137. After the reactor accident in spring 1986, these areas had the most radioactive caesium deposited on the ground in a Germany-wide comparison.

Caesium content also depends on the type of mushroom

Even in these more highly contaminated areas, not every mushroom species is equally affected. In the BfS measurements of the past three years (2020–2022), hedgehog mushroom (Hydnum repandum) and terracotta hedgehog (Hydnum rufescens) reached peak values of over 4,000 Bq caesium-137/kg fresh mass in individual cases.

The BfS detected maximum values above 1,000 Bq/kg in various woodwax (Hygrophorus) species as well as in yellowfoot (Craterellus tubaeformis), red cracking bolete (Xerocomellus chrysenteron), bay bolete (Imleria badia), sooty milkcap (Lactarius lignyotus), common yellow russula (Russula ochroleuca), tawny grisette (Amanita fulva), amethyst deceiver (Laccaria amethystina), and brown and yellow bolete (Boletus subtomentosus).

In contrast, the measured values of the following species always remained below 10 Bq/kg – even at the most contaminated sampling sites during the study period: long-stemmed puffball (Lycoperdon excipuliforme), blue roundhead (Stropharia caerulea), red-capped bolete (Xerocomellus rubellus), date amanita (Amanita spadicea), scurfy deceiver mushroom (Laccaria proxima), entire russula (Russula integra), the prince (Agaricus augustus), bleeding agaricus (Agaricus fuscofibrillosus), chestnut bolete (Gyroporus castaneus), honey fungus (Armillaria mellea), woodear (Auricularia auricula-judae), cauliflower mushroom (Sparassis crispa), slimy spike-cap (Gomphidius glutinosus), stunted cavalier (Melanoleuca brevipes), Coal brittlegill (Russula anthracina), monk’s head (Infundibulicybe geotropa), common funnel (Clitocybe gibba), clustered domecap (Lyophyllum decastes), giant polypore (Meripilus giganteus), rusty bolete (Xerocomus ferrugineus), shaggy parasol (Macrolepiota rhacodes), sulphur polypore (Laetiporus sulphureus), banded amanita (Amanita battarrae), Macrolepiota rhodosperma, blewit (Lepista nuda), agaricus silvaticus (Agaricus silvaticus), common stump brittlestem (Psathyrella piluliformis), Leucocybe connata, Clitopilus geminus, bicoloured deceiver (Laccaria bicolor), banded amanita (Amanita battarrae) From a radiation protection point of view, they can be consumed throughout Germany in any quantity without hesitation.

BfS President Dr Inge Paulini

Limit value applies only to trade

"Mushrooms on the market must comply with the limit value for radioactive caesium-137 of 600 Bq/kg. Anyone who collects mushrooms themselves is not protected by this limit", explains BfS President Inge Paulini. She therefore advises people to inform themselves before eating mushrooms and to consume wild mushrooms they have collected themselves only in moderation – especially in the areas mentioned. "It is ultimately a personal decision: The occasional consumption of more highly contaminated mushrooms leads only to a small additional radiation dose. However, this can be easily avoided by leaving mushroom species with potentially high levels of contamination in the forest."

An adult who consumes 200 g of mushrooms containing 2,000 Bq caesium-137/kg every week receives an additional radiation dose of 0.27 mSv/year. That's about as much as about 20 flights from Frankfurt am Main to Gran Canaria.

Soil contamination with caesium-137 in 1986. The current values can be determined by multiplying the numbers by 0.43.

165 species of mushrooms studied

The BfS Mushroom Report is published annually. It provides information on which wild edible mushrooms can have high caesium-137 levels and which regions of Germany are still particularly affected by the Chernobyl reactor accident of 1986. The current edition covers the years 2020 to 2022. When preparing the report, the BfS examined 165 species of mushrooms collected at selected sites in southern Germany.

Cultivated mushrooms such as champignons and oyster mushrooms were not examined. They grow on substrates that contain only small amounts of caesium-137. Like other agricultural products, cultivated mushrooms therefore contain extremely little caesium-137.

Caesium-137 is a radioactive isotope of the element caesium that does not occur in nature. Among other things, it is produced during nuclear fission in nuclear power plants. It has a half-life of approx. 30 years. This means that the amount of caesium-137 deposited on the ground in Germany in 1986 has decreased by more than half.