The mushrooms we see are the fruiting bodies of fungi. The real body of the fungus is a network of fine threads called hyphae, which together form the mycelium. The cells of the mycelium have simple walls that act like sponges, readily absorbing substances from the soil or substrate they grow in. If they grow in a medium contaminated by heavy metals, acid rain, slurry or other pollution, they can absorb and accumulate those substances.
Fungi are so good at this that they are studied for cleaning up contaminated soils – a process known as mycoremediation. But it also means that the growing environment of mushrooms we eat must be carefully controlled.
Choosing certified organic mushrooms means they have been grown according to organic production rules, without synthetic pesticides or fertilisers, with controls on soils and substrates. For mushroom supplements, specific laboratory analysis of each batch – including heavy metals – is also important, which is why we test every batch.