Mycotoxins are poisonous compounds made by various fungi (molds) as secondary metabolites. It is believed that one of their primary functions is to give mold a competitive advantage over other microorganisms, while the damage to human health is coincidental. Mycotoxin exposures resulting in recognized toxicoses in humans have been limited almost entirely to agricultural situations, where they occur either by ingestion or rarely, by inhalation.
The health effects of mycotoxin exposure in contaminated indoor environments, however, remain controversial. In spite of this controversy, the potential health effects of mycotoxins has led to their testing as part of some indoor air quality investigations. Understanding the testing limitations and controversy surrounding mycotoxins can help the investigator make informed decisions about the applicability of mycotoxin testing in individual situations.
As indicated, most of the data on mycotoxins and their ability to cause illness and death in humans and animals has come from the agricultural field. Exposure in these cases is usually large and by ingestion, causing an acute effect. A classic example is ergotism, a disease caused by a fungus that grows on cereal plants and replaces the grains. The fungus and its toxins are ingested at the same time as the harvested grain. Symptoms of ergotism in humans include convulsions, gangrene, hallucinations and death.
Other well known examples of mycotoxicoses include alimentary toxic aleukia which killed thousands of people in the USSR during the 1940s and Turkey X disease that killed more than 100,000 turkeys in the United Kingdom in 1960. It was Turkey X disease that really sparked an interest in mycotoxin research. Other diseases caused by mycotoxin ingestion have been documented, such as equine leukoencephalomalacia (ELEM) and porcine pulmonary edema (PPE), both caused by the consumption of contaminated feed.
Two Schools of Thought
More recently, scientists have tried to determine the effects of mycotoxins on human health in an indoor environment. Exposure in this setting is usually chronic and by inhalation, as opposed to the acute ingestion exposures that occur in agriculture. The real controversy right now is whether chronic exposure to mycotoxins through inhalation has a negative effect on human health.
In regards to inhalation mycotoxin exposures in indoor environments, two diametrically opposed schools of thought have developed. One school recognizes mycotoxins as dangerous due to their associative symptoms and their health effects in agricultural situations. The opposite school of thought states that the evidence is all anecdotal because it is typically based on differential diagnoses with general disease symptoms, e.g., gastrointestinal effects, headaches, and neurological effects to some extent. In these cases, causality has not been established because the symptoms are based on a person's word and are hard to prove medically. This group argues that toxicological effects require much larger doses than observed in indoor environments and thus are not of concern. However, the fact that chronic sub-acute exposures have not been sufficiently studied makes the evidence for the second school just as anecdotal. The resulting lack of evidence supporting either camp suggests that the most responsible attitude is to treat mycotoxins as though they could potentially cause ill health effects in indoor environments.
A compounding difficulty is the lack of baselines for a person before exposure to the contaminated indoor environment. For example, if a person's IQ after exposure to mycotoxins is 78, one may be led to believe that the mycotoxins had a deleterious effect on intelligence. However, the person may have started with an IQ of 77 and the mycotoxins actually increased cognitive functioning slightly. As this example shows, without an accurate baseline, conclusions regarding potential exposures can be flawed.
Another argument against the first school of thought is that the majority of scientific studies analyzing the effects of mycotoxins involve acute exposures and/or animal studies. Extrapolating these results to human chronic exposure provides questionable conclusions. Additionally, it is difficult or often impossible to determine what levels of specific mycotoxins people are actually being exposed to, due to the fact that levels are far below the detection limits of the most sensitive analytical method available: high-performance liquid chromatography. This is confounded by lack of knowledge on chronic exposure what are the accumulations; what are the detoxifications; is there increased sensitivity; are there interactions with other mycotoxins, additional organisms or other environmental factors?
While there is no conclusive evidence for either school of thought, it should be noted some other accepted agents of disease also lack irrefutable causality. For instance, it is widely accepted that smoking causes cancer. Yet there is no dose response established for cigarettes and cancer. It is not known how many cigarettes it takes to cause 50 percent of the population to develop cancer of the same type. Cigarettes contain known carcinogens, but which ones caused the cancer? Yes, there is a strong association, but it is still an association and not a proven causality. Another example is that drinking while pregnant may cause birth defects; again, this is an epidemiological association and not a proven causality.
Sampling Limitations
Important in this discussion is an understanding of the limitations of sampling methodologies. A real quandary exists here because present technology usually cannot collect enough spores from the air to obtain sufficient toxin for detection. People try to get around the limitations of air sampling by analyzing bulk samples or by culturing the organism in the lab and showing that the fungus can make mycotoxins. Regrettably, neither of these methods can be related to actual exposure. With bulks, there is no way of extrapolating results to what is actually in the air. Aerotech Laboratories has evidence showing isolates of the same species of organism, taken from different areas in a room or building, can have profoundly different toxin profiles. Thus, in cases of severe contamination, one cannot quantify the potential toxicity of the fungal contamination without costly and extensive testing. Even if potential toxicity is estimated, one cannot extrapolate how much toxin is airborne since it is impossible to determine the percentage of bioaerosol contributed by each of the isolates.
Extrapolation of results from cultures is more complicated than from bulks. In addition to the differing isolate problem, the fungus is put into an artificial environment: the temperature in the lab may be different from the investigation site, the growth media may have different nutrients from the initial growth substrate, or the fungus may or may not be competing with other organisms, which reportedly has been conducive to mycotoxin production. Since mycotoxin production is at least partially dependent on environmental conditions, its fabrication by a laboratory culture cannot be used to show there were mycotoxins in the air at the sampling site. Therefore, it cannot be used to extrapolate to an actual exposure, but can demonstrate a potential exposure existed.
In spite of its interpretive limitations, sampling for mycotoxins can be an appropriate and important analytical tool. For instance, mycotoxin analysis can be useful when trying to establish there is a potential exposure, especially in cases of litigation. It may also be useful when making a case based upon a medical aspect such as trying to determine the potential cause of symptoms exhibited by building occupants.
Rather than analyzing for mycotoxins, some investigators simply determine the species of fungus present and report their potential mycotoxins. For instance, certain species of Fusarium, Stachybotrys, Aspergillus, Penicillium and Chaetomium are considered indicators of potential toxicity. While their presence in an indoor environment does not necessarily imply exposure to mycotoxins, it does suggest its potential.
Caution, Research Needed
If not careful, people can go beyond the bounds of scientific knowledge and use one of the viewpoints listed earlier to promote their own agenda. Claiming that mycotoxins have no health effect or that they are dangerous in indoor environments are both positions that have not been scientifically validated. The bottom line is that one cannot say there is or is not a health effect associated with mycotoxins from contaminated indoor environments. However, since there could be a potential health effect, proper precautions to protect people must be taken.
Additional research needs to be conducted in order to make a more definitive case about the health effects of indoor exposure to fungi and their mycotoxins. Such research would have to involve long-term chronic exposures. Unfortunately there does not seem to be any impetus for the scientific community to resolve this controversy. In the meantime, mold and mycotoxin analyses continue to be strategic tools in preserving the health of building occupants.
R. Vincent Miller, Ph.D., directs all research and development projects for Aerotech Laboratories Inc., Phoenix. His more than 24 years of experience in microbiology and chemistry allow him to validate and develop new analytical methods. He is the co-inventor of two patents and co-author of 19 publications and 22 proceedings at national and international conferences. Prior to joining Aerotech, he served as vice president of Mycogenesis, where he managed multiple projects on antifungal pharmaceuticals. Before that, he helped found EcoPharm, the precursor to Mycogenesis and a developer of natural products with antifungal applications. He holds a Master of Science degree in biology from New Mexico State University and a Ph.D. in plant pathology from Montana State University.