The amount of radioactive cesium (cesium-137) in mushrooms can be reduced during cooking, using common mushroom treatment methods.

When mushrooms are soaked or boiled in water, most of the radioactive cesium in them is released into the water. The reduction of cesium-137 content in mushrooms is based on throwing away the water in which the mushrooms were soaked or boiled.

As much as 70–80 per cent of the cesium in mushrooms can be eliminated by soaking or boiling the mushrooms in water. The treatment can be made more efficient by using more water than instructed in the general instructions or by repeating the treatment. This can remove as much as 90–95 per cent of the cesium. Soaking dried or salted mushrooms in cold water overnight is more efficient than brief soaking in hot water. Drying mushrooms without soaking them does not reduce the amount of cesium.

Just rinsing fresh mushrooms in cold water does not reduce the cesium-137 concentration much, while soaking them in cold water overnight can reduce it by as much as 70 per cent.  

Squeezing water out of frozen mushrooms after thawing can reduce the amount of cesium-137 in them by more than 50 per cent, depending on the amount of water.