Mold: To test or not to test?

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Submitted by MIAQC Member, Ron Lessard.  Ron is a Certified Industrial Hygienist and Certified Safety Professional with Foresight EHS in Brunswick Maine.  He currently serves on the MIAQC Board of Directors and is chairperson of the Council’s Communications Committee.

How much mold is too much mold? Is the mold I see going to make my family sick? Is the mold that I see what is making me feel sick? I’ve lived in that building for 10 years and never had a problem. Now my tenants are complaining that mold is making them sick. Are my tenants crazy? How can I prove that I have a mold problem (or prove that I don’t have a problem)? We at the Council frequently hear these types of questions and people who have these questions invariably want someone to test for airborne mold so they can get answers. This article provides a brief description of mold testing and what “mold” actually is and then provides guidance on when mold testing can provide valuable information and when it cannot.

Testing for airborne mold involves moving air through collection devices that are then sent to a special “mycology” lab for analysis. After analysis, the lab will send the investigator a report that lists the types and amounts of mold that the lab identified on each collection device. There a several air testing methods that can be used to collect mold samples. Each method has a unique ability to collect certain types of mold and provide us with certain types of information. No one test method or even collection methods can capture and detect all of the mold types and amounts that might be present in the air. It’s critical to understand that the lab report lists the types and numbers of mold that were captured and detected on the collection devices and does not necessarily indicate all of the numbers and types of mold that might have been present in the air during testing.

Mold is ever-present in our natural, outdoor environment and it’s neither possible nor desirable to completely eliminate mold from our built environments. Our goal is simply to keep our buildings clean, warm, and dry. If we are successful in this endeavor, the mold that is present in our buildings will be temporary visitors from the outdoor, natural environment and will be unable to establish permanent colonies inside and thus indoor mold will present no greater hazard than the mold that is present in our natural, outdoor environment.

If you do end up with mold growing in your building, its likely that the mold colonies that you see are self-contained ecosystems comprised of various species of mold, bacteria, and insects like dust mites; all of which are feeding, metabolizing, reproducing, and dying. The mix of species that are present will change as the colonies evolve with time and changing conditions. These colonies are capable of producing a wide assortment of potential airborne contaminants including mold fragments, mold spores, microbial volatile organic compounds  (mVOCs), particulates containing digestive enzymes produced by mold, particulates containing toxins that mold excrete to protect their food source from other species (mycotoxins), toxic particles from certain types of dead bacteria (endotoxins), dust mite body parts, and dust mite feces. The concentrations of any of these potential airborne contaminants will vary significantly over time. Some of them may not be present at all and some may be undetectable in air samples even though they may be present in the air or in the mold colonies.

There is tremendous variability in the numbers and types of contaminants that might be present in a mold-contaminated building and individual sensitivities to these contaminants can vary widely. Several of the contaminants described above can trigger allergic and asthmatic responses. People who suffer from allergies or asthma may have adverse reactions to relatively low concentrations of these airborne contaminants while people who are not affected by allergies and asthma may have no adverse health effects even when the concentrations of these contaminants are relatively high. Other contaminants have the potential to cause a variety of other health effects. All of this variability has prevented scientists from figuring out what constitutes a maximum safe airborne concentration (exposure limit) for the vast majority of these contaminants including mold spores and mold fragments.

Without exposure limits, we simply can’t use air testing to determine if airborne mold is a health hazard or if its causing someone’s symptoms. Fortunately, we don’t need air testing to tell us that we should take action. Any conditions in a building that could support the growth of mold should be remediated regardless of any air test results or presence of visible mold colonies. Such conditions include excess dampness that could be caused by plumbing leaks, water intrusion from outside, and condensation of water vapor on cold building surfaces. A good mold investigator will be able to anticipate, recognize, and evaluate conditions that can support mold growth and then recommend control methods for the remediation of those problems.

Testing for airborne mold can be very useful when indoor mold growth is suspected but there are no obvious, visible colonies. Testing can be done in these situations to compare the types and numbers of mold from complaint areas to those from non-complaint areas and the outside. Indoor test results that are similar to outdoor and non-complaint area test results might indicate that the mold found indoors came from outside. Indoor tests that are very different from outdoor and non-complaint area tests might indicate that mold is indeed growing in the building thus justifying more expensive and destructive investigative techniques. Of course we don’t need to do this testing if we can see the mold. If you see mold, spare the time and expense of mold testing and simply remediate the problem.

Comparative testing can also be used to support the decision to “clear” an area for re-occupancy following a mold remediation. Mold test results from the remediated area and the outside that are pretty similar might support the hypothesis that any mold that is now present in the remediated area came from the outside. Comparative mold testing should never be used as the only or even primary source of information in a mold investigation or remediation clearance but it can provide valuable information if the investigator has the skill to interpret the information properly.

In summary, resources that might be spent on inconsequential air sampling to determine if airborne mold is presenting a hazard to occupants or is causing their symptoms should be diverted toward identifying and eliminating conditions that can support mold growth and remediating areas where indoor mold growth has occurred. Mold tests that compare the types and numbers of mold in complaint areas, non-complaint areas, and the outside can provide valuable information during mold investigations and clearing spaces for re-occupancy following remediation but should never be used as the only or even primary source of information in these situations. Better yet, all of this becomes a moot point if we keep our buildings clean, warm, and dry.


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