Mold and Health
Mold is a serious health risk in the dilapidated housing that characterizes much of the shelter available to the indigenous ("First Nations") people of Canada. Mold has been well documented as occurring in First Nations housing, but its health consequences remain implicit and the actual types of mold are understudied and largely unanalyzed. This article reviews the relevant conditions conducive to mold growth, what is known about the kinds of risks mold represents, the socioeconomic and historical factors that have led to this situation, and the circumstances that require action on the part of multiple levels of governance in Canada to address this issue.
Molds include all species of fungi that grow as multicellular filaments called hyphae. Over 100,000 types of mold are classified in the Zygomycota, Deutermycota, and Ascomycota phylums. Mold grows on solid culture media and gains nutrients through the decomposition of dead organic matter. Reproduction occurs both sexually and asexually within microscopic spores, which may contain one or several nuclei. Some spores can remain airborne indefinitely and are capable of surviving extreme levels of pressure and temperature variation. It is only when mold colonies grow as an interconnected group of hyphae called mycelium that mold becomes visible. Mycelium is far more widespread at low concentration levels than simple visual inspection would suggest (Prezant, Weekes, & Miller, 2008).
All molds secrete hydrolytic enzymes that break down starch, cellulose, and lignin into simpler substances that they can absorb. The ability of molds to decompose organic matter makes them invaluable components in the nutrient cycle. Many molds also secrete mycotoxins, however, which, along with the enzymes used to process organic matter, have evolved to inhibit the growth of other microorganisms (such as bacteria or insects) competing for the same nutrients. Some of these mycotoxins are neurotoxins, which gravely disrupt the nervous systems of competing organisms such as insects and also impact other organisms including humans. Some mycotoxins can be very dangerous when inhaled due to their effect on human respiratory (Hope & Simon, 2007) and neurological functions (Campbell, Thrasher, Gray, & Vojdani, 2004).
The impacts of mycotoxins on human health include allergic rhinitis, asthma, mucosal irritation, common cold symptoms, fatigue and weakness of concentration, general weakening of the immune system, and even death. Due to these dangers, mold is often treated as a hazardous material (Park & Cox-Ganser, 2011). Mold is dangerous to human health in several other ways. Mold spores are sufficiently small enough to be inhaled into the bronchial tubes, bypassing the mucosal barrier; consequently, some mold spores commonly yield allergic reactions including conjunctivitis, allergic coryza, inflammation of the respiratory tract, bronchial asthma, skin eczema, and "nettle rash" (Hardin, Kelman, & Saxon, 2003; Portnoy, Kwak, Dowling, VanOsdol, & Barnes, 2005).
Mold mycelium is also dangerous and is associated with mycosis and mycotoxicoses. Mycosis is the growth of a mold fungus on a human host, which can cause infectious diseases such as aspergillosis and penicilliosis (Jacob et al., 2002). Mycotoxicosis is anthropogenic intoxication due to the inhalation of the toxic by-products of mycelium metabolism, which can lead to delirium (Fung & Clark, 2004).
The adverse affects of mold (like most environmental illness) are age related and particularly pronounced in children (Ahluwalia & Matsui, 2011; Bearer, 1995; Jones, Recer, Hwang, & Lin, 2011; Koskinen, Husman, Meklin, & Nevalainen, 1999). This is due to a combination of their immature size, immune system vulnerabilities, confined exposure (they are kept inside), and misinterpretation of symptoms as sequential rhinoviruses (common colds). The public health risk of mold has been well documented for Europe (Bornehag et al., 2004) and for the U.S. (Institute of Medicine, 2004) in studies that have concluded that a direct association exists between mold in buildings and risk to their occupants and that this risk extends beyond the respiratory system (asthma, in particular) to other poor health outcomes. The economic and individual suffering associated with mold is simply staggering: Mudarri and Fisk (2007), for example, estimated the annual cost of asthma in homes attributable to mold to be $3.5 billion for the U.S.
Environmental Influences of Mold Growth
Mold growth is influenced by many factors. The decisive criterion for mold growth is sufficient moisture provided either by water liquid or vapor. Different molds thrive at different levels of relative humidity, i.e., the ratio of actual vapor density in an air-vapor mixture to the vapor density at saturation. Relative humidity between 70% and 80% provides adequate moisture for the growth of nearly all species of mold (Lstiburek & Carmody, 1996; Sedlbauer, 2000).
Temperature is another important growth criterion. Each mold has a specific temperature range in which it is able to grow. Generally, all species grow within the 0[degrees]C to 50[degrees]C range (Sedlbauer, 2000). Temperature also impacts the relative humidity at which mold is able to grow. As temperature increases, lower relative humidity levels become adequate for mold growth (Lstiburek & Carmody, 1996; Sedlbauer, 2000).
The substrate (medium) on which mold grows also influences growth rates. The nutrient contents of substrates vary widely: some substrates provide ideal nutrients (e.g., decaying fruit), some provide moderate nutrients (e.g., wood or wall paper), and some provide no nutrients (e.g., plastic).
The duration of favorable environmental conditions is also important. Some molds are able to grow quickly in favorable environmental conditions while others require lengthier periods (Sedlbauer, 2000). Other criteria of lesser importance also influence mold growth. These criteria include pH and salt content of the substrate, oxygen content of air, surface conditions of the substrate, and other biotic influences, such as the presence or absence of other organisms (Sedlbauer, 2000).
Mold and Buildings
Negative health impacts of mold result when humans are in close proximity to mold in an enclosed environment where concentrations of mycotoxins are able to increase. Thus, mold growth in buildings is particularly dangerous to human health. Mold spores typically enter buildings through windows and doors in air currents or by attachment to clothes and pets (Canada Mortgage and Housing Corporation [CMHC], 2005). Once spores are inside a building, spores germinate and mycelium grows provided favorable indoor environmental conditions exist.
The crucial condition--sufficient moisture--can be generated inside the home in various ways. Rainwater may enter through openings or cracks in the building envelope, faulty eaves troughs, defective plumbing, or on the clothes of residents and the fur of pets. Insufficient use of insulation, multi-paned windows, or vapor barriers can result in condensation on interior envelope surfaces during the winter months. Inadequate use of ventilation and increased levels of indoor moisture generation due to resident activities (e.g., breathing, cooking, showering, etc.) increase humidity levels in indoor air. Increased humidity in indoor air further increases the condensation on interior envelope surfaces (Prezant et al., 2008).
Over 200 species of mold are known to occur in buildings and the majority are not harmful to humans. The most frequently occurring mold species causing harmful mycosis are Absidia, Aspergillus, Basidiobolus ranarum, Cephalosporium, Cladosporium, Fusarium, Mortierella, Mucor, Penicillium, Rhizopus, Scopulariopsis, and Verticillium (Sedlbauer, 2000). The most frequently occurring of these causing harmful mycotoxicoses (including via food contamination) are Aspergillus, Penicillium, and Fusarium (Felicio, Freitas, Rossi, & Goncalez, 2011) and are associated with esophageal cancers (i.e., Fusarium; Sydenham et al., 1990) and respiratory distress (i.e., aspergillosis; Bennett, 2010). Penicillium, which while beneficial as an antibiotic, causes a highly allergic response, penicilliosis, in up to 10% of individuals (Bhattacharya, 2010).
Present Research on Environmental Conditions in Buildings and Mold
Mold growth and moisture balance in buildings are currently active research fields. Several authors have identified the toxic mold species found within homes and the types of substrates on which they grow (Adan, 1994; Clarke et al., 1999; Nielsen, 2002; Pasanen et al., 2000; Sedlbauer, 2000). Some researchers have designed mold spore detection techniques and technologies (Moon, 2005; Schleibinger, Laussmann, Eis, & Ruden, 2005). Others have developed moisture generation and transfer models for the building envelope and interior space dependent on indoor and outdoor environmental conditions (Holm, Kuenzel, & Sedlbauer, 2003; Kumaran, 1999; Kunzel, Holm, Zirkelbach, & Karagiozis, 2005; Krus & Kiebl, 1998; Lu, 2003; TenWolde, 1988).
Researchers have also grown mold in a laboratory setting to correlate environmental conditions to the probabilities of mold growth (Clarke...