Mycotoxins

What are mycotoxins?
The name mycotoxin is derived from the Greek word 'mykes' meaning fungus and the Latin word 'toxicum' meaning poison. Mycotoxins are secondary metabolites produced by fungi (including moulds) that cause illness or death in humans or animals, typically through ingestion. Some mycotoxins are also toxic to plants or other microorganisms (called antibiotics). Fungi produce many different secondary metabolites as a product of their metabolism. The reason why fungi produce mycotoxins for themselves is still not clear. It may be a mechanism to secure a food source from their competitors; chemical warfare at its most basic form.

Fungi are a natural part of the environment with most species living on dead organic matter that they help to decompose, while many others may cause diseases in plants. More than 250 mycotoxins have been detected from over 200 fungal species. For most, their toxicological characteristics have not been fully described. The Food and Agricultural Organization of the United Nations (FAO) has estimated that 25% of the world's crops are contaminated with mycotoxins, and certain diseases have been linked to ingestion of food and feed contaminated with mycotoxins. New evidence that indoor air pollution from toxigenic fungi may play a role in
human illness has implicated that mycotoxins could have a much bigger role in chronic disease than was previously thought possible (CAST 2003).

Historically, the first fragmentary information of fungal poisoning was in ancient Greco- Roman times although it was not until the Renaissance that more precise descriptions are found. Modern mycotoxicology really began with the discovery of aflatoxin in the early 1960's as the chemical compound responsible for causing "Turkey X" disease. Over 10,000 turkeys were killed after consuming contaminated peanut meal.

What are the significant toxins?
Mycotoxins have traditionally been studied in the agricultural and food industries but in recent years their association with indoor mould contamination has been of great interest. The major classes of mycotoxins are aflatoxin, trichothecenes, fumonisins, zearalenone, ochratoxin A and ergot alkaloids. The mycotoxins found in indoor air are usually concentrated in the aerosolized fungal spores but may also be in mycelia and contaminated substrates. Table 1 lists toxigenic fungi commonly isolated from water-damaged buildings.

Table 1.

Toxins in boldface are of high potency. Abstracted from Advances in experimental medicine and biology. Vol.504; 43-52. Edited by J.W. DeVries, M.W. Trucksess and L.S. Jackson.

How are they produced?

Mycotoxins can be produced by a variety of different fungal species and it is a generally accepted phenomenon that the occurrence of mycotoxins is unpredictable. Two important points need to be emphasized. First, the presence of a mould or evidence of prior fungal contamination does not in itself indicate the presence of mycotoxins. There is a possibility that the fungus is genetically incapable of toxin production or, if the organism is capable, the conditions may not be the right ones to trigger off and stimulate toxin production.

Mycotoxin production is affected by a multitude of variables that are interactive and in a state of dynamic change. Environmental, genetic and physiological factors play a key role. These factors include weather conditions, invertebrate vectors, strain type, and spore load. Physical factors for mycotoxin production are time of exposure, temperature, humidity, insect predation and other damage. Chemical factors for production include nutrients, aeration (O2 and CO2 ratio), type of substrate, and pH.

Health considerations
Mycotoxins can be carcinogenic (causes cancer), teratogenic (causes birth defects), mutagenic (causes mutation or damage to genetic material), immunosuppressive (decreases the immune system), tremorgenic (causes tremors or damage to the central nervous system), hemorrhagic (causes bleeding), hepatotoxic (damages the liver), nephrotoxic (damages the kidneys) and neurotoxic (damages nerve tissue).

Human exposure to mycotoxins can occur by several ways, including ingestion, contact, and inhalation. Table 2 lists some human diseases in which analytic and/or epidemiological data suggest or implicate mycotoxin involvement from ingestion of contaminated substrates.

Table 2.

CAST (2003).

Dose-response relationships between exposure to mycotoxins in the indoor environment through inhalation and health effects to occupants have still not been established. We know that there are significant health effects when mycotoxins are ingested, we do not know what it takes to elicit any effect through breathing contaminated air.

Sampling Considerations
The Indoor Air Quality (IAQ) professional may select different types of sampling procedures depending on the project’s scope. The most common sampling procedure used is swab or wipe sampling. The sample would consist of swabbing a known area, usually 10 square inches or centimeters with a sterile swab or gauze. An acceptable swab/wipe solvent is PBS solution, sterile water, or methanol. Building materials with visible fungal growth can also be submitted to a laboratory for mycotoxin analysis. Clearance testing can be performed with swabs by swabbing the surfaces of flat areas such as desks, baseboard molding, or HVAC vents. The presence or absence of toxins can provide guidance to the remediation contractor as to the extent
and effectiveness of the cleanup procedures used.

Air samples can also be taken although this type of sampling is used less frequently than the swab or wipe. The investigator would employ the same spore collection techniques as those used for PCR analysis. This collection method uses a 37 mm polycarbonate (0.45 um) filter cassette and a high volume pump, sampling at 10-30 liters/minutes for 500-1000 liters.

The identity of the fungal species is required to complete the mycotoxin analysis. The investigator would collect and submit samples to the laboratory for fungal identification by direct examination or by PCR (polymerase chain reaction) analysis first before mycotoxin analysis.

If toxins are found you know that you either have the mold present currently or it was there prior. Also, if young children or the immunocompromised such as the elderly or the sick are exposed, the IAQ professional should view this finding of toxin presence as an indicator parameter of potential concern. If a home or office is classified as unhealthy due to non-specific complaints, the toxins could be indicative of a potential problem. Classifying the levels of toxins found as “toxic or unhealthful” is a difficult challenge. Attributing health problems solely to airborne exposures or classifying environments as “toxic” or “unhealthy” is a difficult job for the IAQ professional because of the lack of research data in the literature.

Laboratory Selection
Mycotoxin analysis can only be performed by a handful of environmental microbiology laboratories in the US. Some veterinarian schools offer mycotoxin analysis on samples of grains and feeds to the agricultural industry but these procedures may be of little use to the IAQ professional. Selection criteria for laboratories should include industrial hygiene experience, fungal speciation experience, and experience in handling highly toxic compounds.

Mycotoxin analysis can be performed using routine instrumentation or very sophisticated instrumentation. The differences in instrumentation used by the laboratory can drastically affect the cost per sample for analysis. For example, the cost per sample for ochratoxin analysis can range from $100 per sample to thousands of dollars per sample. Ideally, laboratories should be obtaining the same result although the analytical procedures employed may be different. It is crucial when selecting a laboratory for mycotoxin analysis to discuss with them your project goals and how that will affect the quality of data and price.

Method Selection – Why are there so many different ways to analyze for mycotoxins?
As with most scientific disciplines, there are many ways to analyze for substances. Some procedures yield good data without the sacrifice of high cost. Generally, higher cost means more sophisticated instrumentation and procedures. New techniques are being developed that can reduce the cost of analysis but still yield quality data.

Enzyme-linked immunosorbent assay (ELISA) techniques have been developed for the identification of certain mycotoxins. Monoclonal antibody isolation chemistry has been used in the livestock feed industry for years with great success. These techniques can provide the IAQ professional with useful data for only a fraction of the cost than that of more sophisticated techniques that use liquid chromatography with mass spectrometry (LC/MS). LC/MS is useful for very low level detection and identification of certain mycotoxins and metabolites where no standard reference material is available. For the more common Aspergillus and Penicillium species, aflatoxins and ochratoxin A can be identified and quantified using ELISA or monoclonal antibody isolation techniques.