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    Molds in Indoor Air and health effect

    Excertp from McNeel and Kreutzer, 1996, Fungi & Indoor Air Quality

    Molds in Indoor Air

    Fungi are ubiquitous organisms that make up approximately 25% of earth's biomass. They can be subdivided somewhat artificially by gross morphology into yeasts, mushrooms and molds - the fungi of most importance for indoor air. Molds are very adaptable and can colonize dead and decaying organic matter (e.g. textiles, leather, wood, paper) and even damp, inorganic material (e.g. glass, painted surfaces, bare concrete) if organic nutrients such as dust or soil particles are available. Because various genera grow and reproduce at different substrate water concentrations and temperatures, molds occur in a wide range of habitats.

    Constituents of indoor air are determined by both outdoor and indoor sources (Table 1). Likewise mold types and concentrations indoors are primarily a function of outdoor fungi and substrate water (related to indoor humidity level). Higher concentrations of outdoor molds and other fungi occur where trees, shrubs and landscape irrigation occur close to exterior building walls. (While most indoor molds originate from exterior sources, some species of Aspergillus and Penicillium can grow and reproduce effectively indoors and are commonly found in air samples of normal, "dry" buildings.)

    Molds are composed of linear chains of cells (hyphae) that branch and intertwine to form the fungus body (mycelium). All fungal cell walls contain (1-3)-beta-D-glucan, a medically significant glucose polymer that has immunosuppressive, mitogenic (i.e. causing mitosis or cell transformation) and inflammatory properties. This mold cell wall component also appears to act synergistically with bacterial endotoxins to produce airway inflammation following inhalation exposure in guinea pigs (Fogelmark et al., 1994).

    Under certain metabolic conditions, many fungi produce mycotoxins, natural organic compounds that initiate a toxic response in vertebrates. While some mycotoxins have been found to be associated with hyphae, the primary mode of human exposure to mycotoxins and is inhalation of spores and mold-contaminated material. Molds that are important potential producers of toxins indoors are certain species of Fusarium, Penicillium, and Aspergillus. In water-damaged buildings Stachybotrys chartarum (a.k.a. atra) and Aspergillus versicolor may also produce toxic metabolites. A large body of information is available on the human and animal health effects from ingestion of certain mycotoxins (Beasley, 1994; Sorenson, 1989; Smith and Henderson,1991), but investigators have only recently begun to explore the health implications of inhalation exposure to these substances. Two classes of mycotoxins have been isolated from house dust samples: aflatoxins from some strains of Aspergillus flavus and trichothecenes from some species and strains of Fusarium, Cephalosporium, Stachybotrys and Trichoderma. In laboratory animals, inhalation of trichothecene mycotoxins causes severe inhibition of protein synthesis and immunosuppression (Beasley, 1994). Several case reports have associated overgrowths of trichothecene-producing fungi with human health effects such as cold and flu-like symptoms, sore throats, headache and general malaise (Croft et al., 1986; Johanning et al., 1993; Nikulin et al., 1994). However, isolation of a toxigenic fungus from a building does not imply the presence of mycotoxin, since the physical conditions necessary for mycotoxin production are very specific, and are often different from those required for growth of the parent mold. Likewise, failure to produce toxins in vitro does not mean that a mold known to be toxogenic will not produce toxins in a field situation.

    Molds also produce a large number of volatile organic compounds (VOCs). These chemicals are responsible for the musty odors produced by growing molds. There is little evidence that fungal VOCs cause specific human health effects (Batterman, 1995), but the most common VOC, ethanol, is a potent synergizer of many fungal toxins.

    Health effects associated with molds

    Molds produce acute health effects through toxin-induced inflammation, allergy, or infection. There is no information at this time on the effects of chronic, low dose inhalation exposure to mycotoxins.

    Toxin-induced inflammation: Repeated or high exposures to airborne mycotoxins can cause mucous membrane irritation characterized by eye, nose and throat irritation (Richerson, 1990). When small diameter spores (2-4 ¦Ìm) are inhaled, they may reach the lung alveoli and induce an inflammatory reaction, creating toxic pneumonitis. Severe toxic pneumonitis can cause fever, flu-like symptoms and fatigue (organic toxic dust syndrome). Hypersensitivity pneumonitis, a particular form of granulomatous lung disease, is a syndrome caused by inhalation of large concentrations of dust containing organic material including fungal spores. It is generally an occupational hazard in agriculture, but has been reported in individuals exposed in the home (Flannigan, et al., 1991). Other symptoms attributed to mycotoxin or fungal-origin VOCs include headache, dizziness, dermatitis, diarrhea and impaired or altered immune function.

    Allergy: Indoor fungal allergens probably affect fewer people than do allergens from cats, mites or cockroaches. Yet a significant proportion (10-32%) of all asthmatics are sensitive to fungi. More thorough discussion of fungal allergens is available elsewhere (Horner, et al. 1995; Einarsson, et al. 1992; Burge, 1985).

    Infection: Opportunistic fungal pathogens such as Aspergillus are common in indoor air. A normal, healthy individual can probably resist infection by these organisms regardless of dose, although high exposures may cause hypersensitivity pneumonitis. However, any mold that can grow at body temperature can become a pathogen in an immuno-compromised host. Individuals undergoing chemotherapy, organ or bone marrow transplantation or those with HIV/AIDS are especially susceptible to invasive infection by Aspergillus species.




    More info of this article can be found on the web at: This link was broken when checked on Dec. 2006http://www.dhs.cahwnet.gov/org/ps/deodc/ehib/EHIB2/topics/fungi_indoor.html




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