By Jeffrey C. May
Although I take many air and dust samples in my indoor air quality investigations, I’m going to play the Devil’s Advocate in this article and discuss what I believe are the weaknesses and pitfalls in many areas of mold testing.
First, air samples alone won’t identify the location of mold growth.
Sometimes the source can be something minor, such as a small patch of mold on a bathroom wall or ceiling.
The solution is to clean the area with a diluted bleach solution or with any suitable product, and then reduce the humidity in the bathroom by operating the ceiling exhaust fan as well as an oscillating fan for an hour or two after showering, to re-move moisture from the air and speed up drying of surfaces. And yet, if the air sample taken in a room near the bathroom showed a high level of spores, a potentially major and costly remediation of several rooms in the house might be recommended.
The results of air testing for mold spores can be falsely reassuring. Let’s assume that a carpet in a finished basement playroom is contaminated with mold that is subsisting on the dust captured in the carpet fibers. If someone takes an air sample in the room without walking across the carpet, the air sample will seem fairly clean. But if the person happens to walk across the carpet first and then takes the air sample, the results will tell a very different story.
Dust trapped in HVAC systems or on baseboard heating convectors can be contaminated with mold growth, which an air test may not detect if the HVAC system is not running or the dust on the convectors is not disturbed. Then the building occupant who may be suffering health symptoms is left without a remediation plan, which could be as simple as cleaning the baseboard convectors or as extensive as cleaning the HVAC system or replacing the air handler and even some of the ducts.
The person doing the mold testing has to know what he or she is doing. Some testers will sample in a mold-contaminated basement first, and then go around and sample other areas of the building – all the while carrying spores on his or her clothing from the basement that can be picked up in samples taken in other rooms. Then the lab results could suggest that the mold problem is wide-spread, rather than in just one location.
Lab results can be inaccurate. In a recent study, the authors (Robertson L. and Brandys, R.) sent identical spore-trap samples to seven different labs. At each lab, the most experienced microscopist examined 100% of the samples (most analysts routinely look at only 25% to 50% of a sample). Spore counts for identical types of mold differed in some case by as much as a factor of 10, and only 50% of the labs successfully identified Pen/Asp (Penicillium or Aspergillus) spores—the most common mold growth associated with damp buildings.
I have seen many serious identification errors from even some of the bigger labs, where inexperienced microscopists may have rushed through samples. One lab identified spray-paint spheres as Aspergillus mold spores, and another lab identified candle soot as “toxic black mold.”
Many samples are culturable, meaning that they gather living spores, which labs then count. Dead spores are still allergenic, though, so even if the mold counts in a culturable sample are low, building occupants may still be experiencing ex-posure to allergenic spores. Read the full article in the January 2017 issue of Healthy Indoors Magazine.