Living organisms are classified into groups called kingdoms. There are five kingdom classifications; Monera, Protista, Plants, Animals and Fungi. Mushrooms, mold, mildew, slimes and rusts are included within the kingdom of Fungi. Throughout history, mankind has developed useful applications for some fungi. We have incorporated fungi into our diet in the form of red wine, beer, mushrooms and blue cheese. We have extracted fungi byproducts to develop and manufacture medications such as antibiotics (Penicillin) and organ transplant anti-rejection drugs (Cyclosporine). Fungi also facilitates the decomposition of organic waste in our landfills and compost bins. Other fungi, in particular molds, have been identified as pathogenic and mold exposure poses a serious threat to our health.
Mold has been a companion of humanity since the beginning of human history, but for a number of reasons has become a major health concern today. Modern construction techniques have resulted in energy efficient structures that fresh air cannot infiltrate. For this reason, pollutants can more easily reach critical concentrations, threaten our indoor environments and cause adverse health effects. Furthermore, we use building materials that are composed of cellulose, which is the nutrient that molds require to grow. Finally, media attention and consumer education have made us acutely Intune to the dangers of mold contamination.
Conditions Affecting Mold Contamination
Healthy indoor environments should host a balanced fungal ecology; interior mold samples should reflect outside reference samples in lower concentrations. Weather conditions, time of year and geographical location are variables that can alter this norm. Multiple factors affect mold growth including temperature, light, PH, nutrients and water.
Molds are highly adaptable and can thrive over wide temperature ranges, examples are mold growth on food left in the refrigerator as well as those that flourish in arid desert regions. Molds that we encounter in water damaged buildings are called mesophilic, a mesophile is an organism that grows best at moderate temperatures.
The belief that mold contamination only occurs in the absence of light is a myth. Molds often proliferate in dark environments due to availability of moisture and a scarcity of ventilation. Many molds will begin disseminating spores when exposed to light as a result of declining available moisture.
Most molds prefer a moderately acidic environment.
Cellulose in an ideal nourishment to support mold colonization. Molds growing on cellulose rich materials will secrete enzymes that dissolve the building material, releasing the cellulose for absorption through the membrane walls. These actions not only support mold growth and proliferation, it also compromises structural integrity.
Free water is the most important factor relating to mold growth. Different strains of mold require varying degrees of available moisture in order to grow.
Fungi are Heterotrophs and saprophytic, which means they must rely on an external food source high in cellulose. Molds can however, grow on any surface capable of supporting organic residue known as bio-film.
Moisture & Mold Contamination
Water activity is the amount of free water available on a substrate to support mold growth. Different strains of fungi have varying moisture requirements, the type of mold found indoors is dependent on the moisture content of the material supporting the mold colony. Healthy moisture content of wood is 8% to 12%, when moisture content exceeds 16% the wood surface can support mold contamination. If the moisture content exceeds 20%, fungal rot can occur.
Molds are classified into 4 categories based on moisture requirements.
Hydrophilic (water loving) molds require a tremendous amount of moisture to thrive. Examples of hydrophilic molds include Fusarium, Rhizopus and Stachybotrys chartarum. Stachybotrys sp. is a slow growing hydrophilic mold that takes between 7 and 12 days to establish and become viable. Stachybotrys in not easily detected using air sampling methods as it does not become readily air born. Stachybotrys, like many molds, is black with sooty appearance when growing on building materials. Air sample and tape lift testing is important to determine what mold contamination is present. The presence of hydrophilic mold growth such as Stachybotrys sp. indicates a chronic moisture problem and is only one strain of hydrophilic molds that can produce dangerous mycotoxins.
Mesophilic molds prefer moderately wet conditions and are present in virtually all water damaged environments where mold contamination is present. Mesophilic molds include Penicillium, Aspergillus, Cladosporium, Epicoccum and Alternaria.
Species of Penicillium and Aspergillus are known to produce respirable spores, which are 5 microns or less in size and can be breathed deeply into the lungs and become lodged. Penicillium and Aspergillus can colonize within 48 to 72 hours and certain species can produce potent mycotoxins. Aspergillus fumigatus produces aflatoxins, which are the most potent carcinogen chemical known. Certain species of Aspergillus are pathogenic and can cause diseases such as Aspergillosis, which is a respiratory disease caused by exposure Aspergillus fumigatus that results in a large fungal mass growing in the respiratory system.
Xerotolerant molds prefer relatively dry conditions. Examples of Xerotolerant molds are Aspergillus glaucus and some species of Penicillium. This category of mold can grow on house dust given high relative humidity levels.
This type of mold prefers very dry conditions and can colonize dry materials such as high sugar foods and some building products. Some species of Aspergillus and Penicillium are classified as Xerophilic.
There are multiple avenues of exposure to the toxic and allergenic components of microorganisms. The most common include:
• Dermal – Occurs from absorption through the skin, mucus membranes or abrasions.
• Inhalation – This is the primary route of mold exposure.
• Ingestion – This is the primary route of exposure due to poor hygiene.
• Injection – Occurs due to injury such as puncture wounds that allow pathogens to enter the body.
By-Products of Mold Contamination
Molds can produce several by-products that can result in human illness and allergic reactions.
Microbial volatile organic compounds (mVOCs) are chemicals produced during fungal metabolism as a waste by-product. The chemicals released give off a musty odor that is often associated with mold contamination. Microbial VOC’s are considered irritants and result in symptoms such as burning eyes, scratchy throat, skin rashes and headaches. The presence of mVOCs is an indicator of active mold growth.
Fungal spores are microscopic, a massive amount of spores can be produced and released by a single mold colony. Fungal spores present in water damaged environments are generally between 2 and 20 microns in size, a micron being 1/1,000,000 of a meter.
Actively growing fungi produce and release spores for dissemination and survival, a process known as sporulation. Whether viable or non-viable, fungal spores may contain allergens and mycotoxins that can compromise health. Viable spores can remain dormant for extended time periods, some more than 20 years. When suitable conditions for germination arise; spores will activate, colonize and produce additional spores.
Molds produce mycotoxins to gain a competitive advantage over other microorganisms competing for resources. Some of these chemicals are toxic, carcinogenic and can suppress the immune system. Symptoms associated with mold exposure include skin rashes, headaches, dizziness, fatigue, muscle and joint pain, nausea, depression, memory loss, vomiting and diarrhea. Mycotoxins can also affect the vascular system by damaging the outer lining of blood vessels. Fungal mycotoxins are located within or on the surface of the cell walls of spores and hyphae.
Environments suffering from mold contamination often support various molds, which can combine to amplify toxic effects. Known as synergistic effects, this phenomena occurs when the toxic properties of certain microorganisms are intensified when in concert with others.