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Written by Robert E. Sheriff, MS, CIH, CSP, President
Updated April 19, 2019
The more appropriate terms are: Is it Viable? or Non-Viable?
Viable/non-viable are better descriptive terms since these molds act like plants in terms of growth. A mold spore is like a seed—if the right combination of food, heat, and moisture are present, the spore can grow and multiply—just like a seed that can be dormant for long periods and then begin to grow.
What’s different between a mold spore and a seed is that if one is allergic to the particular mold (spore), it can produce the allergic response whether it is living or dead (Viable or Non-Viable). The real difference is that it cannot multiply if it’s non-viable. That may be important in some cases. If it is viable, then it can multiply and increase in concentration and create a stronger effect on a person or affect more people.
Another important fact is whether it is actively growing (multiplying!) or is it from a past condition that favored growth but is no longer present. This situation—non-viable and from past growth—is not unusual—but just taking a viability sample for incubation will not necessarily answer the question. Is it from a past growth or present growth? The reason is—what if the mold spores are viable even from a past growth environment? They can grow! Thus, if a viability test—using a culture media—is used—if no growth occurs, one can conclude it is likely from a past condition. But if it does grow (it’s viable), we don’t know if it was from the past or present!
Although we are often asked this question—is the mold a result of past growth or current growth? There is no valid way to differentiate between old mold and new mold! About the best that can be done is a determination if conditions for growth are present or not (moisture, food, temperature), at the time our inspection and testing were performed.
In the short term, often some conclusions can be drawn—yeast grows often in a matter of hours, then Basidiospores in a day or two, then Penicillium/Aspergillus in two to five days, then Stachybotrys in a week or two. Most molds will grow in a few days often dependent on growth conditions (marginal acceptable optimal perfect).
As a general rule, if testing is desired, just do a microscopic examination of an air sample or surface sample to see what it is and how much is present. Is there visible evidence of mold growth? (Those little circular green, white, black, or brown colonies on a surface). A qualified laboratory has microscopist who can identify the mold genes and sometimes even the species.
Is there evidence of flooding, or water damage? Finally, is there any odor of dampness—or moldiness?
If there is no such visible evidence of mold growth but air samples reveal high mold counts (compared to outdoors, of course) or it smells musty, then viability testing/sampling may be of value in determining if it is from past growth—remembering that only a negative viability test (no growth) will tell us it was from the past.
This is just one aspect of determining the situation involving molds and humans’ reaction to them. Often an experienced professional is required to make sense of any type of test result! Viable? Non-Viable? Surface? Air? Indoors? Outdoors? Seasonal? Toxic? Old? New? There are very few easy answers.
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