Characteristics of Commonly Encountered
In general indoor levels of molds are usually 30-80% of outdoor levels and the distribution of
spore types should be similar. The presence of higher levels of certain types of molds indoors
when compared to outdoor levels may indicate that mold contamination is present indoors.
The following are some of the commonly encountered fungal genera and possible causes and sources
of elevated levels of certain mold genera:
Specimens of Alternaria are often found growing on carpets, textiles and horizontal surfaces such as window frames. It is commonly found in soil, seeds and plants. It is known to be a common allergen. It appears as a velvety tuft with long soft hairs and is often confused with Ulocladium as its color ranges from dark olive green to brown. Alternaria is a dry spore and is readily found in air samples as well as on tape lift samples.
Alternaria is commonly found in water damaged buildings, and a significant increase in its numbers compared to outdoor levels can be a sign of growth.
Ascospores refers to a category of spore types rather than a mold genus. There are many different types of Ascospores and they are found virtually everywhere. The spores of Penicillium and Aspergillus fall within this category, however they are normally identified separately on a report.
Many types of Ascospores have wet spores, which are dispersed by rain or other moisture. Outdoor levels of Ascospores often get very high after a rain event as many of the molds in this groups discharge spores when they get wet. High levels indoors is not usually a problem if outdoor levels are also high. There can sometimes be a delay in how indoor levels of spores correspond to changes in outdoor levels, especially if the house does not get a lot of ventilation with outdoor air. Indoor levels of Ascospores may sometimes be higher than outdoor levels if it had rained in the few days prior to sampling, but was dry on the day of sampling.
This genera is found on many different textiles and organic materials such as soil, compost, stored grain, wood and paper and its moisture requirements vary widely with some preferring dryer conditions. If is often found in water damaged carpet. It is a dry spore and spores may be carried in the air making Aspergillus a common cause of respiratory irritation and infection.
The mold may be woolly or cottony in texture and shades of green, brown or black in color. The spores are similar to Penicillium spores and sometimes indistinguishable through non-viable analysis, and as such, are often classified as Penicillium/Aspergillus.
Elevation of any one species of Aspergillus in viable samples can be an indication of the growth of that mold inside a building. Species, such as A. niger, A. versicolor, A. fumigatus, and A. flavus, are most commonly found in water damaged buildings. If elevated levels of Aspergillus species or Penicillum/Aspergillus spores (non-viable sampling) are reported in a building, but not visible mold is observed, the source if often in the carpeting. Aspergillus and Penicillium are the most commonly reported molds found if water damaged carpeting is present. These molds feed well on the jute backing of carpeting, the glues in the carpet padding, and on the organic dust that accumulates in carpet. High levels of moisture vapor emitted from slab foundations will frequently cause elevated levels of Penicillium and Aspergillus.
Sometimes the presence of higher levels of spores indoors than outdoors is not due to the presence of mold growth indoors. Aspergillus species have dry spores that get washed out of outdoor air during rain events or periods of high fog, which drastically reduces outdoor levels. There can often be a lag in the change in indoor levels, which can lead to higher levels indoors when compared to outdoor levels. As long as the level is still within the normal range for the mold elevated indoor levels may not be a problem. Since the spores of these molds are a common part of carpet dust, recent vacuuming without a HEPA filter can also temporarily cause elevated levels indoors.
Basidiospores is the name of a category of mushroom spores and not a genus of mold. They are very common outdoors, and like Ascospores, outdoor levels increase dramatically during periods of rain, sometimes greater than 30,000 spores/m3. Many species are plant pathogens and they can grow on decaying plant matter indoors and outdoors. One type of Basidiospore is the agent of dry rot and high levels of Basidiospores in wall cavity samples may be a sign of dry rot inside the wall. Like the Ascospores, levels of Basidiospores may be higher indoors than outdoors if there have been recent changes in outdoor weather conditions.
This fungus is an allergenic mold genus. Although it is not well documented it is known to cause hay fever and other common allergy symptoms and is sometimes associated with nail infections. It thrives on cellulose containing materials such as paper and plant compost. It is quite commonly found on wet sheetrock paper. It grows very quickly and may be cottony in appearance. It will range in color from white to gray, to olive green and olive brown, to black. It has small brown oblong shaped spores that are easily spread by wind, insects and water splash.
It is the most common mold found in outdoor environments. It is also found indoors on the surface of fiberglass duct liners and the interior of supply ducts as well as on dead plants. It is drawn to food, straw, soil, paint, wood, textiles, and grows well on moist windowsills. Cladosporium grows at 0º C so it is commonly associated with refrigerator foods. It is a common cause of hay fever, asthma and is a known allergen. It has a distinctive appearance and yields an olive to brown pigmentation. The spores are dry and easily become airborne if disturbed. The mold is moderately fast growing, and may look velvety or woolly.
This mold can be present at high levels outdoors at times, especially in the fall months when levels of outdoor organic debris is high. This is often the mold that is tracked for use in the daily allergy level reports in the newspapers and evening news. The presence of high levels indoors may not be a problem as long as the levels are less than the outdoor levels. High wind and outdoor activities like lawn mowing or raking leaves can drastically increase outdoor airborne levels. Since this molds grows on organic debris outdoors, the location of the outdoor sample may also effect the evaluation of the indoor samples if there is a large difference in the level of organic debris from one outdoor location to the next.
This mold is found in soil, and on many plants. It requires very wet conditions to grow and is often found in humidifiers. It is known to produce trichothecene toxins, which effect the circulatory, alimentary, skin and nervous systems. On grains, it produces vomitoxin, which can effect you through ingestion and inhalation. Exposure to Fusarium can lead to hemorrhagic syndrome (symptoms include nausea, vomiting, dermatitis, and extensive internal bleeding). Fusarium is allergenic and is often associated with eye, skin and nail infections, and readily infects burn victims. Colonies of Fusarium appear in shades of pink, orange and purple, tan, yellow and red. It is a wet spore so it does not generally appear in air samples. Fusarium also has a high moisture requirement for growth, similar to Stachybotrys, and it is not often found growing on surfaces that experience only periodic moisture.
This mold is commonly found in air samples as well as in soil, food, grains, paint, compost piles, wallpaper and interior fiberglass duct insulation. It is often found in water damaged carpets. It can produce mycotoxins, which are allergenic and infect the skin. This soft mold is most commonly found in shades of blue, green and white, and may be velvety, woolly or cottony. Worldwide it is one of the most commonly found fungal genera and is accompanied by a heavy musty odor. Identification to the species level can be difficult and the spores are very similar to Aspergillus spores.
Like Aspergillus, Penicillium is often associated with water damaged carpeting. Penicillium also has dry spores, which are affected by rain and outdoor humidity. See Aspergillus above.
Stachybotrys is found in building materials with high cellulose content. It is found indoors and grows well in damp straw, wicker and other wood or paper products. It is not known to compete well with other molds, but if there is a high level and constant availability to water for an extended period of time it may become the dominant mold. It grows very well on sheet rock that has sustained significant water damage, and is often found inside wall cavities that have sustained water intrusion. Stachybotrys appears distinctively from other molds and is a dark gray to black color, sometimes with green, and is shiny when wet.
Stachybotrys is not normally found in the air outside, although it can grow on a variety of outdoor substrates. This mold has very sticky spores, which do not often become airborne unless they are disturbed. Even when the spores are airborne, they are usually present at levels much lower than the other molds commonly found inside. The presence of any airborne Stachybotrys inside a house should warrant further investigation if a source is not obvious. This mold has a high moisture requirement for growth, so it is usually found when significant and/or sustained water damage has occurred.
This mold is found on gypsum board, tapestries, wood and other organic materials. It is a potential allergen and produces symptoms such as hay fever and asthma. It is a dry spore and is detected by air samples as well as tape samples. Ulocladium has an appearance similar to Alternaria but tends to appear more brownish whereas Alternaria more often appears as a dark olive green color. Colonies grow rapidly and have a texture similar to velvet.
Ulocladium is commonly found in water damaged buildings, and a significant increase in its numbers compared to outdoor levels can be a sign of growth.
Rusts or Smuts
These are groups of fungi that are plant pathogens, which do not normally grow
indoors. They are brought inside homes as part of the normal influx of dust
particles. The presence of large amounts of dust can lead to elevated levels
of these molds, as well as recent dusting.