Mold (and other microorganisms) can grow on many different substrates and exploit a wide spectrum of environmental niches. During the growth process, mold may produce a gas that you and I can smell, called Microbial Volatile Organic Compounds (MVOCs). These MVOCs are some specific metabolites which are released as volatile compounds into the indoor air. These odorous compounds have been described as “earthy”, “musty”, and “fruity”. Depending on the compound generated, one may identify MVOCs with one or more of these (or other) descriptive terms. For example, the fungal metabolite 1-octen-3-ol has been described as “like mushrooms” and “like old paper”; while, 2-octen-1-ol, produced by some Aspergillus and other mold species, has been described as “a strong musty, oily odor” and the benzyl cyanide, produced by Botrytis cinerea, has been described as “grassy”. 

What we do know is that during primary metabolism, the organism breaks down food in the environment to extract nutrients needed for the maintenance of the cell structures and, in the process, creates MVOCs as by-products. In secondary metabolism, the production of MVOCs is driven by the competition for resources in a nutrient-poor environment. The list of potential MVOCs is too long to provide in this blog. Sufficient for this blog is this short list of MVOCs and the microorganisms that produce them: 

As to MVOCs’ ability to instigate disease, the answer depends on the nature and concentration of the MVOC(s) produced and the sensitivity of the person (or persons) exposed. When attempting to determine the risk that a given environmental stressor poses to a person or group of persons in a given building, one must consider the biological sensitivity of the person or group of persons to the stressor observed at the concentration it was observed. Knowing the biological sensitivity data allows the industrial hygienist (IH) to interpret the laboratory data in relation to the occupant(s) risk due to exposure and develop a site-specific, risk-specific corrective action plan (i.e., protocol for remediation) that will lead to: (1) a safe remediation project, (2) a sustainably safe environment for occupant(s), and (3) remove the unwanted risk from the subject building. Anything less is not a risk assessment. (In a future blog I’ll discuss the difference between a hazard and risk assessment.) There’s one catch to all of this, though, and that is this: MVOC sampling methodologies are, primarily, established for research purposes (to determine what VOCs microorganisms produce under defined laboratory culture conditions) and are not particularly useful as a means to establish whether microbial growth is impacting the health of building occupants, thus justifying mold remediation. This is why many mold assessors and IHs do not perform MVOC sampling during a mold assessment, choosing, instead, to focus on other, more reliable, indicators of (1) the building’s condition relative to mold, (2) the extent of mold contamination in a subject building, and (3) the potential risk to building occupants as a result of the determined type and concentration of mold.