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.
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.
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.