Airborne Fungal Toxins Can Develop More Readily than Previously Suspected

View by microscopy of a sporulating Aspergillus, showing numerous light spores that can be easily aerosolized and inhaled together with mycotoxins. [Sylviane Bailly/Université de Toulouse]

A team of French investigators has uncovered some new alarming evidence that will likely have major implications on the sick building syndrome (SBS) hypothesis—a medical condition where people in a building suffer from symptoms of illness or feel unwell for no apparent reason. The researchers found that toxins produced by three distinct species of fungus growing indoors on wallpaper may become aerosolized and easily inhaled. The findings from the new study were published recently in Applied and Environmental Microbiology, in an article entitled “Aerosolization of Mycotoxins after Growth of Toxinogenic Fungi on Wallpaper.”

The incentive for the current study was the scarcity of data pertaining to the potential health risks from mycotoxins produced by fungi growing indoors. To study the effects of indoor mycotoxins, the investigators built an experimental bench that simulates an airflow over a piece of contaminated wallpaper, controlling speed and direction of the air. Then they analyzed the resulting bioaerosol.

“We demonstrated that mycotoxins could be transferred from a moldy material to air, under conditions that may be encountered in buildings,” explained co-senior study investigator Jean-Denis Bailly, D.V.M., Ph.D., professor of food hygiene at the National Veterinary School of Toulouse, France. “Thus, mycotoxins can be inhaled and should be investigated as parameters of indoor air quality, especially in homes with visible fungal contamination.”

The researchers employed three fungal species in their study: Penicillium brevicompactum, Aspergillus versicolor, and Stachybotrys chartarum. These species, long studied as sources of food contaminants, are commonly found as indoor contaminants. Each fungus produces different mycotoxins, and their mycelia—thread-like projections that seek nutrition and water from the environment—are very different from one another, likely leading to differences in the quantities of mycotoxins they loft into the air.

“Most of the airborne toxins are likely to be located on fungal spores, but we also demonstrated that part of the toxic load was found on very small particles—dust or tiny fragments of wallpaper, that could be easily inhaled,” Dr. Bailly noted.

The investigators findings raised some interesting scientific questions that the scientists felt needed to be addressed. First, there is almost no data on the toxicity of mycotoxins following inhalation, with the research team noting that most research has focused on such toxins as food contaminants. Additionally, the different fungal species put different quantities of mycotoxins in the air, most likely related to mycelium organization but also possibly related to the mechanisms by which mycotoxins from different fungi become airborne—for example via droplets of exudate versus accumulation in spores. Such knowledge could help in prioritizing those species that may be of real importance in wafting mycotoxins.

“We demonstrated that mycophenolic acid, sterigmatocystin, and macrocyclic trichothecenes (sum of 4 major compounds) could be produced at levels of 1.8, 112.1 and 27.8 mg/m², respectively on wallpaper,” the authors wrote. “Moreover, part of the produced toxins could be aerosolized from the substrate. The propensity to aerosolization differed according to the fungal species. Thus, particles were aerosolized from wallpaper contaminated with P. brevicompactum when air velocity of just 0.3 m/s was applied, where S. chartarum required air velocity of 5.9 m/s. A. versicolor was intermediate since aerosolization occurred under air velocity of 2 m/s.”

Interestingly the scientists noted that the push for increasingly energy-efficient homes might aggravate the problem of mycotoxins indoors, as such homes are strongly isolated from the outside to save energy, yet various water-using appliances such as coffee makers could lead to favorable conditions for fungal growth.

“The presence of mycotoxins in indoors should be taken into consideration as an important parameter of air quality,” Dr. Bailly concluded.