Mushroom farming is not only a source of nutritional rich food but also a provider of effective medicinal products. In the last decades, mushroom cultivation has become very popular among people all over the world. 31 billion tons was the number of the world’s total edible and medicinal mushroom registered in 2012. Different cultivating techniques have developed throughout the years and this has contributed to an increase in mushroom production. Cultivation has evolved from a relatively primitive method to a highly technological industry. The basic principles are the same for all mushrooms, but the practical approaches differ depending on the species. A person who decides to grow mushrooms for the purpose of consumption has to be aware that even though he or she does not skip any step of the grow process, toxic substances may still be present within the resulted frutibodies, and they should not be neglected. As one starts out in this field, the strategy should be identifying a strain that is compatible with the climate conditions in that specific area, is able to grow on the available substrates, has a quick production and requires a decent cost and infrastructure to sustain harvest consistently.
The presence of toxic substances like heavy metals in soil, air, water and organisms has always been of great concern and considered a threat to human health. They are cytotoxic, carcinogenic and mutagenic. Some of them are toxic even at trace levels. They tend to accumulate in tissues and organs and cause serious harm.
Interest is shown especially in the content of these substances found in edible mushrooms. Although cooking and preservation might decrease the levels it does not make them disappear. Fungi are indicators of heavy metal concentration in the environment. They reflect the level of contamination through different metabolic and morphological characteristics. Exposure to the heavy metal content results in physical, neurological and muscular disorders. There are several factors that contribute to the accumulation ability like species, heavy metal identity, the substrate’s pH, age of culture mycelia, etc. EFSA (European Food Safety Authority) has listed some safe levels for heavy metal ingestion known as TDI (tolerable daily intake). Nickel, a naturally occurring metal can be found in food and water as a result of industrial contamination. The TDI is 2.8 µg/kg of body weight. Mercury, a heavy metal of elevated risk is tolerable in 1.3 µg/kg of body weight. Cadmium, another very popular metal is labeled at 2.5 µg/kg of body weight TWI (tolerable weekly intake). Lead is an environmental contaminant whose occurrence is sustained by different human activities. Regulations have decided that the maximum levels present in mushroom should be of 0.30 mg/kg wet weight.
Researchers have found that the content of heavy metals in fruitbodie increases in polluted areas. What’s peculiar about this is that some species of mushroom are not affected by the pollution and the content of heavy metals found in them is significantly lower compared to others. Also, it was discovered that the cap held higher concentration than the stalk in most cases. A study performed on distinct species of mushrooms and conducted by several scientists found out that the highest cadmium concentration was signaled in Agaricus arvensis, 117 mg/kg. The highest nickel, Pleurotus ostreatus, 145 mg/kg. Concerning the concentration of mercury, an amount of 120 mg/kg was found in only one sporophore of Lycoperdon utriforme. Most species accumulate cadmium, lead and nickel. There are some types of mushrooms that can present two metals in high concentrations: Agaricus bisporus, Lepista nuda (lead and nickel), Marcolepiota procera (lead and mercury), Agaricus sylvicola (cadmium and nickel).
Apart from heavy metals, fungi can also carry insecticides. Sugarcane bagasse is used in mushroom compost production. In order to prevent and combat pests, people use a substance called fipronil. It effectively controls insects but using it might lead to the formation of toxic metabolites. Exposure to insecticides is neurotoxic. Sun mushrooms have the tendency to accumulate fipronil from the compost if available and this poses threat to human consumption. Studies have revealed that the presence of fipronil in the compost did not lead to accumulation in fruit bodies. On the other hand, when added to the soil casing layer, the results showed bioaccumulation in the mushrooms. One interesting fact is that fipronil adsorption is higher in soils rich in organic matter.
Mushrooms are also vulnerable to radiocesium contamination occurring from a radioactive fallout. Boletus badius is commonly known to hold affinity for contamination with radioactive substances. After the Chernobyl nuclear incident, researchers have gathered samples of mushrooms from different parts of Poland and analyzed them for nuclear traces. The abundance of radiocesium in mushroom can be attributed to three factors: soil contamination, the specific uptake of various species and mushroom requirements. The radioactive compounds are adsorbed and deposited on the top organic layer of the soil. Some fungi with simplistic mycelia can accumulate these elements readily and in considerable amounts.
It is highly important to take into consideration every minor aspect when deciding to grow mushrooms. Growing them organically, even though it might imply more funds, tests and regulations, has more benefits on the long run but even with this on we won’t be absolutely sure that the mushrooms that we eat are clean.
A report by Malina Puia
“Organic Mushroom Farming and Mycoremediation: Simple to Advanced and Experimental Techniques for Indoor and Outdoor Cultivation” book by Tradd Cotter
- Chang, S. P. Wasser, “The Cultivation and Environmental Impact of Mushrooms”, 2017
Mogildea Daniela, “BIOACCUMULATION OF TOXIC HEAVY METALS IN MUSHROOMS – A REVIEW”, 2016
- A. Carvalho et al., “Bioaccumulation of insecticide in Agaricussubrufescens”, 2014
- Falandyz, et al., “Evaluation of the radioactive contamination in fungi genusBoletus in the region of Europe and Yunnan Province in China”, 2015
- Das, “Heavy metals biosorption by mushrooms”, 2005
- D. Raj, et al., “MUSHROOMS IN THE REMEDIATION OF HEAVY METALS FROM SOIL”
- Dulay, M. De Castro, “CADMIUM AND CHROMIUM TOLERANCE ANDMYCOREMEDIATION ABILITYOF TIGER SAWGILL MUSHROOM, Lentinustigrinus”, 2016