The Subjective Science of Mold Testing

May 17, 2023 Bob Krell

By Bob Krell

Having just come off the road from a few of this year’s national industry events, the topic of mold testing came up multiple times—as usual.  Many people vocalized their opinions on the pros and cons of the various sampling and analysis methodologies currently being used.  Spore traps and mycotoxins got their usual panning from some well-known faces, but what was mostly missing was what I believe to be a glaring question: Are we looking at the right parameters regarding indoor mold and occupant exposures?

Now, I need to preface all this by noting I have been around for some time, in fact, before the now commonly used spore trap cassettes even existed. Back in my day, besides having to walk miles to school, uphill, both ways, we actually had to apply a coating of lithium grease to glass slides to collect spore trap samples.  It was messy and easy to mess up your collected air samples.  The common air sample methodology in the early 1990s when I began actively involved with consulting for mold-related indoor environmental projects was using a single-stage Anderson N-6 impactor and Petri dishes with various agar mediums. Spore traps we less commonly used back then.

I’ve said it hundreds of times before, but it bears repeating: Mold sampling (as we mostly do it) is a subjective science.

Bob Krell, CIEC, CMRS, Founder & Publisher of Healthy Indoors Magazine

The advent of the spore trap cassette changed things dramatically by making the field collection of these types of samples significantly easier to do. Of course, mold spore traps and culture air samples have limitations and blind spots.  Since spore traps are analyzed via direct microscopy, the delay of growing out the culture plate samples is removed—a spore trap can be analyzed immediately rather than taking a week or longer culture. However, that plus is often overshadowed by the fact that many spores look the same under a microscope in a spore trap trace. Small, round, spherical spores get lumped together in catch-all classifications of Pen-Asp-like, Amerospores, etc., making genus-level identification difficult, and species-level IDs almost impossible.  Of course, culture samples don’t pick up any non-viable spores or fragments, and the agar growth mediums used for them are somewhat target specific for mold types.  And both have questionable collection efficiencies when you collect field samples. There are numerous other parameters to utilize for testing air and surfaces, but most appear to have gaps.

But the real question is do any of the widely used environmental mold sampling methodologies have a real correlation to the physiological effects on a building’s occupants? Are spores per cubic meter or CFUs per cubic meter a measure of the healthiness of a particular space for its occupants? Perhaps not. And that is a big problem for the industry.  My editorial space is limited, so I will pause here after figuratively throwing a hand grenade into the discussion, LOL. This topic has been burning in my brain for some time now, and I believe it warrants a full article (which I will pen for Healthy Indoors in the near future)…stay tuned!

Healthy Indoors Magazine, April 2023 Editorial:

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