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mycotoxin

[mahy-koh-tok-sin]

Toxin produced by a fungus. Numerous and varied, mycotoxins can cause hallucinations, skin inflammation, liver damage, hemorrhages, miscarriage, convulsions, neurological disturbances, and/or death in livestock and humans. The best-known mycotoxins are aflatoxin, ergot toxin, and the agents of mushroom poisoning.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

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Mycotoxin

Mycotoxin (from the Greek μύκης (mykes, mukos) "fungus") is a toxin produced by an organism of the fungus kingdom, which includes mushrooms, molds and yeasts. Most fungi are aerobic (use oxygen). Fungi are found almost everywhere in extremely small quantities because of their spores, and are most commonly microscopically small. They consume organic matter, wherever humidity and temperature are sufficient.

Where conditions are right, fungi proliferate into colonies and mycotoxin levels become high. Toxins vary greatly in their severity. Some fungi produce severe toxins only at specific levels of moisture, temperature or oxygen in the air. Some toxins are lethal, some cause identifiable diseases or health problems, some weaken the immune system without producing symptoms specific to that toxin, some act as allergens or irritants, and some have no known effect on humans. Some mycotoxins generally have more negative impacts on farm animal populations than on humans. Some mycotoxins are harmful to other micro-organisms such as other fungi or even bacteria; penicillin is one example.

Mycotoxins can appear in the food chain as a result of fungal infection of crops, either by being eaten directly by humans, or by being used as livestock feed. Mycotoxins greatly resist decomposition or being broken down in digestion, so they remain in the food chain in meat and dairy products. Even temperature treatments, such as cooking and freezing, do not destroy mycotoxins.

Buildings are another source of mycotoxins. Public concern over mycotoxins increased following multi-million dollar toxic mold settlements in the 1990s. The negative health effects of mycotoxins are a function of the concentration, the duration of exposure and the subject's sensitivities. The concentrations experienced in a normal home, office or school are often too low to trigger a health response in occupants.

Food-based mycotoxins were studied extensively worldwide throughout the 20th century. In Europe, statutory levels of a range of mycotoxins permitted in food and animal feed are set by a range of European directives and Commission regulations.

Various wild mushrooms also contain an assortment of mycotoxins that can cause noteworthy health problems for humans who eat wild mushrooms without first properly identifying the specimens as safe edibles, in such cases sometimes causing mild to catastrophic mushroom poisoning. The bulk of this article, however, is about mycotoxins that are found in fungi other than mushrooms.

Major groups of food toxins

Aflatoxins are produced by Aspergillus species, and are largely associated with commodities produced in the tropics and subtropics, such as groundnuts, other edible nuts, figs, spices and maize. Aflatoxin B₁, the most toxic, is a potent carcinogen and has been associated with liver cancer.

Ochratoxin A is produced by Penicillium verrucosum, which is generally associated with temperate climates, and Aspergillus species which grow in warm humid conditions. Aspergillus ochraceus is found as a contaminant of a wide range of commodities including cereals and their products, fruit and a wide range of beverages and spices. Aspergillus carbonarius is the other main species associated in warm humid conditions found mainly on vine fruit and dried vine products particularly in the Mediterranean basin. It causes kidney damage in humans and is a potential carcinogen.

Patulin is associated with a range of fungal species and is found in moldy fruits, vegetables, cereals and other foods. It is destroyed by alcoholic fermentation and so is not found in alcoholic drinks. It may be carcinogenic and is reported to damage the immune system and nervous systems in animals.

Fusarium toxins are produced by several species of the genus Fusarium which infect the grain of developing cereals such as wheat and maize. They include a range of mycotoxins including the fumonisins, which affect the nervous systems of horses and cause cancer in rodents; and the trichothecenes, including deoxynivalenol, and zearalenone, the last two of which are very stable and can survive cooking. The trichothecenes are acutely toxic to humans, causing sickness and diarrhea and potentially death.

Stachybotrys and Penicillium

Mycotoxin binding agents and deactivators

In the feed and food industry it has become common practice to add mycotoxin binding agents such as Montmorillonite or bentonite clay. To reverse the adverse effects of mycotoxins, the following criteria are used to evaluate the functionality of any binding additive:

Efficacy of active component verified by scientific data
A low effective inclusion rate
Stability over a wide pH range
High capacity to adsorb high concentrations of mycotoxins
High affinity to adsorb low concentrations of mycotoxins interactions between toxins
Affirmation of chemical interaction between mycotoxin and adsorbent
Proven in-vivo data with all major mycotoxins
Non-toxic, environmentally friendly component

Since not all mycotoxins can be bound to such agents, the latest approach to mycotoxin control is mycotoxin deactivation. By means of enzymes (esterase, epoxidase), yeast (Trichosporon mycotoxinvorans) or bacterial strains (Eubacterium BBSH 797), mycotoxins are detoxified to non-toxic metabolites.

Mycotoxins killing humans

In 2004 in Kenya 125 people died and nearly 200 others were treated after eating aflatoxin contaminated maize. The deaths were mainly associated with homegrown maize that had not been treated with fungicides or properly dried before storage. Due to food shortages at the time, farmers may have been harvesting maize earlier than normal to prevent thefts from their fields, so that the grain had not fully matured and was more susceptible to infection.

Mycotoxins in pet food

There have been outbreaks of pet food containing mycotoxins in North America.

Mycotoxins in fiction

A fictional application of a mycotoxin occurs in William Gibson's seminal novel Neuromancer, in which Case, the anti-hero, is punished by some of his business partners for stealing from them by being administered a "Russian war-time mycotoxin", which alters his nervous tissue and renders him unable to access cyberspace.