Mycotoxins and indoor environment : Aerosolization of mycotoxins during development of toxigenic species and development of tools for monitoring in habitats
Mycotoxins are secondary metabolites produced by many fungal species. Health effects induced by the ingestion of these substances are well documented and some mycotoxins are now regulated for their maximum tolerable levels in foods. However, other routes of exposure to these contaminants are possible. Thus, if irritating or allergenic reactions related to the inhalation of fungal spores or mycelial fragments have been demonstrated, inhalation of mycotoxins is also suspected to be causing certain respiratory disorders or certain pathologies. Indeed, mycotoxins can be found in spores but also on finer particles which are easily aerosolized and therefore likely to be inhaled. However, data on the hazard associated with human exposure to mycotoxins by inhalation are still very fragmented. In this context, our main objective was to characterize the aerosolization of mycotoxins during the colonization of different materials encountered in indoor environments by toxinogenic molds. First we studied growth and production of mycotoxins during the colonization of building materials (wallpaper, painted fiberglass wallpaper, vinyl wallpaper, fir, fiberglass) by three fungal species of interest: Aspergillus versicolor, Penicillium brevicompactum, Stachybotrys chartarum. These species were chosen because of their frequent presence in indoor environments and their diverse mycelial organization. In addition, these three species produce different toxins: sterigmatocystin, mycophenolic acid and macrocyclic trichothecenes for A. versicolor, P. brevicompactum and S. chartarum, respectively. These studies have shown that, during their development on tested materials, three species produce mycotoxins. The most favorable material for fungal development and toxinogenesis is wallpaper. Mycophenolic acid, sterigmatocystin and macrocyclic trichothecenes can thus be produced at levels of 1.8, 112.1 and 27.8 mg/m2, respectively, on this material. These toxins can then be partially aerosolized. We have shown that aerosolization depends on species and their mycelial structure, but also on culture conditions and airflow. This transfer to air is nevertheless observed after aeraulic solicitations which can be easily encountered in indoor environments because theycorrespond to the movement of people in a room (0.3 m/s), speed of air in ceiling diffusers (2 m/s), slamming doors or air drafts when opening windows(6 m/s). P. brevicompactum showed to be the easiest to aerosolize. The major part of the aerosols’ toxic charge is found in particles whose size corresponds to that of spores or mycelial fragments. However, for macrocyclic trichothecenes, toxins were also found in particles smaller than spores, which could easily be inhaled by occupants and penetrate deep into the respiratory tract. In order to better characterize the actual hazard associated with inhalation of these compounds, cytotoxicity studies have been performed using lung cells and comparing with results observed on digestive cells. Pulmonary toxicity is comparable to that observed in digestive cells. Macrocyclic trichothecenes are much more toxic than other tested toxins with IC50 in order of ng/ml. In parallel, we analyzed the VOCs specifically produced during active mycotoxinogenesis in order to identify potential biomarkers of the actual production of mycotoxins that could be used as tools for monitoring of indoor environments. Unfortunately, this approach has not, for the moment, led to the identification of specific targets. In the end, we evaluated the persistence of these contaminants during application of bleach, the most frequently used decontamination process. We have shown that a normal cleaning procedure allows only partial removal of mold
