Mushrooms accumulate harmful heavy metals from soil

We eat edible mushrooms. Fine. 

Mushrooms are  low in calories and fat and cholesterol-free, mushrooms contain a modest amount of fiber and over a dozen minerals and vitamins, including copper, potassium, magnesium, zinc and a number of B vitamins such as folate. They are good for health we think. 

But do you know that some mushrooms and other fungi are used in phycoremediation to clean up contaminated soils. Part of this is the ability of fungi to break down organic compounds.

The nutrient profile of a mushroom varies depending on the type and the method of cultivation (4).

Mushrooms can also sequester heavy metals from the environment in their mycellium (1). The results of researchers  showed the concentrations of seven heavy
metals which include Mercury(Hg), Iron (Fe), Zinc (Zn), Lead (Pb), Copper (Cu),
Nickel (Ni) and Cadmium (Cd) in four edible mushrooms which include Pleurotus
squarrosullus, Volvariella volvacea, Schizophyllum commune and Auricularia
auricular sold in Benin City. There was a variation in the composition and
concentration of the heavy metals in the different edible mushroom samples analysed. The heavy metal concentration ranged from 2.50 to 5.75 mg/kg for Ni, 2.25-4.88
mg/kg for Cd, 1.55-1.86 mg/kg for Cu, 1.25-1.88 mg/kg for Pb, 6.46-27.33 mg/kg for
Zinc and 8.25-58.25 mg/kg for Fe. The results from this investigation showed that
edible mushroom can serve as a bioremediation agent because of its ability to bio
accumulates substances such as heavy metals, thereby removing them or reducing their
concentration which may be harmful or hazardous from the polluted soil. This
investigation also revealed the need for public awareness on edible mushrooms and
their bioaccumulation ability especially in areas with frequent pollution like crude oil
pollution in the Niger Delta area of Nigeria.

“Researchers in Spain have analyzed the presence of heavy metals in 12 species of mushroom collected from non-contaminated natural areas, and has found that the levels vary depending on the type of mushroom. The results of the study show that the largest quantities of lead and neodymium are found in chanterelles.” (2)

“Stamets (2005) reported that mushroom channels heavy metals from land to fruity bodies for removal from the soil/ environment. This is first by denaturing the toxins and finally absorbing such heavy metals. Mushroom are hyper accumulators of heavy metals and radioactive metals that are toxic to consume and are thus eliminated from the environment. These are bio concentrated in solid forms in the mushroom (Wasser et al., 2003; Sasek, 2003). Similarly, Arica et al., (2003) reported, the use of Turkey tail mushroom and Phoenix oyster mushroom mycelia to eliminate 97% mercury ion from water. Mushroom is a fungus, which feeds by secreting enzymes and digests food externally and absorb the nutrients in net like chain called hypha. The net like chain (hypha) is exposed to stimuli in their ecological niche and act as a conscious intellect and respond to stimuli. Dense and regular branching of hypha endows fungi with potentials to pervade any substrate thoroughly (Hudson, 1986). The higher the mycelium thickness, the higher the rate of mechanical penetration and breaking down of substrate. This culminates at the higher the rate of digestion of substrate through the secretion of extra- cellular enzymes. This shows the potentials of bioremediation capabilities of mushroom (Bouchez et al., 1996; Juhaz and Naidu, 2002). This hypha/mycelium penetrates contaminated soils, thus placing a mat on them; it is the process of breaking down and adsorption of toxic products or pollutants. Generally the bonds in hydrocarbon and petroleum products such as PMS and AGO are similar to bonds that hold the plant materials together. The enzymes produced by mushroom which are lignin peroxidase, manganese peroxidase and laccase penetrate, break and digest or mineralizes these hydrocarbon, petroleum products and pesticides to primary non-solid products and are liberated in the forms of water and carbon (iv) oxide (Schliphake et al., 2003). These enzymes act singly or collectively in aiding mycelium to break down natural or human made resistant materials (Stamets, 2005). Similarly, Hitivani and Mecs (2003), reported that the mycelium of Shiitake mushroom exposed to heavy metals of cadmium, copper, lead, mercury and zinc increased the production of enzymes laccase, decolorized them and subsequently absorbed the heavy metals.”

Bioaccumulation of Heavy metals and pollutants by edible mushroom…

U.Udochukwu, B.O Nekpen2, O.C.Udinyiwe, and F.I. Omeje

The ingestion of vegetables and mushrooms contaminated with heavy metals causes serious human health issues, such as gastrointestinal cancer, fragile immunological mechanisms, mental growth retardation, and malnutrition (6). Heavy metals can accumulate in human bones or fatty tissues through dietary intake, thereby leading to the depletion of essential nutrients and weakened immunological defenses. Certain heavy metals (e.g., Al, Cd, Mn, and Pb) are further suspected to cause intrauterine growth retardation (6).

Experts are very concerned with the heavy metals, as these can be sequestered in the mushroom. (3)

Therefore, they are recommending that  cultivation of mushrooms in heavy metal-free soil should be encouraged (5). Home-grown mushrooms should be encouraged instead of growing them in heavy metal prone polluted areas. 

CITATIONS:

1. https://www.ijcmas.com/vol-3-10/U.Udochukwu,%20et%20al.pdf

2. https://www.sciencedaily.com/releases/2009/10/091030102151.htm

3. https://www.sciencedirect.com/science/article/abs/pii/S014765131300...

4. https://www.ncbi.nlm.nih.gov/pubmed/28530594

5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6221449/

6. https://www.sciencedirect.com/science/article/pii/S0160412018327971