Wild mushrooms still partly contaminated with radioactive caesium

A basket with bay boletes Source: Tarabalu/Stock.adobe.com

Wild mushrooms in southern Germany can still be contaminated with radioactive caesium above the limit value. This can be seen in the current mushroom report of the Federal Office for Radiation Protection (BfS) for which the levels of caesium-137 in edible wild mushrooms are investigated on an annual basis. The caesium comes mainly from the Chernobyl disaster in 1986. But a small proportion can be traced back to the above-ground nuclear weapons tests of the 1950s and 1960s.

A limit of 600 becquerels of caesium-137 per kilogram of fresh mass applies to mushrooms that are sold on the market. However, this limit does not protect you if you go into the forest to collect mushrooms yourself.

Wild mushrooms should be consumed in moderation

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

"Those who collect mushrooms for their own consumption can use the mushroom report of the Federal Office for Radiation Protection for orientation", explains BfS President Inge Paulini. The report shows which edible mushroom species may have high caesium levels and which regions of Germany are particularly affected by the Chernobyl disaster.

"In these areas – such as the Bavarian Forest, the edge of the Alps, and the Donaumoos southwest of Ingolstadt – mushrooms you collect yourself should be eaten only in moderation so that unnecessary radiation exposure can be avoided", says Paulini.

Edible mushroom species with higher levels of contamination

The mushroom report summarises the survey results for 2019 to 2021. Particularly high values of up to more than 4,000 becquerels of caesium-137 per kilogram of fresh mass were found in wood hedgehog (Hydnum repandum) and terracotta hedgehog (Hydnum rufescens) during this period.

The measured values of various woodwax (Hygrophorus) species, 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), blue spot knight (Tricholoma columbetta), amethyst deceiver (Laccaria amethystina), and brown and yellow bolete (Boletus subtomentosus) were above 1,000 becquerels per kilogram.

Harmless mushroom species

With less than 10 Bq/kg, the following were only slightly contaminated: long-stemmed puffball (Lycoperdon excipuliforme), pear-shaped puffball (Lycoperdon pyriforme), agaricus silvaticus (Agaricus silvaticus), red-capped bolete (Xerocomellus rubellus), date amanita (Amanita spadicea), common ink cap (Coprinopsis atramentaria), chestnut bolete (Gyroporus castaneus), honey fungus (Armillaria mellea), woodear (Auricularia auricula-judae), stunted cavalier (Melanoleuca brevipes), monk’s head (Infundibulicybe geotropa), giant polypore (Meripilus giganteus), shaggy parasol (Macrolepiota rhacodes), abruptly-bulbous agaricus (Agaricus abruptibulbus), shaggy inkcap (Coprinus comatus), midnight blue bolete (Boletus pulverulentus), Macrolepiota rhodosperma, Leucocybe connata, Clitopilus geminus, jelly tooth (Pseudohydnum gelatinosum), bicoloured deceiver, (Laccaria bicolor), and banded amanita (Amanita battarrae).

Cultivated mushrooms such as button mushroom (Agaricus bisporus) and oyster mushroom (Pleurotus ostreatus) were not investigated for the report. Their caesium-137 content is extremely low and comparable to that of other agricultural products.

Mushrooms with a high caesium content should be avoided

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

In addition to the caesium-137 content of the mushrooms, the amount consumed is also decisive for the radiation exposure of humans. If wild edible mushrooms are consumed in the usual quantities, the additional radiation exposure is comparatively low.

Nevertheless, it is worth avoiding particularly highly contaminated mushroom species if you regularly eat mushrooms you have collected yourself. An adult who eats 200 g of mushrooms containing 2,000 Bq of caesium-137 per kg every week will experience an additional annual radiation dose equivalent to about 20 flights from Frankfurt to the Canary Islands. Expressed in figures, this is 0.27 millisieverts.