Concern about mold exposure in buildings continues to be a significant issue. The bottom line is that mold has been around for eons and is not going away. It will grow whenever and wherever buildings get wet and materials suitable for microbial growth are present. So what is mold exactly and its effect on buildings? This article provides a general overview on this topic.
What is Mold?
Molds are members of the biological kingdom Fungi. This is distinguished, along
with bacteria, from the other kingdoms. This is due to the way it grows and derives nutrients (through absorption rather than ingestion). There are over 100,000 identified species of molds.
It is likely that another 100,000 have yet to be discovered. Of these, only a relative handful of molds have been studied for their benefits and health risks.
Mold requires moisture to grow. In the presence of sufficient moisture, molds secrete enzymes. These enzymes break down the nutrient source (commonly cellulose for the molds that most frequently grow in buildings). This allows it to serve as food, which supports continued growth. The key to controlling mold growth is to control the moisture.
Mold spores range from ~1 micron to over 100 microns in size. Most molds associated with water-damaged buildings have spores that range from 2 to 10 microns in size.
Common Mold Species in Buildings
Several species of concern (a term used to describe molds associated with health risks), are also associated with water-damaged buildings. Stachybotrys chartarum is probably the best known mold. It has been a great press agent, having been dubbed “killer mold” or “black mold” in the news media, which in the public perception tends to make it public enemy #1. Interestingly, though, a number of other mold species may be equally hazardous. There are hundreds of molds that are “black” in color. In fact, the color of many molds varies with food source and other factors. As far as Stachybotrys being a “killer mold” or “black mold,” while there have been some cases where Stachybotrys or other molds have been suspected as the primary cause of death in a healthy individual, these instances are very rare.
There are several other groups of molds related to water-damaged buildings. These include species of the Penicillium, Aspergillus, Chaetomium, Trichoderma, and Cladosporium genera, to name a few. Many of these species may, when conditions are appropriate, produce chemicals called mycotoxins during their growth cycle. Mycotoxins may be capable of causing adverse health effects at very low concentrations. Not all molds produce mycotoxins. Those that do may only produce them some of the time. This is usually as a result of competition with other species for a food source or when stressed out by other environmental factors. The application of biocides may actually increase the production of mycotoxins as it could be considered a stressor.
What is that musty odor you notice when you enter a moldy building? That is actually gasses produced by active mold growth. Microbial volatile organic compounds (MVOC’s) are a byproduct of mold digesting its food and are the cause of these malodors. There are continuing studies related to MVOC’s, many of which are known irritants. Exposure to MVOC’s from molds has been reported to cause certain symptoms. These include headaches, nasal irritation, dizziness, fatigue, and nausea (taken from EPA Mold Remediation in Schools and Buildings). Research on MVOC’s is still in the early stages. Time will tell how these metabolites impact occupant health.