Testing Your Environment for Mold

There are 5 main mold testing methods:

Gravity Plates

A popular method of environmental mold testing is gravity plates, also known as petri dishes, settle plates, or Gradient Agar Plates. This testing method uses a specialized gel which sits on a plate, and collects and grows a sample of mold spores from the air. Gravity Plate testing facilitates easy and inexpensive passive testing of air quality for as few or as many rooms or areas as desired, including cars (a surprisingly common source of mold exposure!)

However, plates can only capture a limited group of spores (i.e., the ones closest to the plate, the ones most likely to be airborne, and the heaviest ones that are more likely to settle onto the plates), and not all types of mold will grow on all types of media, many spores and types of mold will often go undetected when testing using plates. You just won’t get a clear picture to be able to determine if the sample is or isn’t representative of what is going on in your environment.

The volume of mold growth on a plate is not indicative of anything beyond how fast that particular spore grows in the type of culture medium provided on the plate. The color of the mold on the plate is also irrelevant, as mold color alone cannot be used to determine type, quantity, or toxicity.

What else your plate or mold test kit won’t tell you:  

• What spores are responsible for either the visible mold you are seeing and/or the symptoms you are experiencing. You don’t know if it is the spores that were detected or the ones that were undetected that are causing issues. 
• If you have spores that don’t grow on plates. They can still trigger reactions, but won’t be detected by settling plates, and can outnumber spores that do grow by as much as 50x.
• If you have fragments of spores and of growth, which can also trigger reactions and can be as much as 1000x more plentiful than what grows on a plate.
• If the mold is producing mycotoxins or other mold toxins.
• The location of the mold growth that is producing the spores. Without that information you can’t know where to remediate.

So, are the results from plates useless or misleading?

Well, while they are not proof of a problem (or lack thereof), and can’t determine if action is needed, the results from settling plates can often be sufficient to trigger further investigation with an on-site assessment, which can then provide the rest of the information needed to answer your critically important questions about necessary next steps. In other words:

• If the mold plate test looks bad, you definitely have more investigation to do.
• If the mold plate test looks good, you might still have a mold problem and need to do more investigation.

Mold testing with plates is NOT accurate enough to rely upon as the sole method of testing. If you’re going to use settling plates to test for mold, make them merely one step in a comprehensive assessment.

Direct Examination

Another type of mold testing is direct examination, which allows for the immediate determination of the presence of mold spores, as well as what types of mold are present. Tape and swab sampling are the techniques typically used for direct examination. Direct examinations should only be used to sample visible mold growth in a contaminated area, since most surfaces collect a mixture of mold spores that are normally present in the environment.

Tape Sampling

Tape sampling is the most common technique used to test surfaces for mold during a mold inspection. It provides valuable information, as the species of mold, the relative degree of contamination, and the potential for airborne spore production may all be determined by tape sampling.  

Advantages of Tape Sampling

1. Tape sampling is quick and easy.
2. It is inexpensive.
3. It requires no set-up time.
4. It requires no complex equipment.
5. Many samples can be collected in a short period of time.
6. Samples showing hyphae fragments and reproductive structures can provide proof of mold growth.
7. Tape sampling allows for the quick identification of genera and species by a laboratory.
8. Tape samples provide more data than air samples.
9. Tape sampling is usually non-destructive.

Disadvantages

1. While tape sampling is an excellent way to collect samples where mold is easy to see, light-colored and highly airborne genera, such as Aspergillus and Penicillium, may not be as obvious and can be missed using only tape sampling.
2. Some smaller, airborne mold spores do not readily settle onto flat surfaces, so tape samples may not accurately represent their presence.
3. If a tape sample is collected from dust rather than an area of actively growing mold, or if the sample is taken at the most spore-packed part of a growth area, it is possible that only spores will be collected.  This can make determination of the species more difficult.
4. Using tape of any kind on certain types of materials, such as paper and varnished wood, may damage the item.
5. Tape sampling is meant to be used for qualitative rather than quantitative analysis.  Tape sampling can aid in the identification of mold, but cannot accurately determine the scope and severity of the mold problem.

Swab Sampling

When there is visible mold, surface sampling by collecting mold samples with a simple swab test combined with lab analysis can determine if mold is present at amplified levels and exactly what type of mold you are dealing with. The lab analysis from the swab can pinpoint the type of molds present, many of which are not easily detected in air samples, such as Stachybotrys and Chaetomium (two of the most common and most health-destructive molds present in mold-contaminated buildings).

Swab sampling can help to identify sources of mold so that they can be addressed via basic clean-up or full-blown remediation. Swab sampling can reach deep into recessed corners, into carpets, and in many other areas that are difficult to test with tape sampling. One area where swab testing is particularly enlightening is heating and cooling system air handlers. Determining whether visible discoloration, dust, or debris seen on condensers and on HVAC registers is mold growth will provide important information about the path forward for the proper cleaning of the HVAC system.

Spore Trap

Spore trap samplers function by pulling air through a sample slit and onto a small glass slide that is covered with a sticky sampling media (like flypaper or a glue trap).

Advantages of Spore Traps

• Capable of capturing a majority of spores and particulate matter in the air, making it possible to accurately characterize problem environments where spores are present, including those that are no longer alive, or are species that do not culture well. (These are two situations where culturable sampling techniques, if used alone, may miss a potential indoor air quality problem.)
• Can also be used to quantify pollen, fiberglass, hyphal fragments, hair, skin cells, etc., present in the air.
• Samples can be analyzed immediately.

Disadvantages

• While many mold spores have unique characteristics and can be identified by direct microscopic examination, others do not and are thus more difficult to identify. These latter types must be counted in broader spore groups. In certain situations, this grouping may mask an indoor air quality problem.

ERMI