Mushrooms And Arsenic: A Toxic Relationship

Mushrooms are known to accumulate arsenic, with levels varying depending on the environment in which they are grown. Arsenic is a metalloid that can be toxic to humans, and mushrooms can absorb and bioaccumulate it from their growth substrates. The arsenic content in mushrooms is a concern for consumers and regulatory authorities, especially in light of the absence of limits for arsenic in foods in the European Union. While arsenic levels in mushrooms are typically within the normal range in unpolluted areas, they can be significantly higher in polluted environments, posing a potential health risk. Studies have been conducted to investigate arsenic concentrations in mushrooms and assess the associated health risks, particularly in regions like Bangladesh, where arsenic toxicity is prevalent.

Mushrooms can accumulate arsenic depending on the substrate

Mushrooms can accumulate arsenic, and the amount of arsenic accumulated depends on the substrate on which they are grown. Arsenic is a metalloid, and mushrooms can capture and bioaccumulate heavy metals and trace elements present in their growth substrates. The arsenic compounds in edible mushrooms are a concern for consumers and regulatory authorities.

The Violet Crown Cup, or Sarcosphaera coronaria, is a mushroom that was once considered edible but caused several poisonings in the early 20th century. Arsenic has been proposed as a possible explanation for its toxicity, as Crown Cups can contain high amounts of arsenic.

Mushrooms cultivated in Bangladesh have been found to contain arsenic, with a mean concentration of 0.51 mg/kg. The substrate used for mushroom cultivation in Bangladesh, rice straw, is known to have high arsenic content. The arsenic concentration in the mushrooms was lower than that of the substrate, with the substrate in Savar containing an average of 0.563 mg/kg of arsenic, and the mushroom powder containing 0.15-0.36 mg/kg.

A study on the importance of low substrate arsenic content in mushroom cultivation found that edible fungal species grown on substrates containing different arsenic species exhibited different accumulations of total arsenic. The highest accumulation was found in Pleurotus ostreatus HK35 and Pleurotus eryngii, while Agaricus bisporus accumulated the lowest amount of arsenic. A. bisporus is potentially able to take up only certain forms of arsenic, effectively excluding others, which is likely behind its high tolerance.

The normal levels of arsenic in wild mushrooms are usually less than 1 mg/kg dw, but there are exceptions. For example, Laccaria amethystina has been found to contain arsenic levels between 4 and 146 mg/kg dw, and even extreme levels of 1420 mg/kg dw in polluted areas.

Arsenic toxicity in mushrooms is a health risk

The Violet Crown Cup, or Sarcosphaera coronaria, is a mushroom species that was once considered edible but has been linked to several poisonings in the early 20th century. While the reason for its toxicity remains unresolved, arsenic has been proposed as a possible explanation due to the high levels of arsenic that this species can absorb. Analyses have detected arsenic concentrations of up to 0.9% in dry mass, with the presence of both the less toxic methylarsonic acid (MA) and the highly toxic methylarsonous acid [MA (III)].

The impact of arsenic toxicity extends beyond individual mushrooms. In Bangladesh, for example, rice is the staple food, and it is a significant source of arsenic poisoning for the population. Consequently, rice straw, a common growing medium for mushrooms in the region, often contains high levels of arsenic. Studies have confirmed the presence of arsenic in mushrooms cultivated in Bangladesh, raising concerns about the associated health risks.

The health risk index, calculated as the ratio of estimated exposure to oral reference dose, is used to assess the safety of mushroom consumption. An index value exceeding 1.0 indicates a potential hazard to human health. Analyses of ground mushroom samples in Bangladesh revealed arsenic concentrations ranging from 0.15 to 0.36 mg/kg, highlighting the presence of arsenic in commercially available mushrooms.

To mitigate the health risks associated with arsenic toxicity in mushrooms, it is crucial to ensure the use of low-arsenic substrates in mushroom cultivation. By minimizing the metalloid residue levels in the substrate, the accumulation of arsenic in mushrooms can be reduced, thereby lowering the potential health hazards for consumers.

Arsenic levels vary in different mushroom species

Arsenic levels do indeed vary across different mushroom species. Mushrooms are known to accumulate various concentrations of arsenic, depending on the metalloid residue level in the substrate. The Violet Crown Cup, or Sarcosphaera coronaria, is a mushroom that was once considered edible but caused several poisonings in the early 20th century. Arsenic has been proposed as a possible explanation for its toxicity, as Crown Cups can contain high amounts of arsenic, with some studies finding up to 0.9% arsenic by dry mass.

The normal levels of arsenic in wild mushrooms are usually less than 1 mg/kg dw, but notable exceptions exist. For example, Laccaria amethystina has been found to contain arsenic levels between 4 and 146 mg/kg dw, and even extreme levels of 1420 mg/kg dw in polluted areas. The inedible Sarcosphaera coronaria species has been measured at 2130 mg/kg dw. Cultivated Agaricus bisporus, which is sold in Switzerland, was reported to have arsenic levels between 0.05 and 1.50 μg As/g dry mass.

A study of arsenic concentrations in mushrooms from Bangladesh found that the mean arsenic concentration was 0.51 mg/kg. Ground mushroom samples of P. ostreatus and P. high-king available in markets in Bangladesh were analysed, and the arsenic concentrations were found to be between 0.15 and 0.36 mg/kg. In another study, edible fungal species (Agaricus bisporus, Pleurotus ostreatus, Pleurotus eryngii, and Hericium erinaceus) were grown on substrates containing different arsenic species at different concentrations. The lowest arsenic accumulation was found in A. bisporus, while the highest was in P. o streatus HK35 and P. e ryngii.

The variation in arsenic levels across different mushroom species is influenced by factors such as the metalloid residue level in the substrate and the ability of certain mushroom species to selectively take up specific forms of arsenic while excluding others.

Mushrooms can contain inorganic and organic arsenic

Mushrooms can accumulate different concentrations of arsenic species, including both inorganic and organic forms, depending on the metalloid residue level in the substrate. Arsenic is taken up by the mycelium of the fungus, which can capture and bioaccumulate heavy metals and trace elements from its growth substrate. This accumulation can occasionally occur in high concentrations.

The arsenic content in mushrooms has been studied in various regions, including Galicia in northwestern Spain, Bangladesh, and Brazil. In Galicia, arsenic levels in wild mushrooms are typically below 1 mg/kg dw, but higher values have been recorded in certain species, such as Laccaria amethystina, which can contain up to 146 mg/kg dw in unpolluted areas. In polluted areas, arsenic levels in this species can reach as high as 1420 mg/kg dw. The inedible Sarcosphaera coronaria species has been found to have even higher arsenic levels, measuring 2130 mg/kg dw.

Mushroom samples from Bangladesh showed arsenic concentrations ranging from 0.15 to 0.36 mg/kg, with higher levels found in ground mushroom samples purchased from the market compared to those collected directly from growers. The arsenic content in the mushrooms was influenced by the growing medium, with rice straw, a common substrate in Bangladesh, known to have high arsenic levels.

Agaricus bisporus, a commercially cultivated mushroom species, has been found to have lower arsenic accumulation compared to other species. Studies have shown that this species can selectively take up certain forms of arsenic, effectively excluding others, which contributes to its high tolerance to arsenic. In Brazil, the arsenic levels in A. bisporus were considered safe for consumption.

Some mushrooms are safe to eat due to low arsenic uptake

Mushrooms are known to accumulate arsenic, particularly when grown in polluted areas. However, not all mushrooms absorb arsenic to the same degree, and some are considered safe to eat due to their low arsenic uptake.

The accumulation of arsenic in mushrooms depends on the metalloid residue level in the substrate on which the mushrooms grow. Arsenic toxicity is a significant health problem, and certain forms of arsenic are more toxic than others. For example, the highly toxic form of arsenic, methylarsonous acid [MA (III)], was detected in the Violet Crown Cup mushroom (Sarcosphaera coronaria), which was linked to poisonings in the early 20th century.

However, some mushroom species exhibit low arsenic uptake, making them safer to consume. For instance, the cultivated mushroom Agaricus bisporus, sold in Switzerland, was found to have relatively low arsenic levels, ranging from 0.05 to 1.50 μg As/g dry mass. This species is considered highly resistant to arsenic accumulation due to its low metalloid uptake. Similarly, in a study from Bangladesh, ground mushroom samples of Pleurotus ostreatus and P. high-king had arsenic concentrations ranging from 0.15 to 0.36 mg/kg and 0.15 to 0.45 mg/kg, respectively, which were lower than those found directly from growers.

The ability of certain mushrooms to selectively take up specific forms of arsenic, while excluding others, contributes to their safety. For example, A. bisporus was found to have very low levels of As(V) and was able to effectively exclude other forms of arsenic. This mechanism is believed to be responsible for its high tolerance to arsenic rather than the biotransformation of inorganic forms into less toxic compounds.

In conclusion, while mushrooms can accumulate arsenic, certain species are considered safe to eat due to their low arsenic uptake and their ability to selectively exclude certain toxic forms of arsenic. However, it is important to note that the arsenic content in mushrooms can vary depending on the growth conditions and substrate, and further research is needed to fully understand the toxicity and health risks associated with mushroom consumption.

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