Growth of commonly occurring moulds in foods and building materials may result in production of toxic complex secondary metabolic by-products referred to as mycotoxins.
Moulds that produce mycotoxins are said to be toxigenic (or incorrectly toxic moulds). According to experts, five kinds of mycotoxins are important in human health: aflatoxins, ochratoxin A, fumonisins, certain trichothecenes and zearalenone. It is believed the effect of mycotoxins as a cause of human mortality is underestimated. They can elicit a wide range of toxic responses including acute and chronic systemic effects in humans and animals that cannot be attributed to mould growth within the host or allergic reactions to foreign proteins.
Exposure to mycotoxins can occur through ingestion, contact or inhalation of airborne particulates containing mycotoxins, including dust and mould components such as spores and mycelial fragments. In agricultural settings, mycotoxicoses (mycotoxin poisoning) in both farm animals and humans can result from oral, dermal, or exposure through inhalation of mycotoxin-contaminated grain or dust.
The most widely known mycotoxins are the aflatoxins whose toxic effects were first realized in England in the 1960s when an outbreak of the so called turkey X disease killed over 100,000 fowls following consumption of contaminated peanuts. Aflatoxins are still a problem in developing countries. In mid 2004 more than 100 people died in an East African country after consuming grains contaminated with aflatoxins.
Aflatoxins are mainly produced by two species of Aspergillus, Aspergillus flavus and A. parasiticus, in several agricultural commodities, including corn and nuts. Two structural types of aflatoxins are known (B and G types), of which aflatoxin B1 is a class 1 carcinogen and is considered the most toxic. In laboratory mammals, symptoms associated with mycotoxins can be induced by systemic, oral, dermal, subcutaneous, or exposure through inhalation.
In experimental animals, exposure through breathing has been shown in some cases being several orders of magnitude more toxic than dermal or even systemic administration. Levels of mycotoxins in air in indoor environment have not well been established and neither the contribution of airborne mycotoxins to sick-building syndrome.
What Factors Favour Mycotoxin Production?
Mycotoxins are produced by a few strains of moulds at some point during their growth under suboptimal growth conditions or limited nutrients. Production occurs preferentially on materials that both allow toxigenic moulds to grow and provide the conditions for mycotoxin production.
From the many studies of the production of mycotoxins by mould isolates derived from agricultural environments, a great deal is known about the mould species that are capable of producing known mycotoxins and about the growth media and conditions that induce production. Conditions that favour production of one type of mycotoxins may not be favourable for production of another type.
For example, aflatoxin production by Aspergillus is dependent on concentrations of O2, CO2, zinc, and copper, as well as physical location while ochratoxin production relates to air exhaustion. Understanding the conditions under which mycotoxins are produced is important since presence of toxigenic moulds in any environment does not prove the presence of a mycotoxin.
What do we know about mycotoxins in indoor environment and their health effects?
Frequently, toxigenic moulds have been isolated from building materials and air samples in buildings where residents have suffered from non-specific symptoms possibly related to mycotoxin production, such as cough; irritation of eyes, skin, and respiratory tract; joint ache; headache; and fatigue.
It is only recently that the presence of some mycotoxins has been confirmed in crude building materials. Most mycotoxins have yet to be extracted from either air samples or bulk material derived from indoor environments. Also, very few studies have been conducted to show correlation between mycotoxin exposure and building-related illnesses.
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