Mold sampling Strategy in Indoor Environment

Jan. 12, 2009 - PRLog -- Molds are types of fungi. Tiny particles of molds are found everywhere in indoor and outdoor air. In nature, molds help break down dead materials, and can be found on plants, foods, dry leaves, and other organic material. Molds are also very common in buildings and homes. Mold needs moisture to grow. Indoors, mold growth can be found where humidity levels are high.

Molds release thousands of microscopic cells called “spores”, which are lightweight, easily airborne and spread to surrounding areas through the air. Mold growth on surfaces can often be seen as a colored spot, frequently green, gray, brown, black or white. It commonly appears as a powdery, fuzzy, or hair-like material. Actively growing molds typically produce odors, sometimes described as earthy, moldy or mildew. The spores must have both food and moisture to actually start growing, similar to plant seeds.

Mold Sampling
The method of choice for assessing potential exposures to airborne molds and mycotoxins in indoor environments involves the collection and identification of fungal propagules. Currently, there are numerous sampling methods available to measure fungal concentrations in the environment. Source sampling, which includes methods such as swab, tape, bulk, and dust, is commonly used to identify indoor fungi. These source sampling methods are “necessary adjuncts” to air sampling, especially when air sampling might result in false-negative findings. However, these surface-based methods cannot identify hidden sources of mold.

Air sampling is one of the most common methods used to assess fungal levels in indoor environments. Many studies have related human health effects, such as increases in allergic and asthmatic respiratory symptoms, to airborne fungal spores. As the health effects of fungal exposure are mainly respiratory, air sampling is believed to be adequate to represent the exposure. However, fungal spores have been found to exhibit varying patterns in their release into the air depending on several environmental factors.

Spatial or Location Variables


Sampling strategies can be affected by the layout of building components or zones. Thus, the objective of sampling may be to determine whether mold spores from a damp attic are being dispersed into occupied zones. Consequently, during the inspection prior to sampling, it is important to determine whether pathways occur that would allow for transport of spores from the attic to occupied zones. In this example, collection of air samples in the attic and in occupied areas should occur after development of a sampling plan based on a thorough physical inspection.

Indoor activities such as vacuum cleaner operation are known to elevate bioaerosol concentrations. Other activities such as walking around and sitting up and down on upholstered furniture can result in a “personal cloud effect” wherein the airborne particle level in other parts of the same room will be low. It may be important, therefore for the investigator to determine whether personal or area sampling is appropriate. If the intent of the evaluation is to document the personal cloud around the active occupant, then a personal sampling strategy is required.


Temporal (Time) Variables


Sampling results in a building are potentially affected by variables including human activity patterns, AHU system operation, and climatic or seasonal variations such as alternating rainy and dry periods.

For example, sampling for culturable fungi during a prolonged dry season will be less likely to detect water indicatior fungi from leak prone envelope walls than will sampling during a rainy period when the building envelope is leaky and wet. Similarly, sampling for human shed bacteria in a office room during unoccupied nighttime hours will yield different results than will sampling in the same office room with many active occupants.

Temporal changes in the building envelope affect air sampling results. Solar heating of the building envelope causes air near perimeter walls to warm and move upward. Thus, divergent bioaerosol sampling results can occur in the morning as compared to the afternoon. In this case sampling should be repeated at least several times daily (morning and afternoon) at each testing site. Seasonal changes in moisture levels including condensation potential on the inner surface (closet to occupants) of the envelope wall can affect the ecology of molds on the wall surface and in room air. Thus, during warm, humid, seasons condensation and active mold growth can occur on the wall surface especially in depressurized buildings. However, surface and air sampling results obtained in the same areas during the heating season may be different because of the absence or dampness.

Complaint and Non Complaint Zones


Occupant complaints in buildings may be environmentally based (dampness, water leaks, visible mold growth, etc.), health related (example: upper respiratory irritation, allergy, infection), or both of these. It should be recognized that results of microbial sampling alone cannot be used to determine whether adverse health outcomes have occurred. However, careful inspection of a building for dampness/moisture damage can lead to a microbial sampling strategy, the results of which can provide useful information to a physician or epidemiologist in associating environmental conditions with occupant health complaints.

Additional factors to consider with regard to microbial sampling strategy in complaint/noncompliant areas include the timing of the sampling evaluation as well as the methodology to collect the samples.

The methodology used to collect samples in complaint/noncompliant zones should simulate normal occupant exposure conditions. Collection of air samples from a wall cavity in a complaint zone when wall board or other material are being aggressively disturbed (example: by drilling or pounding) does not represent normal bioaerosol exposure of room occupants. An appropriate sampling strategy should specify “normal occupant activities and conditions” at the time of air sample collection in both complaint and non complaint areas.

To understand more about old and its effects, please visit http://www.iaqsg.com/mold-microbes-and-indoor-environment...

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