Importance of Outdoor Mold Assessment as a Background Control
Mold and mold spores are everywhere around us and outdoor air is the ultimate source for many fungal spores, that can eventually contaminate indoor air. Soil and plant materials are major sources of outdoor mold and the levels vary greatly by region, season, weather conditions, and air movement. These microscopic contaminants can get indoors through a number of sources including: doors, windows, structural cracks, ventilation intakes and also spores in the outside air attach themselves to people, both with the air surrounding them and on their clothes, shoes and bags making convenient vehicles for transporting indoors.
When mold spores drop on places with excessive moisture, such as where leakage may have occurred in roofs, pipes, walls, or plant pots or where flooding may have occurred, molds will grow and produce thousands of new spores utilizing organic material in these sites.
Many building materials provide suitable nutrients that encourage mold to grow. Wet cellulose materials, including paper products, ceiling tiles and wood materials are particularly conducive for the growth of some molds. Other materials such as dust, paints, wallpaper, wallboard, carpet, fabric and upholstery commonly support mold growth. In order to determine whether the indoor mold is different from that outdoors, one must understand the variability factor and transmission route.
Indoor environments are never entirely free of molds. As a general rule of thumb, in a “healthy building” the concentration of spores and the mix of mold species tend to be similar to outdoor environment levels.
A key component of any IAQ investigation is the outdoor air sample. It provides crucial information that helps to determine whether indoor contaminants are being generated within the structure or are from infiltration of outdoor contaminants. Because of the enormous potential for variability in the outdoor aerosol, the errors involved in comparing indoor and outdoor samples are enormous. This makes it essential that outdoor samples be collected as close as possible to the entry point of the specific indoor environment and as close as possible in time.
Exposure Standard of Mold in Air
There is no health based standard or a specific level that defines either of safe or unsafe mold exposure inside a home or other building. Because of the huge discrepancies person to person in mold sensitivity, what might be a harmless amount of mold exposure to one occupant can be devastating health-wise to another person.
Usually, mold infestation is considered to be high if indoor mold samples show higher mold counts and different types indoors than in an outdoor mold control test. Mold infestation usually affects pregnant woman, infants, elderly and people with severe immune deficiency, such as bone marrow transplant patients. But day in and day out, cumulative exposure to mold infestation can make healthy adults quite sick.
Possible Health Effects of Mold Exposure
Health effects associated with mold fall into four groups as follows:
- No effect: Physiological mechanisms in healthy people may allow exposure to mold at low and high levels.
- Allergic sensitization and immune responses: These can include allergic rhinitis (hay fever), asthma, hypersensitivity pneumonitis (inflammation of lung tissue), and allergic skin diseases.
- Infectious growth of the mold in or on the body: People with compromised immune systems may be more vulnerable to infections by molds. Healthy individuals are usually not vulnerable to infections from airborne mold exposure.
- Disruption of cellular function: This level occurs with toxigenic effects by toxic compounds produced by certain molds.
Interpretation of sampling results
The outdoor sample establishes a baseline for comparative evaluation of the indoor air samples. Because there are no federal standards for mold spore count levels in indoor environment.
It is important to interpretate indoor and outdoor relationships by individual spore types and levels detected in different environments. Usual comparisons are indoors to outdoors or complaint areas to non-complaint areas. Specifically, in buildings without mold problems, the qualitative diversity (types) of airborne fungi indoors and outdoors should be similar.
However, in problem buildings where there is fungal contamination, one or two spore types may dominate the air samples. Often these are not present in the outdoor air or present in low concentrations, may indicate a moisture problem and the indoor air quality is considered to be degraded.
Also, the consistent presence of certain fungi such as Stachybotrys chartarum, Aspergillus versicolor or various Penicillium species over and beyond background concentrations may indicate the occurrence of a moisture problem and a potential atypical exposure and it needs additional investigation, supplemental testing or corrective measures.
Generally, indoor mold types should be similar and levels should be no greater than outdoor and/or non-complaint areas. Analytical results from bulk material or dust samples may also be compared to results of similar samples collected from reasonable comparison areas.