Mushrooms That Absorb Radioactive Cesium 137 and Other Radionuclides

The lingering effects of the Chernobyl nuclear catastrophe in 1986 in Ukraine continue to affect entire eco-systems in Europe. An example of such effects is the radioactive contamination (cesium-137 contamination) of wild mushrooms in certain European countries. With the recent developments at the Fukushima Daiichi nuclear plant in Japan and the uncertainty of the consequences of the disaster, the topic of nuclear contamination of food has re-gained considerable public attention over the past weeks.

Mushrooms' Affinity for Cesium-137 and Other Radionuclides

Fungi, which lack stems and roots, use absorption to obtain nutrition from the atmosphere through their surface cells. As a result, they are prone to absorbing radioactive substances such as cesium-137 (also known as caesium-137, radiocaesium-137 and 137 Cs) and other radionuclides. Cesium is one of the by-products of nuclear fission processes in nuclear reactors and nuclear weapons testing. The Chernobyl power plant released significant amounts of radiocesium-137 into the environment, but also the nuclear weapons tests in the 1950s and 1960s released some cesium.

Mushrooms are sensitive to nuclear contamination

Radiocesium can cause genetic mutations in humans and animals, and consequently, a high consumption of nutrition contaminated by cesium can lead to cancer or cause deformations to embryos and fetuses. The European Commission recommends that the UK, Ireland and other member countries of the European Union should not sell natural products that exceed the permitted maximum level of radioactive cesium-137 which the Commission has set to 600 becquerel per kilogram. In Japan, the maximum limit has been set to 300 becquerel per kilogram. Becquerel, Bq, is a unit of radioactivity, and one Bq unit is defined as the radioactivity in which one nucleus decays per second. The becquerel was named after Antoine Henri Becquerel (1852-1908), a French physicist, who shared a Nobel Prize with Pierre and Marie Curie for their work in discovering radioactivity.

The European Commission also states that in regions where foodstuffs may exceed the maximum level of radioactive cesium permitted, member states shall inform the population of the health risks involved. In addition to wild mushrooms, foods that have been significantly affected by the nuclear fallout from the Chernobyl nuclear plant meltdown in several European countries include bilberries (wild blueberries), raspberries, cranberries, blackberries, cloudberries, wild strawberries, wild game, deer meat, and carnivorous freshwater fish from lakes (e.g. perch and pike).

Level of Nuclear Contamination Depends on Mushroom Type

The amount of cesium in wild mushrooms varies significantly between mushroom species. There are about 14,000 species of mushrooms in the world, most of which fall into one of the following categories: gilled, non-gilled, and puffballs and their relatives. In general, mushrooms that are gilled or have pores or pines under their caps as well as mushrooms that have stalks are more prone to accumulating radiocesium and other other radionuclides. Typically, the names of these mushrooms contain one or more of the following words or word pairs: roof, common meadow, crumble, web, inky cap, milk, tricholomas, ringstalks, sheath, mottle, pink, and brittle gills, tooth, death, waxy.

The following tables list mushrooms that have shown a greater affinity for radioactive cesium-137 and mushrooms that appear less sensitive to cesium accumulation. The lists have been created by HealWithFood.org based on accumulated data from three sources: 1) a study conducted by the Finnish Food Safety Authority and the Finnish Radiation and Nuclear Safety Authority, 2) a cesium-137 measurement campaign carried out by the German the Federal Office for Radiation Protection, and 3) a review of edible mushroom radioactivity compiled by Pavel Kalac from University of South Bohemia, Czech Republic.

* Fulfilled one or more of the following definitions of "high radioactivity" and none of the "low radioactivity" definitions: a) the German researchers reported values exceeding 1 000 Bq/kg Cs-137 b) the level of cesium-137 was commonly in excess of 600 Bq/kg, measured by the Finnish researchers, even in areas of minor fallout from the Chernobyl nuclear plant, c) a "high" radiocaesium ranking by the Czech researcher.
** Fulfilled one or more of the following definitions of "low radioactivity" and none of the "high radioactivity" definitions: a) the German researchers always reported below 10 Bq/kg Cs-137 b) the Finnish researchers found that the cesium-137 levels were in excess of 600 Bq/kg only on a random basis c) a "low" radiocaesium ranking by the Czech researcher.

Nuclear Contamination of Mushrooms and Type of Soil

In addition to the structure of the mushroom determined by the species it belongs to, the type of soil in which the mushroom has grown affects how much cesium-137 it contains. Sandy pine needle covered soils appear to promote the uptake of cesium-137 and other radionuclides in mushrooms, while fungi grown in deciduous woods and meadows typically show lower levels of nuclear contamination. This is because the fertile soil in decidious areas is richer in minerals that appear to absorb cesium better than sandy soil. The depth at which underground portions of the mushrooms inhabit soil has also been shown to affect the uptake of radioactive substances by mushrooms. Yoshida et al. (1994) concluded that the highest average concentration of cesium-137 was in mushrooms that inhabited the surface soil layer (0-5 cm or 0-2 inches).

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