Wednesday, August 16, 2006

3 Common Methods Used to Detect Mold in Buildings


Commonly used methods used to detect the presence of mold in a building include bulk sampling, surface sampling (swab or tape), and air monitoring for bioaerosols.

Bulk Sampling

Bulk sampling involves collection of material samples in a building from areas where mold is apparent or if no mold can be found, where conditions exist for the growth of mold such as water-damaged floors or walls. To prevent mold from one sample getting onto another sample, samples are collected and bagged using sterile equipment4. In the lab, samples are washed to transfer the mold into a solution. A portion of this solution is then stained so that when illuminated with fluorescent light, the mold can be more easily seen under a microscope. By viewing the mold in a microscope, the types of mold that were on the building materials can be determined. Another portion of the solution is put into a dish that contains the nutrients molds need to grow. After being incubated, the organisms in the solution that are alive will form visible colonies in the dish that can be identified and counted . The disadvantage to the bulk sampling method is that parts of building materials need to be removed or damaged in order to obtain a sample5.

Surface Sampling

Surface sampling allows the identification of molds that are growing on a surface in addition to molds that settle out of the air onto surfaces. The two techniques used for sampling surfaces are swab sampling and tape sampling. Swab sampling involves using a sterile swab to wipe a known area of a surface to collect the mold, and tape sampling involves using a clear piece of adhesive tape to strip a surface suspected of having mold on it.

The analysis of the swab method is similar to that used in the bulk sampling method. The mold is transferred into solution and then subsequently one portion is viewed under the microscope and another is grown in a dish with nutrients. This analysis is performed to identify both the types of mold present and the number of viable or live organisms that were in the solution. The adhesive tape is viewed directly under a microscope to identify the types of mold present on the sampled surface.

There are disadvantages involved with surface sampling. The smoother the surface sampled, the more effectively the tape or swab can pick up the mold. It is hard to sample surfaces using these methods if they are rough, uneven, or porous. Using swabs to sample limits the identification of mold types because some of the organisms are destroyed during the sampling whereas using tape to sample keeps the structure of the organisms in tact for identification. The downside of using the tape, however, is that the mold cannot be removed from the tape after it is sampled. This means that samples taken using the tape method cannot be cultured to see what portion of the mold organisms are living. Tape sampling also requires that the surface being tested not have a lot of other debris on it. A tape sample that contains a large amount of debris makes it hard to identify the mold.

There are also advantages to using surface sampling methods. Because multiple samples can be taken from stationary surfaces, surface sampling can determine either the presence or absence of mold in certain areas, and be used to compare the amount of contamination in one area to another. Furthermore, unlike bulk sampling, both swab sampling and tape sampling are nondestructive methods which do not include the removal or damage of any materials in the building. Surface sampling requires little in the way of costly materials or equipment, it’s relatively easy to perform, and the results of the sampling can be obtained quickly.

Air Monitoring

As with all areas to sampled, there are a number of ways to monitor the air for bioaerosols. A passive method used to determine the types of mold in a given area involves only exposing a dish filled with nutrients, settling dish, to the air. This process requires little effort on the part of the operator, but it does not give a representative view of the number or type of organisms in the air only the ones with enough mass to settle out of the air onto the plate.

Active methods collect samples using a pump that draws air across a nutrient dish, through a filter, or over a greased slide. If a dish of nutrients is used it can be incubated directly to identify the types and quantities of mold in the air. Using a filter or a slide to collect a sample versus a nutrient dish has the advantage of allowing the total amount of mold in air to be accounted for and not just the viable or living portion. After mold is collected on a filter, it is suspended into solution were it either can be viewed under a microscope or incubated in a nutrient dish4. A sample collected on a greased slide sometimes referred to as a spore trap can be viewed directly under a microscope, but this method has the disadvantage of not being able to quantify the viable spores.

As with other methods, the results of the air sampling methods alone cannot eliminate the possibility that contamination exists2. One reason why data from air sampling methods cannot conclusively prove the absence of mold is that different varieties of mold favor different methods of sampling and analysis. Another reason that an air sample may not represent the molds that are present in a building is that sampling may have been performed during a time when the mold was inactive.


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